Quantity of Heat Lab

 The principle of heat exchange is often demonstrated by heating a metal sample in boiling water, then adding the metal to a known quantity of water. The temperature of the water is measured before and after adding the metal sample. The heat lost by the metal is gained by the water. The following equation can then be used:

 m_metal  x  Dt_metal  x  c_{p metal}  =  m_water  x  Dt_water  x  c_{p water}

 Procedure: Immediately begin boiling water in the beaker. Place precisely 100.0 mL of water in the styrofoam cup (a cup within a cup) and the determine the mass and temperature of that water. Record these measurements. Mass the dry metal samples. Record. Heat the metal samples in the beaker. Heat the samples in boiling water until the temperature remains constant for 3-4 minutes to insure that the samples are heated evenly throughout. DO NOT RUSH THIS IMPORTANT STEP.  Record the temperature of the boiling water (we are assuming the metal samples are at the same temperature). Using the string pick up the mesh containing the metal samples. Holding it immediately above the boiling liquid, allow it to drain FOR A FRACTION OF A SECOND. Immediately place it in the water the styrofoam cups as quickly and safely as possible. This step should not allow the samples to cool. As you read the thermometer swish the water gently for a few moments. Record the highest temperature reached by the water.

 Data:

sample material .. ......................
mass of metal sample .... . ............
specific heat capacity (metal) ...........

mass of 100.0 mL of water................
initial temp. of water (in cup) ..........
initial temp. of metal (boiling water)...
final temp. of water/samples (in cup) ....

 2. Repeat above experiment with 100.0 mL of permanent antifreeze. Remember that the samples must be thoroughly reheated in boiling water before being added to the antifreeze.

 Data:

 mass of 100.0 mL of antifreeze ............
specific heat capacity (antifreeze) ......
initial temp. of antifreeze (in cup) .....
initial temp. of metal (boiling water)...
final temp. of antifreeze/samples (cup)..

3. Repeat original procedure using 100.0 mL of the 50/50 mixture of water and antifreeze.

Data:

mass of 100.0 mL of 50/50 mixture .........
specific heat capacity (50/50 mixture)...
initial temp. of mixture (in cup) ... ....
initial temp. of metal (boiling water)...
final temp. of 50/50 mix/samples (cup)...

Safety Awareness: Be careful with the boiling water and the hot metal samples. Thermometers must be allowed to slowly adjust to changes in temperature. This is especially true in going from boiling temperatures to room temperatures.  Be certain to return the pure antifreeze to the proper container as well as returning the 50/50 mixture to its original container.

Analysis:

1. Why use boiling water as the method of heating the metal samples each time. Why not just hold the samples over a burner?

2. List the materials used in this lab in order, from lowest to highest, in specific heat capacities?

3. How does the quantity of heat transferred depend on specific heat, mass, and initial temperature?

4. List the liquids, from lowest to highest, based on the amount of change in temperature. Can this be explained?

5. How did the heat lost by the metal samples in each run compare? List this and explain.

6. Which of the liquids would be the most effective coolant in a car's radiator. Why?

7. Should one run 100% coolant (antifreeze) in a car's radiator in the summer? Why?

8. How would your results differ if you ran the experiment again with a different metal?

9. Explain briefly how specific heat capacities could be used to identify an unknown metal or liquid?

10. Given a true 50/50 mixture of ethylene glycol and water and without using the lab scales, how could

you calculate the mass of the mixture. (The given density of pure ethylene glycol is 1.1157 g/cm³)

Calculations:

1. Calculate the specific heat capacity of water. Use the specific heat capacity for your metal. See the chart on the board for densities and specific heat capacities.

m_metal  xDt_metal  x  c_{p metal}  =  m_water  x  Dt_water  x  [c_{p water}]

Calculate the percentage error between that of the actual value for water and what you found.

% error = theoretical value - experimental value; x 100 =   %
                             theoretical value

 2. Calculate the specific heat capacity of the metal you used. This time you must use the actual value for water.

 m_metal  xDt_metal  x [ c_{p metal} ] =  m_water  x  Dt_water  x  c_{p water}

 Calculate the percentage error for the metal.

 3. Calculate the specific heat capacity of the pure antifreeze. Use the actual value for the metal. The anti here indicates antifreeze.

 m_metal  xDt_metal  x  c_{p metal}  =  m_antifreeze  x  Dt_antifreeze  x  [c_{p antifreeze}]

 Calculate the percentage error for the pure ethylene glycol. Additives may have changed the value.

 4. Calculate the specific heat capacity of the 50/50 mixture. Use the actual value for the metal. The 50/50 here indicates the mixture.

 m_metal  xDt_metal  x  c_{p metal}  =  m_50/50  x  Dt_50/50  x  [c_{p 50/50}]

 

Lab Write-up: As usual you may substitute your notecard for the procedure and data table. You may leave out the equipment listing and safety rule section. Be prepared for an extensive calculation and result section. Remember to answer all the questions in the discussion section.