# Question 9609d

Oct 17, 2016

$\text{0.1 g NaCl}$

#### Explanation:

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

Now, a $\text{10 mM}$ solution contains $10$ millimoles of solute for every $\text{1 L}$ of solution. Since you know that

$\text{1 mol" = 10^3"mmol"" }$ and $\text{ " "1 L" = 10^3"mL}$

you can say that $\text{200 mL}$ 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"))))

$= \text{ 0.0020 moles NaCl}$

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.