Counterfeiting money is one of the oldest types of crime. In some ancient cultures, penalties for counterfeiting ranged from hand amputations to death sentences. In the Roman Empire, counterfeiters were burned at the stake.
Historically, counterfeiting money has been a problem in the United States. In the 1800s, each bank issued its own currency. With approximately 1600 different banks producing 7000 different types of paper money, counterfeiting money was easy to do and difficult to detect. It is estimated that by the 1860s, approximately one-third of all circulating currency was counterfeit.
To solve this problem, a national currency was adopted in 1863. Counterfeiters still were at work, and the United States Secret Service was established in 1865 to eliminate counterfeiting. Many counterfeiters are caught and prosecuted, but this crime remains a problem. The importance of detection has increased, as criminals no longer limit themselves to reproducing money, but also counterfeit such things as credit cards, identification papers, and tickets for transportation or entertainment.
Methods to detect currency counterfeiting include investigating the detail used in legal currency. For example, some of the printing on paper currency is raised. Much counterfeit currency is missing the fine detail present in legal currency, such as detail in faces and outer borders or, in coins, even and distinct corrugated outer edges. Investigators also check for repeated serial numbers in paper currency. One common coin-counterfeiting scheme involves altering the date, or mint mark, on a coin, changing it to a date or mint location that has more value than the one on the original coin.
Detection methods also include investigating the materials used by counterfeiters. Genuine paper currency uses a certain type of paper that is illegal for use by anyone except those authorized to produce paper money. Paper used for currency contains tiny, embedded red and blue fibers. Counterfeit coins might contain alloys that differ in composition from those in official coins.
As times change and counterfeiting methods improve, so do methods of prevention and detection. You may be familiar with the new paper money that contains a hidden image, which is difficult to counterfeit, and is printed on paper that turns a certain color when marked with a special marker. Scientists also have many methods of analysis that can determine whether money is counterfeit or not. In this set of labs, you will use several methods that will help you investigate evidence and determine facts about a crime involving counterfeiting.

Scene of the Crime

---

The police discovered a coin counterfeiting ring and arrested several people. The detectives discovered an old warehouse where they think the coins were being made. Although no suspects were found at the scene, the detectives collected evidence for analysis. Evidence collected included metal cylinders and some powder of unknown composition, including two different white powders. After questioning Mr. Skittle, the owner of the warehouse, and people in the neighborhood, the detectives identified four suspects. Once laboratory chemists identified the evidence, it was compared to evidence taken from each suspect, and the guilty party was identified and arrested. Your task is to analyze the samples and prepare an evidence report for the scheduled trial. This project may include fingerprint techniques described by your teacher.

What metal can it be?

Problem

How can the physical properties of specific heat and density be used to identify an unknown metal?

Objectives

• Determine the specific heat and density of a metal.
• Identify an unknown metal by using specific heat and density data.

Materials

metal sample
plastic-foam cup
lid to fit the cup, with a hole for the thermometer
400-mL beaker
250-mL beaker
100-mL graduated cylinder
thermometer
laboratory balance
hot plate
tongs

Safety Precautions

---

• Always wear safety goggles and a lab apron.
• Use caution when handling hot water.
• Never use a thermometer as a stirrer.
• Use caution when using the hot plate.

Pre-Lab

1. What is a physical property?
2. List three physical properties.
3. Why isn't the ability to burn a physical property?
4. Describe how to find the average of three numbers.
5. Read the entire laboratory activity. Form a hypothesis about how the physical properties of a substance can be used to identify it. Record your hypothesis on page 3.

Tools of the Trade

Specific Heat To change the temperature of a substance such as water, heat must be added or removed. Some substances require little heat to cause a change in temperature. Other substances require a great deal of heat to cause the same temperature change. For example, it requires 4.184 J of heat to raise the temperature of 1 g of water one Celsius degree. Joule (J) is a unit commonly used to measure energy. It requires 0.902 J to raise the temperature of 1 g of aluminum one degree Celsius. The heat required to raise one gram of a substance one degree Celsius is called the specific heat (c_p) of the substance. The subscript p indicates that the temperature measurement is made at constant pressure.
Specific heat is a characteristic physical property of a substance. Every substance has its own value for specific heat. Therefore, specific heat can be used to identify an unknown substance. For example, if substance A has a specific heat of c_p = 0.920 J/(g°C) and substance B has a specific heat of c_p = 0.710 J/(g°C), you can conclude that A and B are not the same substance.
The law of conservation of energy states that any heat lost by something must be gained by something else. Transfer of energy takes place between two things that are at different temperatures until the two reach the same temperature. The amount of energy transferred from or to a sample of matter can be calculated from the relationship

q = m × ΔT × c_p,

where q is the quantity of heat gained or lost, m is the mass in grams, ΔT is the change in temperature, and c_p is the specific heat.
In this experiment, you will determine the specific heat of a metal. A heated sample of this metal will be placed into cool water contained in a covered plastic-foam cup. Because foam is a good insulator, heat cannot easily escape to the surroundings. Shortly after mixing, the water and the metal will be the same temperature. Therefore, the heat lost by the metal is equal to the heat gained by the water.
The specific heat of water is known, c_p,water = 4.184 J/(g°C). The temperature changes of the water and of the metal can be measured, as can the mass of the water and the mass of the metal. Using this data, the specific heat of the metal can be calculated using the following equation.

m_water × ΔT_water × c_p,water
                                        = m_metal × ΔT_metal × c_p,metal

This equation can be rearranged to solve for c_p,metal.

Density An object made of cork feels lighter than a lead object of the same size. What you are actually comparing in such cases is how massive objects are compared with their size. This property is called density. Density is the ratio of mass to volume.

D = m/V

Density is a characteristic physical property of a substance. Density does not depend on the size of the sample because as the sample's mass increases, its volume increases proportionally. The ratio of mass to volume for a substance is constant at a specific temperature. Therefore, density can be used to identify a substance. For example, if substance A has a density of 0.86 g/mL and substance B also has a density of 0.86 g/mL, you can conclude that A and B may be the same substance.

Procedure

Part A: Specific Heat

1. Add 250 mL of tap water to a 400-mL beaker. Place the beaker on a hot plate and bring the water to a slow boil. While the water is heating, proceed to step 2.
2. Measure the mass of a metal sample. Record this mass in Part A of the Data and Observations section.
3. Place the metal sample in the boiling water for at least 10 minutes. Proceed to step 4 while the metal is heating.
4. Carefully measure 100.0 mL of distilled water in a graduated cylinder, and pour the water into a plastic-foam cup. Place the cup in a 250-mL beaker for support.
5. After the metal has been heating for at least 10 minutes, record the temperature of the water in the cup. Record this value as the initial temperature for water in Data Table 1.
6. Assuming the temperature of the metal is the same as that of the boiling water, measure the temperature of the boiling water and record it as the initial temperature of the metal.
7. Using tongs, carefully remove the metal from the boiling water. Immediately add the metal to the water in the cup. Place the lid on the cup, and put the thermometer into the cup through the hole in the lid. Gently swirl the cup and its contents. Note the temperature after it stops changing. Record this temperature as the final temperature for both the water and the metal in Data Table 1.
8. Repeat the experiment. If time permits, perform a third trial. Be sure you use the same metal sample for all trials.

Part B: Density

1. Record the mass of the metal sample in Data Table 2.
2. Add 50.0 mL of water to a 100-mL graduated cylinder. Record this initial volume in Data Table 2.
3. Add the metal to the 50.0 mL of water in the graduated cylinder. Measure the volume, and record this value as the final volume in Data Table 2.
4. Repeat steps 1-3 for two more trials.

Hypothesis

Cleanup and Disposal

1. Dry the metal samples for reuse.
2. Dry all equipment and return it to its proper place.
3. Be sure the hot plate is turned off and unplugged.

Data and Observations

Part A: Specific Heat

Volume of water added to the cup for each trial: __100.0 mL

Mass of metal: __70.81_ g

Part B: Density

Analyze and Conclude

Part A: Specific Heat

1. Measuring and Using Numbers
   
   
   1. Calculate the changes in temperature of the water (ΔT) for each trial. Record the values in Data Table 1. Trial 1: (28.9°C - 24.3°C) = 4.6°C; Trial 2: (28.5°C - 24.0°C) = 4.5°C; Trial 3: (29.1°C - 24.5°C) = 4.6°C

      ---

      
      
   2. Calculate the changes in temperature of the metal (ΔT_l) for each trial. Record the values in Data Table 1. Trial 1: (100.0°C - 28.9°C) = 71.1°C; Trial 2: (100.0°C - 28.5°C) = 71.5°C; Trial 3: (100.0°C - 29.1°C) = 70.9°C

      ---

   3. Record c_p for water in Data Table 1. See Data Table 1.

      ---

2. Measuring and Using Numbers
   1. Remember that the heat gained by the water is equal to the heat lost by the metal. Use the data for ΔT, c_p,water from Data Table 1, and the information in Tools of the Trade to calculate the specific heat of the metal for each trial. Record the values in Data Table 1. Trial 1: c_p = (100.0g)(4.6°C)[4.18J/(g°C)] (70.81g)(71.1°C) = 0.382 J/(g°C)

      ---

      Trial 2: cp = (100.0g)(4.5°C)[4.18J/(g°C)] (70.81g)(71.5°C) = 0.372 J/(g°C)

      ---

      Trial 3: cp = (100.0g)(4.6°C)[4.18J/(g°C)] (70.81g)(70.9°C) = 0.383 J/(g°C)

      ---

   2. Calculate your average value for the specific heat of the metal.
      0.382 J/(g°C) + 0.372 J/(g°C) + 0.383 J/(g°C) = 1.137 J/(g°C) 1.137 J/(g°C)/3 = 0.379 J/(g°C)
      

      ---

      
      
3. Drawing a Conclusion Compare the average specific heat for your unknown metal to the specific heats of the metals listed. Which metal do you believe to be the identity of your unknown?
   copper
   

   ---

   
   

   ---

Part B: Density

4. Measuring and Using Numbers
   
   
   1. Calculate the volume of metal for each trial by subtracting the initial volume from the final volume. Record these values in Data Table 2.
   2. Calculate the density of the metal for each trial. Record these values in Data Table 2.
   3. Calculate the average density.
      Trial 1: 58.0 mL - 50.0 mL = 8.0 mL Trial 2: 58.2 mL - 50.0 mL = 8.2 mL Trial 3: 57.8 mL - 50.0 mL = 7.8 mL
      

      ---

      Trial 1: 70.81 g/8.0 mL = 8.85 g/mL Trial 2: 70.81 g/8.2 mL = 8.64 g/mL Trial 3: 70.81 g/7.8 mL = 9.08 g/mL
      

      ---

      8.85 g/mL + 8.64 g/mL + 9.08 g/mL = 26.57 g/mL 26.57 g/mL/3 = 8.86 g/mL
      

      ---

      
      
5. Drawing a Conclusion Compare the average density for your unknown metal to the densities of the metals listed. Which metal do you believe to be the identity of your unknown?
   copper
   

   ---

   
   

   ---

   
   
6. Error Analysis How do your answers for questions 3 and 5 compare? Explain possible causes of error.
   Answers will vary. Sources of error may include that the metal was wet when mass was measured of that water splashed out of the cup or graduated cylinder when the metal was
   

   ---

   placed in either container.
   

   ---

   
   

   ---

   
   

   ---

   
   

   ---

Gathering the Evidence

Write about how the results of this lab apply to counterfeiting coins. Save the results of this lab until all labs relating to the crime are completed.

Many valuable coins are made of silver. If someone tried to duplicate a silver coin, they would use a metal that is similar in appearance to silver, such as aluminum or zinc. Both metals are the same color as silver and could be buffed to have the same degree of luster. The same emblems could be then be stamped onto the aluminum or zinc coin. In appearance, the counterfeit coins may look identical to silver coins, but if you were to determine the density and the specific heat of the counterfeit coins and compare their findings to the density and specific heat of silver, you would see that the values don't match.