RQP chemistry

Making Soluble Salts – Method

1. Add excess insoluble base (e.g., copper oxide) to dilute acid in a beaker.

2. Heat gently using a Bunsen burner to speed up reaction.

3. Stir until no more base reacts (excess remains).

4. Filter to remove unreacted solid.

5. Pour filtrate into evaporating basin and heat to evaporate water.

6. Leave to cool to form crystals, then dry them.

Variables

• Independent: Type of acid or base used.

• Dependent: Amount of salt produced (crystals formed).

• Control: Same acid volume/concentration, same temperature, same amount of base added.

Common Errors & Fixes

• Not adding excess base → ensure some solid remains before filtering.

• Overheating → heat gently to avoid losing product.

• Wet crystals → dry properly after crystallisation.

Titration – Method

1. Rinse burette with acid, fill it, and record initial reading.

2. Use pipette to measure fixed volume of alkali into conical flask.

3. Add a few drops of indicator (e.g., phenolphthalein).

4. Slowly add acid from burette while swirling flask.

5. Stop at end point (permanent colour change).

6. Record final reading and calculate volume used; repeat for concordant results.

Variables

• Independent: Not typically changed (aim is accurate concentration).

• Dependent: Volume of acid needed to reach end point.

• Control: Same volumes, same indicator, same concentrations, same technique.

Common Errors & Fixes

• Overshooting end point → add acid dropwise near end.

• Reading error → read burette at eye level (bottom of meniscus).

electrolysis - method

1. Set up power supply with two electrodes in electrolyte (molten or solution).

2. Connect positive electrode (anode) and negative electrode (cathode).

3. Switch on DC power supply to pass current.

4. Ions move: cations to cathode, anions to anode.

5. Products form at electrodes (observe gases or deposits).

6. Record products formed at each electrode.

Variables

• Independent: Type of electrolyte used.

• Dependent: Products formed at each electrode.

• Control: Same voltage/current, same electrode material, same concentration (if solution).

Common Errors & Fixes

• Wrong electrode connections → check anode (+), cathode (−).

• Impure electrolyte → use correct, pure substance.

• Misidentifying products → test gases (e.g., hydrogen pop test).

Temperature Change Practical – Method

1. Measure a fixed volume of reactant (e.g., acid) into a polystyrene cup.

2. Record the initial temperature using a thermometer.

3. Add the second reactant (e.g., alkali or solid) quickly.

4. Stir the mixture and start timing.

5. Record the highest (or lowest) temperature reached.

6. Calculate temperature change (ΔT).

Variables

• Independent: Type of reaction or reactants used.

• Dependent: Temperature change (ΔT).

• Control: Same volumes/concentrations, same starting temperature, same insulation (cup).

Common Errors & Fixes

• Heat loss → use lid/insulated cup.

• Slow measurement → read temperature quickly and continuously.

• Inaccurate volumes → measure carefully with measuring cylinder.

Chromatography – Method

1. Draw a pencil baseline near bottom of chromatography paper.

2. Place a small spot of the sample on the baseline.

3. Put paper in solvent (baseline above solvent level).

4. Allow solvent to travel up the paper.

5. Remove paper before solvent reaches the top and mark solvent front.

6. Let dry and observe separated spots.

Variables

• Independent: Type of solvent or sample used.

• Dependent: Distance travelled by substances (Rf values).

• Control: Same paper, same baseline position, same solvent level, same temperature.

Common Errors & Fixes

• Ink baseline → use pencil (insoluble).

• Submerged spots → keep baseline above solvent.

• Large spots → use small, concentrated spots.

Purifying Water – Method

1. Add insoluble solids to water to simulate dirty water.

2. Filter the water to remove insoluble particles.

3. Collect the filtrate in a clean container.

4. Set up distillation apparatus (flask, condenser, heat source).

5. Heat the filtrate so water evaporates and then condenses.

6. Collect the distilled (pure) water.

Variables

• Independent: Type/amount of impurities in water.

• Dependent: Purity of water collected.

• Control: Same volume of water, same apparatus, same heating conditions.

Common Errors & Fixes

• Incomplete filtration → use proper filter paper setup.

• Heat too strong → heat gently for controlled distillation.

• Loss of water vapour → ensure condenser is working properly.