Density

• What are the aims of the density practical?

  To determine the densities of regular and irregular solid objects and liquids.

  (The volume of objects should be determined from the dimensions of regular shaped objects and by a displacement technique for irregularly shaped objects.)
• What equipment is needed for the density core practical?

  - Various regular and irregular shaped objects

  - A suitable liquid (e.g. water)

  - 30cm ruler (smallest division is millimetres)

  - Digital balance

  - Displacement/ Eureka can

  - A variety of measuring cylinders

  - Two 250cm3 beakers

  - Cotton/thin string
• What procedure would you follow to calculate the density of a regular shaped object?

  Calculating the Density of Regular Objects:

  1. Measure the length, height and width of the object, recording your values to the

  nearest millimetre.

  2. Calculate the volume by multiplying the length, height and width, giving your value in

  cm3

  3. Measure the mass of the object, using the mass balance. (Electronic balance) Remember to reset the balance with nothing on the scales to reduce zero errors.

  4. To calculate the density, use the equation:

  P= m/v

  where p is the density, measured in kg m^3

  (You must convert from g/cm' to kg/m)
• In order to calculate the density of a regular shaped object, what would you do first?

  Firstly, use a balance to measure the mass of the regular shaped object in grams (x3)
• After you've measure the mass of the regular shaped object, using a digital balance, what would you do next?

  Using a 30 cm, measure the dimensions of the regular shaped object (x3)
• How would you work out the density of the regular shaped object once you know the mass and the volume?

  To work out the density (once you know the volume(cm^3) and the mass (g), substitute these values into the equation :

  density = mass/volume
• Why do you need to ensure that the digital balance is on zero before usage?

  To avoid zero-error
• What procedure would be followed to work out the density of a liquid?

  1 -Turn on the digital balance and make sure it's on 0, then measure the mass of a measuring cylinder, using the mass-balance.

  2. Pour 100cm*^3 of the liquid into the measuring cylinder .

  3. Measure the combined mass of the measuring cylinder and the liquid.

  4. To calculate the liquid's mass, subtract the mass of the beaker from the mass of the

  combined beaker and liquid.

  5. Calculate the density of the liquid using the density equation;

  density = mass/volume
• In order to measure the density of a liquid, what would you do first?

  Turn on the digital balance and make sure it's on 0, then measure the mass of a measuring cylinder, using the mass-balance.
• After you measure the mass of the measuring cylinder, what would you do next to find out the density of a liquid?

  Pour 100cm*^3 of the liquid into the measuring cylinder - measure carefully at eye-level to avoid parallax error.
• What procedure would be followed to calculate the density of an irregular object?

  1. Fill the displacement/ eureka can with room temperature water and align a measuring beaker with the spout. Make sure that the level of water lies below the level of the spout, but that there isn't too much of a gap between the two levels.

  2. Place the irregular shaped object slowly into the can with a string , ensuring not to drop it from a height or cause it to splash.

  3. Collect the displaced water and measure the volume of water displaced. The volume of water displaced will equal the volume of the object that caused the

  displacement.

  4.Measure the mass of the object using a mass-balance

  5. Calculate the density of the irregular object, using the density equation in step 4 of

  the method above.
• How would you measure the mass of an irregular shaped object?

  Measure the mass of the object using a digital balance.
• How would you measure the volume of an irregular shaped object?

  - Fill the displacement/ eureka can with room temperature water and align a measuring beaker with the spout. Make sure that the level of water lies below the level of the spout, but that there isn't too much of a gap between the two levels.

  - Tie the object to a piece of cotton and very carefully lower it into the displacement (don't do this from a height as it will splash) so that it is completely submerged.

  - Collect all of the water that comes out of the spout in the measuring beaker.

  - Collect the displaced water and measure the volume of water displaced. The volume of water displaced will equal the volume of the object that caused the displacement.

  (repeat)
• What sources of error are there in the density core practical?

  - Some water may have been spilled before putting the object in.

  - Measuring cylinders have a low resolution (1ml can't see 1.4ml)

  - Zero error when using scales

  - Measurements may not have been read correctly
• Why should this experiment be repeated?

  To identify any anomalies and to find the mean
• What are the risks when carrying out the density core practical?

  - glass equipment can break, this is hazardous because sharp glass fragments can cut the skin

  - spillages of water can be a hazard - clean any spillages
• How do you find the uncertainty?

  You divide the smallest increment by two (ex. If the beaker goes up by ones, the uncertainty is 0.5)

  or...

  range/2
• Resolution

  smallest change a piece of equipment can measure.