Question

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

hydrogen gas of STD. If silver remained unsolved calculate the percentage Composition of the alloy .
( Alamic masses of Zn: 65, H:1)​

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 (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* Ar\\\\mass=0.00759* 65\\\\mass=0.49335~g`

Mass Silver :

`\tt 2.55-0.49335=2.05665~g`

Percent composition :

• Zn

`\tt (0.49335)/(2.55)* 100\%=19.35\%`

• Ag

`\tt (2.05665)/(2.55)* 100\%=80.65\%`