Lab #1: Measurements and Density

Name: ______

Objectives:

  1. Learn to measure masses using the top-loading balance.
  2. Learn to measure volumes using a two pieces of glassware.
  3. Learn to use correct significant figures when recording measurements.
  4. Learn to use density to calculate volume from mass.
  5. Learn the difference between accuracy and precision.
  6. Determine the density of solid samples using water displacement method.

Notes:

  1. Measure water volume at the bottom of the meniscus.
  2. Use the same balance for the entire lab (do not move the balance!)
  3. Remember to use correct significant figures throughout when recording measurements and in calculations.

Pre-lab:

  1. Prepare your lab notebook (as described in the lab notebook handout)
  2. Hand in the answers to the following questions on a separate sheet before lab begins:

a)If a mass is measured as 44.012 g, how many significant figures are there?

b)If a graduated cylinder has markings every 1 mL, how many decimal places should be recorded for a volume measured with that cylinder?

c)What is the water displacement method?

d)Why is it important to use at least 1.00 mL of metal?

Procedures (Part A):

1. Weigh a 50 mL graduated cylinder and record this as the dry mass.

2. Place as close to 20.0 mL of distilled water as you can into the cylinder and record this as volume 1.

3. Weigh the cylinder with the water in it and record this as the mass of cylinder + water.

4. Calculate the mass of the water by subtracting the dry mass from the mass of cylinder + water.

5. Calculate the volume of the water using the mass and the density of water (d = 0.99876 g/mL) and record this as volume 2.

6. Repeat steps 2-5 two more times and record the data and calculations.

7. Calculate the error for each run by taking the absolute difference between volume 1 and volume 2. Record this as the error.

8. Repeat the whole process (steps 1-7) with a 50 mL beaker.

Procedures (Part B):

1. Choose an unknown metal, weigh a few pieces (the pieces should fit into your 10 mL graduated cylinder and have a volume between 1.00 mL and 3.00 mL) and record the mass.

2. Place about 5 mL of water in your 10 mL graduated cylinder. Record the water volume.

3. Tilt the graduated cylinder and gently slide the metal pieces down inside it. Record the new water volume.

4. Calculate the volume of the metal and record.

5. Calculate the density of the metal and record. Also record the density on the class computer.

6. Repeat steps 1-5 for each unknown metal.

7. Compare the class densities (or your own) to those in the table given out in lab to determine the identity of each unknown metal.

Data (Part A):

Fill in the tables below. (Numbers requiring calculations are in bold. Show your work for one of each type of calculation.) Calculate the average volumes and errors and record below.

50 mL Cylinder / Run 1 / Run 2 / Run 3
Dry Mass (g)
Volume 1 (mL)
Mass of container
+ H2O (g)
Mass of H2O (g)
Volume 2 (mL)
Error (mL)

For 50 mL cylinder:

Average Volume 1 (mL)Average Volume 2 (mL) Average Error (mL)

______

50 mL Beaker / Run 1 / Run 2 / Run 3
Dry Mass (g)
Volume 1 (mL)
Mass of container
+ H2O (g)
Mass of H2O (g)
Volume 2 (mL)
Error (mL)

For 50 mL beaker:

Average Volume 1 (mL)Average Volume 2 (mL) Average Error (mL)

______

Calculations (Part A):

Data (Part B):

1. Fill in the table below.

2. Show a sample of each type of calculation.

Metal A / Metal B / Metal C / Metal D / Metal E
Mass of metal(g)
Volume of water
Volume of water
+ metal (mL)
Volume of metal (mL)
Density of metal (g/mL)
Class average
Density (g/mL)
Class error (g/mL)
Identity of metal

Calculations (Part B):

Post-Lab Questions:

1. Why is it important not to move the balance?

2. For part A, consider volume 2 to be the true value for the volume of water in each experiment.

a) Based on your data, which is more accurate, the cylinder or the beaker?

b) Based on your data, which is more precise, the cylinder or the beaker?

3. Based on the class data, what can you say (in general) about the accuracy and/or precision of the experiments in part B?

4. Is it better to use the class average density to identify the metal, rather than your own data? Explain.