# Question ec7e1

Apr 29, 2016

Here's how you can do that.

#### Explanation:

All you have to do here is use the given weight by volume percent concentration, $\text{% w/v}$, as a conversion factor to help you determine how many milliliters of solution would contain $\text{2.5 mg}$ of solute.

A solution's weight by volume percent concentration tells you how many grams of solute you get for every $\text{100 mL}$ of solution.

In your case, the solution is said to be $\text{0.80% w/v}$, which means that you get $\text{0.80 g}$ of solute for every $\text{100 mL}$ of solution.

Now, the problem tells you that you have a mass of solute of $\text{2.5 mg}$. Before doing anything else, convert this from milligrams to grams by using

$\textcolor{p u r p \le}{| \overline{\underline{\textcolor{w h i t e}{\frac{a}{a}} \textcolor{b l a c k}{\text{1 g" = 10^3"mg}} \textcolor{w h i t e}{\frac{a}{a}} |}}}$

You will have

2.5 color(red)(cancel(color(black)("mg"))) * "1 g"/(10^3color(red)(cancel(color(black)("mg")))) = "0.0025 g"

So, you know that the solution contains $\text{0.80 g}$ of solute per 100 mL" of solution. Use this as a conversion factor to find the volume of the solution that would contain $\text{0.0025 g}$ of solute

0.0025 color(red)(cancel(color(black)("g solute"))) * overbrace("100 mL solution"/(0.80color(red)(cancel(color(black)("g solute")))))^(color(blue)("= 0.80% w/v")) = "0.3125 mL solution"

Rounded to two sig figs, the answer will be

"volume of solution" = color(green)(|bar(ul(color(white)(a/a)"0.31 mL"color(white)(a/a)|)))#