Question #8baf6

1 Answer
Stefan V.
Feb 17, 2017

"0.255 moles K"_2"Cr"_2"O"_7

Explanation:

The first thing you need to do here is to figure out how many grams of potassium dichromate you have in your sample.

You know that your solution is 15.00%, presumably by mass, which tells you that you get "15.00 g" of potassium dichromate for every "100 g" of solution.

This means that your sample will contain

500. color(red)(cancel(color(black)("g solution"))) * ("15.00 g K"_2"Cr"_2"O"_7)/(100color(red)(cancel(color(black)("g solution")))) = "75.0 g K"_2"Cr"_2"O"_7

Now all you have to do is use the molar mass of potassium dichromate to convert the number of grams to moles

75.0 color(red)(cancel(color(black)("g"))) * ("1 mole K"_2"Cr"_2"O"_7)/(294.185color(red)(cancel(color(black)("g")))) =color(darkgreen)(ul(color(black)("0.255 moles K"_2"Cr"_2"O"_7)))

The answer is rounded to three sig figs, the number of sig figs you have for the mass of the solution.

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