KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

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Karnataka SSLC Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 1.
Someone in the family is suffering from the problem of acidity after overeating. Which of the following would you suggest as a remedy — lemon juice, vinegar or baking soda solution? Why?
Answer:
Acidity is caused by excessive production of hydrochloric acid in the stomach. In order to give relief to the person suffering from hyperacidity, drinking baking soda solution is suggested. Baking soda is basic in nature and hence will neutralize the acid in the stomach and give relief.

Question 2.
What is an acid? List a few general properties of acids.
Answer:
Any chemical compound that is sour to taste and has excessive H+ ions in aqueous state is called an acid. Acids have the following general properties:

  1. They are sour to taste.
  2. They turn blue litmus red.
  3. They conduct electricity in aqueous state.
  4. They react with bases to form salt and water.
  5. They are corrosive.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 3.
What is a base? Give a few general properties of bases.
Answer:
Any chemical compound that is bitter to taste and has excessive OH ions in aqueous state is called a base. General properties of bases include the following:

  1. They are bitter to taste.
  2. They are soapy to touch.
  3. They turn red litmus blue.
  4. They conduct electricity in aqueous state.
  5. They react with acids to form salt and water.
  6. They are corrosive.

Question 4.
What is an indicator? What is its use? Give examples of natural indicators.
Answer:
Indicators are substances that change their colour or odour when added into an acid or an alkaline solution. They are used in chemical tests. Litmus, for example, is a natural indicator that becomes red in the presence of acids and blue in the presence of bases. Turmeric is another example of a natural indicator.

Question 5.
What are olfactory indicators? Give examples.
Answer:
Those substances whose odours change in acidic or basic medium are called olfactory indicators. Vanilla, onion and clove are examples of olfactory indicators.

Question 6.
While eating food, you spill some curry on your white shirt. You immediately scrub it with soap. What happens to the yellow colour of the curry on scrubbing with soap? Why? What happens to this stain when the shirt is washed with plenty of water?
Answer:
On scrubbing, the colour changes from yellow to reddish brown. This is because soap is basic in nature and the colour of turmeric changes from yellow to reddish brown in basic medium. When the shirt is washed with plenty of water, the stain turns yellow again.

Question 7.
What is litmus? How is it obtained? What is it used for?
Answer:
A dye obtained from certain lichens that are red under acidic conditions and blue under alkaline conditions is called litmus.

Litmus solution is a purple dye, which is extracted from lichen, a plant belonging to the division Thallophyta, and is commonly used as an indicator. It is used in the laboratory as indicator to test whether a given solution is acidic, basic or neutral.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 8.
You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Answer:
We know that acids turn blue litmus red and bases turn red litmus blue. Distilled water does not change the colour of either of the two litmus papers.
Step 1:
Now, dip the given red litmus paper into each of the three given test tubes. One of them will turn the colour of the litmus to blue. This test tube contains basic solution.

Step 2:
Now, dip blue litmus paper obtained in step 1 into the other two test tubes. One of them will change the colour to red and the other does not change the colour. The test tube in which the colour of blue litmus paper changes to red contains acidic solution.

Step 3:
The test tube in which the colour of both red litmus and blue litmus remained unchanged contains distilled water.

Question 9.
Can we use olfactory indicators to test for acids and bases? How?
Answer:
Yes, we can use olfactory indicators to test for acids and bases. Take some finely chopped onions in a plastic bag along with some strips of clean cloth. Tie up the bag tightly and leave overnight inside a fridge. The cloth strips can now be used to test for acids and bases. Take two of these cloth strips and check their odour.

Keep them on a clean surface and put a few drops of dilute HC1 solution on one strip and a few drops of dilute NaOH solution on the other. Rinse both the cloth strips with water and again check their odour.

The smell in the acid medium is different from the smell in the basic medium. Thus we can test for acids and bases using locally prepared olfactory indicator. We can also use Vanilla essence or clove oil to distinguish between acids and bases using olfactory senses.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 10.
Why do HCl, HNO3, etc., show acidic character in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

OR

Compounds such as alcohol and glucose also contain hydrogen but are not categorised as acids. Give reason.
Answer:
Acids dissociate in their aqueous state and give hydronium ions [H3O+]. Compounds such as alcohols and glucose do not dissociate in aqueous state and give hydronium ions. [H3O+], Hence they are not categorised as acids.

Question 11.
How do dilute mineral acids react with metals? Name the products formed in such reactions.
Answer:
Dilute mineral acids usually react with metals forming a salt of the metal along with hydrogen gas. Here, metal displaces hydrogen from mineral acids.
Dilute mineral acid + Metal → Salt of the metal + Hydrogen gas.

Question 12.
Draw the diagram of the arrangement of apparatus to show the reaction of zinc granules with dilute sulphuric acid and testing hydrogen gas by burning and label the part that contains zinc granules and sulphuric acid.
Answer:
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 1
Zinc + dil. Sulphuric acid → Zinc sulphate + Hydrogen
Zn + H2SO4 → ZnSO4 + H2

Question 13.
Describe a simple experiment to show that hydrogen is produced when dilute acids react with metals. Show the arrangement of apparatus with a suitable diagram. Represent the reaction with a suitable equation.
Answer:
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 2
Arrange the apparatus as shown in the figure above. Take about 5 mL of dilute sulphuric acid in a test tube. Add a few pieces of zinc granules to it. The acid reacts with zinc forming zinc sulphate and hydrogen gas. Pass the gas being evolved through the soap solution.

Immediately we get soap bubbles containing hydrogen gas. Bring a burning candle near a gas-filled bubble. The bubble bursts with a pop sound. This establishes that the gas evolved is hydrogen.
Zinc + dil. Sulphuric acid → Zinc sulphate + Hydrogen
Zn + H2SO4 → ZnSO4 + H2

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 14.
Using zinc granules and hydrochloric acid, how do you show that hydrogen is produced when dilute acids react with metals? Show the arrangement of apparatus with a suitable diagram. Represent the reaction with a suitable equation.
Answer:
Take about 5 mL of dilute hydrochloric acid in a test tube. Add a few pieces of zinc granules to it. The acid reacts with zinc forming zinc chloride and hydrogen gas. Pass the gas being evolved through the soap solution.

Immediately we get soap bubbles containing hydrogen gas. Bring a burning candle near a gas-filled bubble. The bubble bursts with a pop sound. This establishes that the gas evolved is hydrogen.
Zinc + dil. Hydrochloric acid → Zinc chloride + Hydrogen
Zn + 2 HCl → ZnCl2 + H2

Question 15.
Name the products formed when dilute nitric acid reacts with zinc. Write a balanced chemical equation to represent this reaction.
Answer:
Dilute nitric acid reacts with zinc forming zinc nitrate and hydrogen gas.
Zinc + dil. Nitric acid → Zinc nitrate + Hydrogen gas
Zn + 2 HNO3 → Zn(NO3)2 + H2

Question 16.
What happens when acetic acid reacts with zinc metal? Write a balanced equation for the reaction.
Answer:
Acetic acid reacts with zinc metal forming zinc acetate and hydrogen gas.
Zinc + Acetic acid → Zinc acetate + Hydrogen gas
Zn + 2 CH3COOH → Zn(CH3COO)2 + H2

Question 17.
Which eas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Answer:
The gas usually liberated when an acid reacts with a metal is hydrogen. This can be illustrated by taking zinc and dilute hydrochloric acid. Take some zinc granules in a test tube and add dilute hydrochloric acid to it.

Allow the gas to pass through soap solution. Now soap bubbles are formed which contain the gas produced during the reaction. Bring a burning candle near one of the bubbles. The gas burns with a pop sound. This shows that the gas produced during the reaction is hydrogen.
Zn + 2 HCl → ZnCl2 + H2

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 18.
Write word equations and then balanced equations for the reaction taking place when

  1. dilute sulphuric acid reacts with zinc granules.
  2. dilute hydrochloric acid reacts with magnesium ribbon.
  3. dilute sulphuric acid reacts with aluminium powder.
  4. dilute hydrochloric acid reacts with iron filings.

Answer:
1. Sulphuric acid + Zinc → Zinc sulphate + Hydrogen
H2SO4 + Zn → ZnSO4 + H2

2. Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen
2HCl + Mg → MgCl2 + H2

3. Sulphuric acid + Aluminium → Aluminium sulphate + Hydrogen
3 H2SO4 + 2Al → Al2(SO4)3 + 3 H2

4. Hydrochloric acid + Iron → Ferric chloride + Hydrogen
6 HCl + 2 Fe → 2 FeCl3 + 3H2

Question 19.
Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH, COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?
Answer:
Fizzing occurs more vigorously in test tube A. This is because HCl is a stronger acid than acetic acid. HCl liberates hydrogen gas more vigorously and hence fizzing is more vigorous in test tube A than in B.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 20.
Why should curd and sour substances not be kept in brass and copper vessels?
Answer:
Curd and other sour substances contain acids. They react with brass and copper vessels and form harmful chemicals. This is why curd and other sour substances should not be kept in brass and copper vessels.

Question 21.
Describe an experiment to show the reaction between zinc (a metal) and sodium hydroxide (a base). Write a balanced chemical equation for the reaction.
Answer:
Take a few pieces of granulated zinc metal in a test tube. Add about 2 mL of sodium hydroxide solution. Warm the contents of the test tube. The reaction takes place and we observe the evolution of a gas. Pass the gas being evolved through soap solution.

Immediately we get soap bubbles containing hydrogen gas. Bring a burning candle near a gas-filled bubble. The bubble bursts with a pop sound. This establishes that the gas evolved is hydrogen.
The equation for the reaction above is:
Sodium hydroxide + Zinc → Sodium zincate + Hydrogen gas
2 NaOH + Zn → Na2ZnO2 + H2

Question 22.
Draw the diagram of the arrangement of apparatus to show the reaction of carbon dioxide gas when it is passed through calcium hydroxide solution.
Answer:
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 3

Question 23.
How do metal carbonates and metal hydrogen-carbonates react with acids?
Answer:
All metal carbonates and metal hydrogen-carbonates react with acids forming a corresponding salt, carbon dioxide and water.

Question 24.
How do you show the reaction between sodium carbonate and dilute hydrochloric acid? Write a balanced chemical equation for the reaction.
Answer:
Take about 0.5 g of sodium carbonate (Na2CO3) in a test tube. Add about 2 mL of dilute HCl to it. Reaction takes place and a gas is produced which turns limewater milky.

Therefore, the gas produced is carbon dioxide. Sodium chloride and water are also formed during this reaction. The equation for the reaction is:
Sodium carbonate + dil. Hydrochloric acid → Sodium chloride + Carbon dioxide + Water
Na2CO3 (s) + 2 HCl(aq) → 2 NaCl (aq) + CO2 (g) + H2O (l)

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 25.
How do you show the reaction between sodium hydrogen-carbonate and dilute hydrochloric acid? Write a balanced chemical equation for the reaction.
Answer:
Take about 0.5 g of sodium hydrogen-carbonate (NaHCO3) in a test tube. Add about 2 mL of dilute HCl to it. Reaction takes place and a gas is produced which turns limewater milky. Therefore, the gas produced is carbon dioxide.

Sodium chloride and water are also formed during this reaction. The equation for the reaction is:
Sodium carbonate + dil. Hydrochloric acid → Sodium chloride + Carbon dioxide + Water
NaHCO3 (s) + HCl (aq) → NaCl (aq) + CO2 (g) + H2O (l)

Question 26.
What happens when carbon dioxide gas is passed through limewater? Name the products formed during the reaction. Write the equations for the reactions that occur during the process.
Answer:
Limewater is aqueous solution of calcium hydroxide. It is a clear, colourless liquid. When carbon
dioxide gas is passed through limewater, it turns milky. This is due to the formation of insoluble calcium carbonate. The equation is:
Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l)

If carbon dioxide is passed further, again limewater turns colourless due to the formation of soluble calcium bicarbonate. The equation is:
Calcium carbonate + Carbon dioxide + Water → Calcium hydrogen-carbonate
CaCO3 (s) + CO2 (g) + H2O (l) → Ca(HCO3)2 (aq)

Question 27.
Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The eas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
Answer:
Calcium carbonate reacts with hydrochloric acid and produces carbon dioxide gas with effervescence. Carbon dioxide is neither a supporter of combustion nor a combustible gas. Hence, it extinguishes a burning candle. Therefore, the metal compound A is calcium carbonate. The balanced equation for this reaction is:
CaCO3 + 2 HCl → CaCl2 + CO2 + H2O.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 28.
What are the products formed when an acid reacts with a base?
Answer:
An acid reacts with a base forming a salt and water.
Acid + Base → Salt + Water.

Question 29.
What is a neutralisation reaction? Give two examples.
Answer:
A chemical reaction in which an acid and a base react quantitatively with the intent of producing a neutral pH level is known as neutralization. A salt and water are formed during neutralization reaction.
E.g. 1: Sodium hydroxide reacts with a requisite quantity of hydrochloric acid forming sodium chloride and water.
NaOH + HCl → NaCl + H2O.

E.g. 2: Milk of magnesia (magnesium hydroxide) is a base. It is given as a treatment for acidity problems. Acidity is caused by excessive production of hydrochloric acid in the stomach. This acid produced in the stomach is neutralized by milk of magnesia. The reaction produces magnesium chloride and water as products.
Mg(OH)2 + 2 HCl → MgCl2 + 2H2O.

Question 30.
Explain with a suitable equation the neutralization reaction between sodium hydroxide and hydrochloric acid.
Answer:
Sodium hydroxide (NaOH) is a base. Take about 2 mL of dilute NaOH solution in a test tube. Add two drops of phenolphthalein solution. The colour of the solution now turns pink. Add dilute HCl solution to the above solution drop by drop.

At some point of time, the pink colour disappears and the solution becomes colourless. At this point of time, the solution is neither acidic nor basic. It is a neutral solution containing a salt.

At this stage, the acid is completely neutralized by the base. If we add a few more drops of NaOH, the solution again turns pink. This is because the solution has again turned basic.
NaOH (aq) + HCl (aq) → NaCl (aq) + H2O.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 31.
How do you test whether the given sample of soil is acidic or not?
Answer:
Take about 2 g of the soil to be tested in a test tube. Add 5 mL of water to it. Shake the contents of the test tube. Filter the contents and collect the filtrate in another test tube.

Check the pH of this filtrate with the help of universal indicator paper. Based on the colour of the indicator, determine the pH value. If the pH value is less than 7, the soil has acidic content. If the pH value is more than 7, the soil is alkaline.

Question 32.
Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Answer:
Sometimes the soil in the field turns acidic. This will not only make the soil less fertile, it also adversely affects the yield. In such a situation, farmers add quick lime or slaked lime or chalk which are all basic in nature to the soil to neutralize the acid content in it.

Question 33.
How do metallic oxides react with dilute mineral acids?
Answer:
Dilute mineral acids react with metallic oxides forming a salt and water.
Dil. acid + Metallic oxide → Salt + Water.

Question 34.
Describe an experiment to show the reaction between metallic oxides and dilute mineral acid. Write a balanced equation for the reaction. What does this reaction establish with regard to the nature of metallic oxides?
Answer:
Take a small amount of copper oxide in a beaker. Add dilute hydrochloric acid slowly while stirring. Copper oxide dissolves in the solution and the colour of the solution turns blue-green. This is due to the formation of a salt called copper (II) chloride.

Water is also formed during the reaction. This reaction can be represented by the following equation:
Copper oxide + dil. Hydrochloric acid → Copper chloride + Water
CuO(s) + 2 HCl (aq) → CuCl2 (aq) + H2 (l)
This reaction establishes that metallic oxides are basic in nature.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 35.
How do non-metallic oxides react with bases? Give an example. What does this reaction show with regard to the nature of non-metallic oxides?
Answer:
Non-metallic oxides react with bases forming a salt and water.
For example, carbon dioxide is a non-metallic oxide. It reacts with sodium hydroxide forming sodium carbonate (salt) and water.
Carbon dioxide + Sodium hydroxide → Sodium carbonate + Water
CO2 + 2 NaOH → Na2CO3 + H2O.
This reaction shows that non-metallic oxides are generally acidic in nature.

Question 36.
What do all acids have in common?
Answer:
All acids contain H+ ions and these ions are responsible for their acidic properties.

Question 37.
What do all bases have in common?
Answer:
All bases contain OH ions and these ions are responsible for their basic nature.

Question 38.
Do aqueous solutions of acids conduct electricity? Why? Give examples.

OR

Why does an aqueous solution of an acid conduct electricity?
Answer:
Yes, aqueous solutions of acids do conduct electricity. Mineral acids are ionic compounds. They dissociate into positive ions (H+) and negative ions in their aqueous solutions. The presence of these ions makes them conduct electricity.
E.g.:

  1. HCl → H+ + Cl
  2. H2SO4 → 2 H+ + SO4

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 39.
How do you show experimentally that an aqueous solution of an acid conducts electricity?
Answer:
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 4
Take dil. sulphuric acid in a 100 mL beaker. Fix two nails on a cork and place the cork over the beaker as shown in the figure. Connect the nails to the two terminals of a 6-volt battery through a bulb and a switch.

Now, switch on the current. The bulb begins to glow. This shows that dilute sulphuric acid conducts electricity. The same effect is observed when the experiment is repeated with other acids. This shows that acids in general conduct electricity.

Question 40.
Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an activity to prove it.
Answer:
Compounds such as alcohols and glucose do not ionize in aqueous state. Hence they do not conduct electricity. This can be demonstrated by a simple activity.
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 5
Take some amount of glucose solution in a 100 mL beaker. Fix two nails on a cork and place the cork inside the beaker. Connect the nails to the two terminals of a 12-volt battery through a bulb and a switch.

Now, switch on the current. The bulb does not glow. This shows that glucose solution does not conduct electricity. The same effect is observed when the experiment is repeated with alcohol.

This activity shows that chemical compounds like alcohol and glucose do not contain hydrogen ions although hydrogen is present in their molecule.

Question 41.
Draw the diagram of the apparatus used to demonstrate that acidic solutions conduct electricity. Label the following parts:

  1. The solution taken
  2. Source of electric current.

Answer:
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 6

Question 42.
What are hydronium ions? Give its formula.
Answer:
Hydrogen ions cannot exist independently in an aqueous medium. They combine with water molecules forming positively charged hydronium ions. Hydronium ions are represented by the formula H3O+.
Water molecule + Hydrogen ion → Hydronium ion
H2O + H+ → H3O+

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 43.
How are hydrogen ions usually shown?
Answer:
Hydrogen ions are usually shown as H+ (aq) or hydronium ion (H3O+).

Question 44.
Why do acids not show acidic behaviour in the absence of water?
Answer:
Hydronium ions are responsible for the behaviour of a substance as an acid. Acids do not dissociate into hydronium ions in the absence of water. Therefore, they do not show acidic behaviour in the absence of water.

Question 45.
How can we show that dry HCl gas is not acidic while its aqueous solution is?
Answer:
Take about 1 g of solid NaCl in a clean and dry test tube. Add some concentrated sulphuric acid to the test tube. Cover the mouth of the test tube with a one-holed rubber stopper carrying a delivery tube.

Reaction begins and a gas is evolved which rushes out of the delivery tube. This gas is hydrogen chloride (HCl). Hold a dry blue litmus paper near the free end of the delivery tube. The colour of the litmus paper does not change.

Now try with wet blue litmus paper. HCl gas dissolves in water present on the litmus paper. Immediately the colour changes to red. This shows that dry HCl is not acidic while an aqueous solution of HCl is acidic.

Question 46.
Why does dry HCl gas not change the colour of dry litmus paper?
Answer:
Hydrogen ions in HCl are produced in the presence of water. The separation of H+ ion from HCl molecules cannot occur in the absence of water. Hence, dry HCl gas does not show acidic properties, as it does not contain hydrogen ions (H+). Therefore, it cannot change the colour of dry litmus paper.

Question 47.
How do you show that the dissolution of an acid in water is exothermic?
Answer:
Take 10 mL of water in a beaker. Add a few drops of concentrated sulphuric acid. Swirl the beaker slowly. Touch the base of the beaker. The beaker feels considerably warmer. The same is observed when other concentrated acids are added to water. This shows that heat is evolved when acid is added to water indicating that the process is exothermic.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 48.
What are the precautions to be taken while diluting an acid?
Answer:
The process of dissolving an acid in water is a highly exothermic one. Care must be taken while mixing concentrated nitric acid or sulphuric acid with water. The acid must always be added slowly to water with constant stirring.

If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.

Question 49.
While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Answer:
Mixing an acid in water produces heat, as the process is exothermic. While mixing, if water is added to acid, more heat would be evolved, as there is more acid present in the container.

This may result in the acid splashing out, which may result in injuries. When acid is added to water, water content is more and hence relatively less amount of heat is evolved. Therefore, it is recommended that the acid should be added to water and not water to the acid.

Question 50.
How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?
Answer:
The concentration of hydronium ions (H3O+) decreases when a solution of an acid is diluted.

Question 51.
How is the concentration of hydroxyl ions (OH) affected when we dilute the solution of a base?
Answer:
The concentration of hydroxyl ions (OH) decreases when a solution of a base is diluted.

Question 52.

  1. How do you show that the dissolution of a base in water is exothermic?
  2. How do you show that bases conduct electricity? What is their conductivity due to?

Answer:
1. Take 10 mL of water in a beaker. Add a spoon of sodium hydroxide. Swirl the beaker slowly. Touch the base of the beaker. The beaker feels considerably warmer. The same is observed when other bases are added to water. This shows that heat is evolved when a base is added to water indicating that the process is exothermic.

2. Take an aqueous solution of sodium hydroxide in a 100 mL beaker. Fix two nails on a cork and place the cork over the beaker such that the two nails are partially immersed in sodium hydroxide.

Connect the nails to the terminals of a 6-volt battery through a bulb and a switch. Now, switch on the current. The buib begins to glow. This shows that sodium hydroxide conducts electricity. The same effect is observed when the experiment is repeated with other bases. This shows that bases in general conduct electricity.

Bases in aqueous solution dissociate into positive ions and negative ions (OH). These ions are responsible for their electrical conductivity.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 53.
What are the ions formed in an aqueous solution of

  1. Sodium hydroxide,
  2. Magnesium hydroxide, and
  3. Potassium hydroxide? Give suitable equations for each.

Answer:
1. Sodium hydroxide in its aqueous solution will dissociate into positively charged sodium ions (Na+) and negatively charged hydroxyl ions (OH).
NaOH → Na+ + OH

2. Magnesium hydroxide in its aqueous solution will dissociate into positively charged magnesium ions (Mg++) and negatively charged hydroxyl ions (OH).
Mg(OH)2 → Mg2+ + 2OH

3. Potassium hydroxide in its aqueous solution will dissociate into positively charged potassium ions (K+) and negatively charged hydroxyl ions (OH).
KOH → K+ + OH.

Question 54.
What are alkalis?
Answer:
Some bases dissolve in water while others do not. Bases that are soluble in water are called alkalis. Thus we may say that all alkalis are bases but all bases are not alkalis.

Question 55.
Show with the help of a simple experiment that glucose solution or alcohol is not a conductor of electricity. Give reason for your observation.
Answer:
Take a solution of glucose in a 100 mL beaker. Fix two nails on a cork and place the cork over the beaker such that the two nails are partially immersed in the solution. Connect the nails to the two terminals of a 12-volt battery through a bulb and a switch.

Now, switch on the current. The bulb does not glow. This shows that glucose solution does not conduct electricity. The same effect is observed when the experiment is repeated with alcohol. This shows that glucose and alcohol do not conduct electricity.

Substances such as glucose and alcohol do not dissociate into ions in their aqueous solution. Therefore, they do not conduct electricity.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 56.
Why does distilled water not conduct electricity whereas rainwater does?
Answer:
Rainwater contains acids and many other ionic impurities. The acids present in rainwater produce hydronium ions, which make rainwater to conduct electricity. Distilled water does not contain any ionic substance that can dissociate into hydronium ions. This is why distilled water does not conduct electricity.

Question 57.
What determines the concentration of an acid and a base?
Answer:
The concentration of an acid depends on the concentration of hydrogen ions (H+) or hydronium ions (H3O) contained in it. Similarly, the concentration of a base depends on the concentration of hydroxyl ions (OH) contained in it.

Question 58.
How are dilute acid and weak acid different from one another?
Answer:
An acid that contains higher proportion of molecules of the acid than those of the solvent (water) is called a dilute acid. An acid that ionises to a lesser extent (gives fewer hydrogen ions) in aqueous solution is called a weak acid.

Question 59.
What effect does the concentration of H+(aq) ions have on the nature of the solution?
Answer:
The concentration of H+ (aq) ions determines the acidic nature of the solution. Hence, acidity of a solution increases with increase in concentration of H+ (aq) ions and vice-versa. In other words, more the concentration of H+ ions in a solution, more acidic the solution is.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 60.
Do basic solutions also have H+ (aq) ions? If yes, then why are these basic?
Answer:
Yes, basic solutions also have H+ (aq) ions. However, such solutions are basic because the concentration of hydroxide (OH) will be much higher than the H+ (aq) ions.

Question 61.
How is the concentration of hydroxyl ions (0H) affected when excess of the base is dissolved in a solution of sodium hydroxide?
Answer:
The concentration of OH ions increases when excess base is dissolved in a solution of sodium hydroxide.

Question 62.
What is pH scale? Explain.
Answer:
A measure of acidity or alkalinity of water-soluble substances is expressed in terms of its pH value. pH stands for ‘potential of Hydrogen’. The pH value is a number from 1 to 14, with 7 as the middle (neutral) point.

This means pH of a neutral solution is 7. Values below 7 indicate acidity, which increases as the number decreases, 1 being the most acidic. Values above 7 indicate alkalinity, which increases as the number increases.
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 7

Question 63.
How is the pH value of a solution measured?
Answer:
The pH value (number) of a solution is measured using a universal indicator, which shows different colours at different concentrations of hydrogen ions in a solution. Generally, a paper strip impregnated with the universal indicator is used for measuring pH.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 64.
You have two solutions. A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of these is acidic and which one is basic?
Answer:
An acidic solution has pH value less than 7 and a basic solution has pH value more than 7. Hence, the solution A having pH value 6 is acidic and has more hydrogen ion concentration. The solution B with pH value 8 is a basic solution and has more OH ions.

Question 65.
Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is

  1. Neutral,
  2. Strongly alkaline,
  3. Strongly acidic,
  4. Weakly acidic, and
  5. Weakly alkaline?

Arrange the pH in increasins order of hydrogen-ion concentration.
Answer:

  1. D is neutral, as its pH value is equal to 7.
  2. C is strongly alkaline, as its pH value is 11.
  3. B is strongly acidic, as its pH value is equal to 1.
  4. A is weakly acidic, as its pH value is equal to 4 and more than that of solution B.
  5. E is weakly alkaline, as its pH value is equal to 9 and less than that of C.

The pH values of the given solutions in the increasing order of hydrogen-ion concentration are: C < E < D < A < B.

Question 66.
Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Answer:
Curd is acidic in nature. An acidic substance has less pH value. As the milk turns into curd, the acidic content of milk will increase. Therefore, the value of pH of milk will decrease.

Question 67.
A milkman adds a very small amount of baking soda to fresh milk.

  1. Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
  2. Why does this milk take a long time to set as curd?

Answer:
1. By making the milk little more alkaline, the milk does not set easily into curd. It takes longer time for milk to turn into curd. That’s why the milkman shifts the pH of fresh milk to slightly alkaline by adding a very small amount of baking soda to it.

2. As this milk is slightly more alkaline, the acid that causes curding will be neutralized by baking soda. Hence, the milk takes a longer time to set as curd.

Question 68.
What is the pH value of human blood? What does this value say about the nature of human blood?
Answer:
The pH value of human blood is about 7.3. This indicates that human blood is slightly alkaline in nature.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 69.
What is the pH value of acid rain? How does acid rain affect life forms?
Answer:
The pH value of acid rain is about 5.6. Living organisms including aquatic organisms can survive only in a narrow range of pH. When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.

Question 70.
What is hyperacidity? How is it usually treated?
Answer:
Our stomach produces hydrochloric acid, which helps in digestion of food. The acid also helps to kill bacteria that enter the stomach through food. Excessive production of hydrochloric acid in the stomach causes sharp pain and irritation. This condition is called hyperacidity.

Hyperacidity is treated by administering medicines called antacids. Antacids are chemicals that are basic in nature. They neutralize the excessive acid and give relief to the patient.

Question 71.
Which is the most commonly used chemical to treat hyperacidity? How does it help?
Answer:
The most commonly used chemical to treat hyperacidity is magnesium hydroxide (commonly called milk of magnesia). This chemical is mildly basic in nature. It neutralizes the excessive acid in the stomach and gives relief.

Question 72.
What causes tooth decay? Explain.
Answer:
Tooth enamel is mainly made up of a compound called calcium hydroxyapatite, a crystalline form of calcium phosphate. This is a very hard substance that does not dissolve in water. However, it gets corroded when the pH value in the mouth falls below 5.5.

This situation arises when degradation of sugar and food particles occurs in the mouth due to bacterial activity. This process produces acids and increases the acidity level in the mouth. This hurts the tooth enamel and causes tooth decay.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 73.
Which is the best way to prevent tooth decay?
Answer:
The best way to prevent tooth decay is to clean the mouth after eating food. Using toothpastes which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.

Question 74.
How do some animals and plants use acids for self-defence? How can that situation be met?
Answer:
Some animals such as insects sting and inject an acid as a means of self-defence. This causes pain, irritation and swelling in the victim. Some plants also resort to injecting acids as a defence mechanism.

For example, stinging hair of nettle leaves injects methanoic acid which causes burning pain. Use of a mild base like baking soda on the stung area gives relief.

Question 75.
Name the acid present in the stinging hair of nettle leaves.
Answer:
Methanoic acid is present in the stinging hair of nettle leaves.

Question 76.
List some naturally occurring acids. Mention their source.
Answer:

Naturally-occurring acid Source of the acid
1. Acetic acid Vinegar
2. Citric acid Orange, Lemon
3. Tartaric acid Tamarind
4. Oxalic acid Tomato
5. Lactic acid Sour milk (curd)
6. Methanoic acid Ant sting, Nettle sting

Question 77.
Write the formulae of the following salts: Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate and ammonium chloride.
Answer:

Name of the salt Molecular formula
1. Potassium sulphate K2SO4
2. Sodium sulphate Na2SO4
3. Calcium sulphate CaSO4
4. Magnesium sulphate MgSO4
5. Copper sulphate CuSO4
6. Sodium chloride NaCl
7. Sodium nitrate NaNO3
8. Sodium carbonate Na2CO3
9. Ammonium chloride NH4Cl

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 78.
Name the acid and base from which the following salts can be obtained: Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate and ammonium chloride.
Answer:
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 8

Question 79.
Salts having the same positive or negative radicals are said to belong to a family. How many families can you identify among these salts: Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate and ammonium chloride?
Answer:
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 9

Question 80.
You are given a salt. How do you determine the pH value of this salt?
Answer:
Take a pinch of the given salt and test for its solubility in water (use distilled water only). If soluble, prepare a solution of the salt. Use a litmus paper to test whether the solution is acidic, basic or neutral.

Use pH paper (universal indicator) to find the pH value. If the salt solution turns blue litmus to red, the salt is acidic and its pH value is less than 7. If the salt solution turns red litmus to blue, the salt is basic in nature and its pH value is more than 7. A neutral salt will not change the colour of the litmus paper and its pH value would be 7.

Question 81.
State the solubility, reaction to litmus paper, pH value, nature and the acid and base involved in the following salts: sodium chloride, potassium nitrate, aluminium chloride, zinc sulphate, copper sulphate, sodium acetate, sodium carbonate and sodium hydrogen-carbonate.
Answer:
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 10

Question 82.
State the relationship between strength of the acid and base involved in the formation of a salt and its pH value.
Answer:
Salts of a strong acid and a strong base are neutral with pH value of 7. Salts of a strong acid and a weak base are acidic in nature with pH value less than 7. Salts of a strong base and a weak acid are basic in nature, with pH value more than 7.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 83.
What is the chemical name of common salt? Mention its molecular formula. Name the acid and base from which this salt can be obtained.
Answer:
The chemical name of common salt is sodium chloride. Its molecular formula is NaCl. Sodium chloride can be obtained by the reaction between hydrochloric acid and sodium hydroxide.

Question 84.
What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Answer:
Sodium hydrocarbonate is also known as sodium bicarbonate. Sodium hydrocarbonate decomposes on heating into sodium carbonate, water and carbon dioxide gas.
2 NaHCO3 → Na2CO3 + H2O + CO2

Question 85.
Why is sodium chloride considered a neutral salt? Which is its biggest natural source?
Answer:
Sodium chloride is obtained when hydrochloric acid reacts with sodium hydroxide. Hydrochloric acid is a strong acid and sodium hydroxide is a strong base. Salts of strong acid and strong base are neutral salts.

Therefore, sodium chloride is also a neutral salt. The solution of sodium chloride does not change the colour of litmus paper as its pH value is 7. Seawater is the biggest natural source of common salt (sodium chloride).

Question 86.
What is rock salt? What is its colour due to?
Answer:
A naturally occurring brownish mineral called halite, which contains mainly sodium chloride, is called rock salt. The brownish colour of rock salt is due to the impurities contained in the mineral.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 87.
Name a few chemical compounds that can be obtained by using sodium chloride as the raw material.
Answer:
Common salt is used as a raw material for preparing various chemical compounds including sodium hydroxide, baking soda, washing soda, and bleaching powder.

Question 88.
How is sodium hydroxide manufactured from sodium chloride in chlor-alkali process? How does this process get its name? What are the products formed during the process? Write a balanced chemical equation for the reaction.

OR

Draw the diagram of the apparatus used to test the conductivity of sodium chloride solution and label the graphite rod and the part where sodium chloride solution is present.
Answer:
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 11
Sodium chloride is also known as brine. Sodium hydroxide is manufactured in chlor-alkali process by the decomposition of brine solution using electricity.

During the process, chlorine and an alkali (NaOH) are produced. Hence, the process gets its name (chlor for chlorine and alkali for sodium hydroxide).

This process yields chlorine gas, hydrogen gas and sodium hydroxide as products. The reaction involved is represented by the following equation:
2 NaCl (aq) + 2 H2O (l) → 2 NaOH (aq) + Cl2 (g) + H2 (g).

Question 89.
From where are chlorine, hydrogen and sodium hydroxide obtained during the electrolytic decomposition of brine solution?
Answer:
During the electrolytic decomposition of brine solution, hydrogen gas is obtained at the cathode, chlorine gas is collected at the anode and sodium hydroxide remains in solution in the voltameter.

Question 90.
During the manufacture of sodium hydroxide from sodium chloride, hydrogen gas is collected at the cathode. List three uses of this gas.
Answer:
Hydrogen collected at the cathode is used

  1. As fuel,
  2. To manufacture a substance called margarine (a substitute for butter), and
  3. To manufacture ammonia, which is in turn used to manufacture fertilizers.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 91.
During the manufacture of sodium hydroxide from sodium chloride, chlorine gas is collected at the anode. List three uses of this gas.
Answer:
Chlorine gas collected at the anode is used

  1. In the treatment of drinking water,
  2. To disinfect swimming pools,
  3. In the manufacture of PVC, and
  4. In the manufacture of CFCs and pesticides.

Question 92.
List some of the uses of sodium hydroxide.
Answer:
Sodium hydroxide is used:

  1. As a raw material in the manufacture of soaps and detergents.
  2. As a cleaning agent to remove grease from metal parts.
  3. In the manufacture of paper.
  4. To make artificial fibres.

Question 93.
There is no change in the colour of red litmus and blue litmus paper when introduced into an aqueous solution of sodium chloride. After passing direct current through the same solution, red litmus changes to blue colour. Which product is responsible for this change? Mention any two uses of this product.
Answer:
Sodium chloride solution is a neutral solution. Hence, it does not change the colour of litmus. The compound formed when an electric current is passed through aqueous sodium chloride is sodium hydroxide. Sodium hydroxide is a base. It is the formation of sodium hydroxide that turns red litmus to blue.
For uses of sodium hydroxide

  1. As a raw material in the manufacture of soaps and detergents.
  2. As a cleaning agent to remove grease from metal parts.
  3. In the manufacture of paper.
  4. To make artificial fibres.

Question 94.
What is the common name of the compound CaOCl2?
Answer:
The chemical name of the compound CaOCl2 is calcium oxychloride. It is commonly known by the name ‘bleaching powder’.

Question 95.
Name the substance which on treatment with chlorine yields bleaching powder.
Answer:
Calcium hydroxide or dry slaked lime [Ca(OH)2] yields bleaching powder (CaOCl2) when treated with chlorine.
Ca(OH)2 + Cl2 → CaOCl2 + H2O.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 96.
How is bleaching powder manufactured?
Answer:
Bleaching powder is produced by the action of chlorine on dry slaked lime which is nothing but calcium hydroxide [Ca(OH)2].
Ca(OH)2 + Cl2 → CaOCl2 + H2O.

Question 97.
List any three uses of bleaching powder.
Answer:
The following are some of the uses of bleaching powder:

  1. Bleaching powder is used for bleaching cotton and linen in the textile industry, wood pulp in paper factories, and washed clothes in laundry.
  2. It is used as an oxidising agent in many chemical industries.
  3. It is used to make drinking water free of germs.

Question 98.
What is baking soda? Write its formula.
Answer:
Baking soda is the common name of a chemical called sodium hydrogen carbonate. Its molecular formula is NaHCO3. It is also called sodium bicarbonate.

Question 99.
What are the raw materials used for nut king baking soda?
Answer:
Baking soda is obtained by using sodium chloride, water, ammonia and carbon dioxide as raw materials.

Question 100.
How is baking soda prepared from sodium chloride? Write the equation for the reaction.
Answer:
Baking soda (sodium hydrogen carbonate) is prepared by bubbling ammonia gas and carbon dioxide one after the other in that order through a strong brine solution (NaCl + H2O).
The reaction yields baking soda and ammonium chloride as products.
Sodium chloride + Water + Carbon dioxide + Ammonia → Ammonium chloride + Sodium hydrogen carbonate
NaCl (Brine) + H2O + CO2 + NH3 → NH4Cl + NaHCO3.

Question 101.
What will happen if a solution of sodium hydrogen carbonate (baking soda) is strongly heated? Write the equation for the reaction.
Answer:
Sodium hydrogen carbonate decomposes on heating and yields sodium carbonate, water and carbon dioxide.
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 12

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 102.
What property of baking soda is used to treat the problem of excessive acidity?
Answer:
Baking soda (sodium hydrogen carbonate) is a mild non-corrosive basic salt. This property is used to treat the problem of excessive acidity in the stomach as it neutralises the acid.

Question 103.
List some of the uses of baking soda.
Answer:
The following are some of the uses of baking soda:

  1. It is used in antacids to remedy the problems of acidity in the stomach and related problems.
  2. It is used to make baking powder, which is used in baking industry.
  3. It is used in soda-acid fire extinguishers.

Question 104.
What is baking powder? How is it prepared?
Answer:
A mixture of sodium bicarbonate and tartaric acid is known as baking powder. It is sodium salt of tartaric acid. Baking powder is obtained by mixing sodium bicarbonate and tartaric acid.

Question 105.
In a bakery, baking powder was not added while preparing cake. The cake obtained was hard and small in size. What is the reason for this?
Answer:
Baking powder is a mixture of baking soda (sodium hydrogen carbonate) and a mild edible acid such as tartaric acid. While preparing the dough, baking powder is added to the flour.

When baking powder mixes with water, then sodium hydrogen carbonate (NaHCO3) reacts with tartaric acid to evolve carbon dioxide gas. This CO2 gas causes the cake to rise and become soft and spongy. As baking powder was not added, the cake obtained was hard and small.

Question 106.
What is washing soda? Write its molecular formula.
Answer:
Washing soda is the common name of a chemical compound called sodium carbonate. Its molecular formula is Na2CO3.10H2O.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 107.
How is sodium carbonate prepared? Write the equation for the reaction.
Answer:
Sodium carbonate is obtained from sodium chloride. First, sodium hydrogen carbonate is prepared by passing ammonia and carbon dioxide through a strong brine solution. Later, sodium carbonate is prepared by the thermal decomposition of sodium hydrogen carbonate.
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 13

Question 108.
What is the chemical nature of sodium carbonate?
Answer:
Sodium carbonate is basic in nature.

Question 109.
List the uses of washing soda.
Answer:
The following are some of the uses of washing soda:

  1. Sodium carbonate (washing soda) is used in glass, soap and paper industries.
  2. It is used in the manufacture of sodium compounds such as borax.
  3. It is also used as a cleaning agent for domestic purposes.
  4. It is used to remove permanent hardness of water.

Question 110.
Name the sodium compound that is used for softening hard water.
Answer:
The compound of sodium used for softening hard water is sodium carbonate (Na2CO3). This compound is commonly known as washing soda.

Question 111.
Give two important uses of washing soda and baking soda.
Answer:
Important uses of washing soda include the following:

  • Washing soda is used to soften hard water.
  • It is used in making soap.

Important uses of baking soda include the following:

  • Baking soda is used to make baking powder, which is used in baking industry to make bakery products.
  • It is also used in soda-acid fire extinguishers.

Question 112.
What is meant by water of crystallization of a salt? Explain with an example. Why is it essential?
Answer:
Many salts contain a certain fixed number of water molecules in their formula unit. The fixed number of water molecules present in one formula unit of a salt is known as water of crystallization.

For example, the formula of sodium carbonate is Na2CO3.10H2O. This means a molecule of sodium carbonate contains 10 molecules of water. This means 10 molecules of water are present in one formula unit of sodium carbonate.

Water of crystallization is necessary for certain salts to crystallize out from their aqueous solutions. This water makes it possible for them to form crystals, and it is responsible for the shapes of their crystals.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 113.
How do you show the presence of water of crystallization in copper sulphate crystals?
Answer:
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 14
Test tube holder Boiling tube Water droplets Copper sulphate crystals The molecular formula of crystalline copper sulphate is CuSO4.5H2O. It is a blue-coloured chemical.

Take a few crystals of copper sulphate in a dry boiling tube. Note the colour of copper sulphate. Heat the boiling tube strongly. Now copper sulphate turns into a white powder. Several water droplets get collected near the mouth of the boiling tube.

Now, add two or three drops of water into the boiling tube. Now the blue colour of copper sulphate is restored. This activity shows the presence of water of crystallization in copper sulphate crystals.

Question 114.
What is gypsum? How many water of crystallization is present in its molecule? Write its molecular formula.
Answer:
Gypsum is the common name of a chemical compound called calcium sulphate. The water of crystallization in the formula of calcium sulphate is 2. Its molecular formula is CaSO4 . 2 H2O.

Question 115.
What is Plaster of Paris? What is its chemical name?
Answer:
A white powder mainly made of calcium sulphate hemihydrate that forms a paste when mixed with water, and then, thickens and hardens is known as Plaster of Paris.
The chemical name of Plaster of Paris is calcium sulphate (CaSO4\frac{1}{2}H2O).

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 116.
Explain the preparation of Plaster of Paris with the help of balanced chemical equation.
Answer:
When gypsum is heated to a temperature of 373 K, it loses water molecules and becomes calcium
sulphate hemihydrate (CaSO4\frac{1}{2}H2O), which is called Plaster of Paris.
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 15

Question 117.
How does Plaster of Paris react with water? Write an equation to show the reaction between Plaster of Paris and water.
Answer:
Plaster of Paris forms a fine paste when mixed with water. Later, it solidifies to form a hard mass. This hard mass is calcium sulphate.
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 16

Question 118.
The formula of Plaster of Paris is CaSO4. 1/2H2O. Can a formula unit of a compound contain half molecule of water? Explain.
Answer:
In Plaster of Paris, two formula units of CaSO4 share one molecule of water. This is why the formula of Plaster of Paris is written as CaSO4.\frac{1}{2}H2O.

Question 119.
Plaster of Paris should be stored in a moisture-proof container. Explain why.
Answer:
Plaster of Paris easily turns into a hard mass of gypsum on reacting with moisture present in air.
KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts 17
This is why Plaster of Paris should be stored in a moisture-proof container.

Question 120.
List any three uses of Plaster of Paris.
Answer:
Plaster of Paris is used for making toys, casts of statues, decorative materials etc. It is also used to make surfaces smooth. Doctors also use it as plaster for supporting fractured bones in the right position.

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Fill In The Blanks

1. The chemical name of washing soda is sodium carbonate
2. Sodium chloride is commonly known as common salt
3. Hydrogen ion combines with a water molecule to give hydronium ion
4. The pH value of pure water is seven
5. As the hydrogen ion concentration of a solution increases, its pH value decreases
6. The common ion given by alkalis in aqueous state is hydroxyl ion
7. The common product of all neutralization reactions is water
8. Chemicals used to treat acidity are known as antacids

Multiple Choice Questions

Question 1.
Which of the following statements is true for acids?
(A) Bitter and change red litmus to blue
(B) Sour and change red litmus to blue
(C) Sour and change blue litmus to red
(D) Bitter and change blue litmus to red
Answer:
(C) Sour and change blue litmus to red

Question 2.
A sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the pH paper yellowish-orange. Which of the following would change the colour of this pH paper to greenish-blue?
(A) Lemon juice
(B) An antacid
(C) Vinegar
(D) Common salt
Answer:
(B) An antacid

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 3.
Which of the following are present in a dilute aqueous solution of hydrochloric acid?
(A) H3O+ and Cl
(B) H3O+ and OH
(C) Cl and OH
(D) un-ionised HCl
Answer:
(A) H3O+ and Cl

Question 4.
A solution turns red litmus blue. Its pH is likely to be
(A) 1
(B) 4
(C) 5
(D) 10
Answer:
(D) 10

Question 5.
Which of the following gives the correct increasing order of acidic strength?
(A) Water < Hydrochloric acid < Acetic acid
(B) Acetic acid < Water < Hydrochloric acid
(C) Water < Acetic acid < Hydrochloric acid
(D) Hydrochloric acid < Water < Acetic acid
Answer:
(C) Water < Acetic acid < Hydrochloric acid

Question 6.
A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains
(A) NaCl
(B) HCl
(C) LiCl
(D) KCl
Answer:
(B) HCl

Question 7.
An aqueous solution turns red litmus solution blue. Excess addition of which of the following solutions would reverse the change?
(A) Baking powder
(B) Lime
(C) Ammonium hydroxide solution
(D) Hydrochloric acid
Answer:
(D) Hydrochloric acid

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 8.
If a few drops of a concentrated acid accidentally spill over the hand of a student, what should be done?
(A) Wash the hand with saline solution.
(B) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogen carbonate.
(C) After washing with plenty of water apply solution of sodium hydroxide on the hand.
(D) Neutralise the acid with a strong alkali.
Answer:
(B) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogen carbonate.

Question 9.
10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be
(A) 4 mL
(B) 8 mL
(C) 12 mL
(D) 16 mL
Answer:
(D) 16 mL

Question 10.
One of the constituents of baking powder is sodium hydrogen carbonate, the other constituent is
(A) hydrochloric acid
(B) tartaric acid
(C) acetic acid
(D) sulphuric acid
Answer:
(B) tartaric acid

Question 11.
The pH of the gastric juices released during digestion is
(A) less than 7
(B) more than 7
(C) equal to 7
(D) equal to 0
Answer:
(A) less than 7

Question 12.
Which of the following salts does not contain water of crystallisation?
(A) Blue vitriol
(B) Baking soda
(C) Washing soda
(D) Gypsum
Answer:
(B) Baking soda

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 13.
What happens when a solution of an acid is mixed with a solution of a base in a test tube?
(i) The temperature of the solution increases.
(ii) The temperature of the solution decreases.
(iii) The temperature of the solution remains the same
(iv) Salt formation takes place.
(A) (i) only
(B) (i) and (iii)
(C) (ii) and (iii)
(D) (i) and (iv)
Answer:
(D) (i) and (iv)

Question 14.
Which one of the following types of medicines is used for treating indigestion?
(A) Antibiotic
(B) Analgesic
(C) Antacid
(D) Antiseptic
Answer:
(C) Antacid

Question 15.
Sodium carbonate is a basic salt because it is a salt of
(A) strong acid and strong base
(B) weak acid and weak base
(C) strong acid and weak base
(D) weak acid and strong base
Answer:
(D) weak acid and strong base

Question 16.
Which of the following is used for dissolution of gold?
(A) Hydrochloric acid
(B) Sulphuric acid
(C) Nitric acid
(D) Aqua regia
Answer:
(D) Aqua regia

Question 17. Which of the following is acidic in nature?
(A) Antacid
(B) Human blood
(C) Lime juice
(D) Lime water
Answer:
(C) Lime juice

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Question 18.
During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through the guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is
(A) To absorb moisture from the gas
(B) To absorb the evolved gas
(C) To moisten the gas
(D) To absorb Cl ions from the evolved gas.
Answer:
(A) To absorb moisture from the gas

Question 19.
The pH values of four solutions P, Q, R and S are 7.8, 1.0, 13.0 and 1.4 respectively. The solution having highest hydrogen ion concentration among them is
(A) P
(B) Q
(C) R
(D) S
Answer:
(B) Q

KSEEB Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts

Match The Following

Question 1.

Column A Column B
1. Washing soda a. Calcium sulphate
2. Baking soda b. Sodium carbonate
3. Plaster of Paris c. Sodium chloride
4. Gypsum d. Calcium oxychloride
5. Bleaching powder e. Sodium hydrogen carbonate
f. Calcium sulphate hemihydrate

Answer:
1 – b, 2 – e, 3 – f, 4 – a, 5 – d.

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