Matter exists in three main states:

• Solid — Particles are tightly packed and vibrate in fixed positions (e.g., ice, iron, stone)
• Liquid — Particles are close together but move freely (e.g., water, juice, kerosene)
• Gas — Particles are far apart and move quickly in all directions (e.g., steam, air)

Experiment 1: Melting of Ice (Solid → Liquid)

Objective: To observe the change from solid to liquid when heat is applied.

Materials needed:

• Ice cubes (from a freezer or vendor)
• A clean beaker or glass
• A heat source (sunlight or warm water bath)
• Thermometer (if available)

Procedure:

1. Place a few ice cubes in the beaker.
2. Observe and record the appearance of the ice at the start.
3. Leave the beaker in sunlight or place it in warm water.
4. Observe the ice every 2 minutes.
5. Record your observations until all ice has melted into water.

Expected observations:

• Ice (solid) gradually loses its shape
• Water droplets form around the ice
• Eventually, all ice becomes liquid water
• No new substance is formed—ice and water are both H₂O

Experiment 2: Freezing of Water (Liquid → Solid)

Objective: To observe water changing to ice when heat is removed.

Materials needed:

• Water
• A small container (plastic cup or glass)
• A freezer or ice box

Procedure:

1. Fill the container with room-temperature water.
2. Place the container in a freezer.
3. After 1–2 hours, remove and observe the water.
4. Touch the result gently to test its state.

Expected observations:

• Liquid water becomes solid ice
• The process is reversible (ice melts back to water when heated)

Experiment 3: Evaporation of Water (Liquid → Gas)

Objective: To observe water changing to vapor when heated.

Materials needed:

• Water
• A clean beaker
• A heat source (spirit lamp or stove—teacher demonstration only)
• A glass plate or lid

Procedure:

1. Pour a small amount of water into the beaker.
2. Heat the water carefully (teacherdemonstration).
3. Observe as bubbles form and steam rises.
4. Place a cold glass plate above the steam and observe condensation.

Expected observations:

• Water boils and changes to steam (gas)
• Steam condenses on the cold glass plate back to liquid water

Experiment 4: Sublimation of Iodine (Solid → Gas)

Objective: To observe a solid changing directly to gas without becoming liquid.

Materials needed:

• Iodine crystals (from laboratory)
• A clean dry test tube
• A heat source (spirit lamp—teacher demonstration)
• A watch glass or white paper

Procedure:

1. Place a few iodine crystals in the dry test tube.
2. Hold the test tube gently above the flame (avoid direct contact).
3. Observe the crystals heat up.
4. Place a white paper or watch glass above the tube to collect any sublimed vapor.

Expected observations:

• Dark purple vapor rises from the solid
• No liquid iodine forms during this process
• On cooling, the vapor deposits back onto the tube as solid crystals

Experiment 5: Testing for Water (Using Anhydrous CuSO₄)

Objective: To use a chemical test to confirm water presence.

Materials needed:

• Anhydrous copper(II) sulfate (white powder)
• Water
• A clean watch glass

Procedure:

1. Place a small amount of white anhydrous CuSO₄ on the watch glass.
2. Add a few drops of water.
3. Observe the color change.

Expected observations:

• White CuSO₄ turns blue
• This shows that water was added (a physical change, as the blue CuSO₄ can be heated to recover white CuSO₄)

• Changes of matter from one state to another are physical changes
• No new chemical substance is formed—the material remains the same (e.g., H₂O)
• These changes are generally reversible
• Adding heat typically causes: solid → liquid → gas
• Removing heat typically causes: gas → liquid → solid

• Handle hot apparatus with care; use tongs or heat-resistant gloves
• Do not taste or touch laboratory chemicals
• Perform heating experiments under teacher supervision
• Iodine vapor is toxic—work in a ventilated area

In Tanzania, understanding changes of matter is useful in everyday life. For example, when selling maziwa ya mtindi (fermented milk) in local markets, vendors must store it in cool places to prevent it from turning into liquid due to heat. Similarly, fishermen in Lake Victoria use ice to keep fish fresh—observing how ice (solid) melts to water (liquid) when the weather is hot, helping them plan how much ice to bring for their daily catch.