10th Class PS 2nd Lesson Acid Bases and Salts Textbook Questions and Answers

10th Class PS 2nd Lesson Acid Bases and Salts Textbook Questions and Answers

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Question 1.

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:

Divide the red litmus paper in three parts and dip each part in three test tubes. The test tube in which red litmus paper turns blue contains basic solution. The blue litmus paper so obtained is dipped into the remaining two solutions. The one which turns blue litmus paper red again is an acidic solution. The third tube in which there is no change of colour contains water. 

Question 2.

Why should curd and sour substances not be kept in brass and copper vessels ?

Answer:

Curd and sour substances are acidic and acids react with brass and copper and so are not kept in brass and copper vessels.

Question 3.

Which gas 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:

H2 gas is liberated when an acid reacts with a metal.

Illustration : Set up an apparatus as shown in figure. Take some zinc granules in the test tube. Add some 5 ml dilute hydrochloric acid slowly. Soon the reaction between zinc and hydrochloric acid starts and hydrogen gas is evolved.
Zn + HCl → ZnCl2 + H2

Test for H2 gas : H2 gas is not soluble in water. When passed through soap solution, it gets trapped into bubbles which burn with explosion.

Question 4.

Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

Answer:

Since the end product is calcium chloride and the gas formed extinguishes a burning candle, it is CO2, the metal compound A must be calcium carbonate. Hence, the reaction between calcium carbonate and hydrochloric acid is as follows.
 
Question 5.

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

Answer:

H+ ions in aqueous solution are responsible for acidic character. HCl, HNO3 etc. generate H+ ions in water while alcohol and glucose do not do so, and hence do not show acidic character.

Question 6.

Why does an aqueous solution of an acid cortduct electricity ?

Answer:

Acids give ions in aqueous solution and in solution current is carried through ions. Thus aqueous solution of an acid conducts electricity.

Question 7.

Why does dry HCl gas not change the colour of the dry litmus paper ?

Answer:

Dry HCl gas does not generate H* ions and hence does not change the colour of dry litmus paper.

Question 8.

While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?

Answer:

When an acid is mixed with water, there is evolution of a large amount of heat. Therefore, acid is slowly added to water. If on the other hand, water is added to acid, it might spill on your body and cloths due to explosion and evolution of sudden and large amount of heat. 

Question 9.

How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted ?

Answer:

Concentration of hydronium ions (H3O+) decreases when a solution of an acid is diluted.

Question 10.

How is the concentration of hydroxide ions (OH–) affected when excess base is dissolved in a solution of sodium hydroxide ?

Answer:

Concentration of hydroxide ions (OH+) increases. When excess base is dissolved in a solution of sodium hydroxide.


Question 11.

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 this is acidic and which one is basic ?

Answer:

Solution A has more hydrogen ion concentration. Solution A is slightly acidic and solution B is slightly basic.

Question 12.

What effect does the concentration of H+ (aq) ions have on the nature of the solution?

Answer:

More the concentration of H+ ion, higher the acidic nature of the solution higher the acidic nature of the solution. 

Question 13.

Do basic solutions also have H+ (aq) ions ? If yes, then why are these basic ?

Answer:

Yes, basic solutions also have H+ ions. However, their concentration is less as compared to the OH– ions that makes the solution basic.

Question 14.

Under what sdil 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:

Plants work well in the pH range 6 – 8. So, when the soil becomes acidic farmers treat the soil fields with bases like quick lime or slaked lime or chalk.

Question 15.

What is the common name of the compound CaOCl2 ?

Answer:

Bleaching powder.

Question 16.

Name the substance which on treatment with chlorine yields bleaching powder.

Answer:

Dry slaked lime (Ca(OH)2). 

Question 17.

Name the sodium compound which is used for softening hard water.

Answer:

Washing soda, i.e., sodium carbonate (Na2CO3.10H2O)

Question 18.

What will happen if a solution of sodium hydrogen carbonate is heated ? Give the equation of the reaction involved.

Answer:

Sodium hydrogen carbonate on heating gives sodium carbonate and CO gas is evolved.
2NaHCO3 → Na2CO3 + CO2 + H2O

Question 19.

Write an equation to show the reaction between Plaster of Paris and water.

Answer:

 

10th Class PS 2nd Lesson Acid Bases and Salts Textbook Questions and Answers