Density of Water

Density of Water

What is the density of water, and how does it depend on temperature? Answers to such interesting questions are provided in this article.
The term 'density' is a characteristic property of every object, and it forms a basic topic of study in science. An interesting anecdote that is related to the concept of density is the running of Archimedes, naked in the streets of Greece, shouting 'Eureka, Eureka', after he discovered a method to determine the volume of an object with an irregular shape. This discovery indirectly paved the path for study and analysis of volume and density in the subsequent years.

Water, with its unique physical and chemical properties, has various interesting characteristic features, and one of them is its density. It is a very fluctuating parameter that depends on various factors like mass and volume of water, temperature, and atmospheric pressure. In chemistry, density of water at room temperature is used as a parameter to compare the densities of various other objects.

Does a substance float or sink in water? This gives us an idea about the density of a substance. For instance, a log of wood floats in water, but a rock sinks in it. This tells us that density of water at room temperature or normal average temperature is more than the wood and less than the rock. Simply said, wood is less dense than water, and rocks are denser than water.

Explanation
Density can be defined in a qualitative form as the relative heaviness of various objects with constant volume. Mathematically stated, density is mass per unit volume of a substance. Although, mass and weight are generally interchangeably used terms, there is a fundamental difference between them, and understanding this is necessary to avoid any confusion. Mass is a measure of the quantity of matter contained by an object, and it is independent of any external factor. Thus, mass is a fixed quantity all over the Universe. On the other hand, weight is proportional to mass, but it depends on the position of the object. Weight is the gravitational force exerted on the object (generally by Earth). In physics, specific gravity or relative density is another term used to define the density of a substance relative to water.

Density (ρ) = Mass (m)/Volume(V),

where,
m = mass of the body
V= volume occupied by the body

Density of an object depends on the temperature. An increase or decrease in temperature causes the expansion or contraction, respectively, in the size of the object. This leads to changes in volume, and hence, also in density. According to the SI system of units, the unit of density is kilogram per cubic meter or Kg/m3. This unit can be easily derived by putting the SI units of mass and volume in the density formula, which are kilogram and cubic meter. In CGS system, the unit of density is gram per cubic centimeter or g/cm3.

What is the Density of Water?
At room temperature (20° C), the density value is 1 g/cm3 or 1000 kg/m3. This value is stable and constant at any particular temperature, when the water is devoid of any impurities. Density is an intensive property at any particular temperature. However, with changes in temperature, pressure, and addition of impurities, the density of water also changes. Water expands after freezing, increasing its volume by 9%, and that is why the density of ice is less than that of water. Thus, ice floats on water. An interesting fact about water is that it is the only substance where the density in solidified form is less than its liquid form. Besides that, it is the only substance on Earth, to exist in all the three general phases of matter, which are solid, liquid, and gas.

Density of Water at Different Temperatures
It is highest at 4° C (39.2° F), and it equals to approximately 1000 kg/m3.

Density of Water
Temperature (t° C)Density (ρ kg/m3)
0999.9
51000
10999.7
20998.2
30995.7
40992.2
50988.1
60983.2
70977.8
80971.8
90965.3
100958.4

Except for a point at 4 °C, the density of water decreases with increase in temperature, i.e., water has the highest density at this temperature.