Question

2.55 gram of an alloy of silver and zinc on treatment with excess dilute hydrochloric acid gave 170 CC Of

Answer 1

The percentage composition of the alloy : 19.35% Zn, 80.65%Ag

Further explanation

Given

2.55 gram of an alloy

170 cc (170 ml=0.17 L) of  Hydrogen gas(H₂)

Ar Zn = 65. H=1

Required

The percentage composition

Solution

Silver remained unsolved⇒no reaction

Hydrogen gas from reaction of Zn

Zn+2HCl⇒ZnCl₂ + H₂

mol H₂ at STP (STP⇒1 mol = 22.4 L) :

$\tt \dfrac{0.17}{22.4}=0.00759~moles$

From equation, mol ratio Zn : H₂ = 1 : 1, so mol H₂ = 0.00759

Mass Zn :

$\tt mass=mol\times Ar\\\\mass=0.00759\times 65\\\\mass=0.49335~g$

Mass Silver :

$\tt 2.55-0.49335=2.05665~g$

Percent composition :

• Zn

$\tt \dfrac{0.49335}{2.55}\times 100\%=19.35\%$

• Ag

$\tt \dfrac{2.05665}{2.55}\times 100\%=80.65\%$