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### 6th Edition E27, First Part

Posted: Thu Oct 04, 2018 11:43 pm
I'm stuck on the first part of the question in title. How do you convert 1 H20 molecule to moles?

### Re: 6th Edition E27, First Part

Posted: Thu Oct 04, 2018 11:47 pm
All you do is divide 1 by Avogadro's number. The calculation should looks like this: 1/(6.02 x 10^23).

### Re: 6th Edition E27, First Part

Posted: Thu Oct 04, 2018 11:47 pm
You divide 1 H2O molecule by Avogadro's constant (6.02 * 10^23) to convert to moles, then multiple by molar mass to convert to grams.

### Re: 6th Edition E27, First Part

Posted: Thu Oct 04, 2018 11:51 pm
Oh hey, quick reply guys! Thanks. To catch you guys here, is the reason why it is 1 / (6.022 x 10^23) moles because of the need to cancel out the units via dimensional analysis?

### Re: 6th Edition E27, First Part

Posted: Fri Oct 05, 2018 12:10 am
you use the Avogadro's constant to convert from mass per mol to mass per molecule. It should be (1/6.022x10^23 molecules.mol^-1 ) so you would be able to get g.molecule^-1 for the mass of the H2O molecule.

### Re: 6th Edition E27, First Part

Posted: Sun Oct 07, 2018 5:09 pm
Converting one H2O molecule to moles using dimensional analysis:
=1 molecule * 1 mol / 6.022*10^23 molecules
=1.66 * 10^-24 mol of H2O

Solving E27(a) using dimensional analysis:
Mass of 1 water molecule = (1.008*2 + 15.999)g/1mol * 1mol/6.022*10^23 molecules = 2.99 * 10^-23 g