Density of Water - Formula, Factors, Temperature, FAQs

Examples based on water density

• Ice floats on water because the density of ice is less than that of water. When ice freezes, it expands, and molecules of water arrange themselves in open crystal structures, which makes them occupy more space. Due to this expansion, ice becomes less dense than water.
• The boats and ships float on water because the overall density of those ships is less than the density of water.
• In our daily lives, when we cook, we see vegetables floating over the surface of the water. This is because the density of vegetables is less than the density of water.
• During swimming, the human body floats over the water because the density of water is more than the density of the human body.
• Density of water is useful in metallurgical processes. Because there are many materials whose density is less than that of water, the powder of the ore is mixed with water, and material having less density than water comes to the surface of the water, which can be removed easily.

What is density?

The density of any material can be measured by dividing the mass of that material by its volume. Basically, the density of any material measures the mass of any material in a particular volume.

The mathematical expression for density is shown below:

Density $=\frac{\text { Mass }}{\text { Volume }}$

SI unit for density = kilogram per cubic meter, i.e., kg/m³

CGS unit for density = gram per cubic centimeter, i.e., g/cm³

For example, if there are two materials that are of the same volume but different densities, the higher-density material will be heavier than the material that possesses lower density. The floating property of any material is based on the density of that material, whether it will sink or float.

What Is the Density of Water?

The density of water can be calculated by dividing the mass of water by the volume of water. The density of water is approximately 997 kg/m³. This means that 997 kilograms of water is present in 1 cubic meter (1 m³). The density of water is temperature-dependent.

Why is Water's Density Unique?

The density of water is unique because its density varies with the increase or decrease in temperature. But the density of water shows different behavior from other substances. For example, when the temperature of any substance is decreased, then generally they become more dense, and as they further cool, the density increases, but it's not the same for water. The density of water becomes maximum at 4°C. On further decrease of the temperature of water, its density tends to decrease. Due to this phenomenon, the ice floats on the water's surface because ice freezes at 0°C, and at this point, the density of ice is lower than the density of water.

Water shows this strange behavior due to its molecular structure. The space occupied by water molecules when it is in a liquid state is lower than the space occupied by water molecules in its frozen state (or solid state). This occupied more space, leading to a lower density of the frozen state of water because volume is indirectly proportional to the density; as the volume increases, the density will decrease at this point. Hence, the ice will float on the water surface. This ice floating on the surface of the water insulates the outer region over the ice surface and the lower liquid water region below the ice surface and helps protect aquatic life in the cold regions.

Few properties of Water

Factors Affecting the Density of Water

There are a few factors that affect the density of water. Some of these are mentioned below:

Temperature

This is mentioned above in the article as well, that temperature affects the density of water. This is because the density of water depends upon its crystal structure, and if the temperature varies, the space occupied by the molecules of water also varies.

Salinity

Salinity means the amount of salts dissolved in water. Seawater is denser than normal freshwater. This is because there is a huge amount of salt dissolved in the seawater, which increases the density of the seawater. So, it becomes heavier than nonsaline freshwater. This is the reason why some objects float in seawater but not in freshwater.

Pressure

The density of water is affected by pressure in very small amounts. This is because the water is incompressible. But still, water becomes a little denser when pressure is increased.

Density vs Temperature

There is no absolute density of water because the density of water is dependent on temperature. The density of water in the liquid phase is higher than the density of water in the solid phase. The temperature versus density graph is shown below to understand how the density varies with temperature:

Density of Water at Various Temperature Scales

The table shown below represents the density of water at different temperatures (two different scales) in different units.

The information from the table mentioned above indicates that the density of water decreases with an increase in temperature. The density of water is highest at 4°C (39.2°F).

Density of Water Experiment

To better understand the density of water, here's an experiment shown below. For which we need a large glass tube or a glass container, honey, water, coconut oil, and a few food colorings.
Firstly, pour one-fourth cup of honey.
Then, gently pour one-fourth cup of colored water over the honey.

And in the last, cover the colored water with one-fourth cup of coconut oil.

It's important to note that different compounds have varied densities, which means that even for the same volume, they weigh differently. For example, heavier substances, like honey, tend to settle at the bottom, while lighter substances, like oil, prefer to float at the top.

Density of Several Liquids

The table shown below indicates the density of a few liquids:

Note:

• The specific gravity (SG) of any substance is the ratio of the density of a substance to the density of water (at 4°C, where water has a density of 1 g/cm³).
• The substances that have a specific density of 1 have the same density as the density of water.
• The substances that have a value of specific gravity less than 1 are lighter than water, while the substances that have a value of specific gravity more than 1 are heavier than water.