Question

Asolution is made by dissolving 14.0g of potassium chloride to a final volume of 78.9mL solution. What is the weight /volume % of the solute?

Answer 1

`17.7%`

Explanation:

The thing to remember about a solution's mass by volume percent concentration, `"m/v %"`, is that it is calculated by taking the number of grams of solute present in `"100 mL"` of solution.

This implies that you can find a solution's mass by volume percent concentration by determining how many grams of solute you get in `"100 mL"` of solution.

`color(blue)(|bar(ul(color(white)(a/a)"% m/v" = "no. of grams of solute / 100 mL solution"color(white)(a/a)|)))`

Now, you know that your solution is made by dissolving `"14.0 g"` of potassium chloride, `"KCl"`, which constitutes your solute, in enough water to make the final volume of the solution equal to `"78.9 mL"`.

You can use this information as a conversion factor to calculate the number of grams of potassium chloride present in `"100 mL"` of solution

`100 color(red)(cancel(color(black)("mL solution"))) * overbrace("14.0 g KCl"/(78.9color(red)(cancel(color(black)("mL solution")))))^(color(blue)("given by the problem")) = "17.744 g KCl"`

Since this is how many grams of solute you get in `"100 mL"` of solution, you can say that the solution has a mass by volume percent concentration equal to -- don't forget to add the percent symbol, `%`.

`"% m/v" = color(green)(|bar(ul(color(white)(a/a)color(black)("17.7% KCl")color(white)(a/a)|)))`

The answer is rounded to three sig figs.