Question

The density of water is greater at:
A) ${\text{90}}{{\text{ }}^0}{\text{C}}$
B) ${\text{0}}{{\text{ }}^0}{\text{C}}$
C) ${\text{4}}{{\text{ }}^0}{\text{C}}$
D) ${\text{78}}{{\text{ }}^0}{\text{C}}$

Answer 1

Hint: The water shows different values of density at different temperatures. The density value is calculated as the mass of a substance divided by the volume occupied by the substance. One can think about this concept and relate this concept with different temperatures given in the options.

Complete step by step answer:
1) First of all let's learn about how the density gets affected by the temperature change. As we know the density is the value which we calculate by mass divided by the volume, the increase in the temperature will evaporate some solvent of the solution which will make the decrease in the total volume and the reverse will happen in the case of a decrease in temperature.

2) As we increase the temperature the solvent quantity will decrease which means the volume decreases but as mass particles don’t get evaporated the mass quantity will increase. So, we can say that the density increases as we increase the temperature and vice-versa.

3) But in the case of pure water where the solvent and solute are both the water molecule, the concept of density applies here differently. As there is an increase in the temperature there will be a decrease in the density.

4) The water is turned to ice at below the temperature of ${\text{0}}{{\text{ }}^0}{\text{C}}$ which is a solid form of water. At the solid state of water which is ice, the density is lowest as the water molecules form gaps between them.

5) At the temperature of exact ${\text{0}}{{\text{ }}^0}{\text{C}}$ there are some ice crystals that lower the density. The ice crystals start forming at the temperature of ${\text{4}}{{\text{ }}^0}{\text{C}}$ and further lowering of temperature turns it into ice. At this temperature of ${\text{4}}{{\text{ }}^0}{\text{C}}$ there is no ice crystal formed and the water molecules are closest to each.

6) Hence, at ${\text{4}}{{\text{ }}^0}{\text{C}}$ temperature the water has a greater density .

Hence, option C is the correct answer.

Note:
The water does not have a specific density as it varies with the temperature and that’s why we generally take the density value of water as ${\text{1}}$. The ice has a lower density than water and that’s the reason for ice floating on the water surface.