Question

Question #5498c

Answer 1

`"428 mL"`

Explanation:

As you know, the molarity of a solution tells you the number of moles* of solute present for every `"1 L"` of the solution.

`"molarity" = "moles"/"1 L"`

If you keep in mind that you have

`"1 mol" = 10^3color(white)(.)"mmol" " "` and `" " "1 L" = 10^3color(white)(.)"mL"`

you can say that the molarity of a solution tells you the number of millimoles of solute present for every `"1 mL"` of the solution.

`"molarity" = (color(red)(cancel(color(black)(10^3)))color(white)(.)"mmoles")/(color(red)(cancel(color(black)(10^3)))color(white)(.)"mL") = "mmoles"/"1 mL"`

This means your solution, which has a molarity of `"0.642 M"`, contains `0.642` mmoles of sodium thiosulfate, the solute, for every `"1 mL"` of the solution.

You can thus say that `275.` mmoles of sodium thiosulfate will be present in

`275. color(red)(cancel(color(black)("mmoles Na"_2"S"_2"O"_3))) * "1 mL solution"/(0.642 color(red)(cancel(color(black)("mmoles Na"_2"S"_2"O"_3)))) = color(darkgreen)(ul(color(black)("428 mL solution")))`

The answer is rounded to three sig figs.