Kemmi is practicing a calculation of the theoretical percent water in a hydrate.

Question

Kemmi is practicing a calculation of the theoretical percent water in a hydrate. Her compound is calcium chloride dihydrate and the formula is CaCl22H2O. Help her with the calculations. Report all the answers with three significant digits and with appropriate units.

A) Calculate the mass of water in the hydrate, based on the formula. Remember there are two water molecules present. (Three significant digits, units of g)

B) Calculate the total molecular mass of the hydrated salt. Remember to include the salt and the water portion. (Three significant digits, units of g)

C) Calculate the percent water in the hydrate. Use the equation in Part H of the Module 3 Lab 1 Procedure to help. (Three significant digits, units of %)

Explanation / Answer

There are two molecules of water present is CaCl2. 2H2O.

Molar mass of water is 18.01528 g/mol.

So, mass of two moles of water is 2 * 18.01528 g = 36.03056 g.

Now, molar mass of CaCl2. 2H2O is 147.0146 g/mol

So, mass percent of water in CaCl2. 2H2O is

(36.03056 g/147.0146 g)*100 % = 24.51 %

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