Question #78d59

1 Answer
Stefan V.
Nov 14, 2016

#"0.002271 moles K"_2"Cr"_2"O"_7#

Explanation:

By defition, a #"0.1885-M"# solution of potassium dichromate, #"K"_2"Cr"_2"O"_7#, contains #0.1885# moles of solute for every liter of solution.

Since you know that

#color(blue)(ul(color(black)("1 L" = 10^3"mL")))#

you can say that your solution will contain

#"0.1885 M K"_2"Cr"_2"O"_7 = ("0.1885 moles K"_2"Cr"_2"O"_7)/(10^3"mL solution")#

You can thus use the molarity of the solution as a conversion factor to take you from volume of solution to moles or vice versa.

In your case, you have

#12.05 color(red)(cancel(color(black)("mL"))) * ("0.1885 moles K"_2"Cr"_2"O"_7)/(10^3color(red)(cancel(color(black)("mL")))) = color(darkgreen)(ul(color(black)("0.002271 moles K"_2"Cr"_2"O"_7)))#

The answer is rounded to four sig figs.

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