COPPER SULFATE HYDRATE DETERMINATION LAB:
The Average Atomic Weight listed with each of the elements on the periodic table is a
measure of the mass of an average atom of that element in AMU. Because we don’t have a
balance for measuring AMU because it is WAY TOO SMALL, we have to mass things in grams
instead. If, however, I measure things in grams I will be massing many atoms of that element
and not single atoms.
Think about this: the average atomic mass of Hydrogen is 1.008amu and the average atomic
mass of Oxygen is 15.999amu. If I were to mass out 1.008grams of Hydrogen and
15.999grams of Oxygen on a balance, what would I be able to say about the number of H
atoms compared to O atoms? Can you see that even though we don’t know how many actual
atoms there must be of each, we can say that the number of atoms of each element must be
the same? One way or another, we know that we are dealing with a HUGE number of atoms
of each element.
Even though we don’t know the actual number of atoms we’re dealing with, let’s refer this
number of atoms as a “unit” of atoms. So, if I have the mass of an element (that we get from
periodic table) in GRAMS, I will have 1 unit of that element. So, 1 unit of any element is going
to be a whole lot of actual atoms but will be the same “whole lot” of atoms for each element.
When we write formulas for compounds, we refer to the number of units of each element in a
compound (i.e. for H2O, 2 units of H (2 x 1.008g) would react with 1 unit of O (1 x 15.999g)).
1. How much would 1 unit of H2O weigh (in grams)?
2. How many units of water would I have if I only had 10.2g of Water?
3. How much would 1 unit of CuSO4 weigh (in grams)?
4. How many units of CuSO4 would I have if I had only 14.0g of CuSO4?
NOW, related to the lab:
5. Sometimes, water molecules will stick to compounds in a crystal structure. How much
would 1 unit of CuSO4w/1H2O attached to it weigh (in grams)?
6. How many units of CuSO4w/1H2O would I have it I had only 2.0g of CuSO4w/1H2O?
7. What is the percent of H2O in CuSO4w/1H2O?
8. If I had 2.0g of CuSO4w/1H2O, how many grams of that 2.0g would be the water?
Determine the Percent H2O in each of the following crystal structures:
9. CuSO4w/2H2O:
10. CuSO4w/3H2O:
11. CuSO4w/4H2O:
12. CuSO4w/5H2O:
13. CuSO4w/6H2O:
14. CuSO4w/7H2O:
Now, let’s collect some data to figure out which one it actually is:
1. Get the following data:
a. Weight of a clean, dry 150 mL beaker
b. Weight of a clean, dry 150 mL beaker with approximately 2 grams of hydrated
copper sulfate
2. Set up a ring stand, Bunsen burner and wire gauze. Make sure the ring stand is VERY far
away from where your flame is going to be
3. Heat your hydrated copper sulfate SLOWLY!
4. After about 15 minutes of heating, remove the beaker from the flame using HOT
HANDS. Let cool for about 2 minutes.
5. Mass of the beaker with copper sulfate: (1)
6. Heat the hydrated copper sulfate slowly again for about 5 minutes.
7. Mass of the beaker with copper sulfate: (2)
8. If the mass of (1) and (2) are within +/- .05 of each other, you can stop here. Otherwise
repeat steps 6 and 7 until you get two readings that are within +/- .05 of each other:
9. Mass of the beaker with copper sulfate (3)
10. Mass of the beaker with copper sulfate (4)
11. Mass of the beaker with copper sulfate (5)
Calculations:
1. What is the mass of your water?
2. What is the percent of water in your hydrate?
3. What is the formula of the hydrate you had?