Question

5g sample of brass was dissolved in 1 litre dil H2SO4. 20ml of this solution was mixed with KI and the liberated iodine required 20ml of 0.0327 M hypo solution for titration. Calculate the percentage of copper in the alloy?

Answer 1

Reaction between copper and iodine and hypo is as follows: 

2Cu2+ (aq) + 2I- (aq) ---> 2 Cul (s) + l2(aq) 

2 s203 - (aq) + l2 ---> s4O6 2- (aq) + 2 l- (aq) 

Iodine generated by 2 moles of Cu oxidizes 2 moles of hypo 

 

 

N1V1 (hypo) = N2V2 (Cu+Kl) 

N2 = N1xv1(hypo)/v2(cu+k1) = 0.0327x20/20 = 0.0327 

Weight of Cu in sample = 0.0327 x molar mass of Cu 

= 0.0327 x 63.5460 = 2.077 g 

 

Percent of Copper in brass = 2.077/5 x 100 = 41.54%

Answer 2

copper reacts with iodine as;

2Cu²⁺  + 2I⁻ →2 Cul + l₂ 

2 S₂0₃⁻+ l₂ →S₄O₆²⁻ + 2 l⁻  

Iodine generated by 2 moles of Cu oxidizes 2 moles of sulphur oxide

 

 

N₁V₁ (S2O3) = N₂V₂ (Cu+Kl) 

N₂ = N₁ x V₁/V₂

= 0.0327x20/20 

= 0.0327 

Weight of Cu in sample = 0.0327 x molar mass of Cu 

= 0.0327 x 63.5460 = 2.077 g 

Percent of Copper in brass = 2.077/5 x 100 

= 41.54%