when few drops of liquid "X" are added to distilled water, it observed that the pH of water decrease. identify the liquid sample X and al So give the reason for the change in the distilled water
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NCERT IN–TEXT QUESTIONS SOLVED
Q1. 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?
Ans. Add few drops of solution from all three test tubes on the red litmus paper separately. The solution which turns red litmus to blue contains basic solution. Use this blue litmus paper to test the solutions in other two test tubes. The solution from the test tube which turns blue litmus paper to red will be the acidic solution and solution of the test tube which do not change either red or blue litmus paper contain water.
Q2. Why should curd and sour substances not be kept in brass and copper vessels?
Ans. Curd and sour substances contain acids which can react with copper vessels and brass to form toxic compounds.
Q3. 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?
Ans. When an acid react with a metal it liberates hydrogen gas.
E.g., Zn(s) + 2HCl(aq) → ZnCl2 (aq) + H2(g)
To test the presence of H2 gas, bring a burning splinter near the mouth of the test tube where H2 gas is released, the match stick bums with a pop sound.
Q4. 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.
Ans. Metal compound A is CaCO3
Gas evolved is CO2
Balanced equation:
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
Q5. Why do HCl, HNO3 etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Ans. Solutions like HCl, HNO3 etc. get ionised in aqueous solutions and due to the presence of H+ ions they show acidic characters. While solutions of compounds like alcohol and glucose do not form any such ions so they do not show acidic characters.