How to Understand Errors in Stoichiometry – Part 1

Stoichiometry is the relationship between the quantities of reactants and products before, during, and after chemical reactions.



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Question:

An experiment was performed to determine the moles of H2(g) formed (collected over water) when an acid reacts with Mg metal. To do this. A piece of dry Mg was weighed. Then 50 mL of H2(g) was collected. Next Mg was dried to remove about 0.1 mL of water and weighed again to see how much Mg had reacted. The volume of H2(g) was measured and converted into moles of H2(g). Which mistake will give the largest error in the result?

A. Forgetting to dry Mg before weighing
B. Failing to take the vapor pressure of water (23 torr at 250C) into account
C. Missing to convert 0C to K
D. Reading the gas-collecting container to 20 mL

Solution:


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Eerie error❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com❗

References:

‌(1)    Brown, C.; Ford, M. Higher Level Chemistry, 2nd ed.; Pearson Education: Harlow, Essex, 2014.

‌(2)    Jespersen, N. D.; Barron's Educational Series, Inc. Barron’s AP Chemistry; Barron’s Educational Series: Hauppauge, N.Y., 2012.

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