Chemistry 11 Lab #2

Basic Measurements and Devices I

The lab will be set up with a number of work stations. You can do these in any order you choose. It is crucial to get reading errors for each measurement. If you are aiming at a better mark you will do repeated measurements where feasible to get a more accurate error. Ask me about how to do this if you are not sure.

A note on error calculations and an equation

What to do with reading errors when you have to do calculations with the quantities that have errors on them? Well, there are a couple of simple rules to follow:
  1. When you add or subtract quantities you simply add up the reading errors of the quantities.
  2. When you multiply or divide quantities you simply add up the RELATIVE errors of the quantities and equate that to the RELATIVE error of the calculated quantity.
  3. So what the heck is relative error? A quantity with reading error has relative error = reading error/quantity.
  4. Quantities without any error are treated the same way as any other, just set their error to be zero.
  5. The equation for mass density is: mass density = mass/volume.

Station #1 Volume

Compare two methods for calculating the volume of a regular solid (in this case a metal cylinder). 
  1. Use the steel ruler and calipers to find the height and diameter of the cylinder and calculate the volume via the known formula.  If you do not remember it, look it up in a book or on the internet.
  2. Use the beakers and graduated cylinders to measure the volume via the displacement method.
  3. Discuss the precision of the two methods by comparing their calculated errors. Also discuss their other strengths and limitations.
Station #2 Density

Compare two methods of calculating the density of a liquid (saltwater).
  1. Use the pan balance to mass the empty 500 mL graduated cylinder.
  2. Mass the cylinder filled to no more than 500 mL with saltwater.  Make an accurate reading of the volume.
  3. Use the above masses and volume to find the density of the saltwater.
  4. Use the hydrometer (a specific gravity meter - it looks like a thermometer) to find the density directly.
  5. Discuss the precision of the two methods by comparing their calculated errors. Also discuss their other strengths and limitations.
Station #3 Massing

Compare the triple beam balance to the electronic balance
  1. Mass the standard cylinder from Station 1 using the triple beam balance.
  2. Mass the same mass using the electronic balance.
  3. Discuss the precision of the two devices by comparing their calculated errors. Also discuss their other strengths and limitations.
Extra Work

Use the data from Stations 1 and 3 to find the density of the cylinder. Compare the density to those listed below and decide if the cylinder could be made of one of the metals listed. If so state which metal.
Densities of Metals
Magnesium 1,700 kg/m3
Aluminum 2,700 kg/m3
Copper 8,700 kg/m3
Gold 19,300 kg/m3
Iron 7,800 kg/m3
Lead 11,300 kg/m3
Platinum 21,400 kg/m3
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