Question

What is the mass of \[mercury\] in \[grams\] and in \[kilograms\] if the density of \[mercury\] is \[13.6gc{m^{ - 3}}\] ?

Answer 1

Hint: To find the answer to the above question we need to be familiar with the basic density formula first. Then using the unitary method of conversion we can simply convert the answer in the given formula unit.

Complete answer:
Density of a substance is its amount of mass per unit volume. Density offers a convenient means of obtaining mass of a body from its volume or vice versa. Different materials usually have different densities, and density may be relevant to buoyancy, purity and packaging. For a pure substance the density has the same numerical value as its mass concentration. The density of material varies with its temperature and pressure, this variation is small for solid and liquids but much greater for gases. Increasing the pressure decreases the volume of the substance which increases the density. It is given by the formula-
\[density = \dfrac{{mass}}{{volume}}\]
For the S.I. unit of density, it can be obtained by –
\[S.I{\text{ }}unit{\text{ }}of{\text{ }}density = \dfrac{{S.I{\text{ }}unit{\text{ }}of{\text{ }}mass}}{{S.I{\text{ }}unit{\text{ }}of{\text{ }}volume}}\]
\[S.I{\text{ }}unit{\text{ }}of{\text{ }}density = \dfrac{{kg}}{{{m^{ - 3}}}}\]= \[kg{\text{ }}{m^{ - 3}}\]
Since this unit is quite large, therefore a chemist often expresses density in \[gc{m^{ - 3}}\], where mass is expressed in \[grams\] and volume is expressed in \[c{m^3}\]
From the formula of density we can obtain the mass formula as well. It will be-
\[Mass = Volume \times density\]
Here the
Volume = \[1L\]= \[1000c{m^3}\]
Density= \[13.6gc{m^{ - 3}}\]
Mass= \[1000 \times 13.6\]= \[13600g\]
For the mass in \[kilograms\]
\[1kg = 1000g\]
\[13600g = 13.6kg\]
One must know that the unit \[litre\] is not an S.I. unit, which is used for measurement of volume of liquids.

Note:
We often get confused between mass and weight. One must remember that mass is the amount of matter present in it while weight is the force exerted by gravity on an object. Weight may vary from one place to another whereas mass of a substance is constant.