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# C3.8d Moles in life help watch

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1. I am struggling with a question (higher tier, extension):

The legal limit in the UK for the amount of alcohol that a driver can have in their blood is 80mg/100cm^3 of blood. What is this in mol dm^-3?

Btw, alcohol has an RFM of 46.

2. You first need to work out what 80mg (0.08g) is in moles. You should know how to do this already.

You also need to convert 100cm3 to dm3, do this by dividing by 1000.

Once you have a value for amount and volume, you can work out concentration by using c=n/v.

Spoiler:
Show

0.08g/46gmol-1 = 0.00174mol
100cm3 = 0.1dm3
Concentration = 0.00174mol/0.1dm3 = 0.0174moldm-3

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Updated: November 12, 2016
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