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LAB – Coffee Cup Calorimeter
INTRODUCTION: A coffee cup calorimeter is essentially a polystyrene (Styrofoam) cup. The cup is partially filled with a known
volume of water and a thermometer is inserted through the lid of the cup so that its bulb is below the water surface. When a chemical
reaction occurs in the coffee cup calorimeter, the heat of the reaction if absorbed by the water. The change in the water temperature is
used to calculate the amount of heat that has been absorbed (used to make products, so water temperature decreases) or evolved (lost
to the water, so its temperature increases) in the reaction.
Heat flow is calculated using the relation: q = mcT, where q is heat flow, m is mass in grams, and ΔT is the change in temperature.
The specific heat (c) is the amount of heat required to raise the temperature of 1 gram of a substance 1 degree Celsius. The specific
heat of water is 4.184 J/(g·°C).
PURPOSE: To experimentally determine the amount of heat that is either given off or needed when NH 4Cl dissolves in water.
MATERIALS:
NH4Cl
CaCl2
Water
Styrofoam cups
250 ml Beaker
Scupula
thermometer
Electronic Balance
Weighing cup
100 ml graduated cylinder
SAFETY:
1.
2.
3.
Goggles and apron are required throughout this entire lab.
NH4Cl and CaCl2 are both skin irritants. Both are harmful if ingested.
Wash hands at the end of the lab.
PROCEDURE:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Pour 100.0 ml H2O into a Styrofoam cup and place the cup inside the 250 ml beaker.
Determine the mass using the density of water (1.00 g/ml).
Record the temperature of the water.
Weigh out approximately 5.0 g. of NH4Cl in a weighing cup.
Pour in the NH4Cl in the Styrofoam cup.
Stir with the thermometer and observe the temperature every 5 seconds until the temperature no longer changes.
Record the temperature that is the biggest difference from the starting point.
Discard the solutions in the sink. Rinse the cup.
Repeat steps 1-8 with CaCl2
Do not throw away the cups
DATA TABLE:
Mass of NH4Cl
g
Mass of CaCl2
g
Mass of H2O
g
Mass of H2O
g
Initial Temperature of water
o
C
Initial Temperature
of water
o
Final Temperature of water
o
C
Final Temperature of
water
o
T (Tfinal – Tinitial)
o
C
T (Tfinal – Tinitial)
o
C
C
C
CALCULATIONS:
Show ALL work including equations and units. Round all answers to the correct number of significant figures.
1.
Calculate the heat gained (+) or lost (-) by the water in Joules after the NH4Cl is added.
#1 Answer:
2.
If the heat gained/lost by the NH4Cl is equal but opposite in sign to the heat determined above, calculate the heat of
solution/mole (Hsolution = qNH4Cl/mol NH4Cl) for NH4Cl
#2 Answer:
3.
If the heat of solution of NH4Cl is 14.7 kJ/mol, calculate the % error of your experimental data.
#3 Answer:
4.
Calculate the heat gained (+) or lost (-) by the water in Joules after the CaCl2 is added.
#4 Answer:
5.
If the heat gained/lost by the CaCl2 is equal but opposite in sign to the heat determined above, calculate the heat of
solution/mole (Hsolution = qCaCl2/mol CaCl2) for CaCl2
#5 Answer:
6.
If the heat of solution of CaCl2 is -80.1 kJ/mol, calculate the % error of your experimental data.
#6 Answer:
7.
Discuss at least two unavoidable sources of error. Do not include human error.