Question

If 10 ml of a 9 g/L stock solution of ferric chloride are added to a Hach container that has 5 L of water, what will be the concentration of ferric chloride in the water?

Answer 1

The new concentration will be 18 mg/L.

Explanation:

We can use the dilution equation to solve this problem.

`color(blue)(bar(ul(|color(white)(a/a) c_1V_1 = c_2V_2color(white)(a/a)|)))" "`

where

`c_1` and `c_2` are the initial and final concentrations, and
`V_1` and `V_2` are the initial and final volumes.

We can rearrange this formula to get

`c_2 = c_1 × V_1/V_2`

In this problem,

`c_1 = "9 g/L"; V_1 = "10 mL" color(white)(mmmll) = "0.010 L"`
`c_2 = ?;color(white)(mm) V_2 = "5 L + 0.010 L" = "5.010 L"`

∴ `c_2 = "9 g/L" × (0.010 color(red)(cancel(color(black)("L"))))/(5.010 color(red)(cancel(color(black)("L")))) = "0.018 g/L" = "18 mg/L"`