What is the molarity of a #KCl# solution made by dissolving 24.7 g of #KCl# in a total volume of 500. mL?

Question

What is  the molarity of a #KCl# solution made by dissolving 24.7 g of #KCl# in a total volume of 500. mL?

Jeremiah Adams · Accepted Answer

#"0.663 mol L"^(-1)#

To determine the molarity of a solution, two things must be known.

The problem provides you with a #"24.7-g"# sample of potassium chloride, #"KCl"#, and a total volume of a solution of #"500. mL"#.

Use the compound's molar mass, which, as you are aware, indicates the mass of one mole of potassium chloride, to determine the number of moles of your solute.

#24.7 color(red)(cancel(color(black)("g"))) * overbrace("1 mole KCl"/(74.55color(red)(cancel(color(black)("g")))))^(color(purple)("molar mass of KCl")) = "0.3313 moles KCl"#

Now, molarity is expressed per liter of solution. Since you dissolve #0.3313# moles of potassium chloride in #"500. mL"# of solution, you can say that #"1.0 L"# will contain

#1.0color(red)(cancel(color(black)("L"))) * (10^3color(red)(cancel(color(black)("mL"))))/(1color(red)(cancel(color(black)("L")))) * "0.3313 moles"/(500. color(red)(cancel(color(black)("mL")))) = "0.6626 moles KCl"#

This indicates that the solution's molarity will be

#c = color(green)("0.663 mol L"^(-1))#

Three sig figs are used to round the result.

Jose Ayala · Answer

undefined To find the molarity of the KCl solution, first calculate the number of moles of KCl using its molar mass (39.1 g/mol for K and 35.45 g/mol for Cl). Then, divide the number of moles by the volume of the solution in liters (0.5 L).

Molarity (M) = moles of solute / volume of solution in liters