Solubility test of iron sulphate , copper sulphate , pottasium nitrate

🧪 Lab Experiment: Color and Solubility of Common Salts

In this experiment, we observed the solubility and color changes of three different salts: Iron(II) sulfate (FeSO₄), Copper(II) sulfate (CuSO₄), and Potassium nitrate (KNO₃). These compounds were mixed with cold water in separate conical flasks, and real-life reactions were documented with photographs. This hands-on activity helped students understand how chemical substances behave in aqueous solutions.

📚 Background: What is Solubility?

Solubility is the ability of a substance (solute) to dissolve in a solvent (usually water) and form a solution. When a salt dissolves, its ions break apart and disperse in water. This process is influenced by factors like temperature, nature of the solute and solvent, and particle size.

Color changes often happen due to hydration or chemical interactions with water or air. Transition metals like copper and iron show vivid colors due to d-d electronic transitions.

🟢 Iron(II) Sulfate – Surprising Color Shift

When I took a sample of Iron(II) sulfate, it appeared light green in its dry form. I carefully poured it into a conical flask containing cold water. Surprisingly, the color changed — it became more intense, slightly murky green. This was fascinating for all of us.

Possible reason: FeSO₄ undergoes slight oxidation in air, forming brown Fe³⁺ ions or hydrated iron complexes. This is a classic example of transition metal sensitivity.

🔵 Copper(II) Sulfate – The Blue Beauty

Copper sulfate was deep blue even before mixing. After adding it to water, it dissolved completely, forming a clear blue solution. This is due to the formation of [Cu(H₂O)₆]²⁺ ions – a hydrated complex responsible for the blue color.

This part of the experiment was very visual and enjoyed by students. It confirmed that CuSO₄ is highly soluble and reacts immediately in water.

⚪ Potassium Nitrate – Totally Transparent

Potassium nitrate (KNO₃) is a colorless crystalline compound. When added to water, it dissolved instantly, forming a transparent solution. There was no color change observed. This is expected as KNO₃ is a neutral salt formed from a strong acid and base (HNO₃ + KOH).

Its dissociation was complete, releasing K⁺ and NO₃⁻ ions into solution. Students found this salt visually boring but scientifically important.

📊 Scientific Concepts

To understand ionic behavior in solution, chemists use the molar conductivity formula:

Λ_m = Λ_m⁰ − A√c

Where:

• Λ_m = molar conductivity at concentration c
• Λ_m⁰ = molar conductivity at infinite dilution
• A = constant depending on ion interaction
• c = concentration in mol/L

This formula is useful in comparing how easily different salts conduct electricity in solution.

👩‍🔬 Student Observations & Reactions

Students were excited to see visible changes in the lab. Some comments:

• "I didn’t know iron salt could change color so fast!"
• "Copper salt is so beautiful, like blue ink."
• "Potassium nitrate looks like nothing happened, but it’s all inside the solution!"

The use of real lab tools and flasks made this experiment memorable. Even students who were afraid of chemistry found it approachable.

🌱 Real-Life Applications of These Salts

• FeSO₄: Used in iron supplements and soil treatment for iron deficiency in plants.
• CuSO₄: Used as a fungicide in agriculture and to clean aquarium water.
• KNO₃: Used in fertilizers, food preservatives, and fireworks due to its oxidizing properties.

Understanding how these behave in water helps us see their importance in industry and daily life.

🧠 Extension Activity

You can extend this experiment by:

• Measuring temperature changes during dissolution
• Adding acids or bases to the solutions and observing reactions
• Testing electrical conductivity using a simple circuit

This builds deeper understanding of ionic chemistry and thermodynamics.

🔗 Related Articles

• Empirical Formula & Calculations
• 🎮 Limiting Reagent Spin Game
• How Fireflies Create Light (Bioluminescence)

✅ Conclusion

This lab experiment was a great success. It visually demonstrated how different salts dissolve, react, and behave in water. From the vibrant blue of copper sulfate to the neutral clarity of potassium nitrate, students witnessed chemistry in action.

Taking pictures, noting color changes, and discussing applications made the lesson more than just theory — it became an experience. Such hands-on activities should be a regular part of learning.