MYSTERY METAL LAB
PRELAB
Read the entire lab and answer the following questions.
1. Use your periodic table to list the specific heat capacity and density for the following metals: copper, Pb, Al, Cd, and Zn. Construct a table the lists the element symbol, Cp (with units) and density (with units) for each metal.
2. Which of the metals in the table (question 1) would be the best conductor of heat and why?
3. A metal 23.0 gram metal sample was heated to 95.0°C and then dropped in to a calorimeter containing 50.0 ml of water at 23.0°C. If the final temperature of the system was 26.4°C, what is the specific heat of the metal?
4. What equipment do you need to make a calorimeter? Explain the purpose of each piece of equipment.
5. Define specific heat capacity.
OBJECTIVES
To identify a mystery metal sample by performing a density analysis and a specific heat analysis and comparing to theoretical density and specific heat values.
BACKGROUND
Density and specific heat are both intensive physical properties that can be used to identify substances. In the second part of today’s lab, you will determine the density of the sample using the water displacement method to find the volume of the mystery metal. The density data will be used as a secondary means of identifying your metal.
The primary means of identifying the metal sample will be through a determination of its specific heat capacity. In the first part of today’s lab, you will determine the specific heat capacity of the metal using a calorimeter. Heat is a form of energy that cannot be measure directly. However, changes in heat can be determined by measuring changes in temperature. To calculate the amount of heat absorbed or lost by a substance as it changes temperature use the following equation:
q = m x Cp x DT
q = heat lost or gained
m = the mass of the substance (in grams)
Cp = specific heat capacity
DT = T final – T initial
Metals with low specific heat capacities tend to heat up and cool down quickly because it takes les energy to raise their temperature. Water, on the other hand, has a specific heat of 4.184 J/ g°C, which means that it takes 4.184 Joules of energy to raise 1 gram (or 1 ml) of water 1°C.
Measurements in a calorimeter are base on the assumption that all of the heat lost by the metal as it cools must be absorbed by the water. However, some heat is lost because it is impossible to insulate perfectly. For our purposes, we will assume that – q metal = + q water, or that the heat lost by the metal = the heat gained by the water. Given the specific heat of water, we will then be able to solve the equation for the specific heat of the metal, Cp.
MATERIALS
Metal samples (cylinders or looses pieces) – about 15 grams
Coffee cup calorimeter (2 nested coffee cups and a lid)
Thermometer
50 ml graduated cylinder
Balance
Test tube clamp
Test tubes
400 ml beaker for hot water bath
250 ml beaker to hold calorimeter
Electronic balance
PROCEDURE
PART I: Calorimetric determination of specific heat
1. Use a graduated cylinder to measure about 50 ml of cold water. Record the exact volume to the nearest 0.1 ml in your data table.
2. Pour the cold water into your coffee cup calorimeter and allow the water to reach room temperature. Measure the temperature every minute until the temperature stays the same for 3 minutes. Record this temperature in the initial temperature for the calorimeter.
3. Plug in the hot plate and place about 200 ml of water in a beaker and allow it to warm on the hot plate.
**You may want to work on part II of the lab while you are waiting for the hot plate to warm up or while you are waiting for the water to boil for 10 minutes.
4. Obtain a metal sample, record its letter identity and find its mass. If you are using the loose metals, place them in a test tube after finding their mass.
5. Add the metal samples to the hot water bath using tongs. The loose metal pieces should be in a test tube while heating. Allow the water to boil. After 10 minutes of boiling, take the temperature of the hot water bath. You can assume that this is the temperature of the metal sample. Record this temperature in the data table.
6. Using test tube tongs or tongs, remove the metal sample from the boiling water bath and quickly add the metal to the coffee cup calorimeter.
7. Quickly place the lid on the calorimeter and insert the thermometer. Gently swirl the beaker holding the calorimeter for 30 seconds. Record the highest temperature attained by the water in the calorimeter.
8. Remove the metal sample from the colorimeter and place it on a paper towel to dry. Refill the calorimeter with 50 ml or tap water and record its initial temperature.
9. Repeat steps 6-10 for 2 more samples of the same metal.
10. Turn off the boiling water and allow it to cool or carefully pour it down the drain wing hot hands. DO NOT attempt to move the hot plate, just unplug it. Dry all metal samples and return to the beakers (or bags) at the front desk.
PART II: Density determination
1. Find the mass of you metal and the volume of the metal using water displacement. Use three different samples of the same metal and repeat the density determination three times.
DATA
Please add units in the ( ) or in the columns provided.
QUALITATIVE DATA
Letter of metal sample:
Description:
DENSITY DATA
Trial / Mass of metal( ) / Final volume water
( ) / Initial volume water
( ) / Volume of the metal
( ) / Density of metal
( ) / Deviation from average =
|density – average density|
1
2
3
Average density
Average deviation of density
Theoretical density
% error
Sample Calculations:
1. Density calculation
2. Average density
3. average deviation of density
4. % error
SPECIFIC HEAT DATA
Units of measurement / Trial 1 / Trail 2 / Trial 3Mass of test tube and metal or weighing boat and metal
Mass of empty test tube or weighing boat
Mass of metal
Initial temperature of the metal
Final temperature of the metal (final temp. of the calorimeter.)
H2O volume used
H2O density (see appendix in text)
H2O mass (use D = m/v)
Initial temperature of water
Final temperature of the water (in the calorimeter)
Specific heat of metal (experimental)
Average specific heat
Average deviation
Theoretical specific heat (from prelab or periodic table)
% error
Sample calculations:
1. calculate the mass of water given density
2. Using – q metal = + q water to find Cp for metal (show all steps and units)
3. average deviation of specific heat values
4. percent error calculation
DISCUSSION:
See formal lab write up to determine what should be written here. Think especially about the calorimeter used and its drawbacks.
QUESTIONS:
1. State the scientific law that is the basis for the assumption that the heat energy lost by the metal as it cools will be equal to the heat energy gained by the water.
2. If a specific heat value is given in the CRC handbook as 7.50 calorie/ g°C, you need to convert this to J/ g°C. Show this conversion.
3. How does the specific heat capacity of your metal compare to the specific heat of water. Which would absorb the greater amount of heat with a greater change in temperature, the metal or the water?
4. A house wares company is trying to make pots and pans that will quickly reach cooking temperatures. Explain which of the following metals is the best choice: aluminum, copper, iron, or nickel. Please use numerical data to support your claim.
5. Which test, density or specific heat determination, provided the best results? Why do you think this is the case?