Stoichiometry of a Precipitation Reaction

Hands-On Labs, Inc.
Version 42-0201-00-02

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.

 

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.

 

 

D.        Determine the quantity (g) of pure MgSO₄ in 2.4 g of MgSO₄•7H₂O.

 

 

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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