how many ml of 50% acid should be added to 100% acid to get 20 ml of 70% acid

Question

how many ml of 50% acid should be added to 100% acid to get 20 ml of 70% acid

Answer 1

Alligation is a method (used mostly in pharmacy) that can help you do these problems. You set up a table with what you HAVE, what you WANT, and the PARTS to use (see below). In this case, we HAVE 50% and 100% and we WANT 70%.

HAVE........ WANT......... PARTS

50 .....................................30

.....................70....................

100.................................. 20

We get the PARTS by subtracting diagonally.

Thus, we need 30 parts of 50% and 20 parts of 100%. This is a total of 50 parts. Since we want to make 20 mls total, we set 20 mls = 50 parts and each part then becomes 0.4 mls

30 parts of 50% = 12 mls of 50%

20 parts of 100% = 8 mls of 100%

Answer 2

F is the fifty percent acid. H is the 100% acid.

70% of 20ml = 14 ml of acid in the final product.

F + H = 20

.5F + H = 14

Subtract the second from the first.

.5F = 6

F = 6/.5 = 12

H = 20 - 12 = 8

8 ml of the 100% acid and 12 ml of the 50% acid.