[fudawala]

Hi,

I have a question that troubles me. I want to calculate the number of particles per milliliter of Cadmium Selenide? The thing is that I don't know where to start? Can I someone help me please.

Thanks

[Borek]

Will you be able to calculate number of molecules knowing mass of the substance?

[fudawala]

Hi,

The molar mass of the substance is 191.37 grams per mole. How do I get the number of molecules from this mass?

Thanks

[nj_bartel]

(Mass_Sample) / (Molar Mass)

[fudawala]

What do you mean about the mass of the sample? Is this the right way to calculate the number of molecules per millimeter? Thanks.

[Borek]

If you know number of moles, can you calculate number of molecules?

If you know mass sample and molar mass of the substance, can you calculate number of moles?

[fudawala]

Yes you can. So the mass of the sample is 50 milligrams and the molar mass is 191.37 grams per mole. Now if I divide the mass sample over the molar mass I should get the number of moles right. If I multiply the number of moles with avogrado's number I should get the number of molecules per milliliter right.

[Borek]

So the mass of the sample is 50 milligrams and the molar mass is 191.37 grams per mole. Now if I divide the mass sample over the molar mass I should get the number of moles right. If I multiply the number of moles with avogrado's number I should get the number of molecules per milliliter right.

Mostly OK, but 50 mg is not mass of one milliliter of the CdSe. To calculate that you need one more information, about the solid density.

[fudawala]

Well the solid density is about 5.816 g per cubic centimeter.

[Borek]

And you still don't know what to do next?

[fudawala]

No, I don't know what to do next. Can you explain to me please. Thank You.

[fudawala]

Hi Borek,

The solid density is about 5.816 grams per cubic centimeter. Do I convert the 50 milligrams to grams and the cubic centimeter to one milliliter?

What I know so far is that: 1 milligram = .001 grams, and 1 milliliter = 1 cubic centimeter.

[Borek]

You are asked to calculate number of molecules in 1 mL. What is mass of the substance in 1 mL? Number of moles in this mass? Number of molecules in this number of moles?

[fudawala]

Hi Borek,

How do you claculate the mass of a substance of one milliliter?

Thanks

[sjb]

Hi Borek,

How do you claculate the mass of a substance of one milliliter?

Thanks

I'm not Borek, but do your previous insights below help?

Hi Borek,

The solid density is about 5.816 grams per cubic centimeter. Do I convert the 50 milligrams to grams and the cubic centimeter to one milliliter?

What I know so far is that: 1 milligram = .001 grams, and 1 milliliter = 1 cubic centimeter.

and

Well the solid density is about 5.816 g per cubic centimeter.