The Thickness of a Thin Aluminum Sheet Introduction: In science, we make use of large and small numbers many times. In addition, we must often use one set of measurements and known properties to indirectly measure other quantities. One example of this type of measurement will be found in this experiment. The tools necessary to measure the thickness of a piece of aluminum foil would not normally be found in a chemistry laboratory. We, however, will be able to indirectly measure the thickness through a series of measurements and calculations. You are probably wondering why it is important to know the thickness of aluminum foil. Well, guess what? It isn t important. What is important is that you are able to use measuring instruments with accuracy. The other purpose of the lab is to apply the rules of significant figures and scientific notation properly. Background information: The formulas that will enable you to find the thickness of the foil are familiar to you: The volume of a regular object is found using the formula: = L x W x H where L = length, W = width and H = height. Imagine that the regular object is a rectangular shaped piece of aluminum foil and that the height of the foil is the thickness (T). The formula could be written as: = L x W x T where T = thickness of the foil. Going one step further, the area of the foil can be expressed as A = L x W, so our formula for volume can be restated as: = A x T Since this experiment involves finding thickness, it would be better to rearrange the formula once again. Dividing both sides of the equation by A, we get the new equation: T A The next problem will be to find the volume and area of the piece of foil. Remember that the formula for density is: M D The density of aluminum is a known property (you computed the density of Al in Expt. 4, and it is listed in a chart of the properties of elements in the back of your text and lab manual). The mass of a piece of aluminum foil can be measured with a balance. The volume of the aluminum foil can then be calculated by using the rearranged equation: M D
Pre-Lab Questions Do the following problems prior to coming to the lab. Please express your answers in the correct number of significant figures. You must show all calculations and include units in your answer. 1. What is the volume of a block that has the dimensions: l = 8.20 cm w = 2.25 cm h = 1.00 cm 2. If the density of a substance is 0.525 g/cm 3, and the volume of a sample of this substance is 18.25 cm 3, what is the mass of the sample? 3. A piece of paper is known to have an area of 30.2 cm 2 and has a volume of 5.2 x 10-3 cm 3. What is the thickness of this paper?
Objectives: 1. To correctly apply the principles of significant figures in calculating the thickness of aluminum foil. 2. To correctly use scientific notation in expressing the results of the thickness calculation. Materials: 3 pieces of aluminum foil per lab pair 2 centimeter rulers per lab pair Electronic balance Procedure: 1. Pick up one set of aluminum foil pieces (3) and two rulers. 2. Using the centimeter scale, carefully measure the length and width of each piece of foil. Record the measurements in the data table. How precise can your measurements be? Think carefully before you record your results. 3. Measure the mass of each piece of foil using the electronic balance and record the masses in the data table. Data Table 1: Foil Piece Foil #1 Foil #2 Foil #3 Length (cm) Width (cm) Area (cm 2 ) Mass (g) 4. Compute the Area (A), the olume (), and the thickness (T) for each piece of aluminum foil. Record your answers in Data Table 2. Show all work. Your answers should have the correct number of significant figures and be expressed in scientific notation where appropriate.
Data Table 2: Foil Piece Density (g/cm 3 ) Area (cm 2 ) olume (cm 3 ) Thickness (cm) Foil #1 2.6989 Foil #2 2.6989 Foil #3 2.6989 Results and Conclusions: 1. Compare your answers with those of other students, or, if available, look at the box from the aluminum foil. How do your answers compare? Can you determine how accurate your measurements are? Why or why not? Please answer in complete sentences. 2. How precise are your answers? Recall the definition of precision. Please answer in complete sentences. 3. If you had used a very crude balance that allowed only one significant figure, how would that have affected your results? Area? olume? Thickness?
Going Further: Please answer questions in complete sentences and show any calculations necessary to solve the problems. 1. Could the method used in this lab to determine the thickness of the foil be used to determine the thickness of an oil spill? What information would be needed? 2. A very thin layer of gold plating was placed on a metal tray that measured 25.22 cm by 13.22 cm. The gold plating increased the mass of the plate by 0.0512 g. Calculate the thickness of the plating (The density of gold is 19.32 g/cm 3 ). 3. By mistake a quart of oil was accidentally dumped into a swimming pool. The swimming pool measures 25.0 m by 30.0 m. The density of the oil was 0.750 g/cm 3. How thick was the resulting oil slick? Be careful with significant figures and scientific notation. (Hint: 1.06 quarts = 1.00 liter = 1000 cm 3 ). 4. How might this method of finding thickness be used in finding the size of molecules? (your next lab.)