Question

How many molecules of H2O are there in 1.0 g of H2O?

Answer 1

Answer : The number of molecules of
`H_2O` are,
`3.31* 10^(22)`

Explanation : Given,

Mass of
`H_2O` = 1.0 g

Molar mass of
`H_2O` = 18 g/mole

First we have to calculate the moles of
`H_2O`.

`\text{Moles of }H_2O=\frac{\text{Mass of }H_2O}{\text{Molar mass of }H_2O}=(1.0g)/(18g/mole)=0.055moles`

Now we have to calculate the number of molecules of
`H_2O`.

As, 1 mole of
`H_2O` contains
`6.022* 10^(23)` number of
`H_2O` molecules.

So, 0.055 mole of
`H_2O` contains
`0.055* 6.022* 10^(23)=3.31* 10^(22)` number of
`H_2O` molecules.

Therefore, the number of molecules of
`H_2O` are,
`3.31* 10^(22)`

Answer 2

Avogadro's number represents the number of units in one mole of any substance. This has the value of 6.022 x 10^23 units / mole. This number can be used to convert the number of atoms or molecules into number of moles. This will be used for the conversion to be done.

1.0 g H2O ( 1 mol / 18.02 g ) ( 6.022 x 10^23 molecules / mol) = 3.3 x 10^22 molecules