Question 403725

a container has 2 liters of 21% solution sodium hydroxide.

what is the amount and concentration you must add to this in order to

end up with 7 liters of 51% solution?
.
Well, you know you must add 5 liters so the only question is the concentration.
Let x = concentration
then
.21(2) + 5x = .51(7)
.42 + 5x = 3.57
5x = 3.15
x = 0.63
.
Solution: 5 liters of 63% solution sodium hydoxide