Question

Question #78d59

Answer 1

`"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.