Question

potassium dichromate k2cr2o7 is used in tanning leather, decorating porcelain, and water proofing fabrics. Calculate the number of oxygen atoms in 128.82 g of k2cr2o7

Answer 1

First we determine the molecular mass of potassium dichromate as follow:

2(39) + 2(52) + 7(16) = 294 g/mol

Now we find the number of moles of potassium dichromate as below:

Moles = mass / mol mass = 128.82 g / 294 g/mol = 0.438 moles

Note from the formula that the number of moles of chromium is twice the number of moles of potassium dichromate.

So you have 2(0.438 moles) or 0.876 moles of chromium.

Then, the number of chromium atoms present will be

.876 moles X (6.02*10^ 23 atoms / mole) = 5.25*10^ 23 atoms