Question

A student mixes together a solution of cobalt(II) chloride with a solution of ammonium hydroxide in the lab. She filters the precipitate and dries it. The observations that she records are:

Reactants

volume of cobalt (II) chloride = 100 mL concentration of cobalt (II) chloride = 0.214 mol/L

volume of ammonium hydroxide = 130 mL concentration of ammonium hydroxide = 0.315 mol/L Products

mass of filter paper = 1.15 g mass of filter paper + dried precipitate = 2.90 g

a. Based on the measurements of each solution used, what mass of precipitate should be

produced in theory?


b. What percent yield has she achieved in this reaction?


c. Identify one reason why she might not have achieved a 100% yield.

Answer 1

CoCl₂+2NH₄OH --> 2NH₄Cl+Co(OH)_2(s);

a. E(CoCl₂)=0.1*0.214/=0.0214 mol/L;

E(NH₄OH)=0.13*0.315/2=0.0205 mol/L;

NH4OH is the limitant reactant;

m(Co(OH)₂)=0.0205*Mr(Co(OH)2)=0.0205*93=1.91 g; - theoretical yield;

b.% yield=(2.90-1.15)/1.91 *100%=91.62%;

c.The reason why she couldn't achive 100% of yield might be impurities (contaminated starting materials)