Chemical Formula Hydrate Lab

[Sarah32]

We did a lab at our school recently but some of the questions regarding the lab confused me.
The data obtained from the lab is here:
Determining the Chemical Formula of a Hydrate

Purpose
Find the molecular formula of the hydrate of Copper (II) Sulfate, CuSO4 x H20.

Prediction
When the solution is heated the hydrate will convert to an anhydrous ionic compound. Then the percentage composition will be determined by weighing the mass of the white crystals.

Materials
• 400ml beaker with hot plate
• Tongs
• Scoopula
• Electronic balance
• Glass rod
• 3g to 5g hydrated Copper(II) Sulfate
• Goggles

Procedure
This experiment was done in order to find the percentage composition of a hydrate compound. The mass of the empty beaker, beaker + hydrated Copper (II) Sulfate, and mass of the beaker + anhydrous Copper (II) Sulfate was found through this procedure.
The mass of a beaker and stirring rod was found. About 4g of hydrated Copper (II) Sulfate was added to the beaker and the weight was recorded. The beaker was placed on a hot plate, heated until the blue crystals lost there blue color. Stirring the compound was essential to making sure all the blue crystals were heated. When the crystals lost their color the heat source was removed and the beaker was left to cool. The mass of the white crystals, when cooled was recorded. The experiment compound was safely disposed of and the materials that were used were properly put away.

Table 1: Masses
Mass of Beaker and Stirring Rod 77.774g
Mass of Beaker + Hydrated Copper(II) Sulfate 81.531g
Mass of White Crystals 80.348g






Mass of CuSO4 x H2O Mass of H2O= 18.0152g Mass of CuSO4= 159.6068g
2(1.00794)
1(15.9994) Mass of Hydrated CuSO4= 3.757g Mass of Anhydrous= 2.574g
1(63.546)
1(32.065)
4(15.9994)
177.62g

Analysis Questions Page 227 in Text

1a.) 3.757 Difference 1.183 / 3.757 x 100% = 31.49%
-2.574
1.183
b.) It is expected that the mass percent of water should be similar in all the groups,
concerning the Hydrated CuSO4 x H2O.

2a.) Table 2: Class Group Results
Group Mass(CuSO4 x H2O) Mass(CuSO4) % H2O
1 3.757g 2.574g 31.49%
2 3.587g 2.277g 36.52%
3 3.871g 2.646g 31.65%
4 3.188g 2.075g 34.91%
5 3.465g 2.168g 37.43%
b.)

3.) CuSO4= 100 - 31.49 H2O Class Average= 34.4%
= 65.6g

34.4g (1 mol/18.01528)
=1.909mols

65.6g (1 mol/ 159.6086) Therefore the Molecular Formula is CuSO4 x 5H2O.
=0.41mols

1.909/ 0.41= 4.66
= 5 H2O molecules
4.) If you were to heat the hydrated ionic compound in a test tube you would expect to
see steam rising which means that the water in the compound is being evaporated into
the air. In our experiment we did see this happen but it would be more evident in a test
tube because it is more confined than the beaker.


Here are my questions that I'm very confused with, your help is much appericiated:

1. You obtained the mass percent of water in the copper sulfate hydrate.
a.) Using your obervations, calculate the percentage composition of the copper sulfate hydrate.
b.) In the case of a hydrate, and assuming you know the formula of the associated anhydrous ionic compound, do you think it is more useful to have the mass perventage composition? Explain your answer.

2. Suppose that you did not compelely convert the hydrate to the anhydrous compound. Explain how this would affect the calculated percent by mass of water in the compound. and the molecular formula you determined.

3. Suppose the hydrate heated too quickly and some of it spatted out of the container and was lost. Explain how this would affect the calculated percent by mass of water in the compound and the molecular formula you determined.
(I understand that it would change, but exactuly how?)

4. Suggest a source of error (not already mentioned) that would result in a value of x that is
a.) higher than the actual value
b.) lower than the actual value

I know this quite a few questions...but i really don't understand. Please help, thank you :)

 

[chemisttree]

What don't you understand?

 

[Blueshift5]

1. To calculate the percentage composition of the copper sulfate hydrate, we need to determine the mass of water and the mass of the anhydrous copper sulfate. From the data, we can see that the mass of water is 3.757g and the mass of the anhydrous copper sulfate is 2.574g. To calculate the percentage composition of water, we use the formula: (mass of water/total mass of compound) x 100%. In this case, it would be (3.757g/6.331g) x 100% = 59.3%. For the percentage composition of copper sulfate, we use the same formula but with the mass of anhydrous copper sulfate instead, which would be (2.574g/6.331g) x 100% = 40.7%.

As for whether it is more useful to have the mass percentage composition, it depends on the purpose of the experiment. If the goal is to determine the molecular formula of the hydrate, then the mass percentage composition is more useful as it helps in calculating the number of water molecules present. However, if the goal is to determine other properties of the compound, such as its molar mass, then the percentage composition may not be as useful.

2. If the hydrate is not completely converted to the anhydrous compound, it means that some water molecules are still present in the compound. This would result in a higher percentage of water in the compound, as the mass of water would be higher than the calculated value. This would also affect the calculated molecular formula, as the number of water molecules present would be higher than the actual value.

3. If some of the hydrate was lost due to spattering, it means that the mass of the compound used in the experiment would be lower than the actual value. This would result in a lower percentage of water in the compound, as the mass of water would remain the same while the total mass of the compound used would be lower. This would also affect the calculated molecular formula, as the number of water molecules present would be lower than the actual value.

4. One possible source of error could be incomplete conversion of the hydrate to the anhydrous compound. This could happen if the heating was not done properly or for a sufficient amount of time. This would result in a lower value of x, as the mass of water would be lower than the