Question #5498c

1 Answer
Oct 22, 2017

Answer:

#"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.