Question

How do I find the amounts of atoms in $1$ liter ${H_2}O$?

Answer 1

The unit liter is used to express the volume of a substance. The substance is in liquid form. The number of atoms is calculated using the mole concept.

Complete step by step answer:
The given substance in this case is water. Water is a liquid and has a molar mass of $18g/mol$. A molecule of water consists of two hydrogen atoms and one oxygen atom.
The volume of water given is $1$ liter. So at first we need to determine the moles of water contained in $1$ liter of water. One liter of water is equal to $1000mL$ of water.
A mole of substance is the ratio of the amount of the substance and the molar mass of that substance. Thus it is written as
$mole = \dfrac{{amount{\text{ }}of{\text{ }}subs\tan ce}}{{molar{\text{ }}mass{\text{ }}of{\text{ }}subs\tan ce}}$
So the moles of water present in $1$ liter = $\dfrac{{1000}}{{18}} = 55.56moles$.
A mole is defined as the amount of substance which contains the number of atoms equal to $6.023 \times {10^{23}}$ . Thus the number of molecule of water present in $55.56moles$ of water is
$= 55.56 \times 6.023 \times {10^{23}} = 334.64 \times {10^{23}}$.
Further the number of atoms in one molecule of water is = $2$ hydrogen atoms + $1$ oxygen atom =$3$.

Hence the total number of atoms present in one liter of water is
$= 3 \times 334.64 \times {10^{23}} = 1.004 \times {10^{26}}atoms$.

Note: The number $6.023 \times {10^{23}}$ is called the Avogadro’s number. It is used to specify the number of atoms or molecules present in one mole of a substance. One mole of a substance is equal to the mass of the substance which is equal to the molar mass of that substance.