# How many grams of oxygen are in 2 moles of potassium dichromate, K_2Cr_2O_7?

Apr 6, 2016

There are $223.9916$ grams of oxygen in 2 moles of potassium dichromate.

#### Explanation:

There are two simple steps you can take to answer your question. The number of grams of a substance can be determined by summing the atomic weights of the individual components and multiplying that result by the number of moles you have.

However, since you are only interested in the amount of grams of oxygen in 2 moles of ${K}_{2} C {r}_{2} {O}_{7}$, you can focus only on the oxygen element.

There are 7 atoms of oxygen denoted by the subscript 7 in the compound. The atomic mass of oxygen is 15.9994 grams per mole.

So in the ${K}_{2} C {r}_{2} {O}_{7}$ compound the atomic mass of the 7 oxygen atoms is:

$15.9994$ $\text{grams"/"mole} \cdot \left(7\right)$

which equals

$111.9958$ $\text{grams"/"mole}$

Since you have 2 moles of ${K}_{2} C {r}_{2} {O}_{7}$, you multiple your atomic mass of the oxygen by 2 and with dimensional analysis you can see the moles cancel out and you are left with grams.

The answer being: $223.9916$ grams