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Lab 2

Stoichiometry and Percent of a Hydrate

Unit 2⏱ 90 minGuided Inquiry

Overview

How can the percent and molar ratio of water in a hydrated salt be determined from a reaction in which a hydrated salt is produced?

Objectives

  • How can the percent and molar ratio of water in a hydrated salt be determined from a reaction in which a hydrated salt is produced?
  • Connect observations to AP Chemistry models and calculations.
⚠️ Wear protective goggles and an apron. Follow your teacher’s safety directions for all chemicals and equipment.

Materials Needed

Procedure

1

DAY 1 Measure exactly 2.19 grams of zinc acetate dihydrate.

2

Record this mass in your data table.

3

Place the zinc acetate dihydrate into a clean 250-mL beaker and add 50 mL of distilled water to it.

4

Stir thoroughly to make sure all of the crystals are dissolved.

5

Rinse off the stirring rod when done.

6

Measure exactly 2.60 grams of sodium phosphate tribasic hydrate.

7

Place the sodium phosphate tribasic hydrate into a clean 100-mL beaker and add 50 mL of distilled water to it.

8

Pour the sodium phosphate tribasic hydrate solution into the 250-mL beaker containing the zinc acetate dihydrate solution.

9

Record your observations.

10

Collect the precipitate that is formed by filtering the solution through a Buchner funnel using suction.

Pre-Lab Questions

1. What is another name for a double replacement reaction? Define the terms hydrated and anhydrous salt. How can you turn a hydrated salt into an anhydrous salt? How can you turn an anhydrous salt into a hydrated salt? Based on the solubility rules, why was zinc phosphate insoluble, but sodium acetate was soluble. Suggest some sources of error in this experiment that would explain why you would got less than 100% yield. Suggest some sources of error in this experiment that would explain why you would get more than 100% yield. Why must you immediately mass your anhydrous salt after heating? How well did your empirical formula agree with that of the hydrated salt? Explain any inconsistencies. How would you name your hydrated salt, Zn3(PO4)2 . XH2O? (where X is the number you calculated).

Post-Lab Questions