After performing a dilution calculation, you determine you need 25.0 milliliters of an aqueous stock solution to make 100.0 milliliters of a new solution. How would this be prepared?

Aug 17, 2016

Here's what I got.

Explanation:

You know that you need $\text{25.0 mL}$ of a stock solution to make $\text{100.0 mL}$ of a new, diluted solution. This basically means that you're going to dilute your stock solution by a factor of

$\left(100.0 \textcolor{red}{\cancel{\textcolor{b l a c k}{\text{mL"))))/(25.0color(red)(cancel(color(black)("mL}}}}\right) = 4$

You thus know that for every $4$ parts of this new, diluted solution, $1$ part is accounted for by the stock solution and $3$ parts are accounted for by water, you diluent.

The trick now is to realize that despite the fact that you'd need

$\text{100.0 mL " - " 25.0 mL" = "75.0 mL}$

of water to make this new solution, you should not add exactly $\text{75.0 mL}$ of water to your $\text{25.0 mL}$ of stock solution. Instead, you should add enough water to make sure that the total volume of the solution is equal to $\text{100.0 mL}$.

So, to prepare this solution, you should add $\text{25.0 mL}$ of stock solution to a volumetric flask, then add water until the total volume is equal to $\text{100.0 mL}$. You just diluted your stock solution by a factor of $4$.