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

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

(b) The number of oxygen atoms are,
`27.099* 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}=(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* 6.022* 10^(23)` number of oxygen atoms.

So, 1.5 mole of
`CrO_3` contains
`1.5* 3* 6.022* 10^(23)=27.099* 10^(23)` number of oxygen atoms.

The number of oxygen atoms are,
`27.099* 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* 3=4.5` moles of oxygen

`\text{Mass of oxygen}=\text{Moles of oxygen}* \text{Molar mass of oxygen}`

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

The mass of oxygen is, 72 grams.