# You collect 100 mL of a stock solution of redehyde with a concentration of 100 M. You need 500 mL...

## Question:

You collect 100 mL of a stock solution of redehyde with a concentration of 100 M. You need 500 mL of a 10 M solution of redehyde. How much of the stock solution will you need to use? How much diluent will you need to add?

## Dilution of Solutions:

Dilution is the technique routinely used to prepare solutions of desired concentrations. We dilute concentrated solutions by simply adding more solvent. The solvent that is often used is water. By adding more solute, the concentrated solution is less concentrated (more diluted). The amount of solute present remains constant regardless of the amount of solvent present.

The first step is to determine the moles of redehyde required. This involves using the given volume of 500 mL and concentration of 10 M:

{eq}\require{cancel} \rm 500~\cancel{mL}\times\dfrac{1~\cancel{L}}{1000~\cancel{mL}}\times\dfrac{10~mol}{1~\cancel{L}} = 5~mol {/eq}

Based on this mole amount, we use the concentration of 100 M to determine how much volume can be supplied to given 5 moles of redehyde:

{eq}\rm \require{cancel} 5~\cancel{mol~redehyde}\times\dfrac{1~L}{100~\cancel{mol~redehyde}} = 0.05~L {/eq}

Thus, to prepare the solution, we need 0.05 L of the stock solution.

The volume of diluent needed can be determined by subtracting the volume of stock solution needed with 500 mL. Assuming volumes are additive, we have:

{eq}\require{cancel} \rm Volume~Diluent = 0.5~L - 0.05~L \\ \rm Volume~Diluent = 0.45~L \; {/eq}

We find that we will need to add 0.45 liters of the diluent.

Calculating Dilution of Solutions

from

Chapter 8 / Lesson 5
69K

Learn what a solution is and how to properly dilute a new solution from a stock solution. Learn the dilution equation that combines molarity, the volume of stock solution and desired solution to determine how much stock solution is needed for the new solution.