Whats the correct answer?

Question

One way in which the useful metal copper is produced is by dissolving the mineral azurite, which contains copper(II) carbonate, in concentrated sulfuric acid. The sulfuric acid reacts with the copper(II) carbonate to produce a blue solution of copper(II) sulfate. Scrap iron is then added to this solution, and pure copper metal precipitates out because of the following chemical reaction:

Fe(s) +CuSO4(aq) →Cu(s)+FeSO4(aq)



Suppose an industrial quality-control chemist analyzes a sample from a copper processing plant in the following way. He adds powdered iron to a 

150.mL

 copper(II) sulfate sample from the plant until no more copper will precipitate. He then washes, dries, and weighs the precipitate, and finds that it has a mass of 

122.mg

.

Calculate the original concentration of copper(II) sulfate in the sample. Round your answer to 

3 significant figures.

Answer 1

The balanced equation Fe(s) +CuSO4(aq) →Cu(s)+FeSO4(aq), indicates that Cu(s) is produced from CuSO4 in the ratio of the molecular mass of CuSO4 to the atomic mass of Cu(s). From the periodic table, this ratio is found to be 159.6 g CuSO4 / 63.546 g Cu.

Using this ratio, the mass of Cu(s) found can be multiplied by the above ratio:

159.6 g CuSO4 / 63.546 g Cu. x 0.122 g Cu = 0.306 g CuSO4 in 150 mL of the sample. To convert this to moles, divide by the molecular mass of CuSO4.

0.306 g / 159.6 g/mole = 0.00192 moles. As this is in 150 mL of solution, the molarity is

0.00192 moles / 150 mL x 1000 mL/L = 0.0128 M.

Please check math.