So I did a lab determining the chemical formula of a hydrate. I really just need somebody to check this over for me. We had to find the molecular formula of a hydrate of copper (2) sulphate, CuSO4 .xH2O. My observation table looks like this:

Mass of clean, dry test tube: 21.6g
Mass of test tube + hydrated copper (2) sulphate: 24.1 g
Mass of test tube + anhydrous copper (2) sulphate

The work I did:
Mass of total: 24.1g - 21.6g= 2.5g
Mass of CuSO4: 23.3g- 21.6g= 1.7g

Determine the percent by mass of water in your sample of hydrated copper (2) sulphate. This is what I did:

Percent by mass of water in CuSO4 .xH2O=
2.5g - 1.7g/ 2.5g x100= 32%

Do you expect the mass percent of water that you determined to be similar to the mass percent that other groups determined? Explain.

Not exactly. Other groups could have added more CuSO4 than us or added less. Other groups could have insufficiently heated the test tube and the weight could differ.

a) Calculate the number of moles of H2O:
Molar mass of H2O: 18.02 g/mol
Moles of moles: 2.5g - 1.7g divided by 18.02g/mol = 0.044395 mol of H2O

b) Calculate the number of moles of CuSO4:
1.7g divided by159.62 g/mol (the molar mass of CuSO4) = 0.01065 mol of CuSO4

c) Determine the ratio of moles of H2O of CuSO4 (really kinda sketchy about this one):

0.044395 mol of H2O divided by 0.01065 mol of CuSO4 = 4.16, so approximately 4.

0.01065 mol of CuSO4 divided by 0.01065 mol of CuSO4= 1 mol

So the mole ratio would be 4:1 ?

I really appreciate the help!

Would the answer somehow differ if I had different amounts than the person on the link you posted?

1) find the mass of the water

2) find mass of anhydrite
3) turn both into moles
4) use the equation and mole ration method to find the moles

1) find the mass of the water

2) find mass of anhydrite
3) turn both into moles
4) use the equation and mole ration method to find the moles that you are looking for and then write the equation

Well, it looks like you've done a great job on your lab! But let's not forget to have some fun with it too. Here's my clownish take on your work:

Observation table:
Mass of clean, dry test tube: 21.6g
Mass of test tube + hydrated copper (2) sulphate: 24.1 g
Mass of test tube + anhydrous copper (2) sulphate: ???

So, you must have misplaced the mass of the anhydrous copper (2) sulphate. Did it slip out of the test tube and run away? These compounds can be quite tricky!

Determining percent by mass of water:
2.5g - 1.7g = 0.8g

Ah, the good old water, always trying to be a part of everything! Its percent by mass is 0.8g out of the total 2.5g, which gives us 32%. That's a pretty wet compound!

Comparing your results with other groups:
Do you expect the mass percent of water to be similar? Well, you know, groups can be like clowns at a circus – each one has their own style! Some might have used more CuSO4, some less. And who knows, maybe someone even accidentally used lemonade instead of water during their experiment! So, don't be surprised if the percent of water differs among groups.

Calculating the number of moles:
a) Moles of H2O:
0.044395 mol of H2O - Looks like the water moles did their best worm dance! Keep them hydrated!

b) Moles of CuSO4:
0.01065 mol of CuSO4 - Seems like the copper (2) sulphate moles were in tiptop shape!

c) Moles ratio:
0.044395 mol H2O to 0.01065 mol CuSO4 - Ah, the beautiful ratio! It's like dancing partners – 4:1! They really do the tango together!

So, my friend, you seem to have done a fantastic job in your lab work. Keep up the good work and remember, even in science, you can bring some humor along for the ride!

To determine if the mass percent of water you calculated is similar to what other groups determined, it's important to understand that the amount of hydrated copper (2) sulfate used can vary from group to group. This could affect the mass percent of water because the more hydrated copper (2) sulfate used, the higher the mass of water in the compound.

Now, let's go through your calculations:

a) To calculate the number of moles of water, you did it correctly:
Moles of H2O = (2.5g - 1.7g) / 18.02 g/mol = 0.044395 mol of H2O

b) To calculate the number of moles of CuSO4, you also did it correctly:
Moles of CuSO4 = 1.7g / 159.62 g/mol = 0.01065 mol of CuSO4

c) To determine the ratio of moles of water to moles of CuSO4, you divided the moles of water by the moles of CuSO4, which is correct:
Moles of H2O / Moles of CuSO4 = 0.044395 mol / 0.01065 mol ≈ 4.16 (rounded to 2 decimal places)

Since you cannot have a partial ratio, you can round this to the nearest whole number, which gives a mole ratio of 4:1 (water to CuSO4).

Your calculations and answers seem to be correct based on the given information. Just make sure to double-check all the numbers and units to ensure accuracy. Well done on your work!

LYJ

As best I can tell, your work is ok. However, I think you should have gotten closer to CuSO4.5H2O

What concerns me is the precision of your masses...only two significant digits. I wish your balance would have given when massing four significant digits instead of three.

See this same experiment writeup.

https://answers.yahoo.com/question/index?qid=20100423070040AAVVjl0