Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Q.1. Assertion (A) : The acid must always be added to water with constant stirring.
Reason (R) : Mixing of an acid with water decreases the concentration of H+ ions per unit volume.
Q.2. Assertion (A) : Copper sulphate crystals are wet because it contains water of crystallisation.
Reason (R) : Water of crystallisation is the fixed number of molecules of water present in one
formula unit of salt.
Answer(d) The Assertion is false. Copper sulphate is not wet. It is an hydrated salt, as it contains water molecules.
Q.3. Assertion (A) : The aqueous solutions of glucose and alcohol do not show acidic character.
Reason (R) : Aqueous solutions of glucose and alcohol do not give H+ ions.
Q.4. Assertion (A) : HCl gas does not change the colour of dry blue litmus paper.
Reason (R) : HCl gas dissolves in the water present in wet litmus paper to form H+ ions.
Q.5. Assertion (A) : Weak acids have low electrical conductivity.
Reason (R) : Strong acids and weak acids have equal concentration of hydrogen ions in their solutions.
Q.6. Assertion (A): Pure water is neither acidic nor basic.
Reason (R) : The pH of a solution is inversely proportional to the concentration of hydrogen
ions in it.
Q.7. Assertion (A) : During electrolysis of concentrated aqueous solution of sodium chloride, hydrogen is produced at anode and chlorine gas is produced at cathode.
Reason (R) : Ions get attracted to oppositely charged electrodes.
Q.8. Assertion (A) : Baking powder is used in making cake instead of using only baking soda.
Reason (R) : Baking powder contains tartaric acid which reacts with sodium carbonate and removes bitter taste.
Q.9. Assertion (A) : The chemical formula of bleaching powder is CaOCI.
Reason (R) : Calcium oxide reacts with chlorine to form bleaching powder.
Q.10. Assertion (A): Plaster of Paris is stored in a moisture proof container.
Reason (R) : Plaster of Paris sets into a hard mass on wetting with water to form anhydrous calcium sulphate.
Q.11. Assertion (A): The chemical name of bleaching powder is calcium oxychloride.
Reason (R): Bleaching powder is used as an oxidising agent in chemical industries.
Q.12. Assertion: The process of dissolving an acid or a base in water is highly exothermic reaction.
Reason: Water must always be added slowly to acid with constant stirring.
AnswerAnswer: (c) The process of dissolving an acid or a base in water is highly exothermic reaction. Acid must always be added slowly to water with constant stirring.
Q.13. Assertion : Phenolphthalein is an acid-base indicator.
Reason: Phenolphthalein gives different colours in acidic and basic medium.
Q.14. Assertion: Calcium sulphate hemihydrate, CaSO4.1/2 H20 is called plaster of Paris.
Reason: Plaster of Paris is used for producing moulds for pottery and ceramics and casts of statues.
Q.15. Assertion : pH = 7 signifies pure water.
Reason: pH of acetic acid is greater than 7.
AnswerAnswer: (c) pH of acetic acid is less than 7.
Q.16. Assertion : HCl is a stronger acid than acetic acid.
Reason: On dissociation, HCl yields lesser hydrogen ions for the same concentration as compared to acetic
AnswerAnswer: (c) On dissociation, HCl yields more hydrogen ions for the same concentration as compared to acetic acid.
Q.17. Assertion : pH of ammonium nitrate solution is acidic.
Reason: Solution of a salt of weak base and strong acid is acidic.
AnswerAnswer: (a) Ammonium nitrate is a salt of ammonium hydroxide (weak base) and nitric acid (strong acid).
Q.18. Assertion : Phosphoric acid is a weak acid.
Reason : Phosphoric acid when dissolved in water dissociates partially and produces very little H* ions.
Q.19. Assertion : Antacids neutralize the effect of extra acid produced in the stomach during indigestion and thus provide relief.
Reason: Antacids are mild bases.
Q.20. Assertion : Acetic acid does not act as an acid in benzene solution.
Reason: Benzene is non-polar.
AnswerAnswer: (a) For ionization of an acid, polar solvents (like water) are required. As ionization does not take place in non-polar solvents (like benzene) so acetic acid does not acts as an acid.
Q.21. Assertion : Bleaching powder reacts with dilute acids to evolve chlorine.
Reason: The chlorine liberated by the action of dilute acids on bleaching powder is called available chlorine.
Q.22. Assertion : Sodium carbonate pentahydrate is also known as washing soda.
Reason: Chief raw materials for the manufacture of washing soda are NH3, NaCl and CaCO3.
Q.23. Assertion: Common salt is used for the preparation of many chemicals such as sodium hydroxide, bleaching powder, baking soda, washing soda etc.
Reason : Main source of sodium chloride is sea water.
Q.24. Assertion : AlCl3 is a basic salt.
Reason: AlCl3 is a salt of strong acid and a weak base.
Q.25. Assertion : Baking soda is prepared by chlor-alkali process.
Reason: Brine decomposes to sodium hydroxide on passing electricity through it.
Q.26. Assertion : Salt of KNO3 is formed by strong base and weak acid.
Reason: Salt of NH4Cl is formed by weak base and strong acid.
Q.27. Assertion : Strength of the acid or base decreases with dilution.
Reason: Ionization of an acid or a base increases with dilution.
Q.28. Assertion : Higher the H ion concentration, lower is the pH value.
Reason: The pH of a neutral solution=7, that of a basic solution < 7 and that of an acidic solution > 7.
Q.29. Assertion : CH3COOH is used as vinegar in cooking and food preservatives.
Reason: Strong acids are those acids which ionise almost completely in aqueous solution and hence produce a large amount of Hions.
Q.30. Assertion : Tooth decay starts when the pH of the mouth is lower than 5.5.
Reason: Enamel starts corroding below 5.5 pH.