Key Science Topics Summary

Collecting Gas from Photosynthesis

• Setup apparatus in sunlight for gas collection.

• Testing for oxygen: glowing splint relights in oxygen.

• Metal reactivity with water results in hydrogen gas production.

Reactivity of Alkali Metals

• Reactivity increases down the group 1:

  • Lithium: moderate fizzing.

  • Sodium: violent reaction.

  • Potassium: explosive reaction.

• All form alkaline metal hydroxides (pH > 7).

Testing for Starch in Leaves

1. Boil leaf to break cell membranes.

2. Immerse in ethanol to remove chlorophyll.

3. Test with iodine (blue-black indicates starch presence).

Observations of Group 1 Metals

• Shared properties:

  • Soft, shiny, low melting points.

  • Highly reactive, form +1 ions.

• Conductivity: Ionic solutions conduct electricity; solids do not.

Measuring Densities of Objects

• Use displacement method for irregular objects.

• Subtract initial water level from final water level to find volume.

Thermal Conduction Experiments

• Heat different rods and observe wax melting at different rates.

• Observations indicate good conductors are more efficient.

• Non-metals (wood/plastic) are poor conductors, affect heating efficacy.

Convection in Fluids

• Heated ink rises and cools to create a convection current.

• Heating causes particles to move faster and spread out.

Transpiration in Plants

• Stomata mainly on the lower leaf surface, affecting water loss.

• Petroleum jelly reduces transpiration by blocking stomata.

Investigating Metal Reactivity

• Test metals with water and dilute acid to determine reactivity levels.

• Vigorous reaction suggests highly reactive metals like Mg or Na.

Crystallization Process

1. Prepare saturated solution (e.g., copper sulfate).

2. Filter off impurities.

3. Evaporate to crystallize the solute after several days.

Neutralization Reaction

• Conduct titration of HCl with NaOH to form a neutral solution.

• Filtrate shows dissolved salts, undissolved residue indicates insoluble compounds.