Question

a) What is universal indicator .

b) What is the chemical equation involved in the preparation of sodium hydroxide. Name the process.

c) Give reason for; Dry hydrogen chloride gas does not turn blue litmus red whereas dilute hydrochloric.

Answer 1

a)A universal indicator is a pH indicator composed of a solution of several compounds that exhibits several smooth colour changes over a pH value range from 0 to 14 to indicate the acidity or alkalinity of solutions, where 7 indicates neutral.

b)Electrolysis of brine solution (NaCl) gives NaOH.

At anode -
2Cl ^- -----> Cl2 + 2 electrons

At cathode -
2H+ + 2 electrons ------> H2

In the solution, Na+ + OH- ------> NaOH

This process is known as Chlor alkali process

C)
This is because gaseous HCl does not dissociate to give up protons and chloride ions. But, in aqueous solutions HCl does dissociate and exist in ionic form:

H2O(l)+HCl(aq)⟶H3O+(aq)+Cl−(aq)

HX2O(l)+HCl(aq)⟶HX3OX+(aq)+ClX−(aq)


Thus it acts as a typical Bronsted acid (proton donor) in an aqueous environment. In this case, water is gaining a proton (H+)(HX+)(HX+), so it is a base, while HCl is giving one away, so it is an acid.

Therefore it is able to turn the blue litmus paper red (a behaviour typical of acids).