# Question 82823

Jul 7, 2016

14%

#### Explanation:

A solution's percent concentration by mass, $\text{% m/m}$, sometimes called mass percent, tells you how many grams of solute you get for every $\text{100 g}$ 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 $\text{100 g}$ of solution.

In your case, you know that you're adding $\text{8.0 g}$ of sodium hydroxide, $\text{NaOH}$, which is your solute, to $\text{50.0 g}$ 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

${m}_{\text{solution" = m_"solute" + m_"solvent}}$

${m}_{\text{solution" = "8.0 g" + "50.0 g" = "58.0 g}}$

So, you know that you have $\text{8.0 g}$ of solute in $\text{58.0 g}$ of solution. Use this as a conversion factor to find the mass of solute that would correspond to $\text{100 g}$ 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 $\text{13.8 g}$ of solute for every $\text{100 g}$ 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.