Question

The molarity of heavy water ${D_2}O$ is (assume density of ${D_2}O$ as $1g/ml$)
A. $55.55M$
B. $55M$
C. $48M$
D. $50M$

Answer 1

Molarity is the amount of a substance in a certain volume of solution. It is defined as the number moles of solute per liter of solution. It is also known as the molar concentration of a solution. Its SI unit is $mol{L^{ - 1}}$ or $mol\,d{m^{ - 3}}$.

Formula used:
Molarity$= \dfrac{{density}}{{molar\,mass}} \times 1000$

Complete step by step answer:
The majority of reactions happen in solutions. So, it is very important to understand how the amount of substance is expressed when it is present in the solution.
One of the most common methods is Molarity. It is one of the most widely used units of concentration and is denoted by M. It is further defined as the number of moles of solute present in one liter of solution.
Now, in the given question, we have to find out the molarity of heavy water ${D_2}O$
So, to calculate the molarity, we need to know the two constants i.e. density and molar mass
Now, molar mass of deuterium oxide i.e. ${D_2}O$ is $20.0276gmo{l^{ - 1}}$ and density is$1g/c{m^3}$.
According to the given formula,
Molarity$= \dfrac{{density}}{{molar\,mass}} \times 1000$
By substituting the given values, we get
Molarity$= \dfrac{1}{{20.0276}} \times 1000$
$= 49.931 \approx 50$
Therefore, molarity of heavy water is $50M$

Hence, option D is correct.

Note: ${D_2}O$ is an integral part of heavy water nuclear reactors, where it is used as a coolant and as a neutron moderator. It is also used in NMR (nuclear magnetic resonance) spectroscopy, which is used to observe the magnetic fields around the nuclei of atoms. Further, the metabolic rate in humans and animals is also tested with the help of ${D_2}O$ and heavy oxygen water.