Lab #1 - Density and Composition of Pennies - Background, Procedure, and Pre-lab PDF

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CHEM&121 – Intro to Chemistry w/Lab

Andrewsky (adapted from Centauri) – Online Fall 2020

Lab #1: Density and Composition of Pennies – Background, Procedure, Pre-lab PURPOSE: A lab report is created to describe the use of common laboratory equipment to examine density of a solid and its composition. (Caution: This is the assignment’s purpose as a teaching tool, not the lab’s purpose.) SKILLS and KNOWLEDGE: After you complete this assignment, you will be able to: • Utilize the electronic balance to make and record mass measurements. • Develop your skills to accurately use a graduated cylinder. • Make qualitative observations and use to make evidence-based claims • Use laboratory data to calculate the mass, volume, and density of a bone segment. TASKS AND DUE DATES:  Wednesday, 30 September, 2020 – by 8:00 am – late submission of Pre-lab is not accepted. 1. Before the lab day, read the Background section and Procedure section to get a good idea of what concepts are studied in this lab experiment. 2. Before the lab day, complete the pre-lab – Lab #1 questions on Canvas. These questions are the same as those provided in the pre-lab assignment on the back page of this document.  Wednesday, 30 September, 2020 – end of lab session (submitted from 8:00 AM until 11:59 PM on Canvas) 1. During your lab session on lab day, complete the measured and observed values in the tables in the Lab #1 Report Form (Lab #1 questions on Canvas) described in this procedure by filling them into the questions on Canvas in the lab assignment.  Wednesday, 7 October, 2020 by 11:59 pm – Submitted on Canvas. 1. After the lab session, complete the post-lab questions in the Lab #1 Report Form and submit them to the Lab #1 Post-lab on Canvas, and turn it in the by the due date.

GRADING CRITERIA: (50 points total) Although you often work in pairs in lab, this experiment and graded assignment components are completed and turn in individually. 1. Lab #1 pre-lab (10 pts – late submission of Pre-lab is not accepted) – submitted on Canvas. 2. Lab #1 lab (20 pts – refer to syllabus for deductions for each day late) – submitted on Canvas on lab day (Wednesday). 3. Lab #1 post-lab (20 pts – refer to syllabus for deductions for each day late): Complete the Calculations and Post-lab questions and turn it in all the pages indicated by 11:59 pm on the due date. The points for each question and table are listed with each problem.

Lab #1: Density and Composition of Pennies – Online

Last Updated: 9/14/2020

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CHEM&121 – Intro to Chemistry w/Lab

Andrewsky (adapted from Centauri) – Online Fall 2020

BACKGROUND The United States one-cent coin, often called the penny, is a unit of currency equaling one-hundredth of a United States dollar. It was first minted in 1793. Since 1909, President Abraham Lincoln’s bust has been featured on one side with the reverse side featuring the Lincoln Memorial. In 2010, the Lincoln Memorial image was changed to the Union Shield. Other than the images on the penny, has anything else changed? You will work to collect property data rapidly on multiple pennies for each year over a number of years. Significant Figures When we buy tomatoes from the grocery store, the clerk uses a scale to find the weight in pounds. We may have already determined the weight from another scale available to customers in the produce aisles. Almost always, these two weights are different because the weighing’s are made with different instruments. In general, results also depend on other factors such as random fluctuations of the instrument and the person taking the measurement. In fact, these factors create uncertainty in all measurements. In scientific work, it is very important to present the results of measurements in such a way as to show the confidence we have in the result. Too few digits suggest the measurement is not as precise as the actual value; too many digits implies a precision beyond what the instrument is capable of. The problem of data presentation is answered with significant figures: we write all the digits we know for certain and one more digit that we must estimate. For example, suppose we place a centimeter ruler next to the line as shown. The ruler is marked in centimeters (cm), and there are ten divisions between 15 cm and 16 cm marks. Each division must be one-tenth of a centimeter or one millimeter (mm). We can say for certain the length is greater than 15.8 cm and less than 15.9 cm, but we can be even more precise by estimating to one more decimal. To the instructor’s eye, the end of Figure 1: Portion of the line extends about three-tenths of the way to the next mark. Thus, the length is written a Centimeter Ruler as 15.83 cm. Someone else might estimate it to be 15.82 cm. In any case, estimation of the distance the line extends between millimeter marks permits the length to be given to four significant figures. Mass Mass is the measure of the amount of matter in an object. The unit gram, abbreviated “g”, is typically used in the chemistry laboratory for mass. An electronic balance is used to determine masses. The electronic balances give mass readings to a certain number of decimal places (depending on the precision of the instrument) where the last digit is the electronic estimate. In fact, this digit can change over time as the electronics drift. In that case, it is up to you to estimate the last digit. If the display spends more time on one digit that another, that digit is probably the best guess. During an experiment, it is important to use the same electronic balance for the entire experiment to minimize measuring errors. Volume Volume is a measure of the amount of space occupied by an object. A graduated cylinder is often used to make measurements of volume. Like with any measuring device, you must first determine the volume represented by the smallest division. Different types of glassware are used for different purposes. Typically, glassware is either categorized as “to contain” or “to measure”. Beakers and Erlenmeyer flasks are examples of glassware used only to contain substances. Graduated cylinders and burets are examples of glassware used to measure volumes.

Lab #1: Density and Composition of Pennies – Online

Last Updated: 9/14/2020

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CHEM&121 – Intro to Chemistry w/Lab

Andrewsky (adapted from Centauri) – Online Fall 2020

Measurement of liquid volumes is frequently complicated by the meniscus. Water in a small tube may look like the figure at the left. Attraction to the glass causes a small amount of water to creep up the side of the container, creating a curved surface. This surface shape is a concave meniscus. Fortunately, the volume of water creeping up the side is usually very small and the volume measured at the bottom of the meniscus is most accurate. Always measure a volume to the bottom of the meniscus. The angle of reading can also affect the accuracy of the volume being measured. To ensure the most accurate reading, put the graduated cylinder on a flat surface and read the meniscus at eye level (you may need to bend down). Figure 2: Reading the Meniscus of a Liquid in a Graduated Cylinder

Density Each substance has a specific density. Because materials that are alike have the same density, densities can be helpful in identifying that material. Density is defined as the mass divided by the volume. For example, if the mass is in grams and the volume is in mL, the unit of density would be g/mL. To determine an object’s mass, we need both its mass and volume. mass m Density (d or ρ) = = volume V Reactivity Pennies are made of copper….aren’t they? The outside is certainly made of copper, but that’s not the whole story. Pre-1982 pennies are composed of pure copper. During 1982, the rising cost of copper caused a penny to cost more than 1¢ to make & the U.S. Treasury was losing money in the production of pennies. The high cost of copper finally resulted in the U.S. Treasury changing the composition of pennies in 1982. Post-1982 pennies are made of an alloy of zinc & copper & then plated with pure copper. Alloys are mixtures of metals. Because of the differences in composition of the pennies, they will have different physical properties and chemical properties. Physical properties are properties of matter that can be observed or measured without trying to change the composition of the matter being studied – no original substances are destroyed and no new substances appear. Examples of physical properties include color, density, boiling point, and magnetism. Chemical properties are those properties that determine how a substance can be converted to another substance by a chemical reaction. Examples include reactions with other substances like acids or heating to decompose (break apart) the original starting material. Percent Composition Percent means parts per 100 parts. We can use the mass of a given metal in the total mass of the alloy to calculate the mass percent of each metal. Mass percent can be calculated using the following formula: %X=

mass X (g) × 100% mass of alloy (g)

SAFETY (If this was a real, face to face lab) Wear goggles at all times. Hydrochloric acid (HCl) is caustic; that is, it can cause burns. Be careful while handling. Acetone may cause respiratory irritation. Acetone is flammable – keep it away from flames. Long hair and loose clothing must be tied back when working with the Bunsen burner.

Lab #1: Density and Composition of Pennies – Online

Last Updated: 9/14/2020

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CHEM&121 – Intro to Chemistry w/Lab Andrewsky (adapted from Centauri) – Online Fall 2020 PROCEDURE You will work individually on this lab. All links to videos will be given in the lab assignment itself. Part A – Qualitative Observations of Pennies 1. Search the internet for images of one penny from each of the following years: 1960, 1975, 1990, 2000, and 2010. Upload images or screen shots of each of these pennies into Table 1 and then record your qualitative observations in Table 1 (under the data and observations). a. Directions on how to upload images on Canvas Part B – Volume and Density 2. Watch the video for part B and fill in the individualized data given in your lab assignment (not the data from the video) into Table 2. Make sure to include the appropriate number of decimal places for each measurement. Also, record observations about how the experimenter uses the balance and how they add pennies to the graduated cylinder in the space provided in Table 2. PART C. COMPOSITION OF PENNIES Two tests will be performed to compare the composition of pennies before 1982 and after 1982: reactivity with hydrochloric acid and heating in order to decompose. TEST #1. REACTIVITY WITH HYDROCHLORIC ACID (HCl) 3. Watch the video for part C – Test #1 and fill in the individualized data given in your lab assignment (not the data from the video) into Table 3. Make sure to include the appropriate number of decimal places for each measurement. Also, record observations about the safety precautions taken and treatment of waste done by the experimenters in the space provided in Table 3. TEST #2. HEATING TO DECOMPOSE 4. Watch the video for part C – Test #2 and record your qualitative observations in Table 4 (under the data and observations). Also, record observations about the safety precautions taken by the experimenter in the space provided in Table 4.

Lab #1: Density and Composition of Pennies – Online

Last Updated: 9/14/2020

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CHEM&121 – Intro to Chemistry w/Lab

Andrewsky (adapted from Centauri) – Online Fall 2020

Lab #1 pre-lab question sheet (Answer these questions on Canvas in the pre-lab assignment) Deductions: ____

Section letter: ___

Name: ____________________________

1. (4 pts) Four sentence introduction: A four-sentence lab introduction should be structured as follows in the third person (without using I/we/the student): Sentence 1: Describe the scientific goal of the experiment. Sentence 2: Describe the methods used to make the measurements. Sentence 3: Describe the calculations done with the measurements and include the relevant mathematical equations. Sentence 4: Describe how the post-lab questions will analyze the experimental results. To write your first lab introduction fill in the blanks based on information you gleaned from the procedure, background sections and post-lab questions on the lab report sheet documents for this lab. Introduction sentence 1: The main goal of this lab experiment is to determine the ___________ and ______________ of pennies. (property) (other property) Introduction sentence 2: In order to calculate the _____________, only mass by taring must be measured (property) for each set of pennies. But to calculate ______________, volume by difference must be measured too. (other property) Introduction sentence 3: The mathematical equation to calculate _____________ is _______________. (property) (equation) The mathematical equation to calculate ________________ is _______________. (other property) (equation)

Introduction sentence 4: In the post-lab questions, The _____________ of each of the pennies is (property) analyzed by comparing and contrasting the sets based on _________. The ______________ of each of (criteria) (other property) the penny sets is used to determine the _____________ of the sets of pennies. (criteria)

Lab #1: Density and Composition of Pennies – Online

Last Updated: 9/14/2020

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CHEM&121 – Intro to Chemistry w/Lab

Andrewsky (adapted from Centauri) – Online Fall 2020

2. (1 pts) Lab mindset preparation: hypothetically, if the two sets of pennies (pre- and post-1982) have the same volume but the pre-1982 pennies have a larger mass than the post-1982 a. Will their densities of the pennies be the same or different? Circle one: Same Different b. If they have different densities then which one will be bigger? Circle one: Same

Different

3. (1.5 pts) Lab calculation preparation: A student used lab equipment to determine the density of a metal cylinder. The student obtained the following data: mass of metal, XX.XXX g; initial volume of water in graduated cylinder, XX.X mL; and volume level after adding metal sample to water, XX.X mL. (Note: the X’s are placed here because your numbers will vary from what is in this handout)

On paper – show your work and units and round results to proper significant figures. a. Volume of water displaced by the solid sample

b. Density of metal sample

4. (2 pts) Lab calculation preparation: A XX.X g sample of bronze (an alloy of copper and tin) contains X.X g of tin. What is the mass percent composition of copper in this bronze alloy? Hint: Check back in the background for the equation for percent composition. (Note: the X’s are placed here because your numbers will vary from what is in this handout) On paper - Show your work and units and round results to proper significant figures.

Lab #1: Density and Composition of Pennies – Online

Last Updated: 9/14/2020

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CHEM&121 – Intro to Chemistry w/Lab

Andrewsky (adapted from Centauri) – Online Fall 2020

5. (1.5 pts) Common misconception in lab that results in point deductions: A 10-mL graduated cylinder has marks every 0.1 mL. The second decimal place can be found by estimating between the marks. It can be read with an uncertainty of at least ±0.02 mL by deciding if the meniscus is right on the mark (0/5th), 1/5th, 2/5th, 3/5th, or 4/5ths of the way between the marks. For example, if the bottom of the liquid’s meniscus is two fifths of the 0.1 mL distance between the graduations 7.8 and 7.9 mL, then 2/5 x 0.1 mL = 0.04 mL gives the last estimated digit so the measured reading would be 7.84 mL. (A very experienced reader can estimate to ±0.01 mL.) The last digit recorded is always estimated. Using the appropriate number of digits, what should be the reported volume in the graduated cylinders below? A.

B.

Lab #1: Density and Composition of Pennies – Online

C.

Last Updated: 9/14/2020

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