calculate the mass composition of each constituent element of potassium chromate

Question

Express your answers using four significant figures separated by commas.

Answer 1

Mass composition is the percentage of a particular atom over the whole.

You first need the formula of potassium chromate. Potassium has a charge of +1 and chromate, which is CrO4, has a -2 charge. So the formula is K2CrO4. (It doesn't let me do it, here but the 2 and 4 in the formula are subscripts, just so you know!)

Next, you need the molar mass of K2CrO4. You have 2 potassium atoms, 1 chromium atom and 4 oxygen atoms.

Calculation: 2(39.098) + 51.996 + 4(16) = 194.2 grams / mol

Now, to find the mass composition, you take individual masses and divide them by the total of 194.2 grams / mol

We'll do each atom individually:

For potassium, you do 2(39.098) / 194.2 = 0.4027 = 40.27% potassium

For chromium, you do 51.996 / 194.2 = 0.2677 = 26.77%

For oxygen, you do 4(16) / 194.2 = 0.3296 = 32.96%

For checking your work: if you add up all the decimals, you should get 1.

So 0.4027 + 0.2677 + 0.3296 = 1

Another way to check is to add up the percentages, and you should get 100.

Hope this helps =)