Question

A white crystalline salt x' when heated crumbles with a decrepitating noise to form a fusible mass y' which is yellow when hot. A reddish brown gas z' also evolves which has a pungent smell and turns moist blue litmus red.

a.Identify x' , y' and z' (1 )

b.Write the chemical equation for the decomposition of x'. (1)

c.Name the other gas evolved in this

Answer 1

$\bold{GIVEN}$

A white crystalline salt $\bold{X}$ is heated, which gives decrepitating noises, to form a fusible mass$\bold{Y}$ which is yellow when hot.

We know zinc oxide and lead (II) oxide both are yellow when hot and white wgem cold .So, the given salt can either be of zinc or lead.But only lead nitrate is the crystalline salt which when heated produces crackling sounds and forma a buff yellow mass of lead oxide when hot and gives out two gases which are nitrogen di oxide and oxygen.

a) $\bold{x \implies Lead \: nitrate }$

$\bold{y \implies Lead \: (II) \: oxide }$

$\bold{z \implies Nitrogen \: dioxide }$

A reddish brownish gas with pungent smell.

b)

$Pb(NO_3)_2 \longrightarrow 2 PbO + 4NO_2 + O_2$

c) The other gas evolved is oxygen.

Tests:-

◼Neutral to red or blue litmus.

◼Rekindles glowing splinter , when brought in contact with it.