# 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?

Mar 5, 2017

The new concentration will be 18 mg/L.

#### Explanation:

We can use the dilution equation to solve this problem.

$\textcolor{b l u e}{\overline{\underline{| \textcolor{w h i t e}{\frac{a}{a}} {c}_{1} {V}_{1} = {c}_{2} {V}_{2} \textcolor{w h i t e}{\frac{a}{a}} |}}} \text{ }$

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,

${c}_{1} = \text{9 g/L"; V_1 = "10 mL" color(white)(mmmll) = "0.010 L}$
c_2 = ?;color(white)(mm) V_2 = "5 L + 0.010 L" = "5.010 L"

${c}_{2} = \text{9 g/L" × (0.010 color(red)(cancel(color(black)("L"))))/(5.010 color(red)(cancel(color(black)("L")))) = "0.018 g/L" = "18 mg/L}$