Solution concentration problem?

Question

Some home brewed ginger beer is found to contain 0.51% ethanol (CH3CH2OH) Assuming the density of the ginger beer is 1 g ml^-1 calculate:

The mass of ethanol in a 250 ml glass of ginger beer

and

The concentration of ethanol in the ginger beer in mol L^-1

This is in my problems text book and i left the solution sheet at school :(

Any help is appreciated. Thanks. :)

Answer 1

because they wish us to calculate "The concentration of ethanol in the ginger beer in mol L^-1",.... let's use 1 litre & find the moles of alcohol within it

1 litre  is 1000 ml

let's find grams of solution:

1000 ml's @ a density of 1 gram / ml = 1000g grams of solution

let's find grams of alcohol:

0.51% of that 1000 grams of solution is alcohol:

1000 grams @ 0.51 / 100 = 5.1 grams of alcohol is in the litre

let's find moles of alcohol:

5.1 grams @ a molar mass of 46.07 g/mol = 0.111 moles of alcohol are in that litre

your answer is (2 sig figs): 0.11Molar