Question

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

Answer 1

Hint: 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.