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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: jsimpkins on October 16, 2011, 01:56:20 PM

Title: Avogadro's Number?
Post by: jsimpkins on October 16, 2011, 01:56:20 PM

This came from a set of post lab questions.

Find the number of molecules  of benzene (C6H6) in a 34.00ml sample of benzene. The density of benzene is 0.880g/ml.

I'm a bit confused on where to start. C6H6 ----> 78.0g/mol

would I divide 78.0g/mol / 0.880g/ml = 88.6mol/ml?

Thanks in advance for any help.
Jim

Title: Re: Avogadro's Number?
Post by: Wald_ron on October 16, 2011, 02:57:31 PM

Quote from: jsimpkins on October 16, 2011, 01:56:20 PM

This came from a set of post lab questions.

Find the number of molecules  of benzene (C6H6) in a 34.00ml sample of benzene. The density of benzene is 0.880g/ml.

I'm a bit confused on where to start. C6H6 ----> 78.0g/mol

would I divide 78.0g/mol / 0.880g/ml = 88.6mol/ml?

Thanks in advance for any help.
Jim

step 1: find the number of grams of benzene in a 34mL sample
step 2: find the number of mols of benzene in a 34mL sample
step 3: find the number of molecules

Title: Re: Avogadro's Number?
Post by: Sanger on October 18, 2011, 08:42:49 PM

34.00 mL C6H6 x  |  0.880 g    |1 mol C6H6|6.022 x 10²³ molecules|
                        | 1 mL C6H6 |   78.11 g  |        1 mol C6H6        |

Carry this out and you would end up with 3.291 x 10¹⁷molecules.
*Note* I did this on my computer calculator, so this arithmetic may be incorrect