Title TOPIC 4 DENSITY AND RELATIVE DENSITY - WazaElimu.com.pdf ✅

27 TOPIC 4: DENSITY AND RELATIVE DENSITY 1. DENSITY:  This is the mass per unit volume of a substance. NOTE: Density is denoted by a letter ρ The SI-Unit of density is Kg/m3 or g/cm3 . Mathematically Density (ρ) = Mass (M) Volume (V) Example 1 A mass of a substance is 20g. Find the density of a substance if its volume is given as 100cm3 . Solution Data given Volume (V) = 100 cm3 Mass (M) = 20g Density (ρ) =? From: Density (ρ) = Mass (M) Volume (V) Density (ρ) = 20 g 100 cm3 = 0.2 g/cm3 ∴Density of the substance = 0.2 g/cm3 Questions: 1. A glass has a density of 2.5 g/cm3 and volume of 2cm3 . Calculate the mass of a glass. 2. A substance has a mass of 5.4 g and its density is 2.7 g/cm3 . Determine the volume of a substance. 3. A rectangular glass block has a mass of 5 kg and volume of 2 cm3 . Determine the density of the glass block in:- (i) Kg/m3 (ii) g/cm3 NOTE: The table below shows the densities of some substances. SUSBTANCE DENSITY (g/cm3 ) SOLIDS Aluminium 2.7 Copper 8.3 Gold 19.3 Iron 7.8 Lead 11.3 Glass 2.5 Ice (00C) 0.92


30 Data given Mass of solid (M) = 40g Initial volume (V1) = 50 cm3 Final volume (V2) = 70 cm3 Density of the solid object =? From: Density = M (g) ( V2− V1)cm3 Density = 40 g (70−50)cm3 = 2g/cm3 Density of the solid object = 2g/cm3 Question A measuring cylinder was filled with water to 200 cm3 mark. Ten large identical nails were placed in the water and the volume become 320 cm3 . (a) What was the average volume of the nails? (b) If each nail had 2g mass. What was the density of the nail material (Express your answer in kg/m3 ) III. DENSITY OF LIQUIDS  Density of liquids can be determined by using a burette or a density bottle as explained below. a) Density of liquids using a burette. Materials and apparatus (i) Burette (ii) Beaker (iii) Beam balance (iv) Kerosene Procedures 1. Measure the mass of the empty beaker by using a beam balance and record it as M1. 2. Measure the volume of kerosene by using a burette and record it as V cm3 . 3. Pour the known volume of kerosene into the beaker that measured in a burette. 4. Measure the mass of the beaker containing kerosene and record it as M2. Results 1. The mass of kerosene is obtained by subtracting M1 from M2. Thus; Mass of kerosene = (M2 – M1) g 2. The density of kerosene is obtained by dividing the mass of kerosene by the known volume of kerosene. Thus; Density = Mass of kerosine Volume of kerosine But: Mass of kerosine = (M2 – M1) g Volume of kerosine = V cm3 Then; Density of liquid (kerosene) = (M2 − M1) g Vcm3