Question

Question #82823

Answer 1

`14%`

Explanation:

A solution's percent concentration by mass, `"% m/m"`, sometimes called mass percent, tells you how many grams of solute you get for every `"100 g"` of solution.

This means that in order to find a solution's mass percent, all you have to do is figure out how many grams of solute you have in `"100 g"` of solution.

In your case, you know that you're adding `"8.0 g"` of sodium hydroxide, `"NaOH"`, which is your solute, to `"50.0 g"` of water, which is your solvent.

The first thing to do is figure out the mass of the solution by adding the mass of the solute and the mass of the solvent

`m_"solution" = m_"solute" + m_"solvent"`

`m_"solution" = "8.0 g" + "50.0 g" = "58.0 g"`

So, you know that you have `"8.0 g"` of solute in `"58.0 g"` of solution. Use this as a conversion factor to find the mass of solute that would correspond to `"100 g"` of solution

`100 color(red)(cancel(color(black)("g solution"))) * "8.0 g NaOH"/(58color(red)(cancel(color(black)("g solution")))) = "13.8 g"`

Your solution will contain `"13.8 g"` of solute for every `"100 g"` of solution, which means that its mass percent of sodium hydroxide will be

`"% m/m" = color(green)(|bar(ul(color(white)(a/a)color(black)("14 % NaOH")color(white)(a/a)|)))`

The answer must be rounded to two sig figs, the number of sig figs you have for the mass of sodium hydroxide.