Question

A chemist mixes 50 milliliters of a solution that is 20% acid with 75 milliliters of a solution that is 45% acid. How many milliliters of acid are in the resulting mixture

Answer 1

Answer:
81.25 mL
Why?
Total amount of millilitres: 125 mL
Let x represent the millilitres of acid.
Let a represent the amount of acid in the 50 mL solution.
Let b represent the amount of acid in the 75 mL solution.
This means that x = 125 - (a + b)
So, a = 0.2*50
a = 10
So, b = 0.45*75
b = 33.75
Plug it into our equation;
x = 125 - (a + b)
x = 125 - (10 + 33.75)
x = 125 - 43.75
x = 81.25
Therefore, 81.25 mL of the 125 mL mixture is acid.
Alternate solution:
Let x represent the millilitres of acid.
Let a represent the number of millilitres in the mixture.
Let b represent the percentage of acid in the mixture.
This means that x = b*a
So, a = 50 + 75
a = 125
So, b = 0.2 + 0.45
b = 0.65
Plug it into our equation;
x = b*a
x = 0.65*125
x = 81.25
Therefore, 81.25 mL of the 125 mL mixture is acid.

(Hope this helps)