Question

Question #33682

Answer 1

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

Explanation:

Yes, `"Molarity" = "moles"/"litres"`, so

`"3.0 mol/L" = x/"15.0 L"`

`x = "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, `"Molarity" = "moles"/"litres"`.

`"Molarity" = "moles"/x`

`"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.