Hess's Law Virtual Lab

Enthalpy of Hydration: $CuSO_4$ to $CuSO_4 \cdot 5H_2O$

Hess Cycle: $\Delta H_{hyd} = \Delta H_1 - \Delta H_2$
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Lab Manual: Theory, Materials & Procedure
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1. Aim

To determine the enthalpy change ($\Delta H_{hyd}$) for the hydration of anhydrous Copper (II) Sulfate to form Copper (II) Sulfate Pentahydrate using Hess’s Law.

$\text{CuSO}_{4(s)} + 5\text{H}_2\text{O}_{(l)} \rightarrow \text{CuSO}_4 \cdot 5\text{H}_2\text{O}_{(s)}$

2. Principle & Hess Cycle

Direct measurement of hydration energy is impossible without creating a solution. We use an indirect route:

Route 1 (Direct): Anhydrous Salt $\xrightarrow{\Delta H_{hyd}}$ Hydrated Salt

Route 2 (Indirect):
1. Dissolve Anhydrous $\text{CuSO}_4$ in water ($\Delta H_1$)
2. Dissolve Hydrated $\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$ in water ($\Delta H_2$)

$\Delta H_{hyd} = \Delta H_1 - \Delta H_2$

3. Materials Required

  • Anhydrous $\text{CuSO}_4$ (white powder)
  • Hydrated $\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$ (blue crystals)
  • Distilled water ($50\text{g}$)
  • Calorimeter, Thermometer, Stirrer

4. Procedure

Part 1: Anhydrous Salt ($\Delta H_1$)

  1. Add $50\text{g}$ water to the calorimeter.
  2. Record initial temperature ($T_1$).
  3. Add $0.025$ mol of anhydrous salt.
  4. Stir and record the maximum temperature ($T_2$).

Part 2: Hydrated Salt ($\Delta H_2$)

  1. Add $50\text{g}$ water to the calorimeter.
  2. Record initial temperature ($T_3$).
  3. Add $0.025$ mol of hydrated crystals.
  4. Stir and record the final temperature ($T_4$).

5. Calculations

Calculate heat ($q$) using $q = m \cdot c \cdot \Delta T$.
Convert to molar enthalpy: $\Delta H = -q/n$ (where $n = 0.025$).
Finally, subtract $\Delta H_2$ from $\Delta H_1$ to find the hydration energy.

🔮 Predict before you experiment

You will dissolve each salt separately and use Hess's Law (ΔHhyd = ΔH₁ − ΔH₂). Predict the heat effects first, then lock it to unlock Start Test.

⚠️ Safety

  • Copper(II) sulfate is harmful if swallowed and irritating to skin and eyes — wear goggles, do not taste, wash hands after use.
  • Anhydrous CuSO₄ is a strong desiccant — it reacts with water/moisture and can heat up; keep the jar closed and add it to water carefully.
  • Avoid breathing the fine powder; add solids gently to prevent dust and splashing.
  • The calorimeter contents get warm — do not seal the cup tightly; read the thermometer without pulling it out.
  • Copper salts are toxic to aquatic life — collect waste in the labelled container, do not pour down the sink.

Reagent Bench

Anhydrous
Hydrated
1. Select Salt Jar First
50mL $H_2O$

Calorimetry Station

PROBE TEMPERATURE
20.0°C

Observation Log

ANHYDROUS TEST
ΔT: -- ΔH₁: --
HYDRATED TEST
ΔT: -- ΔH₂: --

Logic Monitor

Please click on one of the salt jars on the bench to prepare your sample.

Ready