Question

Question #f0918

Answer 1

`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.