Materials: 25 pennies Electronic, triple-beam, or double-pan balance 20 ml of 6M HCl 2 50-mL beakers

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1 Name Block Atomic Structure Lab 1: Isotopes of Pennium Students should know. the meaning of the terms atomic isotope, average atomic mass, mass number how to use a balance and measure/record the mass of an object with the appropriate number of significant figures and units how to use a graduated cylinder to measure/record the volume of a liquid with the appropriate number of significant figures and units Students will learn. the meaning of the terms qualitative, quantitative, percent frequency, relative frequency how M is used to label solutions evidence to indicate a chemical reaction to predict reactive metals in HCl to calculate percentage & relative abundance/frequency to calculate average atomic mass for an isotope Introduction: All isotopes of an element have the same chemical properties. To account for the different masses of each isotope, average atomic mass is calculated by multiplying the mass of each isotope by its percent abundance and adding all of these values. This allows average atomic mass to reflect not only the different masses, but the mass most likely to be found in a natural sample. Originally, pennies were made of an alloy containing mostly copper with some zinc. Since the late 20 th century, pennies have been made by electroplating zinc blanks. These newer pennies are mostly zinc with a copper coating. These 2 different types of pennies have different masses and can represent isotopes of the element pennium. In this experiment, you will use pennies as a model for an atomic isotope and calculate average atomic mass. Pre-Lab Questions 1.) Define atomic isotopes and provide 3 examples of an isotope to illustrate your point. Use diagrams labeling the subatomic particles of each isotope. 2.) Explain, using a grammatically correct sentence, how one can determine the most common isotope of an element. Provide an example to illustrate your point. Materials: 25 pennies Electronic, triple-beam, or double-pan balance 20 ml of 6M HCl 2 50-mL beakers 25-mL graduated cylinder Tin snips (used w/ teacher s help) Logger Pro graphing software (or some other graphing application)

2 Procedure: 1.) Work in partners to weigh each penny (out of the total 25) to the appropriate number of significant figures. a. In your science notebook, using a data table of your own design, record the year and mass of each penny. b. Each person should have a copy of their own data table to turn in with this lab. c. Using your hard copy data table, transfer this data into an electronic spreadsheet (either Google Docs, Logger Pro, Excel, etc.) d. Get penny data from another group to expand your data collection to a total of 50 pennies. 2.) Notice that there are 2 distinct groups: heavy pennies and light pennies. a. Divide the pennies into these groups as you weigh them. b. These 2 groups of pennies can be viewed as isotopes of an element. Why? 3.) Create two graphs using graphing software a. One graph will compare the year of each penny weighed (x-axis) and the mass of each penny (y-axis). A line graph is best to show a change in a variable over time. In cases where you have more than 1 penny for a given year, plot the average mass of a penny for that year. Show this information on your data table as well. b. A second graph will be a bar graph, showing the mass of each penny weighed (x-axis) and the number of pennies present with that mass (y-axis). This graph will simulate a mass spectrometer reading. 4.) Copy and complete the following data table into your science notebook. Average Mass of Isotope (grams) Number of Isotopes in Sample Number of total pennies weighed Percent Abundance/Frequency of Isotope (out of 100) Relative Abundance/Frequency of Isotope (out of 1) Light Isotope Heavy Isotope What is the difference between percentage abundance/frequency and relative abundance/frequency? What is similar between percentage abundance/frequency and relative abundance/frequency? 5.) Select 1 light penny and 1 heavy penny from your sample. Carefully record any qualitative observations between the 2 pennies in the space below: Compare qualitative observations and quantitative observations: 6.) With the teacher s help, cut a notch into each penny. You should be able to see a cross-section of the penny. 7.) Use the graduated cylinder to pour approx. 10 ml of 6 M HCl into each beaker. a. What does 6 M indicate? 8.) Place each penny in its own beaker of HCl and let it soak overnight. Predict what you think will happen to each penny:

3 Day 2 9.) Record any qualitative observations of the beakers and pennies after letting them soak. 10.) Using tongs or forceps, carefully remove each penny from the beakers. Wash each penny gently with tap water to ensure that all of the acid has been removed. 11.) Observe each penny and note differences in the two pennies. Based on your observations, clearly identify what metal will react with HCl and which one will not. 12.) Using your computer, research the correct chemical equation for the reaction between HCl and each metal discussed in Q11. Provide a separate chemical equation for each reaction: Analysis 1.) Calculate the average atomic mass (in grams) for the element pennium. Show your work below: 2.) Convert your answer to amu. Show your work: 3.) Examine your data. Is there 1 year that is different from the rest? In graph 1, explain what trend can be seen: 4.) What changes are likely to occur in the average atomic mass of a penny as time progresses? For example, how will this activity change for a student in 2030? 5.) What differences did you notice between light pennies and heavy pennies in physical appearance? What about in their reactivity in the HCl? 6.) This model of atomic isotopes has a flaw related to reactivity. Clearly, you saw a difference in reactivity of the two pennies. This is inconsistent with the definition of isotope. Explain: 7.) Does the average atomic mass of the pennium vary among lab groups? Why/why not? Explain your answer!

4 Related Problems Please show all work and pay attention to significant figures in your answers!!! 1. There are three known isotopes of silicon % is 28 Si atomic mass = ; 4.70% is 29 Si atomic mass = ; and 3.09% is 30 Si atomic mass = Calculate an average atomic mass for silicon. 2. Magnesium, Mg, has the following isotopic masses and fractional abundances Mass Number Mass Fractional Abundance Calculate the average atomic mass of magnesium 3. Chromium, Cr, has the following isotopic masses and fractional abundances Mass Number Mass Fractional Abundance Calculate the average atomic mass of chromium 4. Copper has two known isotopes: 63 Cu atomic mass = and 65 Cu atomic mass = The average atomic mass of copper is amu. Calculate the fraction of each of the two isotopes of copper.

5 Answers: 1. = ( x ) + ( x ) + ( x ) = = ( x ) + ( x ) + ( x ) = = ( x ) + ( x ) + ( x ) + ( x )= Let x = fraction of 65 Cu and 1.00-x = fraction of 63 Cu Then X x) = X x = X x = X = X = (30.84%) 1-X = (69.16%) 1.