Question

Question #9609d

Answer 1

`"0.1 g NaCl"`

Explanation:

Your goal here is to find the mass of sodium chloride that would be required to make `"200 mL"` of a `"10 mM"` solution, so focus on finding the number of moles of sodium chloride first.

Now, a `"10 mM"` solution contains `10` millimoles of solute for every `"1 L"` of solution. Since you know that

`"1 mol" = 10^3"mmol"" "` and `" " "1 L" = 10^3"mL"`

you can say that `"200 mL"` of solution will contain

`200 color(red)(cancel(color(black)("mL"))) * (1color(red)(cancel(color(black)("L"))))/(10^3color(red)(cancel(color(black)("mL")))) * (10 color(red)(cancel(color(black)("mmoles NaCl"))))/(1color(red)(cancel(color(black)("L solution")))) * "1 mole NaCl"/(10^3color(red)(cancel(color(black)("mmoles NaCl"))))`

`= " 0.0020 moles NaCl"`

Now all you have to do is use sodium chloride's molar mass to convert the moles to grams

`0.0020 color(red)(cancel(color(black)("moles NaCl"))) * "58.44 g"/(1color(red)(cancel(color(black)("mole NaCl")))) = color(green)(bar(ul(|color(white)(a/a)color(black)("0.1 g")color(white)(a/a)|)))`

The answer is rounded to one significant figure.