Question

have a 700ml solution of 30% acid, needs a 50% solution of acid. How many ml of 100% acid should be added?

Answer 1

hmmm ok. so we're saying that the entire solution needs to be .5 (50%)

Answer 2

so you can solve an equation like this: (.3*700 + 1*x)/(x+700) = .5

Answer 3

so multiplying both sides by x+700, we get : .5x + 350 = x + 210

Answer 4

subtract .5 from both sides, and you get .5x + 210 = 350

Answer 5

so .5x = 140

Answer 6

140/.5 = x = 280

Answer 7

so I'd say 280ml

Answer 8

basically - .5 is the entire fraction of acid in the total solution, hence my equation in the first step - so we know the first part of the end solution since it's given

Answer 9

700ml * .3 is pure acid

Answer 10

what you add to the solution, is also pure 100% acid, so 1*x

Answer 11

the denominator in this case will be the total amount of solution (so the original 700ml plus whatever you added)

Answer 12

and we know that the entire thing - the fraction - is .5

Answer 13

and following that logic the answer is 280ml

Answer 14

i.e. .5 = total ml acid / total ml solution (after you've added everything)

Answer 15

good luck!

Answer 16

Thank you