determine the mole ratio

Question

a chemist reacted measured volumes of a 0.50 M copper nitrate solution with measured volumes of 0.50M sodium carbonate solution. The mass of the precipitate formed was measured and plotted. How do you determine the stoichiometric ratio between the reactants

 

Answer 1

The question is whether it is copper(I) nitrate or copper(II) nitrate.  The former is CuNO₃ and the latter is Cu(NO₃)₂.

If it is copper(I) nitrate, you have the following:

2CuNO₃(aq) + Na₂CO₃(aq) ==> Cu₂CO₃(s) + 2NaNO₃(aq)

 

If it is copper(II) nitrate, you have the following:

Cu(NO₃)₂(aq) + Na₂CO₃(aq) ==> CuCO₃(s) + 2NaNO₃(aq)

 

From the mass of the ppt and the known volumes of reactants, you can determine if the 1 mole copper nitrate reacts with 1 moles of sodium carbonate (second reaction), or if 2 moles of copper nitrate reacts with 1 moles of sodium carbonate (first reaction).  Then you know if the mole ratio between reactants is 1:1 or 2:1