Accuracy and Precision Name ______Metric Measurement Lab Block _____ Date ______

In this experiment, you will practice many of the measurement procedures and calculations that you will do later as you do chemistry labs using the metric system. You will:  Perform measurements using the metric ruler, gram scale, and the graduated cylinder.  Determine the volume of a liquid in two different ways and compare the results.  Demonstrate your ability to convert the original measurements to lower and higher values by conducting dimensional analysis.  Calculate the density of a metals and compare to the accepted reference values.  Calculate percent error (a measure of accuracy) and average deviation mass (a measure of precision) Density  Volume Some tips:  When expressing a volume Observed Value - Accepted Value measurement, milliliters (mL) and Percent Error  100% cubic centimeters (cm3 or cc) mean the Accepted Value same thing.  When recording data, always record one decimal place past the graduations (lines) on the instrument. Read the top half of p. 46 in your book.

Materials Metric Meter Stick Metric Ruler Coins 100 mL graduated cylinder Triple Beam Balance Electronic Balance Density Cubes x 4 Glass Rock

Part 1

Use the metric stick to measure the items listed below. Place your measurements in the spaces below. Above each column write the name of the unit that is abbreviated below it. Circle the unit you used to directly measure with for each item. You will need to convert for the other units.

Diameter of ______M. ______cm. ______mm. ______km. Penny Height of lab ______M. ______cm. ______mm. ______km. counter Width of the ______M. ______cm. ______mm. ______km. Textbook Length of the ______M. ______cm ______mm. ______km. Room

1a. Did you use the same unit to measure each item? Explain why you selected the units you did. Part 2

Use the scale to mass the following materials. Place your measurements in the spaces below. Be sure to check the unit on the scale to verify that you are measuring in grams (g) not oz. or ct. Write the name of the unit above the columns below. Mass of coin ______g. ______cg. ______mg. ______kg. Mass of dollar ______g. ______cg. ______mg. ______kg. Mass of empty 10 ml ______g. ______cg. ______mg. ______kg. graduated cylinder Mass of graduated cylinder ______g. ______cg. ______mg. ______kg. with 10 ml water Mass of 10 ml water ______g. ______cg. ______mg. ______kg.

2a. What is the difference between weight and mass?

2b. Why are they used synonymously on Earth?

Part 3

Use the glassware provided to measure the volume of the following containers. Place your measurements in the space below. In the last column of the chart write which glassware you used to measure the liquid with giving the most precise and accurate measurement.

Volume of the red liquid ______L. ______cl. ______ml. Volume of water ______L. ______cl. ______ml. Volume of the green ______L. ______cl. ______ml. 3a. Do all of the glassware measure with the same degree of accuracy? Explain

3b.What determines which glassware you measure with?

3c. What is a meniscus? Why is it necessary to know about it when measuring liquids?

Part 4 Using the balance, determine the mass of the dry 100-mL cylinder. Record mass in Data Table 1. Fill your graduated cylinder with room temperature tap water to a level between 50 and 100 mL. Accurately read the volume of water in the cylinder and record the volume. Determine the mass of the graduated cylinder with the water in it. Save this water in the graduated cylinder for use in Part 5.

Data Table 1 Mass of empty graduated cylinder

Measured volume of water

Measured mass of water + graduated cylinder

Part 5

Add the green glass stone from the tray to the graduated cylinder containing the water (saved from Part 4). In Data Table 2, accurately record the new volume and the new mass of the cylinder, water, and metal. Data Table 2 Measured volume of water (from Part 4)

Measured mass of water + graduated cylinder (from Part 4)

Measured volume of glass stone + water

Measured mass of glass stone + water + graduated cylinder

Part 6 1) Use the Triple Beam Balance to weigh each of the density cubes (Fe, Br, Al, Cu) and record your answers in the table below. 2) Use the electronic balance to weigh each of the density cubes (Fe, Br, Al, Cu) and record your answers in the table below. 3) Use the metric ruler to measure the measure the length, width, and height for each of the density cubes (Fe, Br, Al, Cu) and record your answers in the table below.

Triple Beam Electronic Length Width Height Fe

Br

Al

Cu

Calculations As usual, show all your work, use correct significant figures, and circle your answers.

Part 1 Perform each of the calculations below:

1a. Multiply the following: diameter of penny in cm. X width of textbook in cm.

1b. Divide the following: Length of room in mm / Height of lab station in mm.

Part 2 Perform each of the calculations below:

2a. Add the following: mass of coin in g. + mass of dollar bill in g.

2b. Subtract the following: Mass of graduated cylinder with 10ml of water – Mass of empty graduated cylinder

Part 4 & 5 3. Determine the volume of the green glass stone using your measurement of the volume displaced by the metal.

4. Using your measurements in Data Table 2, determine the mass of the green glass stone.

5. Calculate the density of the green glass stone. Also, post your answer on the board so classmates can record it for Question 6.

6. Record below the values that you and your classmates determine for the density of your metal. Green Glass Stone Classmate Values:

7. Calculate the average density and the percent error for the green glass stone (your accepted value will be the average density calculated from your classmates)

Part 6

8. Calculate the volume for each of the density cubes and list below:

Fe –

Cu –

Al –

Br –

9. Calculate the density for each density cube using your observed mass measurements. Show your work for each below: Fe –

Cu –

Al –

Br –

10. Using your laptop as a reference, find the accepted density measurements for each of the density cubes listed below and calculate the percent error using your observed measurements.

Fe –

Cu –

Al –

Questions 1. Was the percent error higher in your density calculation or the class average calculation? Which do you think will usually have a higher percent error? Why?

2. Two superstar chemists determined the density of a liquid three times. The values they obtained were 2.84 g/mL, 2.85 g/mL, and 2.80 g/mL. The accepted value is known to be 2.40 g/mL. a. Are these experimental values precise? Explain.

b. Are these values accurate? Explain.

c. Calculate the average of the three measurements, and then determine the percent error in the average.