How much water must be added to 20 L of a 10% solution of boric acid to reduce it to a 4% solution?

Question

15070 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2015-08-13T10:13:41

You have to add 30 litres of water

At the beginning you have 20 L of 10% solution, so it consists of 2L of acid and 18 L of water.

Now you have to calculate the amount of water to add to change the solution to 4%.
To do this you have to solve equation:

#2/(20+x)=4/100#

The equation comes from the fact that the amount of acid is unchanged (2L) and the sum of water and acid is increased by #x# (added water)

#2/(20+x)=2/50#

#40+2x=100#

#2x=100-40#
#2x=60#
#x=30#