By John Brennan | Updated Aug 30, 2022

Overview

Calorimeters quantify the heat change in chemical reactions or physical transformations, such as ice melting. Knowing the calorimeter constant is essential for converting temperature changes into energy values and for accurately interpreting reaction thermodynamics. This guide walks you through a practical, reproducible method for calibrating a simple coffee‑cup calorimeter.

Safety Precautions

• Wear a lab coat, goggles, and gloves.
• Never place hair, clothing, or flammable materials near an open flame.
• Handle hot water (≈80 °C) with care to avoid burns.

Materials

• Coffee‑cup calorimeter (two Styrofoam cups, lid, thermometer)
• Two digital or mercury thermometers
• Bunsen burner, lighter, ringstand, clamp, wire gauze
• Dry 150 mL beaker
• Scale accurate to 0.01 g
• Graduated cylinder
• Spreadsheet software (Excel, OpenOffice Calc)
• Calculator
• Water (room temperature and hot)
• Lab coat, goggles, gloves

Procedure

1. Assemble the calorimeter. Insert one Styrofoam cup into the other, secure the lid, and place a thermometer in the cup through a small hole in the lid.
2. Weigh the empty calorimeter. Record the mass to the nearest 0.01 g.
3. Add 50 mL cold water. Use a graduated cylinder; precise volume is not critical at this stage. Re‑weigh the calorimeter and calculate the water mass from the weight difference.
4. Weigh the beaker. Record its mass. Add 50 mL of water, re‑weigh, and compute the mass of the hot water.
5. Heat the water. Place the beaker on the wire gauze above the Bunsen burner, insert a thermometer, and gently heat to ≈80 °C, avoiding rapid boiling.
6. Stir the calorimeter. Using a clamp, suspend the second thermometer in the cold water and stir for four minutes. Record temperature every minute; the value should be steady.
7. Transfer hot water. At the fourth minute, turn off the burner, note the hot water temperature, and pour it into the calorimeter. Replace the lid and resume stirring.
8. Record temperature. Measure the calorimeter temperature every 30 seconds for the next five minutes.
9. Analyze data. Import the time and temperature data into a spreadsheet. Plot the post‑mixing temperatures (exclude pre‑mixing points) and fit a linear trend line.
10. Extrapolate final temperature. Use the line of best fit to estimate the temperature at 5 minutes (Tf).
11. Calculate temperature changes.
    • Hot water change (ΔTh) = initial hot water temperature – Tf.
    • Cold water change (ΔTc) = Tf – initial cold water temperature.
12. Compute energy changes.
    • Energy lost by hot water: Qh = m_h × 4.184 J g⁻¹ °C⁻¹ × ΔTh.
    • Energy gained by cold water: Qc = m_c × 4.184 J g⁻¹ °C⁻¹ × ΔTc.
13. Determine calorimeter energy. Q_cal = Qh – Qc.
14. Calculate constant. C_cal = Q_cal / ΔTc. The result, expressed in J °C⁻¹, is the calorimeter constant.

Important Notes

• The constant should be positive; a negative value indicates a procedural error.
• Repeat the calibration multiple times and average the results to minimize random error.
• Report the final average ± 2σ, where σ is the standard deviation of the trials.

References

• Atkins, P., & Jones, L. (2008). Chemical Principles: The Quest for Insight, 4th Edition.
• Berniolles, S. (2011). Chemistry 7L Lab Manual.