i have a solution of 70% acid in water solution (70% is acid). How much water to add, to dilute it to 10%?

Question

i have a solution of 70% acid in water solution (70% is acid, 30% is water). How much water do I add to this solution, to dilute it to a 10% acid solution? (Assume I start with 1 tablespoon of my 70% solution.)

Answer 1

Let us use 30 ml as a starting volume (instead of 1 tablepoonful)

 

(.7 * 30)/(30 + x) = .1

because in the initial volume there are 30 * .7 ml of acid which will now be dilute to 30 + x volume which will result in a concentration of .1

 

Then cross multiply: 28 = 3 + .1x 

subtract 3 from each side of the equation

 

25 = .1x

 

Multiply by 10: 250 = x

 

You should now go back and check that the answer satisfies the queston.