Doreen Schmidt is a chemist. She needs to prepare 28 ounces of a 12 % hydrochloric acid solution. Find the amount of 14 % solution and the amount of 7 % solution she should mix to get this solution.

20 ounces of 14% solution and 8 ounces of 7% solution.

Explanation:

Let the amount of 14% solution required be A and the amount of 7% solution required be B.

Mixture of A and B must give 28 ounces:

A + B = 28 ... Eqn 1

Also, mixture of 14% A and 7% B must give 12%, 28 ounces solution:

0.14A + 0.07B = 0.12 (28) = 3.36 ... Eqn 2

From eqn 1, B = 28 - A, eqn 2 becomes:

0.14A + 0.07 (28 - A) = 3.36

0.07A = 3.36 - 1.96

A = 20 ounces

Substitute the value of A into eqn 1 to get B:

20 + B = 28

B = 8 ounces.

Hence, 20 ounces of 14% hydrochloric acid and 8 ounces of 7% hydrochoric acid should be mixed together in order to get 28 ounces of 12% solution.