# Question 33682

May 14, 2017

Add 3.0 L of concentrated phosphoric acid to enough water to make 15.0 L of solution.

#### Explanation:

Yes, $\text{Molarity" = "moles"/"litres}$, so

$\text{3.0 mol/L" = x/"15.0 L}$

$x = \text{3.0 mol"//color(red)(cancel(color(black)("L"))) × 15.0 color(red)(cancel(color(black)("L"))) = "45 mol}$

So, you would add 45 mol of phosphoric acid to enough water to get 15.0 L of solution.

From where do you get the 45 mol of phosphoric acid?

You get it from concentrated phosphoric acid, which has a concentration of 14.8 mol/L.

Again, you use the formula, $\text{Molarity" = "moles"/"litres}$.

$\frac{\text{Molarity" = "moles}}{x}$

$\frac{\text{14.8 mol/L" = "45 mol}}{x}$

x= (45 color(red)(cancel(color(black)("mol"))))/(14.8 color(red)(cancel(color(black)("mol")))//"L") = "3.0 L"#

So, you would carefully add 3.0 L of concentrated phosphoric acid with stirring to about 11 L of water and then add more water until you have 15.0 L of solution.