Question #9609d

1 Answer
Oct 17, 2016

"0.1 g NaCl"0.1 g NaCl

Explanation:

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

Now, a "10 mM"10 mM solution contains 1010 millimoles of solute for every "1 L"1 L of solution. Since you know that

"1 mol" = 10^3"mmol"" "1 mol=103mmol and " " "1 L" = 10^3"mL" 1 L=103mL

you can say that "200 mL"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.