Theory behind this practical:

Density is a way of calculating the mass (number of particles) in a substance for a particular volume. By calculating the density of different sized objects we can compare them to each other, and we can also determine if they would float or sink in water by comparing their density to that of water (if the density is less than water, they will float).

Method:

Density of a regular shape:

• Draw a results table
• Find and record the mass of the object using the top pan balance (g)
• Carefully measure the dimensions of the object and use this formula to calculate its volume: width x height x depth (cm3)
• Use the Density equation (in your book) to calculate the density of the object. Density=mass/volume.
• Record all the data in your table.
• Repeat with another regular object
• From the density you have calculated can you suggest what materials the objects are made from by comparing them to the densities of known materials.

Density of a liquid:

• Draw a results table (or use your first one with extra rows)
• Pour a known volume of liquid into a measuring cylinder (for example 20ml)
• Find the mass of your liquid using the top pan balance (g)
• Record all the data in your table.
• Use the Density equation (in your book) to calculate the density of the liquid
• Repeat with another liquid
• From the density you have calculated can you suggest what the liquids are

Density of an irregular shape:

• Draw a results table (or add to the other one)
• Find the mass of your irregular object using the top pan balance (g)
• Fill the Eureka can with water, so that it is just comes up to the spout
• Put a beaker under the spout
• Gently drop the irregular object into the Eureka can, collect the water that spills out of the spout
• Pour the water into a measuring cylinder, record the amount of water displaced
• Use the Density equation (in your book) to calculate the density of the object
• Record all the data in your table.
• Repeat with another regular object
• From the density you have calculated can you suggest what materials the objects are made from by comparing them to the densities of known materials.

Technician notes:

  • Eureka/displacement cans
  • Measuring cylinders (100 ml and 25 ml)
  • Selection of cubes of different materials
  • Selection of irregular objects on cotton/strings
  • Top pan balances
  • Beakers (100ml)

Safety:

Usual lab rules must be adhered to:

  • Lose hair tied up
  • Goggles on throughout the lesson
  • Bags away and stools tucked under
  • Notify the teacher immediately if any spills or breakages occur

For further/more detailed information, check all reagents and practices at CLEAPSS.