Question

If you have a 150-gram sample of CrO3: • How many moles of CrO3 do you have? • How many oxygen atoms do you have? • How many grams of oxygen do you have?

Answer 1

Answer :

(a) The moles of $CrO_3$ is, 1.5 moles.

(b) The number of oxygen atoms are, $27.099\times 10^{23}$

(c) The mass of oxygen is, 72 grams.

Explanation : Given,

Mass of $CrO_3$ = 150 g

Molar mass of $CrO_3$ = 100 g/mole

Molar mass of oxygen = 16 g/mole

(a) First we have to calculate the moles of $CrO_3$.

$\text{Moles of }CrO_3=\frac{\text{Mass of }CrO_3}{\text{Molar mass of }CrO_3}=\frac{150g}{100g/mole}=1.5moles$

The moles of $CrO_3$ is, 1.5 moles.

(b) Now we have to calculate the number of oxygen atoms.

In $CrO_3$, there are 1 atom of chromium and 3 atoms of oxygen.

According to the mole concept,

1 mole of $CrO_3$ contains $3\times 6.022\times 10^{23}$ number of oxygen atoms.

So, 1.5 mole of $CrO_3$ contains $1.5\times 3\times 6.022\times 10^{23}=27.099\times 10^{23}$ number of oxygen atoms.

The number of oxygen atoms are, $27.099\times 10^{23}$

(c) Now we have to calculate the mass of oxygen.

As, 1 mole of $CrO_3$ contains 3 moles of oxygen

So, 1.5 mole of $CrO_3$ contains $1.5\times 3=4.5$ moles of oxygen

$\text{Mass of oxygen}=\text{Moles of oxygen}\times \text{Molar mass of oxygen}$

$\text{Mass of oxygen}=(4.5mole)\times (16g/mole)=72g$

The mass of oxygen is, 72 grams.