(h) describe how to determine the density of a liquid, of a regularly shaped solid and of an irregularly shaped solid which sinks in water (volume by displacement)


Density is the amount of matter of a body in a fixed volume. The formula to collect density is mass/volume. Its unit is therefore kg/m^3. An object of 1 kg/m^3 density can be said to contain 1Kg of mass in 1m^3 of volume. Different elements and things have specific densities. Therefore,like melting point and boiling point, density can also be used to check the purity of a substance e-g the density of pure water is 1000kg/m^3. The tale of how Archimedes used density to determine whether the king's crown was made of pure gold is well known.

Density of a Liquid

We know that to find density, we need two quantities, mass and volume. To find the mass of a liquid, we need.
  • A beam balance
  • A container (e-g graduated cylinder)
We will first measure the mass of the container using the beam balance. Let us call this mass M1. Now, we will put the liquid in the container, and measure the mass of the container again. Let us name this M2. To get the mass of the liquid, we will subtract M1 from M2. We have the mass of the liquid now.

Now, we need to find the volume of the liquid. For this we will need a:
  • Graduated cylinder
 Finding the volume is pretty simple with the help of a graduated cylinder, and it has already been covered in the previous posts.

Now that we have both the mass and volume of the liquid, we will just use the equation mass/volume. We now have the density of the liquid. This density of the liquid can be used to identify the liquid. Also it tells us what mass of the liquid is present in one cm^3 of that liquid.

Density of a regular shaped solid

The process of finding the mass is the same, that is by using a beam balance. The volume of a regular shaped solid depends on the shape. For example the volume of cube would side*side*side, the volume of a sphere is 4/3*pi*r^3. 

After finding both the quantities, we will once again use the formula mass/volume to find the density of the solid object.

Density of an irregular shaped solid which sinks

The process of finding the mass of the solid is once again the same. 

But to find the volume of an irregularly shaped solid that sinks, we will once again a graduated cylinder. The rest of the process is covered here. Once you have found the volume, the rest is simple. Once again, just use the formula mass/volume.

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