6.9 – NOTES Formula of a Hydrate

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Presentation transcript:

6.9 – NOTES Formula of a Hydrate

C. The formula of a hydrate Hydrate: - salt crystal with water trapped inside In order to determine the formula for a hydrate, you need to determine the mass of water in a sample by performing an experiment. From the masses of the anhydrous compound and the water, the formula can be found from the mole ratio.

Examples: 1. Borax, hydrated sodium tetraborate, Na2B4O7·? H2O, is 52.8% anhydrous sodium tetraborate and 47.2% water. Determine the formula and name the hydrate. Na2B4O7 – 52.8 g (1 mol/ 201.2 g) = 0.26242 / 0.26242 = 1 H2O – 47.2 g (1 mol/ 18.0 g) = 2.6222 / 0.26242 = 10 Na2B4O7  10 H2O

2. A hydrate of cobalt(II) chloride was analyzed in the lab 2. A hydrate of cobalt(II) chloride was analyzed in the lab. The sample had a mass of 3.73 grams, and 1.69 grams of mass was lost. What is the formula of the hydrate? **when calculating the formula of a hydrate, must start with the mass of the ANHYDROUS and water CoCl2 – 3.73 – 1.69 = 2.04g (1 mol/ 129.9 g) = 0.01570 / 0.01570 = 1 (hydrate – water = anhydrous) H2O – 1.69 g (1 mol/ 18.0 g) = 0.09388 / 0.01570 = 6 CoCl2  6H2O

3. From the data below, determine the formula of a hydrate of iron (III) nitrate: Mass of crucible and cover 31.23 g Mass of crucible, cover and Fe(NO3)3 hydrate 35.46 g Mass of crucible, cover and anhydrous Fe(NO3)3 33.76 g Mass of anhydrous – 33.76 – 31.23 = 2.53 g Mass of water – 35.46 – 33.76 = 1.70 g Fe(NO3)3 – 2.53 g (1 mol / 241.8 g) = 0.01046 / 0.01046 = 1 H2O – 1.70 g (1 mol/ 18.0 g) = 0.09444 / 0.01046 = 9 Fe(NO3)3  9 H2O