Density and Relative Density

• Two identical flask are shown one filled with water and the other with kerosene. When measured with an electronic balance the flask filled with water is found heavier than that filled with kerosene. Why?

• The answer is in finding the

  mass per unit volume of 

  kerosene and water 

  in respective flasks.

Density is referred to as the mass per unit volume. It is a measure of how tightly packed and how heavy the molecules are in an object.

• mass (usually expressed in grams)

• volume (usually expressed in cm³ or liters)

• 1000cm³ = 1L => 1cm³= 1mL

• Find the mass of object ; m

• Find the volume of object; v

• Divide Density;ρ= m/v

A block of ice with volume 5.5m³ has a mass of 5060kg.

Find the density of ice.

• Volume of block=5.5m³

  Mass of block= 5060 kg

• Density = mass /volume

                = 5060 kg/5.5m³.

                 = 920 kg/m³.

  The density of ice is 920 kg/m³.

Pure water has its highest density 1000 kg/m³_.

_{This explains why ice floats on water.}

A silver cylindrical rod has a length of 0.5m and radius of 0.4m. Find the density of the rod if its mass is 2640kg.

• Mass of cylinder =2640 kg

  Volume of cylinder = πr²h

                                  = 3.14 x 0.4 ² x 0.5

                                  = 0.2512m³

• Density = mass/volume

           = 2640 kg/0.2512m³

               =10509 kg/m³.

A stone has a mass of 112.5g.When the stone is totally immersed in a measuring cylinder containing water the displaced water moves from 50cm³ to 95cm³.Find the density of the stone.

• Mass of the stone =112.5g

  Volume of stone = 95cm³-50cm³=45cm³

• Density = mass/volume

               = 112.5g/45cm³

               = 2.5g/cm³.

Beaker contain 262.5cm³ of a certain liquid weigh 410g,if the mass of an empty dry beaker is 200g. Find the density of the liquid.

• Mass of liquid=410g-200g=210g

  Volume of liquid=262.5cm³.

• Density=mass/volume

              =210g/262.5cm³

              =0.8g/cm³.

• the density of a substance compared to that of water

• density of substance/density of water

• mass of any volume of a substance/ mass of equal volume of water

• it is a dimensionless quantity

• it can never be zero.

• the density of a substance compared to that of water

• density of substance/density of water

​

• mass of any volume of a substance/ mass of equal volume of water

• it is a dimensionless quantity

• it can never be zero.

• the density of a substance compared to that of water

• density of substance/density of water

• mass of any volume of a substance/ mass of equal volume of water

• it is a dimensionless quantity

• it can never be zero.