SPECIFIC HEAT
Note to Instructors: Have students work in groups of 4 - 5.
Purpose:
To determine the specific heat of an unknown metal.
Materials:
Metal bars of aluminum, magnesium, zinc, copper, and tin, styrofoam picnic cups.
Safety Precautions:
water.
As always, care should be taken with Bunsen Burners/Hot plates and boiling
Introduction
The specific heat (C) of a material is defined as the number of calories of heat required to
change the temperature of one gram of the substance one degree Celsius and is measured
in calories (or joules) per gram per degree (cal/goC). A metal bar is weighed, heated to
the temperature of boiling water, and quickly transferred to a calorimeter containing a
known weight of water at a known temperature. The bar transfers its heat to the water,
and an equilibrium temperature is reached. From the data obtained the specific heat of
the metal can be calculated. The calculation is based on the fact that the heat lost by the
metal is gained by the calorimeter and it contents.
Calories lost by metal = [calories gained by water] + [calories gained by calorimeter]
Cmetal x mmetal x Tmetal = [CH2O x mH2O x TH2O]
The specific heat of water (CH2O ) is 1.00 cal/goC or 4.18 J/goC.
Cmetal = [CH2O x mH2O x TH2O]
mmetal x Tmetal
Scientists often use the Greek letter delta, , to mean "change in," the difference between
final value and initial value. Therefore, T is obtained by subtracting the initial
temperature from the final temperature.
PROCEDURE
1.
Metal bar. Weigh the bar to the greatest accuracy possible on the balance. Carefully place the
metal bar into a large test tube. Prepare a water bath by placing 200 ml of water in a 400-ml
beaker mounted on a ring stand or a hot plate and heat the bar in its test tube to the boiling
temperature of water for five minutes.
While the bar is heating weigh a dry calorimeter on a balance. NOTE: For each trial,
the calorimeter should be emptied, dried, and reweighed. Add about 25 ml of distilled water and
weigh again. The difference is the weight of the calorimeter water.
When the calorimeter is ready, place a thermometer in the test tube containing the bar.
The temperature will slowly rise to between 99oC and 100oC. Continue to heat for at least 5
minutes (when the temperature in the test tube is constant). Record it's temperature to the nearest
0.1oC, leave the test tube and bar in the boiling water, but remove the thermometer from the test
tube. Cool the thermometer to room temperature in water, dry it, and transfer it to the calorimeter,
and read the temperature every 30 seconds until the temperature remains constant. Read the
temperature to the nearest 0.1oC and record this value as the "initial temperature of the water." It
is important that the same thermometer be used for both the test tube and the calorimeter.
Bring the calorimeter to the water bath, remove the test tube with a test tube holder, and
quickly transfer the bar to the calorimeter. Make sure that the entire bar is submerged. Stir the
water with the thermometer and read the temperature every 30 seconds. When it has reached the
maximum, read it to the nearest 0.1oC and record this value as the "equilibrium temperature of the
water + metal." Repeat one more time.
B.
Calculations
Calculate the specific heat of the unknown metal using Equation 2. Remember
that the specific heat of water (CH2O) is 1.00 cal/goC or 4.18J/goC. Look up the
accepted values in the Handbook of Chemistry and Physics and calculate the
percent error.
Name________________________
Date_________________________
Specific Heat
REPORT SHEET
A.
Calorimeter Measurements
Identity of metal =
Sample #1
________
Sample #2
________
Mass of metal =
________
________
Mass of Calorimeter + Water =
________
________
Mass of calorimeter =
________
________
Mass of water =
________
________
Equilibrium temp of water + metal =
________
________
Initial temp of water =
________
________
Temp change (TH2O) of water =
________
________
B.
Calculations
Calculation of specific heat of metal (Cmetal) showing mathematical setup
Sample # 1
Sample # 2
Percent error calculation
Sample #1
________
Sample #2
________
________
________
Percent error = ________
________
Cmetal observed =
Cmetal from literature =