Test: Acids, Bases and Salts - ACT MCQ

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.

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.

According to Bronsted concept of acids and bases, the two conjugate pairs in the above-given equation NH₃ + H₂O ⇌ NH₄ + OH^– are Ammonia – ammonium Ion and water – Hydroxide ion. Here acids are water and ammonium ion.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.