Metal Reactivity Investigation
You are going to investigate the reactions of three metals, X, Y and Z, with aqueous copper(II) sulfate.
Practical Investigation: Temperature Changes in Displacement Reactions
(a)(i) Complete Table 1.1 with your temperature measurements:
| Experiment | Metal | Initial Temp. /°C | Highest Temp. /°C | Temp. Increase /°C |
|---|---|---|---|---|
| 1 | X | 22.0 | 35.5 | 13.5 |
| 2 | Y | 22.0 | 28.0 | 6.0 |
| 3 | Z | 22.0 | 24.0 | 2.0 |
Experiment 4: Add 25 cm³ dilute sulfuric acid to beaker from Experiment 1
(a)(ii) Describe the initial appearance of the aqueous copper(II) sulfate.
(a)(iii) Describe the final appearance of the mixture in the beaker in Experiment 4.
(a)(iv) Explain how your observations show that X is in excess in Experiment 1.
(b) Use your results to arrange X, Y, and Z in decreasing order of reactivity.
(c) A student repeats the experiment using a fourth metal. This metal is the second most reactive of the four metals. Suggest a temperature increase.
(d) The temperature increases calculated are less than the true values. Suggest a reason and improvement.
(e) State and explain the effect of using half the concentration of aqueous copper(II) sulfate.
Practical Solutions
(a)(ii) Blue solution – characteristic color of Cu²⁺ ions in aqueous solution
(a)(iii) Colorless solution with brown solid/precipitate at the bottom – unreacted metal X reacts with acid producing hydrogen gas (effervescence)
(a)(iv) Effervescence/bubbling occurs when acid is added – this indicates unreacted metal X is present and reacting with acid to produce hydrogen gas
(b) Most reactive: X → Y → Z : Least reactive
Explanation: The greater the temperature increase, the more reactive the metal, as more exothermic energy is released in the displacement reaction.
(c) Approximately 9-10°C (between X’s 13.5°C and Y’s 6.0°C)
(d) Reason: Heat loss to surroundings (beaker, air, thermometer)
Improvement: Use a polystyrene cup with lid to reduce heat loss, or use a calorimeter
(e) Effect: Temperature increase would be approximately half
Explanation: Fewer copper(II) ions available to react, so less energy released per mole of reaction
Practical Analysis Strategy
Displacement Reaction Principle:
- More reactive metals displace less reactive metals from their compounds
- Energy released ∝ Reactivity difference between metals
- Temperature change indicates reaction extent and energy release
Metal Reactivity Series (Partial):
Most reactive: K, Na, Ca, Mg, Al, X, Zn, Fe, Y, Pb, [H], Cu, Ag, Z
Key Equations:
Metal + CuSO₄ → Metal sulfate + Cu
Excess Metal + H₂SO₄ → Metal sulfate + H₂
Laboratory Excellence Tips
- Control Variables: Use same volume (25 cm³) and concentration of CuSO₄ for all experiments
- Metal Preparation: Ensure metals are clean and have similar surface area
- Temperature Measurement: Stir continuously and record at consistent time intervals
- Heat Conservation: Use insulation (polystyrene) to minimize experimental error
- Safety: Handle acids with care and wear appropriate PPE
Qualitative Analysis of Solution R
You are provided with solution R and will perform a series of tests to identify its composition.
Systematic Qualitative Analysis
(a) To R + dilute HNO₃ + Ba(NO₃)₂
(b) To R + dilute HNO₃ + AgNO₃
(c)(i) Describe one other observation in the control test with Na₂CO₃ + AgNO₃ + HNO₃.
(c)(ii) Suggest why it is important to add dilute nitric acid in (b).
(d)(i) Record the first flame colour seen with the wooden splint.
(d)(ii) Explain why it is difficult to make a definite conclusion from the flame colour.
(e) To R + NaOH (dropwise then excess) – observations and conclusions
(f) Gently warm the mixture from (e) – observations and conclusions
(g) Suggest the names of the two compounds in solution R.
Analysis Results
Observations: White precipitate forms
Conclusions: Sulfate ions (SO₄²⁻) present
Equation: Ba²⁺ + SO₄²⁻ → BaSO₄(s) [white ppt]
Observations: No precipitate / No change
Conclusions: No chloride, bromide or iodide ions present
(c)(i): The white precipitate dissolves/disappears
(c)(ii): To remove carbonate ions that would interfere (carbonate also forms precipitate with Ag⁺)
(d)(i): Yellow flame
Conclusions: Sodium ions (Na⁺) may be present
(d)(ii): Yellow flame can mask other flame colors; sodium contamination is common
Observations: White precipitate forms, dissolves in excess NaOH
Conclusions: Zinc ions (Zn²⁺) or aluminium ions (Al³⁺) present
Equations: Zn²⁺ + 2OH⁻ → Zn(OH)₂(s) [white]; Zn(OH)₂ + 2OH⁻ → [Zn(OH)₄]²⁻ [soluble]
Observations: Ammonia gas produced (turns damp red litmus blue)
Conclusions: Ammonium ions (NH₄⁺) present
Equation: NH₄⁺ + OH⁻ → NH₃ + H₂O (on warming)
Ammonium sulfate [(NH₄)₂SO₄] and zinc sulfate [ZnSO₄] (or aluminium sulfate)
Qualitative Analysis Strategy
Systematic Approach:
- Test for anions first: Sulfate, halides, carbonate, nitrate
- Test for cations: Flame test, NaOH test, ammonia test
- Confirm with specific tests: Warming with NaOH tests for ammonium
- Eliminate possibilities: Use negative results to exclude ions
Key Identification Tests:
| Ion | Test | Positive Result |
|---|---|---|
| SO₄²⁻ | Acid + Ba(NO₃)₂ | White ppt (BaSO₄) |
| NH₄⁺ | NaOH + warming | NH₃ gas (turns litmus blue) |
| Zn²⁺/Al³⁺ | NaOH (excess) | White ppt, soluble in excess |
Laboratory Excellence Tips
- Apparatus Cleanliness: Always use clean apparatus to avoid contamination
- Systematic Testing: Follow a logical sequence and record all observations
- Flame Test Accuracy: Use cobalt blue glass to filter out yellow sodium light
- Gas Testing: Test gases immediately with appropriate tests (litmus, limewater)
- Precipitation: Add reagents slowly and observe color, texture of precipitates
- Safety: Handle acids and ammonia with care in well-ventilated area
Experimental Planning: Barium Carbonate Decomposition
Plan an experiment to determine the percentage loss in mass when barium carbonate is heated.
Word Equation: barium carbonate → barium oxide + carbon dioxide
Chemical Equation: BaCO₃(s) → BaO(s) + CO₂(g)
Theoretical Mass Loss: 22.3% (44/197 × 100)
Experimental Planning Requirements
Apparatus Setup Diagram
Crucible with lid on pipe clay triangle on tripod stand
Bunsen burner below for heating
Digital balance for mass measurements
Comprehensive Experimental Plan
- Porcelain crucible with lid
- Pipe clay triangle
- Tripod stand
- Bunsen burner
- Heat-resistant mat
- Digital balance (0.01g precision)
- Tongs (crucible tongs)
- Desiccator
- Safety goggles and gloves
- Weigh the empty, clean, dry crucible with lid (mass m₁)
- Add approximately 2-3g of barium carbonate to the crucible
- Weigh the crucible + lid + barium carbonate (mass m₂)
- Set up apparatus: crucible on pipe clay triangle on tripod
- Heat strongly using Bunsen burner for 10-15 minutes
- Keep lid slightly ajar to allow CO₂ to escape but prevent loss of solid
- Allow to cool completely in a desiccator (prevents absorption of CO₂/moisture)
- Reweigh the crucible + lid + contents (mass m₃)
- Repeat heating, cooling and weighing until constant mass is achieved
- Record all masses in a suitable table
- Use digital balance with 0.01g precision for accurate measurements
- Heat strongly to ensure complete decomposition
- Cool in desiccator to prevent absorption of moisture/CO₂
- Heat to constant mass to ensure reaction is complete
- Keep lid slightly ajar to allow CO₂ escape but prevent solid loss
- Use tongs to handle hot crucible to avoid moisture from hands
- Repeat the experiment to check reproducibility
Initial mass of BaCO₃ = m₂ – m₁
Mass after heating = m₃ – m₁
Mass loss = (m₂ – m₁) – (m₃ – m₁) = m₂ – m₃
Percentage loss = (mass loss / initial mass) × 100
Percentage loss = [(m₂ – m₃) / (m₂ – m₁)] × 100
Theoretical Calculation for Comparison:
M(BaCO₃) = 137 + 12 + (3×16) = 197 g/mol
M(CO₂) = 12 + (2×16) = 44 g/mol
Theoretical % loss = (44/197) × 100 = 22.3%
Planning Strategy & Safety
Chemical Principles:
- Carbonates decompose to oxide and CO₂ on strong heating
- Mass loss corresponds to CO₂ gas evolved
- Percentage loss allows comparison with theoretical value
Safety Considerations:
- Barium compounds are toxic – handle with care, avoid ingestion
- Wear safety goggles throughout the experiment
- Use heat-resistant gloves or tongs for handling hot apparatus
- Work in well-ventilated area due to CO₂ production
- Dispose of barium compounds properly according to safety guidelines
Expected Results:
- Experimental percentage loss should be close to theoretical 22.3%
- Lower results may indicate incomplete decomposition
- Higher results may indicate loss of solid or absorption of moisture
Laboratory Excellence Tips
- Constant Mass: Essential to ensure complete decomposition – heat until no further mass change
- Desiccator Use: Critical for accurate results – prevents reabsorption of CO₂/moisture
- Lid Position: Slightly ajar – allows gas escape but minimizes solid loss
- Heating Duration: Sufficient time needed – barium carbonate requires strong heating
- Recording: Record all masses immediately after cooling to room temperature
- Reproducibility: Repeat experiment to check consistency of results