Suggested practical - Determine the densities of a variety of objects

There are different ways to investigate density. In this required practical activity, it is important to:

  • use appropriate apparatus and methods to measure volume and mass
  • make accurate measurements of the mass and the volume of different objects, and use these measurements to calculate densities

Aim

To measure the density of various materials.

Method

Method 1: Regular solids

  1. place the cuboid on the top pan balance and record its mass in grams
  2. use a ruler to measure the length (l), width (w) and height (h) of the cuboid
  3. calculate the volume of the cuboid using: volume = l × w × h (where measurements are in cm and the volume is in cm3)
  4. use the measurements from steps 1 and 3 to calculate the density of the substance

Method 2: Stone or other irregular-shaped object

  1. place the object on the top pan balance and record its mass in grams
  2. fill the displacement can until the water is level with the bottom of the pipe
  3. place a measuring cylinder under the pipe, ready to collect the displaced water
  4. carefully lower the object into the can and wait until no more water runs into the cylinder
  5. measure the volume of the displaced water
  6. use the measurements from steps 1 and 5 to calculate the density of the object

Method 3: Water (or any liquid)

  1. place an empty measuring cylinder on the top pan balance and measure its mass in grams
  2. pour 50 cm3 of liquid into the measuring cylinder and measure the new mass
  3. calculate: mass of liquid = (mass at step 2) - (mass at step 1)
  4. use the volume (50 cm3) and the answer to step 3 to calculate the density of the liquid

Results

Record the results in a suitable table. The one below gives some example measurements.

ObjectMass (g) Volume (cm3)Density (g/cm3) Density (kg/m3)
Steel cuboid 468 60 ......
Stone 17570 ......
Water 5050......

Analysis

Calculate the densities of the different substances using density = \frac{mass}{volume}:

  • density of steel = 468 ÷ 60 = 7.8 g/cm3
  • density of stone = 175 ÷ 70 = 2.5 g/cm3
  • density of water = 50 ÷ 50 = 1.0 g/cm3

Convert the densities to kg/m3:

  • density of steel = 7.8 × 1,000 = 7,800 kg/m3
  • density of stone = 2.5 × 1,000 = 2,500 kg/m3
  • density of water = 1.0 × 1,000 = 1,000 kg/m3

Evaluation

Example

Describe two sources of error in the experiment. For each one, suggest an improvement.

The top pan balance is only precise to ±1 g. A balance that reads to one decimal place (±0.1 g) or to two decimal places (±0.01 g) would be more precise.

The displacement can may not have been set up correctly each time, so another added drop of water would cause some to dribble out of the spout before use. Check that no more water comes out before placing the measuring cylinder under the spout.

Hazards and control measures

HazardConsequenceControl measures
Water spilled from displacement canSlip and fallWork next to a sink and have paper towels ready to mop up any spills