Chemistry Experimental Techniques

🗑️ Chemical Waste Management

Definition

Chemical waste is a product or unwanted material from a chemical reaction or expired product no longer needed for experiments.

Examples of Chemical Waste

Unused chemicals (acids, alkalis, solids)
Broken laboratory glassware
Plastics, waste papers, rubbers
Poisonous gases from reactions

Safe Disposal Methods

Normal waste bins: Non-recyclable plastics, wood, rubber, dirty papers

Special containers: Sharp objects, broken glass, contaminated items

Water drainage: Harmless salts, used acids/alkalis, detergents

Recycling: Unbroken glass, packing waste, paper

Incineration: Syringes, organic solvents, oils

🔬 Scientific Investigation Process

1. Problem Identification

Ask questions about the natural world

Example: What causes rusting?

2. Hypothesis Formation

A guessed answer based on knowledge and experience

3. Experimentation

Series of investigations to test the hypothesis

4. Observation & Data Collection

Record observations with correct units using tables

5. Data Interpretation

Explain observations and trends in relation to experiment aim

6. Conclusion

Confirm or reject hypothesis based on collected data

⚗️ Testing for Purity

Pure Substance: Material with constant composition and consistent properties throughout the sample

🌡️ Melting Point Test

Pure: Specific melting point

Impure: Lower melting point, melts over temperature range

💨 Boiling Point Test

Pure: Fixed boiling point

Impure: Higher boiling point, boils over temperature range

📊 Paper Chromatography

Pure: One spot on chromatogram

Impure: Multiple spots on chromatogram

Relative Flow Values (Rf)

Rf = Distance travelled by substance / Distance travelled by solvent

Always < 1 | Pure substance = 1 Rf value | Impure = multiple Rf values

🧪 Chemical Tests Quick Reference

Testing for Cations (Positive Ions)

With NaOH (Sodium Hydroxide)

Cation	Precipitate Color	In Excess
Cu²⁺	Blue	Insoluble
Fe²⁺	Pale green	Insoluble
Al³⁺	White	Dissolves
Zn²⁺	White	Dissolves

With NH₃ (Ammonia)

Cation	Precipitate Color	In Excess
Cu²⁺	Blue	Dissolves
Fe³⁺	Red-brown	Insoluble
Zn²⁺	White	Dissolves

Testing for Anions (Negative Ions)

Sulphate (SO₄²⁻)

Add dilute HCl + BaCl₂

Result: White precipitate

Halides (Cl⁻, Br⁻, I⁻)

Add dilute HNO₃ + AgNO₃

Cl⁻: White ppt

Br⁻: Pale yellow ppt

I⁻: Yellow ppt

Nitrate (NO₃⁻)

Add NaOH + Al foil, warm

Result: NH₃ gas (blue litmus)

Testing for Gases

NH₃ (Ammonia)

Damp red litmus → blue

CO₂ (Carbon Dioxide)

Lime water → milky

H₂ (Hydrogen)

Burning splint → 'pop' sound

Cl₂ (Chlorine)

Damp blue litmus → bleached

O₂ (Oxygen)

Glowing splint → relights

SO₂ (Sulphur Dioxide)

K₂Cr₂O₇ → purple to colorless

💧 Testing for Water

Anhydrous CuSO₄ Test

White

→

Blue

White to blue indicates presence of water

Anhydrous CoCl₂ Test

Blue

→

Pink

Blue to pink indicates presence of water