You need 560 mL of a 15% alcohol solution. On hand, you have a 70% alcohol mixture. How much of the 70% alcohol mixture and pure water will you need to obtain the desired solution?

Answer 1

Start off by knowing that in a 560 ml solution, to get a 15% Alcohol content, you will need x ml of Alcohol

x/560 = .15 or the amount of Alcohol then will be 560(.15) = 84 ml of alcohol.

But, In 100 ml of the 70% solution, you will have 70 ml of Alcohol & 30 ml of Water

To get 84 ml of Alcohol, multiply by 1.2 to get 120 ml consisting of 84 ml Alcohol & 36 ml of Water

So, 84 + 36 + y = 560 (y = the amount of water to make the 15% concentration)

y = 440 ml.

Check: Concentration = 84 ml Al/(84ml + 36ml + 440ml) = .15 Yes

So, that means that in 120ml of the 70% solution, you need to add 440ml of water to get 15% mixture!