SST Lower Sec IP Science Chemistry Practical Guide Salt Preparation

Visual Lab Guide: Crystallisation & Salt Prep

5-Step Procedure Diagrams, Marking Scheme Keywords, Common Practical Traps & Interactive Mastery Quiz for Lower Secondary & O-Level Chemistry.

✓ 5-Step Illustrated Setups

🎯 Exact Cambridge/IP Keywords Highlighted

⚖️ Thermal Stability Comparison Guide

🏆 8-Question Interactive Mastery Quiz

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Critical Lab Exam Trap: Evaporating to Dryness vs. Saturated Solution

Never heat hydrated or thermally unstable salts (e.g. Copper(II) sulfate) to dryness! Heating past the saturation point drives off water of crystallisation and decomposes the salt into an unwanted anhydrous powder.

🧪 5-Step Practical Walkthrough (With Setups)

Click filter buttons to isolate individual experimental steps

Step 1 Apparatus: Beaker & Glass Stirring Rod

React Acid with Insoluble Substance

Add insoluble base/carbonate (e.g., CuO, CuCO₃) to warm acid (e.g., dilute H₂SO₄) and stir until solid stops dissolving and settles at the bottom.

Key Mark: Add in excess to guarantee all acid has fully reacted.

Step 2 Apparatus: Filter Funnel, Filter Paper & Conical Flask

Filter Out Excess Solid

Pour the warm reaction mixture into a filter funnel lined with filter paper.

Vocabulary Check: Unreacted solid is trapped as Residue; pure salt solution passes through as Filtrate.

Step 3 Apparatus: Evaporating Dish, Tripod, Bunsen Burner & Glass Rod

Heat to Saturated Solution

Heat filtrate in an evaporating dish until concentrated. Check saturation by dipping a cold glass rod.

Golden Rule: Stop heating when a crust of crystals forms on the rod. Never evaporate to dryness!

Step 4 Apparatus: Evaporating Dish at Room Temperature

Cool Slowly to Grow Crystals

Remove from heat and leave undisturbed at room temperature. As temperature drops, solubility decreases and crystals grow.

Theory: Slow cooling gives ions time to assemble into large, regular crystal lattices.

Step 5 Apparatus: Wash Bottle (Cold Distilled Water) & Dry Filter Papers

Wash & Dry Crystals

Filter off crystals. Wash surface with minimal cold distilled water. Gently press between sheets of dry filter paper.

Mark Scheme: Rinse with cold distilled water (avoids re-dissolving) and dry between filter paper.

⚖️ Crystallisation vs. Evaporate to Dryness

How to decide between evaporation and crystallisation based on thermal stability

Method	When to choose it	Typical Example
Method 1 Evaporation to Dryness	Salt is thermally stable (does not decompose when heated strongly) and is anhydrous.	Sodium chloride (NaCl), Potassium chloride (KCl)
Method 2 Crystallisation	Salt is thermally unstable or hydrated (loses water of crystallisation and decomposes on strong heating).	Copper(II) sulfate (CuSO₄·5H₂O), Iron(II) sulfate (FeSO₄)

💡 Top 4 Written Exam Questions & Answers

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Q1: What is a saturated solution? ▼

A solution containing the maximum amount of dissolved solute at a specific temperature.

Q2: Why rinse with COLD distilled water? ▼

To wash away surface impurities while minimising the amount of salt re-dissolving.

Q3: Why not dry crystals with a Bunsen flame? ▼

Heat will remove water of crystallisation, decomposing crystals into an anhydrous powder.

Q4: Why add the solid in excess during Step 1? ▼

To ensure all acid is fully neutralized/reacted, preventing acid impurities in the final salt.

🎯 Full Exam Mastery Quiz

🧪 Practical Revision Self-Assessment (8 Questions)

Test your complete understanding of the crystallisation apparatus setup, saturation criteria, and marking scheme rubrics.

Progress: 0/8 Answered

Score: 0/0

Question 1 Step 1 • Excess Reactant

In Step 1 of preparing copper(II) sulfate crystals, why is excess insoluble copper(II) oxide added to the warm dilute sulfuric acid?

Question 2 Step 2 • Filtration Terminology

In Step 2 (filtration), what are the correct scientific terms for the unreacted solid trapped on the filter paper and the clear solution collected below in the flask?

Question 3 Step 3 • Saturation Test

In Step 3, what is the standard laboratory method to confirm that the heated solution has reached its saturation point?

Question 4 Lab Error • Thermal Stability

What happens if a student accidentally continues heating copper(II) sulfate (CuSO₄·5H₂O) solution to complete dryness instead of stopping at saturation?

Question 5 Step 4 • Crystal Growth Theory

In Step 4, why should the hot saturated solution be cooled SLOWLY at room temperature rather than chilled rapidly in an ice bath?

Question 6 Step 5 • Washing Technique

In Step 5, why are the harvested crystals washed with a minimal volume of COLD distilled water?

Question 7 Step 5 • Crystal Drying

Which of the following is the examiner-approved method to dry the purified crystals?

Question 8 Method Selection • Evaporation vs Crystallisation

Which of the following salts is thermally stable and should be obtained by Evaporation to Dryness rather than Crystallisation?

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