Lab 4: Heat Capacity

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Today we are going to investigate energy flow and specific heat capacity using a coffee cup calorimeter.

Experimental Title: Lab 4:  Heat Capacity

Date of laboratory:  June 24, 2014

Purpose: The purpose of this laboratory is to investigate the flow of thermal energy between substances until they reach thermal equilibrium.

Introduction:

Thermal energy is transferred from an object or substance with higher thermal energy to one at a lower thermal energy, until the two reach thermal equilibrium. 

Chemists often use a calorimeter to study thermal energy transfer. A common set up is called a “coffee cup calorimeter.” It consists of an insulated Styrofoam cup and a thermometer. To improve sensitivity, sometimes two Styrofoam cups are used, one inside the other and a cardboard, plastic or cork lid is added with a hole for the thermometer. This provides further insulation and less loss of thermal energy to the surroundings.

How much the temperature of a given substance increases for a given amount of heat transferred varies from substance to substance. The heat capacity is how much heat (measured in joules) is needed to raise the temperature of a given amount of substance 1°C. The specific heat capacity assumes the amount of the substance is measured in grams.

Equation:  q = m x C x ∆T

  • where q = amount of heat absorbed (joules)
  • m = mass (in g)
  • C = specific heat capacity (j/g °C)
  • ∆T = change in temperature (°C)

The specific heat capacity (C) for water is 4.184 J/g °C  and for copper is 0.385J/g °C.

Special safety concerns for Lab 4:

  • Today we will be wearing eye protection.
  • If boiling water spills on you, run cold water from the sink onto the area immediately. Don’t think, just run to the sink.
  • If the glass thermometer breaks, do not pick it up with your bare hands. Notify your instructor immediately.
  • Be sure to wash your hands when you are finished with this lab.

Materials:

  • Eye protection
  • Stove
  • Oven mitts
  • Pan
  • Thermometer
  • Water
  • Ice
  • Styrofoam cups
  • Graduated cylinders
  • Table top scale
  • Strainer or colander
  • Pennies
  • Spoons
  • Clock
  • Calculator

Procedures:

Part 1:
1.    Pour 100 mL of water at room temperature into a large Styrofoam cup.  Insert the thermometer, taking care not to touch the walls of the cup. Determine the initial temperature of the water and note it in your notebook (see suggested data table below). Remove the thermometer from the cup.
2.    You will be adding 100 mL of boiling water to the cup. Using the initial temperature of the room temperature water, and assuming the temperature of boiling water to be 100°C, predict the final temperature of the mixture when the two samples are combined. Record your prediction in your notebook.
3.    Using a graduated cylinder, measure 100 mL of water. Pour the water into the pan provided and heat on the stove until it boils. Using oven mitts, carefully pour the 100 mL of boiling water into the Styrofoam cup with the room temperature water. If you want to stir the water, use a spoon and not a thermometer.
4. Take a temperature reading every minute until the mixed water reaches thermal equilibrium (when the temperature no longer changes, probably between four and six minutes). Record the final temperature in your notebook.

Part 2:
Repeat Part 1 using 75 mL room temperature water in step 1 and 225 mL of boiling water in step 3.

Part 3:
Repeat Part 1 using 225 mL of room temperature water in step 1 and using 75 mL of boiling water in step 3.

Part 4:
Repeat Part 1 using 100 mL of room temperature water for step 1 and 100 mL ice water for step 3.

Suggested Water Temperature Table (Parts 1-4)

heat-capacity-table-water

Part 5:
1.    Weigh 35 pennies using the scale. Record the mass. (It should be close to 100 g.)
2.    Measure out an equal mass of room temperature water (remember 1 mL water is approx. 1 g). Pour the water into a large Styrofoam cup, insert the thermometer and record the temperature. Remove the thermometer.
3.    Cover the pennies with water in a pot and heat the water to boiling.
4.    While the pennies are heating, predict the final temperature that will result when the hot pennies (assume 100°C) are mixed with an equal mass of water in the cup. Record this value in your notebook.
5.    Drain the pennies in a colander over the sink to remove as much water as possible. Pour the hot pennies into the Styrofoam cup. Measure the final temperature as before and record in your notebook.

Part 6:
1.    Dry the 35 pennies and weigh again.
2.    Measure out an equal mass of room temperature water. Pour the water into a large Styrofoam cup, insert the thermometer and record the temperature. Remove the thermometer.
3.    Cover the pennies with ice water.
4.    While the pennies are cooling, predict the final temperature that will result when the cold pennies (assume near 0° C) are mixed with an equal mass of water in the cup. Record this value in your notebook.
5.    Drain the pennies to separate them from the ice and water and pour them into the Styrofoam cup. Measure the final temperature and record in your notebook.

Water Plus Pennies Temperature (Parts 4 and 5)

heat-capacity-table-pennies

Calculations:

Now calculate the amount of heat (q) for water and pennies. We will work on this together in lab.

Conclusions:

Once you have completed the six parts, sit down and write a sentence or two to explain the results of each part.

Discussion:

Record any thoughts you have about the experiments, including:

  • Why did we perform the experiments in Styrofoam cups?
  • Possible improvements to the procedures or how to tweak techniques
  • How the results differed from your expectations
  • Suggestions for other experiments
  • What key concepts you learned about heat capacity

We’ll go over the key concepts together at the end of lab.

Please leave a comment or send an e-mail if you have any questions before our meeting.

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