Coffee Cup Calorimetry

Measuring enthalpy of neutralization using a simple calorimeter

Thermochemistry Intermediate (High School) 40 min ~$8.00

Objective

Determine the enthalpy of neutralization of HCl and NaOH using a polystyrene cup calorimeter.

Background

A polystyrene cup makes an inexpensive but effective calorimeter because it has low thermal conductivity. By mixing known volumes of acid and base and measuring the temperature change, the enthalpy of neutralization can be calculated. The accepted value for strong acid-strong base neutralization is -57.1 kJ/mol.

Safety Warnings

  • HCl and NaOH are corrosive
  • Wear safety goggles
  • The mixture will get hot

Required PPE

goggles gloves lab_coat

Materials

  • Hydrochloric acid (HCl) (50 mL)
    1M
  • Sodium hydroxide (NaOH) (50 mL)
    1M
  • Distilled water (100 mL)
    For calibration

Equipment

Two polystyrene (Styrofoam) cups (nested) Cardboard lid with hole Thermometer (0.1°C resolution) Graduated cylinder (50 mL) Stopwatch

Procedure

1

Measure 50 mL of 1M HCl and pour into the nested polystyrene cups. Record the initial temperature every 30 seconds for 3 minutes.

5 min HCl is corrosive
2

Measure 50 mL of 1M NaOH in a separate container. Record its temperature.

2 min NaOH is corrosive
3

Quickly pour the NaOH into the HCl, stir gently, and replace the lid with thermometer.

1 min Exothermic reaction
4

Record the temperature every 30 seconds for 5 minutes. Note the maximum temperature.

5 min
5

Plot temperature vs time. Extrapolate the cooling curve back to the mixing time to find the corrected maximum temperature.

5 min
6

Calculate ΔT, then q = mcΔT (assume c = 4.18 J/g°C, mass = 100 g). Calculate ΔH per mole of water formed.

8 min

Expected Results

Temperature should rise by approximately 6-7°C. Calculated ΔH should be approximately -50 to -57 kJ/mol (accepted: -57.1 kJ/mol). Losses to the calorimeter walls typically give lower values.

Cleanup

The neutralized solution is safe to pour down the drain. Rinse and dry the calorimeter cups for reuse.

Details

Category
Thermochemistry
Difficulty
Intermediate (High School)
Duration
40 min
Est. Cost
$8.00
Steps
6
Materials
3

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Frequently Asked Questions

What is the objective of Coffee Cup Calorimetry?
Determine the enthalpy of neutralization of HCl and NaOH using a polystyrene cup calorimeter.
How difficult is Coffee Cup Calorimetry?
This experiment is rated as Intermediate (High School). It takes approximately 40 minutes to complete.
What safety precautions are needed for Coffee Cup Calorimetry?
Key safety precautions include: HCl and NaOH are corrosive; Wear safety goggles; The mixture will get hot.
What materials are needed for Coffee Cup Calorimetry?
The main materials required are: Hydrochloric acid (HCl), Sodium hydroxide (NaOH), Distilled water.
What results should I expect from Coffee Cup Calorimetry?
Temperature should rise by approximately 6-7°C. Calculated ΔH should be approximately -50 to -57 kJ/mol (accepted: -57.1 kJ/mol). Losses to the calorimeter walls typically give lower values.