Percent Yield Lab: Explained & Solutions

Data Table

Analysis

a. Identify the precipitate that was formed in the reaction : Fe _(s) + CuCl_{2 (aq)} → Cu _(s) + FeCl_{2 (aq)}

When solid iron (steel wool) reacts with copper(II) chloride, a single displacement reaction, iron displaces copper in Copper(II) chloride; the new products are solid copper precipitate and aqueous iron(II) chloride.

b. Which reactant was the limiting reactant, and which was the excess reactant?

Therefore, the limiting reactant is Iron (Fe), and the excess reactant is Copper (II) Chloride (CuCl₂)

Calculate the theoretical yield of the precipitate, in grams, using the mass of the steel wool that you measured in Procedure step 5

Mols of Copper: 0.018 mols

Molar Mass of Copper: 63.55 g

               m_Cu = M x n

               m_Cu = (0.018 mol)(63.55 g/mol)

               m_Cu = 1.14 g

The theoretical yield of copper precipitate, given the mass of steel wool utilized, is 1.14g.

• Compare the mass of the precipitate you collected (the actual yield) with the expected theoretical yield; Describe your observations

Mass of Precipitate = 110.02 – 108.43 = 1.59g

Therefore, the actual yield is 1.59 g

The actual yield is 1.59 g as opposed to the expected yield of 1.14 g. The actual yield is higher than the theoretical yield which leads to conclude that there were some errors during the procedure.

The final yield mostly consisted of brown copper precipitate with very slight tints of green iron(II) chloride.

• Calculate the percentage yield of this reaction

% yield = (actual yield / theoretical yield) x 100

             = (1.59 / 1.14) x100

             = 139%

Therefore, the percent yield is 139%

• Suggest reasons why the percentage yield of this reaction was not 100%

A few possible reasons as to why the percent yield was over 100% are:

• The copper might not have dried properly as no heating pads or oven were used to dry the water. The beakers were just left to dry which may have prevented all the water from drying out completely.

• There might have been errors during the decantation process resulting in traces of FeCl₂ still being in the solution,  adding extra mass to the final yield.

• As the experiment was done in an open system and the beaker was left to dry in an open environment, other external factors such as humidity, presence of oxygen and temperature may have had an effect on the final yield.

• Systematic errors caused due to faulty equipment may result in different recordings.