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Posted by **Jessica** on Saturday, January 15, 2011 at 2:19am.

a) how many carbon atoms does the sample contain?

b) what is the total mass of the sample?

- chemistry -
**Dr Russ**, Saturday, January 15, 2011 at 2:33amFrom the formula (C3H8) [please use capital letters for element symbols] we see that there are 3 C atoms for 8 H atoms. If we had 16 H atoms there would be 6 C atoms for example.

Thus is there are 3.84x10^24 H atoms.

a) then there are (3/8)x3.84x10^24 C atoms

b) there are a couple of ways to do this.

If the sample contains 3.84x10^24 H atoms and each molecule contains 8 H atoms then there are 3.84x10^24/8 molecules of propane. Each mole contains 6 x 10^23 molecules so there are

3.84x10^24/(8 x 6 x 10^23 )moles

the molar mass of propane is

(3x12)+(8x1) g mole^-1

hence find the mass as

mass= molar mass x number of moles

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