[Mallatron]

Hello folks,

I am actually a Biotechnology masters student, struggling with a bit of chemistry and was wondering if there was anyone out there that could help?

I need a 1M solution of CuSO4 - MW- 249.68.
I am adding 24.968g to 100ml ddH20. It is producing a blue solution which I would expect, however there is also a precipitate forming at the bottom. Is this normal, is there something that I am doing wrong?

Thanks in advance!

[Borek]

How does the precipitate look?

What you are doing _is_ wrong, for several reasons.

1. Have you really weighed 24.968 g of copper sulfate? It is a waste of time, as its composition (number of hydration waters) is never exactly known, so you can't be sure it is exactly 0.1 moles of the salt. Plus, even in the case of analytical grade reagents you can expect some impurities, which makes weighing with this accuracy unreasonable.

2. Do you really need 1.0000 M solution, or just 1 M solution - the latter means "something around 1 M" (what "around" exactly means depends on the application, but typically ±5% will probably do), the former is a standardized analytical solution.

3. Adding 24.968 g to 100 mL of water doesn't produce 100 mL of the solution, so its final concentration is not what you think it is. Actually it is quite likely you are exceeding the salt solubility.

[cseil]

http://chemicals.etacude.com/c/more/cuso4.html

As you can see, at the temperature of 25°C you can dissolve 21.95 g of CuSO4 into water.
If you want to dissolve more, you have to increase temperature. Of course you have to maintain that temperature in order to keep all the salt dissolved.

We're not talking about 1.0000M solution, I suppose. I don't think you need an analytical precision, am I right?

[knightsljx]

it does look like you possibly exceeded the solubility of CuSO4 at whatever temperature your lab is at.

also, are you using hydrated or anhydrous CuSO4? using hydrated solids would cause your calculations to be off as mentioned by previous comments. your concentration would be lower than what you need

based on your calculations, you need to weigh 24.968 grams of anhydrous CuSO4, which is white in colour

[Borek]

based on your calculations, you need to weigh 24.968 grams of anhydrous CuSO4

No, this number comes from the molar mass of the hydrate (regardless of what the OP wrote in the opening post).

Molar mass of anhydrous CuSO₄ is 159.61 g/mol, molar mass of CuSO₄·5H₂O is 249.69 g/mol.