Name: Period: Date: KIPP NYC College Prep General Chemistry CHEMISTRY LAB #4 THE ILLUSION OF BLING: Using Density to Identify an Unknown Metal 90 MINUTES Do Now Pre- Lab Information: Lab Equipment and Skills Brush Up VOLUME is the amount of space that an object takes up. In science, volume is the term we use when we need to measure the AMOUNT OF LIQUID. The base unit for volume is measured in liter (L). Beakers and graduated cylinders usually measure liquid volume in milliliters (ml). The volume of solids is measured in cm 3. 1 ml is the same volume as 1 cm 3. In the upcoming lab, we will use graduated cylinders to measure the change in volume because we want to be as accurate and specific as possible. We measure the amount of water by standing so that your eyes are directly leveled with the graduated cylinder. The amount of water is determined by reading the meniscus as shown in the picture below. Volume= 66mL MASS in simplest terms is how much matter an object has. People sometimes use mass and weight interchangeably (even though in physics, you will learn that they are not the same thing!). The base unit for mass is measured in grams (g). An electric scale or electric balance is used to measure the mass of an object. Graduated Cylinders Electric scale/ electric balance Pre- lab Questions: Directions: Please answer the questions in COMPLETE SENTENCES. Base your answer off the information given above and in the introduction section of your lab. 1. How much water is present in the diagram below? (Read the scale and determine the interval each line represents on the scale!) ml
2. If an object has a volume of 3 ml, what is the volume in cm 3? 3. If an object has a mass of 2.33 grams and a volume of 4 ml, what is the density of the object? Don t forget your units! 4. What is the density of silver? (Hint: Use your reference table!) 5. We will find the volume of our piece of mineral by using a graduated cylinder. The picture below shows a before and after image of the graduated cylinder after the piece of mineral is dropped into the graduated cylinder. What is the volume of the object? How do you know? Before After
Name: Period: Date: KIPP NYC College Prep General Chemistry CHEMISTRY LAB #4 THE ILLUSION OF BLING: Using Density to Identify an Unknown Metal PURPOSE: To determine the density of an unknown, gold like substance in order to conclude whether or not it is real gold. INTRODUCTION: Density is a physical property that determines how much matter is present in a given volume of space. For example, if we were given three different substances cut out in exact 1cm 3 boxes as shown in figure 1 below, we know that substance A would be most dense because it contains the highest number of stuff (particles) in the same 1 cm 3 volume. In similar fashion, we know that substance C would be the least dense because it has the lowest number of stuff (particles) in the same 1 cm 3 volume. 1 A B C Figure 1 The amount of matter that is present is defined by the term mass, which is measured in grams. The amount of space matter occupies is known as volume, which is measured in ml or cm 3 (1 ml = 1 cm 3 ). While both mass and volume are physical properties, they may vary with different objects made of the same material. For example, we can have two pieces of copper- one piece has a mass of 2 grams and another piece has a mass of 4 grams. We can t, therefore, make the conclusion that all copper has a mass of 2 grams because it depends on the amount of copper we have. Similarly, in terms of volume we can have 1 ml of water or 2 ml of water, but we can t conclude that water has a volume of 2 ml since it depends on how much volume of water we have in a sample. Since mass and volume can change for the same substance, scientists use a property known as density to help identify a substance. Density is the ratio between mass and volume and is represented in a chemical formula: Density is the mass of an object measured in grams, divided by the volume of an object measured in ml or cm 3. The standard unit for density is g/cm 3. Example Problem: If an object has a mass of 3.0 grams and has a volume of 2 ml (2 cm 3 ), when what is the density of the object? Density= = = 1.5 g/ml or 1.5 g/cm 3 Every element has a specific density which is given in Table S of the Chemistry Reference Table and is a common physical property used to identify elements present in an unknown substance. In this lab, you will figure out whether or not a penny is actually pure copper based on its density. If the penny is copper, then the density of the object should equal the value given in Table S of the Reference Table for copper. If the density of the mineral is not the same as the density of copper, we know we have fake pennies.
MATERIALS: 10 pennies Graduated cylinder Electric scale Calculator Water Reference Tables PROCEDURE: 1. Obtain ten pennies 2. Take ten pennies and take the mass of the metal. Record the mass in your data table. 3. Pour water into the graduated cylinder so that it is about half way full. Record the exact volume in your data table. 4. Carefully place the pennies into the water in the graduated cylinder. Record the new volume of the water after the water level has risen. 5. Calculate the volume of the pennies. 6. Calculate the density of the pennies. 7. Pour the water and metal out of the graduated cylinder. 8. Repeat steps 1-7 for ten more pennies. Recording each value in your data table. 9. Clean up by pouring out the water, rinsing the graduated cylinder, turning off the electric scale, drying off the unknown metal pieces, and returning everything to the proper location in the lab.
DATA AND OBSERVATIONS: Observations: In the space below, record observations of the unknown metal pieces. You should include a picture with clear descriptions. Table 1. Mass and Volume Data of Unknown Metals Penny Set 1 Penny Set 2 Penny Set 3 DENSITY Average Density *Record the known density of copper from your reference table:
ANALYSIS QUESTIONS: Directions: Answer the following questions based on your activity in COMPLETE SENTENCES. 1. Is the unknown metal copper? Explain how you know. Use your data to support your answer. 2. Knowing that all three metal pieces were from the same metal, the density of all the pieces should have been the same or similar to one another. Were your results consistent with this expected finding? Why would the densities be the same even if the masses and volumes of the metal pieces were all different? 3. Why is density a better physical property used to describe a substance than mass or volume? Use your data to support your answer. 4. REAL LIFE CONNECTION: Why do you think knowing the physical properties of elements is so important to scientists? 5. CRITICAL THINKING: Why did we have to use a graduated cylinder to measure the volume of the piece of metal instead of using traditional volume equations we learn in math?
CONCLUSION: Directions: Write a one paragraph conclusion. Your conclusion should:! Restate your problem.! Summarize your findings and explain the process in which you arrived at your conclusion.! Discuss one thing you can change to make your results more clear and how they could make your results clearer. (For example, if you did not calculate the same values of density of each of the three metal pieces, then we made some errors along the way. What are some of these errors and how would they have affected our calculations. Please remember that human error is not a sufficient response. Be specific as to what specific human error.)! Makes a connection to how this procedure could be used in real life.
Name: Period: Date Completed: Minutes Earned: CHEMISTRY LAB #4 THE ILLUSION OF BLING: Using Density to Identify an Unknown Metal 90 MINUTES RUBRIC PRE- LAB GRADE: 4 3 2 1! Data is properly recorded in a coherent data table.! Observations are! Data is properly recorded in a coherent data table.! Observations are! Data is properly recorded in a data table.! Observations are Data and Observation specific and includes drawings! Proper calculations are carried out.! Proper units are used. specific! Proper calculations are carried out.! Proper units are used. vague and unclear.! Proper calculations are carried out.! Units are not used throughout. Analysis Questions Conclusion! All answers are correct.! All answers are thoroughly explained and supported by the experimental data.! Answers the purpose of the lab! Summarizes observations clearly.! Includes one thing that could be changed and explains how it would improve the experiment.! Makes a connection to how this procedure could be used in real life.! 4 answers are correct.! Most answers are thoroughly explained and supported by the experimental data.! Answers the purpose of the lab! Summarizes observations clearly.! Includes one thing that could be changed to improve the experiment! 3 answers are correct.! Most answers are thoroughly explained and supported by the experimental data.! Answers the purpose of the lab! Summarizes observations clearly.! No data table present.! Observations are vague and unclear.! Calculations unclear or incorrect.! Less than 3 answers are correct.! Answers the purpose of the lab OVERALL LAB: /12 POINTS (Scaled to 90) PRE- LAB: / 10 POINTS FINAL SCALED SCORE: Complete! Need to Revise