I/GCSE Past Paper Question Analysis Topic: Chemistry - Water
(1) Why does distilled water not conduct electricity, whereas rain water does?
Solution: Distilled water is pure form of water which do not contain any solute in it. Therefore it cannot conduct electricity because it does not contain ions while rain water contains dissolved salts and acids which dissociates in ions and conducts electricity.
(2) Why do acids not show acidic behavior in the absence of water?
- Water is known as a universal solvent as maximum compounds are easily soluble in it.
- In water majority of compounds dissociate into their constituent ions.
- The acidic behavior of acid is due to the presence of hydrogen ions H+ as pH is directly proportional to H+ concentration.
- In the absence of water, an acid will not show its acidic behavior because acids do not dissociate to produce H+(aq) ions.
For example, hydrochloric acid can easily release its H+ ion in water to form hydronium ion H3O+ and Cl− ion.
(3) 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?
1. Add few drops of solution from all three test tubes on the red litmus paper separately.
2. The solution which turns red litmus to blue contains basic solution.
3.Use this blue litmus paper to test the solutions in other two test tubes.
4.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.
Drafted by Quincy (IGCSE Chemistry Prep)