Question #9c19a
1 Answer
Explanation:
Every time you're looking for a solution's molarity, you must determine how many moles of solute you get in one liter of solution.
That is what molarity essentially tells you - how many moles of solute you'd get if you had exactly one liter of solution.
#color(blue)(|bar(ul(color(white)(a/a)"molarity" = "moles of solute"/"one liter of solution"color(white)(a/a)|)))#
Notice that the problem provides you with the volume of the solution and with the mass of the solute, which in your case is potassium fluoride,
Your first goal here will be to use potassium fluoride's molar mass to determine how many moles you get in that sample
#116.2color(red)(cancel(color(black)("g"))) * "1 mole KF"/(58.097color(red)(cancel(color(black)("g")))) ~~"2.00 moles KF"#
So, you know that this solution contains
This means that you can use the number of moles of solute present in this sample as a conversion factor to help you find the number of moles of solute in
#1.00color(red)(cancel(color(black)("L solution"))) * "2.00 moles KF"/(3.00color(red)(cancel(color(black)("L solution")))) = "0.667 moles KF"#
The solution will thus have a molarity of
In other words, every liter of this solution will contain
Notice that you can find the solution's molarity by dividing the number of moles of solute by the total volume of the solution
#color(blue)(|bar(ul(color(white)(a/a)c = n_"solute"/V_"solution"color(white)(a/a)|)))#
In this case, you would have
#c = "2.00 moles"/"3.00 L" = color(green)(|bar(ul(color(white)(a/a)"0.667 mol L"^(-1)color(white)(a/a)|)))#
The answer is rounded to three sig figs, the number of sig figs you have for the volume of the solution.