Is anyone good in Chemistry

[BMichelleB]

I have a question on my lab and google isn't helping

[Am]

[BMichelleB]

okay, so I calculated the mass of a sample of NaCl which was 1.0459 (answer via virtual chem lab through my class). They then asked for the moles of NaCl contained in the sample which I calculated to be .0189moles. The next questions says "calculate the moles of each element in NaCl" so my question is do I use the mass of 1.0459 of NaCl or do I calculate the mass of the sample each of them separately (again through virtual chem lab) then divide by their seperate molar masses....i hope that made sense

[Am]

Originally Posted by BMichelleB okay, so I calculated the mass of a sample of NaCl which was 1.0459 (answer via virtual chem lab through my class). They then asked for the moles of NaCl contained in the sample which I calculated to be .0189moles. The next questions says "calculate the moles of each element in NaCl" so my question is do I use the mass of 1.0459 of NaCl or do I calculate the mass of the sample each of them separately (again through virtual chem lab) then divide by their seperate molar masses....i hope that made sense

If you have 0.0189 moles of NaCl, then you have 0.0189 moles of Na and 0.0189 moles of Cl by default. It's a 1:1 ratio for both elements.

There IS a more difficult way to do it. You figure out the mass percent of each element (divide molar mass of element by molar mass of NaCl) and then multiply that for each by the mass of the sample and convert the answer to moles. It should give you something close to 0.0189 moles of each.

[BMichelleB]

Originally Posted by CarolinaHokie If you have 0.0189 moles of NaCl, then you have 0.0189 moles of Na and 0.0189 moles of Cl by default. It's a 1:1 ratio for both elements. There IS a more difficult way to do it. You figure out the mass percent of each element (divide molar mass of element by molar mass of NaCl) and then multiply that for each by the mass of the sample. It should give you something close to 0.0189 moles of each.

something like this?

Molar mass NaCl = 22.9898 + 35.453 = 58.44 g/mol
% Na = 22.9898 x 100 / 58.44 = 39.3
If we have 1.02 g of NaCl
grams of Na = 1.02 x 39.3 / 100 = 0.401
grams Cl = 1.02 x 60.7 / 100 = 0.619

Moles Na = 0.401 / 22.9898 = 0.0174
Moles Cl = 0.619 / 35.453 = 0.0174
The ratio is 0.0174 : 0.0174 or ( it is the same 1 : 1) and the formula is NaCl


this was on yahoo answers lol i did not do this, I was searching for how to do it


ETA: what about atoms for each element? same thing?

[Am]

Originally Posted by BMichelleB something like this? Molar mass NaCl = 22.9898 + 35.453 = 58.44 g/mol % Na = 22.9898 x 100 / 58.44 = 39.3 If we have 1.02 g of NaCl grams of Na = 1.02 x 39.3 / 100 = 0.401 grams Cl = 1.02 x 60.7 / 100 = 0.619 Moles Na = 0.401 / 22.9898 = 0.0174 Moles Cl = 0.619 / 35.453 = 0.0174 The ratio is 0.0174 : 0.0174 or ( it is the same 1 : 1) and the formula is NaCl this was on yahoo answers lol i did not do this, I was searching for how to do it ETA: what about atoms for each element? same thing?

Thank goodness yahoo has it. I was typing out the math for you. But yeah, that's the math version of how to do it. 0.0174:0.0174 is the same as 1:1. You want the lowest possible ratio.

For atoms, you just multiply moles by Avogadro's number.

[BMichelleB]

Originally Posted by CarolinaHokie Thank goodness yahoo has it. I was typing out the math for you. But yeah, that's the math version of how to do it. 0.0174:0.0174 is the same as 1:1. You want the lowest possible ratio. For atoms, you just multiply moles by Avogadro's number.

thank you so much!! you just saved me. When I did it I got .01788 moles ...i think that's it lol

[Am]

Originally Posted by BMichelleB thank you so much!! you just saved me. When I did it I got .01788 moles ...i think that's it lol

I'm glad I could help.

[BMichelleB]

okay...now im confused again lol don't hate me.

Another questions says "calculate the moles of C12H22O11" (sucrose). I know that the mass (via chem lab) is .9565g. When I get the molar mass for each element do I multiply it by their subscript? Like C has a molar mass of 12.011 Do I multiply that by 12 and add it to the others? I suck at explaining things

[Truegrits81]

Oh my. I failed chemistry. If they didn't have me doing attendance pick up in the mornings to make up the credit, I wouldn't have graduated.