Question #f0918

1 Answer
Jun 12, 2016

Answer:

#6.3%#

Explanation:

The trick here is to realize that a solution's weight by weight percent concentration, #"%w/w"#, is calculated by taking into account the mass of the solute, which in your case is potassium nitrate, #"KNO"_3#, and the total mass of the solution.

You will thus have

#color(blue)(|bar(ul(color(blue)("% w/w KNO"_3 = "mass of KNO"_3/"total mass of solution" xx 100color(white)(a/a)|)))#

You know that your solution contains #"8.4 g"# of potassium nitrate and #"125 g"# of water. This means that the total mass of the solution will be

#m_"total" = m_(KNO_3) +m_(H_2O)#

#m_"Total" = "8.4 g" + "125 g" = "133.4 g"#

The weight by weight percent concentration will thus be

#"% w/w" = (8.4 color(red)(cancel(color(black)("g"))))/(133.4color(red)(cancel(color(black)("g")))) xx 100 = color(green)(|bar(ul(color(white)(a/a)color(black)("6.3% KNO"_3)color(white)(a/a)|)))#

This means that for every #"100 g"# of solution you get #"6.3 g"# of potassium nitrate.