Question

Question #c20c9

Answer 1

`"0.70 g mol"^(-1)`

Explanation:

Your goal here is to figure out the number of moles of solute present in `"1 L"` of solution -- this will give you the molarity of the solution.

Now, you know that your solution contains `"0.26 g"` of potassium chloride, your solute. You can convert this to moles of solute by using the compound's molar mass

`0.26 color(red)(cancel(color(black)("g"))) * "1 mole KCl"/(74.6color(red)(cancel(color(black)("g")))) = "0.003485 moles KCl"`

You can thus say that `"5.00 mL"` of solution contain `0.003485` moles of solute. As you know, solutions are homogeneous mixtures, which implies that the have the same composition throughout.

Consequently, you can use the known composition of the solution to calculate the number of moles of solute present in `"1 L"` of solution

`1 color(red)(cancel(color(black)("L solution"))) * (10^3color(red)(cancel(color(black)("mL"))))/(1color(red)(cancel(color(black)("L")))) * "0.003485 moles KCl"/(5.00 color(red)(cancel(color(black)("mL")))) = "0.70 moles KCl"`

Therefore, you can say that the molarity of the solution is equal to

`color(darkgreen)(ul(color(black)("molarity" = "0.70 g mol"^(-1))))`

The answer is rounded to two sig figs, the number of sig figs you have for the mass of solute present in the solution.