Question 16444
Think about this! 70% acid solution is 30% water and the 50% acid solution is 50% water.

You want to add x liters of water to the 2.5 liters of 30% water/acid solution to make (2.5 + x) liters of 50% water/acid solution. Change the percents to their decimal equivalents 30% = 0.3, 50% = 0.5  Now you can set up your equation to solve the problem.

{{{2.5(0.3) + x = (2.5 + x)(0.5)}}} Simplify and solve for x.
{{{0.75 + x = 1.25 + 0.5x}}} Subtract 0.5x from both sides.
{{{0.75 + 0.5x = 1.25}}} Subtract 0.75 from both sides.
{{{0.5x = 0.5}}} Divide both sides by 0.5
{{{x = 1}}}

The Chemist will need to add 1 liter of water to the 2.5 liters of 70% acid solution to obtain 3.5 liters of 50% acid solution.