Question

There are 80 mL of a 3.5% solution. This solution is added to water to make a total of 160 mL. What is the concentration of the 160-mL solution?

Answer 1

the The concentration of a solute is defined as the quantity of solute per unit quantity of solution,

`\text{Concentration}=\frac{\text{ Quantity of solute}}{\text{ Quantity of mixture}}`

Given that the initial volume is 80 mL and the corresponding concentration is 3.5%. So the quantity (x) of solute can be obtained as,

`\begin{gathered} x=3.5\text{ percent of 80 mL} \\ x=(3.5)/(100)\cdot80 \\ x=2.8 \end{gathered}`

This solution is mixed with pure water, so the quantity of solute in the final mixture remains same since no solute is added.

The final volume of the mixture is 160 mL.

So we know the quantity of solute and the quantity of solution. Therefore, the concentration C of the final solution is calculated as

`\begin{gathered} C=(2.8)/(160) \\ C=0.0175 \\ C=1.75\text{ percent} \end{gathered}`

Thus, the concentration of the final solution is 1.75%.