Question

How many oxygen atoms are present in a tablet weighing $360mg$ of Aspirin (Aspirin-${C_9}{H_8}{O_4}$).

Answer 1

Aspirin is an anti-inflammatory drug used for relieving pain, inflammation and fever. The number of oxygen atoms can be determined using the mole concept.

Complete step by step answer: Aspirin is an organic compound also known as acetylsalicylic acid. The molecular formula of aspirin is ${C_9}{H_8}{O_4}$. It is an aromatic compound containing a benzene ring. The functional groups attached to the benzene ring are one carboxylic ($COOH$) group and one acetyl ($COC{H_3}$) group. The structure of aspirin is

The molecular or chemical formula of Aspirin is ${C_9}{H_8}{O_4}$. The molecular weight of Aspirin is =
$9$ x atomic mass of $C$ atom + $8$ x atomic mass of $H$ atom + $4$ x atomic mass of $O$ atom
=$9 \times 12 + 8 \times 1 + 4 \times 16 = 180g$
A tablet of Aspirin weighs $360mg$. Thus the moles of Aspirin contain in $360mg$ of Aspirin is,
$moles = \dfrac{{weight}}{{molar{\text{ }}mass}}$
$= \dfrac{{360 \times {{10}^{ - 3}}}}{{180}} = 2 \times {10^{ - 3}}$
One molecule of Aspirin contains four molecules of oxygen atom. Thus the moles of oxygen in $2{\text{ }} \times {10^{ - 3}}$ moles of Aspirin = $4 \times 2 \times {10^{ - 3}} = 8 \times {10^{ - 3}}$
According to Avogadro’s law, one gram mole of a substance contains $6.023 \times {10^{23}}$ atoms. Here the number of moles of oxygen is $8 \times {10^{ - 3}}$. Therefore the number of oxygen atoms present in $8{\text{ }} \times {10^{ - 3}}$ moles of oxygen = moles of oxygen x Avogadro’s number
= $8 \times {10^{ - 3}} \times 6.023 \times {10^{23}} = 4.81 \times {10^{21}}$
Hence $4.81 \times {10^{21}}$ number of oxygen atoms is present in a tablet weighing $360mg$ of Aspirin (Aspirin-${C_9}{H_8}{O_4}$).

Note: Before the discovery of aspirin, $2$ -hydroxy benzoic acid was used as a drug. This leads to severe irritation in the stomach after consumption. In order to avoid such irritation the hydroxyl group was protected with acetyl group.