Finding The Formula Of A Hydrate: Lab Report (CE)

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Finding the Formula of a Hydrate – Lab Report (DCP, CE)

Introduction and Overview: A hydrate is a chemical that has water molecules loosely bonded to it. The water molecules are not actually part of the formula, so the formula is written slightly differently. An example would be CaSO4 . 3H2O. This chemical would be called calcium sulfate trihydrate. When finding the mass of this chemical, you find the mass of the calcium sulfate and then add 3 times the mass of water to it. (40.08 + 32.066 + 4(15.999) + 3(2(1.0079) + 15.999)) = 190.19 g/mol.

The water can easily be removed from a hydrate just by heating strongly. You will be weighing a hydrate and heating it to remove the water (now called "anhydrous salt") and weigh it again. You can now find the percent of the anhydrous salt and the water. By finding a mol ratio, you can
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Find the average of your 3-4 trials.
2. Use your average values to calculate the molecular formula of the hydrate (the value of x).
3. What is the molecular formula of this hydrate?

*Answers to questions above...

1) 4.078 + 4.056 + 4.095 + 4.014 = 16.24/4 = 4.061 ±0.008 grams

2.253 + 2.256 + 2.261 + 2.249 = 9.019/4 = 2.255 ±0.012 grams

2) Mass of water = 4.061 – 2.255 = 1.806 ±0.020 grams

Then convert to moles  =1.806 ±0.020 / 18 g = 0.100 ±0.020 mol H2O

Covert to moles of copper Sulfate  =2.255 ±0.012 / 159.6 = 0.0141 ±0.012 mol CuSO4

Finally simplify those values by dividing by the smallest number  =0.0141 ±0.012 / 0.0141 ±0.012 = 1
Then:
0.100 ±0.020 /0.0141 ±0.012 = 8

3) Molecular Formula= CuSO4 x 8H2O

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