NCERT SOLUTIONS CLASS X CH-2 ACID, BASE AND SALT

NCERT INTEXT QUESTIONS

Q.1) You have been provided with three test tubes. One of them contains distilled water and the other two contains 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?

Solution - (a) Put red litmus paper turn by turn in each of the three test tubes. The solution which turns the red litmus paper to blue will be a basic solution. Here, the blue litmus paper formed can now be used to test the acidic solution. 

(b) Put this blue litmus paper in the remaining two test tubes, one by one. The solution which turns the blue litmus paper to red will be the acidic solution.

(c) The solution which has no effect on any litmus paper will be neutral and hence, it will be distilled water.

Q.2) Why should curd and sour substances not be kept in brass and copper vessels?

Solution- Curd and other sour substances should not be kept in brass and copper vessels. This is because curd and other sour substances contains acid which can react with these vessels to form poisonous compounds that can cause food poisoning and damage health.

Q.3) Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test the presence of this gas?  

Solution- When a metal reacts with an acid, usually hydrogen gas is liberated . For example zinc reacts with Dil sulphuric acid as follows

Zn + H2SO4 --> ZnSO4 + H2 

The hydrogen gas evolved can be tested by passing the gas through soap solution and then bringing a burning candle near the soap bubble filled with gas. The soap bubble bursts and hydrogen gas burns with a pop sound. 

Q.4) A metal A reacts with Dil 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.

Solution The gas that extinguishes a burning candle is carbon dioxide. It is formed by the action of Dil hydrochloric acid on a metal carbonate or metal hydrogen carbonate and produce effervescence. Since one of the compounds formed is calcium chloride, this shows that the metal compound is calcium carbonate. It cannot be calcium hydrogen carbonate because calcium hydrogen carbonate is found in solution. Thus, the metal compound A is calcium carbonate

Calcium carbonate reacts with Dil hydrochloric acid to form calcium chloride, carbon dioxide and water.

CaCO3 + 2HCl ----> CaCl2+CO2 + H2O

Q.5) Why do HCl ,HNO3 etc. Show acidic character in aqueous solutions while solutions of compounds like C2H5OH and glucose do not show acidic character?

Solution HCl, HNO3 etc ionise in the aqueous solution to produce H+ ions. Hence, they show acidic character. Compounds like C2H5OH and glucose do not ionise in the aqueous solution to give H+ ions that is hydrogen present in them is non ionisable . Hence, they do not show acidic character.

Q.6) Why does an aqueous solution of an acid conduct electricity?

Solution An acid in the aqueous solution ionise to produce H+ ions and the corresponding negative ions . For example HCl gives H+ and Cl- ions. Due to the presence of ions in the solution, it conducts electricity. 

Q.7) Why does dry HCl gas not change the colour of the dry litmus paper?

Solution Dry HCl gas does not change the colour of the dry litmus paper because it has no hydrogen ions in it.

Q.8) While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid? 

Solution Dilution of concentrated acid with water is highly exothermic process. If water is added into acid , the heat produced is so large that the solution may splash out and the beaker in which it is carried out may break due to excessive heat. Hence, dilution is done by adding acid to water.

Q.9) How is concentration of hydronium ion affected , when a solution of an acid is diluted?

Solution When a solution of an acid is diluted, the concentration of hydronium ion per unit Volume decreases.

Q.10) How is concentration of hydroxide ion affected when excess base is dissolved ta solution of sodium hydroxide?

Solution On dissolving excess base in a solution of sodium hydroxide, concentration of hydroxide ion per unit Volume in the solution increases. 

Q.11) You have two solutions A and B . The pH of the solution A is 6 and pH of the solution B is 8. Which solution has more hydrogen ion concentration? Which of these is acidic and which is basic?

Solution-The pH of a solution is inversely proportional to its hydrogen ion concentration. This means that the solution having lower pH will have more hydrogen ion concentration. Thus, solution A will have more hydrogen ion concentration.

Solution A is acidic and solution B is basic.

Q.12) What effect does the concentration of H+ ions have on the acidic nature of the solution?

Solution water contains exactly the same number of H+ and oH- ions. Acidic solution contains more hydrogen ions than water. Higher the concentration of H+ ions in a solution, more acidic is the solution.

Q.13) Do basic solutions also have H+ ions ? If yes ,then why are these basic?

Solution - Basic solutions also have H+ ions in addition to OH- ions. They are basic because in these solutions OH- ion concentration is greater than H+ ion concentration.