Question #82823

1 Answer
Jul 7, 2016

Answer:

#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.