An aqueous solution has a mass of #490# grams containing #8.5 xx 10^"-3"# gram of calcium ions. What is the concentration of calcium ions in this solution?
1 Answer
Explanation:
Judging by the values you have, the most helpful concentration that can be calculated here is that in parts per million, ppm.
A solution's ppm concentration tells you the number of grams of solute present for every
#10^6 = 1,000,000#
grams of solution. Now, notice that you can approximate the mass of the solution, which is equal to
#"mass solution" = "490 g" + "0.0085 g" #
#"mass solution = 490.0085 g"#
to be equal to the mass of water, the solvent.
#"490.0085 g " ~~ " 490 g"#
You can thus say that, in your case, a
Use the known composition of the solution as a conversion factor to calculate the number of grams of calcium cations present in
#10^6 color(red)(cancel(color(black)("g solution"))) * (8.5 * 10^(-3)color(white)(.)"g Ca"^(2+))/(490color(red)(cancel(color(black)("g solution")))) = "17.35 g Ca"^(2+)#
Since this represents the number of grams of calcium cations present in
#color(darkgreen)(ul(color(black)("concentration" = "17 ppm Ca"^(2+))))#
The answer is rounded to two sig figs, the number of sig figs you have for your values.