Stoichiometry of a Precipitation Reaction
Hands-On Labs, Inc.
Version 42-0201-00-02 Lab Report Assistant
This document is not meant to be a substitute for a formal laboratory report. The Lab Report
Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data
tables that should be addressed in a formal lab report. The intent is to facilitate students’
writing of lab reports by providing this information in an editable file which can be sent to an
instructor. Exercise 1: Stoichiometry and a Precipitation
Reaction
Data Table 1. Stoichiometry Values.
Initial: CaCl2•2H2O (g)
Initial: CaCl2•2H2O (moles)
Initial: CaCl2 (moles)
Initial: Na2CO3 (moles)
Initial: Na2CO3 (g)
Theoretical: CaCO3 (g)
Mass of Filter paper (g)
Mass of Filter Paper + CaCO3 (g)
Actual: CaCO3 (g)
% Yield: 1.0 g
0.0068 mol
0.0068 mol
0.0068 mol
0.8 g
0.68 g
0.9 g
1.5 g
0.6 g
86% Questions
A. A perfect percent yield would be 100%. Based on your results, describe your degree of
accuracy and suggest possible sources of error.
My percent yield was 86 percent. It was not the optimal 100 percent, but it was on the
higher range. It could be possible that I could have had a higher percent yield had the scale
not have gone only to the tenth place. My theoretical yield was 0.68 g. But because the scale
only went to the tenths place I cannot speak with certainty that the weight of my product
was only 0.6 g. It's possible that it could have been 0.68 g but I will never know that. There could have been other sources of error such as not calculating correctly or not weighing
correctly.
B. What impact would adding twice as much Na2CO3 than required for stoichiometric
quantities have on the quantity of product produced?
Excess product of CaCO3 would be produced because there wouldn't be enough CaCl2 to
react with Na2CO3. The purpose of stoichiometric quantities is to know the correct amount
or close to the correct amount of each reactant in order to produce a product that is close to
the theoretical amount and therefore have a higher percent yield. C. Determine the quantity (g) of pure CaCl2 in 7.5 g of CaCl2•9H2O. 7.5 g CaCl 2 •9 H 2O x (1mol CaCl 2 •9 H 2O/273.16 g CaCl 2• 9 H 2 O) x (1mol CaCl 2/1 mol CaCl 2• 9 H 2 D. Determine the quantity (g) of pure MgSO4 in 2.4 g of MgSO4•7H2O.
4 g MgSO 4 •7 H 2 O x(1 mol MgSO 4 •7 H 2O/246.51 g MgSO 4 •7 H 2O)x (1 mol MgSO 4 / 1mol MgSO 4 • E. Conservation of mass was discussed in the background. Describe how conservation of mass
(actual, not theoretical) could be checked in the experiment performed.
According to the background, our established total mass of the reactants should equal the
total mass of our on hand products. Thus we should expect a slightly smaller amount of
product since in practical experimentation a system is seldom completely closed. The
conservation of mass could be checked in our experiment by weighing the reactants and
weighing our product. The total mass of the reactants should be slightly larger than the
weight of the product.

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