Question

A sample of sea water contains $5x{\text{ }}{10^{ - 3}}{\text{ }}g$ of dissolved oxygen in $1{\text{ }}Kg$ of the sample. The concentration of ${O_2}$ in that sea water sample in ppm is:
A. $5 \times {10^4}$
B. $5 \times {10^{ - 3}}$
C. $5 \times {10^{ - 2}}$
D. $5 \times {10^{ - 1}}$
E. $5$

Answer 1

The solubility of gas in sea water is less than that in freshwater. Generally, cold water has been found to contain more dissolved oxygen than warm water. The ppm stands as a measure of concentration in parts per million.

Complete step by step answer: It is given that the sea water contains $5x{\text{ }}{10^{ - 3}}{\text{ }}g$ of dissolved oxygen. The weight of the seawater sample is $1{\text{ }}Kg$. The weight of sea water in grams is $1000g$.
In order to determine the concentration we have to change all the amounts of oxygen and sea water samples in the same units.
The equation can be written as:
$1{\text{ }}Kg$ ($1000g$) of sea water = $5x{\text{ }}{10^{ - 3}}{\text{ }}g$ of oxygen
$1ppm$ is the equivalent to $\dfrac{1}{{{{10}^6}}}$.
Therefore, concentration of oxygen in sea water in ppm will be:
$= \dfrac{{5 \times {{10}^{ - 3}}}}{{{{10}^3}}} \times {10^6}ppm$
$= 5ppm$ .
The correct option is E, i.e. concentration of ${O_2}$ in that sea water sample in ppm is $5ppm$.

Additional information: Dissolved oxygen and carbon dioxide are important constituents for marine life. Marine plants and organisms use dissolved carbon dioxide and oxygen for their survival. Plants using carbon dioxide, sunlight and water, make carbohydrates through the process called photosynthesis thereby releasing oxygen as the byproduct while organisms use this oxygen to release energy from these carbohydrates. Marine animals like fish with gills extract oxygen from the seawater.

Note: The concentration of oxygen in sea water varies from $4 - 9{\text{ }}mg/L$. In addition to oxygen and carbon dioxide, nitrogen gas also has considerable abundance in sea water.