This set of Class 11 Chemistry Chapter 7 Multiple Choice Questions & Answers (MCQs) focuses on “Equilibrium – Acids, Bases and Salts”.
1. Which of the following is not a property of an acid according to Robert Boyle?
a) turns blue Litmus red
b) sour in taste
c) neutralize bases
d) bitter in taste
Explanation: According to Robert Boyle, acids are the substances which have a sour taste, turns blue Litmus red, liberate hydrogen with metals conduct electricity in aqueous solution and neutralize bases. They do not have a bitter taste.
2. Bases turn red litmus blue.
Explanation: Litmus is a mixture of different dyes from lichens that is water soluble. Acids change blue litmus red and bases change red litmus blue. The original colour of Litmus is purple. The pH of a base is in between 7 and 14.
3. HCl is an Arrhenius ___________
Explanation: According to the Arrhenius concept of acids and bases, an acid is a chemical substance which dissociates in aqueous solution to give hydrogen ions or hydronium ions. Therefore HCl is an Arrhenius acid.
4. A proton donor is a ____________ substance.
Explanation: According to the bronsted concept of acids and bases, an acid that is a Proton Donor is proton genic and a base that is a Proton acceptor is protophilic, while an amphoteric substance is both base and acid.
5. Arrhenius theory could not explain the acidic and basic behaviour in non-aqueous solutions.
Explanation: The major drawback of Arrhenius theory is that it fails to explain the acidic and basic behaviour in non-aqueous solutions. It cannot explain the acidic character of aluminium chloride, Boron fluoride and basic character of NH3 PH3.
6. A strong acid has a ______________
a) weak conjugate acid
b) weak conjugate base
c) strong conjugate base
d) strong conjugate acid
Explanation: As per the conjugate pairs in the bronsted concept of acid and bases, strong acid has a weak conjugate base and weak acid has a strong conjugate base. The strong base has weak conjugate acid and the weak base has strong conjugate acid.
7. Which of the following substances cannot act as both acid as well as a base?
a) amphoteric substance
b) amphiprotic substance
Explanation: Amphoteric or amphiprotic substance or ampholytes are the substances which act as an acid as well as a base and example for this is water. It acts as an acid with Ammonia and base with acetic acid.
8. Which of the following is a Lewis base?
b) magnesium chloride
c) aluminium chloride
d) sodium ion
Explanation: Lewis base is a chemical substance which can donate a pair of electrons. Examples are neutral molecules containing lone pairs like ammonia, negatively charged species and the ligands in coordination species.
9. Silver ion is a Lewis acid.
Explanation: Lewis acid is a chemical substance which can accept a pair of electrons. Examples are molecules with an incomplete octet of central atom simple cations like silver Ion molecules in West central atom has vacant d orbitals.
10. Lewis concept does explain the behaviour of __________
c) protonic acids
d) amphoteric substances
Explanation: The major limitations of the Lewis concept is that it does not explain the behaviour of protonic acids such as hydrochloric acid, sulphuric acid and nitric acid. It also does not predict the magnitude of the relative strength of acids and bases.
11. Identify a conjugate pair in the equation: NH3 + H2O \(\rightleftharpoons\) NH4+ + OH–.
a) ammonia and water
b) water and hydroxide ion
c) ammonium ion and hydroxide ion
d) ammonia and hydroxide ion
Explanation: According to Bronsted concept of acids and bases, the two conjugate pairs in the above-given equation NH3 + H2O \(\rightleftharpoons\) NH4 + OH– are Ammonia – ammonium Ion and water – Hydroxide ion. Here acids are water and ammonium ion.
12. Which of the following is the strongest hydracid known?
Explanation: HClO4 which is called Perchloric acid, is the strongest hydracid known and HCN called Formonitrile, is the weakest hydracid known. CsOH called Caesium Hydroxide is the strongest base known.
13. Hydroxide ion is a bronsted base.
Explanation: According to the bronsted concept of acids and bases, acid is a chemical substance that can donate a Proton to some other substance and base is a chemical substance that can accept a Proton from other substance.
14. Water in case of HCl acts as a/an ___________, in case of ammonia acts as a/an ________
a) base, base
b) base, acid
c) acid, base
d) acid, acid
Explanation: Water acts as a base in the presence of hydrochloric acid and acts as an acid in the presence of ammonia. According to bronsted, acid is a chemical substance that can donate a Proton and base can accept a Proton from other substances.
15. Which of the following is not a Lewis acid?
a) aluminium chloride
b) sodium ion
c) sulphur tetrafluoride
d) hydroxide ion
Explanation: Lewis acids are molecules with an incomplete octet of central atoms like aluminium chloride, simple cations like sodium ion, and molecules in which the central atom has vacant d-orbital like sulphur tetrafluoride, but hydroxide ion is a negatively charged species. So it is not a Lewis acid.
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