Determining the Formula of a Hydrate
Introduction:
In this lab, a hydrate was experimented on to determine the percentage composition of water that the hydrate consisted of. A hydrate is usually an ionic compound in the form of a salt that contains water in its crystalline structure. The water molecules, however, are not incorporated directly into the chemical formula and are represented like this: NiSO
4
∙ 6H which known as nickel (II) sulfate hexahydrate. Heating a hydrate will cause the water
2
O molecules to evaporate and leave what is called an anhydrous compound. It is important to find the mass of the hydrate because with that, and the mass of the product, the amount of water that the hydrate consisted of can be calculated. This then leads to being able to calculate the percentage composition among other things.
Testable Question:
What is the percentage composition of water in a hydrate of copper (II) sulfate? What is the chemical formula of CuSO
4
∙ 𝑥H
2
O ?
Materials:
Were those of page 304 of the Nelson Chemistry 11 textbook on Novemeber 15 th , 2013.
Procedure:
Were those of page 304 of the Nelson Chemistry 11 textbook on Novemeber 15 th , 2013.
Observations:
Object(s)/ Substance
Beaker
Test Tube
Beaker + Test Tube + Hydrate
Hydrate
Hydrate after being heated
Anhydrous CuSO
4
Mass of Water (evaporated from Test Tube)
Weight (g)
50.9
19.1
72.8
2.8
1.8
1.8
1

Analyze and Evaluate: a) I am confident that this investigation provided adequate data because all the information that needed to be retrieved was retrieved with ease. Possible sources of error could be that not all of the water was evaporated in the heating process. This would skew the results by having a weight that is incorrect for the calculations. Another possible source of error is that the hydrate reacted with different things in the air forming compounds that were not supposed to be formed. This would also make a difference in what the weight should be making the results slightly off. It is also possible that the hydrate was impure to begin with. Again, this would differ the weight from what it should be. b) The qualitative evidence that suggested that the copper (II) sulfate was converted into its anhydrous form was that all the blue had disappeared. This is because when copper comes in contact with water, it creates a blue tint. The blue colour disappearing c) suggests that all the water has left the hydrate and has become anhydrous. d) e) The calculated value for the percentage of water should be similar because even if f) different amounts of the hydrate were used, the ratio should be the same for everyone. i) ii)

g) h) i) Not heating the hydrate enough would cause there to be still some of the water left.
This would make the percentage by mass of the water higher because the intention was to get rid of all of it when heating it. ii) Overheating the hydrate and producing copper (II) oxide would cause the percentage by mass of water to be lower because there would now be a new compound. Now, the calculations would have to account for the copper (II) oxide because it is part of the whole mass.
Conclusion:
It was experimentally determined that the percentage composition of water in a hydrate of copper (II) sulfate is 35.7%. It was also determined that the chemical formula for
CuSO
4
∙ 𝑥H
2
O is CuSO
4
∙ 5H
2
O .