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### Topic: Calculating the number of particles per milliliter of CdSe  (Read 22242 times)

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#### fudawala

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• Mole Snacks: +0/-2 ##### Calculating the number of particles per milliliter of CdSe
« on: June 26, 2008, 04:04:38 PM »
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 ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #1 on: June 26, 2008, 05:09:28 PM »
Will you be able to calculate number of molecules knowing mass of the substance?
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#### fudawala

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• Mole Snacks: +0/-2 ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #2 on: June 26, 2008, 09:17:44 PM »
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

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• Mole Snacks: +76/-42 ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #3 on: June 26, 2008, 09:20:33 PM »
(MassSample) / (Molar Mass)

#### fudawala

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• Mole Snacks: +0/-2 ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #4 on: June 26, 2008, 09:25:06 PM »
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 ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #5 on: June 27, 2008, 03:34:58 AM »
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?
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#### fudawala

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• Mole Snacks: +0/-2 ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #6 on: June 27, 2008, 09:38:49 AM »
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 ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #7 on: June 27, 2008, 11:06:19 AM »
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.
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#### fudawala

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• Mole Snacks: +0/-2 ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #8 on: June 27, 2008, 11:58:58 AM »
Well the solid density is about 5.816 g per cubic centimeter.

#### Borek ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #9 on: June 27, 2008, 12:35:09 PM »
And you still don't know what to do next?
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#### fudawala

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• Mole Snacks: +0/-2 ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #10 on: June 27, 2008, 02:15:46 PM »
No, I don't know what to do next. Can you explain to me please. Thank You.

#### fudawala

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• Mole Snacks: +0/-2 ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #11 on: June 28, 2008, 07:20:12 PM »
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 ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #12 on: June 29, 2008, 03:54:52 AM »
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?
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#### fudawala

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• Mole Snacks: +0/-2 ##### Re: Calculating the number of particles per milliliter of CdSe
« Reply #13 on: July 01, 2008, 01:59:22 PM »
Hi Borek,

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

Thanks

#### sjb

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« Reply #14 on: July 01, 2008, 02:42:10 PM »
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.