Water is undoubtedly the most abundantly found chemical substance on earth. It is the only compound that exists in all the three phases of matter, viz. gas, liquid, and solid. In contrast to other substances, solid water is less dense than liquid water, or in other words, ice is lighter than water.
Water Density at Room Temperature
In physics, the density of a substance refers to the mass (or weight) per unit volume. This aspect is useful to determine the buoyancy and purity of a material. Represented by the symbol ρ (rho), the SI unit of density is kilograms per cubic meter (kg/m3). Water density is classified under the category of intensive properties. This means that its density at a particular temperature remains the same, every time a measurement is made, irrespective of the sample size.
With respect to the definition, the density formula is represented as Density (ρ) = Mass (m)/Volume (V). At room temperature (i.e., 22° C), the density of water in kg/m3 is 997.77. In other words, at the same temperature, the density of water in g/ml (or g/cm3) is 0.99777. The logic is to divide the value of kg/m3 by 1000 to get pure water density in g/ml. However, it is to be noted that grams per milliliter (g/mL) and gram per cubic centimeter (g/cm3) are not SI units.
While discussing this topic in detail, water density is found to vary with respect to the level of salinity (or other impurities) and fluctuation of temperature. Of course, pressure does play a role in the subject of water denseness. However, as we are discussing the density of water measured in ground level for collected water samples, the pressure attribute is not considered in determining the density. In general, the density of a matter is higher in solid form, as compared to the density of the same matter in liquid form.
The density of water is both directly or indirectly proportional to temperature. To be more precise, water density is higher in colder temperatures, until a certain limit. It is found to be highest when the surrounding temperature is 4° C. When temperature is further cooled down to the freezing point, water solidifies and expands, resulting in low density. This is the reason why ice blocks (less dense than water) floats on the surface of the ocean water. As water freezes to its solid form of ice, the density is reduced to about 9 percent.
Density of Water at Different Temperatures
As the environmental temperature drops down below the room temperature, the corresponding water density is higher than 997.77 kg m3. The actual value will differ based on how cold the temperature is at the time of measurement. A simple example that will help you clear your doubts is the variance in the density at different depths of the sea. As we go deeper, the water temperature gradually decreases. Consequently, water at the sea/ocean bottom is more dense, as compared to the one at surface. For your reference, the table for water density at varied temperatures is given below.
|Density of Water|
|Temperature (° C)||Density (kg/m3)|
As with salinity, higher the level of salt concentration, the more will be the density of water, even at room temperature. In short, density of water is directly proportional to salinity. Thus, water with lower salt content will float over water with higher salt concentration. If you are interested in calculating the density of seawater at different temperatures, there are online tools that are developed for the same purpose. All you need is enter the temperature (both in Celsius and Fahrenheit) and salinity in PPM (parts per million) or mg/L in the suggested fields.
After finding the results, you can correlate the density of water at room temperature for different salinity levels. Likewise, check the water density of samples having same salinity and different temperatures. Direct measurement for density of seawater is done by maintaining the collected water samples in controlled environmental conditions.