Purpose: To determine the empirical and molecular formula of a hydrated salt

1. Lab 5 Determination of the percentage of water in a hydrated salt • Purpose: • To determine the empirical and molecular formula of a hydrated salt • In this experiment you will learn how to: • 1- heat a sample in a crucible with a Bunsen burner. • 2- use the method of “weight-by-difference” to determine mass quantities • 3- convert grams to moles • 4- determine the percent of water lost by heating a hydrated sample.

2. Introduction Hydrated compounds are excellent for demonstrating how mass can be used to determine empirical formula, because, provided the salt is stable enough, all you have to do is heat them up to drive off water. The weight difference between the hydrated salt and the anhydrous salt is the mass of water. MgSO4 + x H2O Anhydrous salt 7 Hydrated salt

3. Procedure • 1- Clean and dry a porcelain crucible. • Weigh the empty crucible and record its weight. W1: Wt of empty crucible • 2- Place about 2 g of the hydrated salt and weigh the crucible with the sample. W2: Wt of crucible + hydrated salt • 3- Put the crucible on the triangle and start heating slowly. • Continue heating for 15 minutes.

4. 4- Cool the crucible at room temperature while covered with its lid. • Weigh the crucible with the sample and record the weight. • 5- Repeat heating gently for another 5 minutes. Cool, reweigh and record the weight until you reach a constant weight. W3: Wt of crucible + anhydrous salt • Calculate the • 1- mass % • 2-number of moles • 3- molar ratio of anhydrous salt to water in its hydrated form. • 4-Suggest the molecular formula of the hydrated salt.

5. Calculation ? ? × 100

6. 3- molar ratio of anhydrous salt to water in its hydrated form. • Hydrated salt : X water 4- Suggest the molecular formula of the hydrated salt Haydratedsalt.X H2O