Question

Question #ec7e1

Answer 1

Here's how you can do that.

Explanation:

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

A solution's weight by volume percent concentration tells you how many grams of solute you get for every `"100 mL"` of solution.

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

Now, the problem tells you that you have a mass of solute of `"2.5 mg"`. Before doing anything else, convert this from milligrams to grams by using

`color(purple)(|bar(ul(color(white)(a/a)color(black)("1 g" = 10^3"mg")color(white)(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 `"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 `"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)|)))`