Secondary 2 Science Scientific Inquiry Quiz

Secondary 2 Science Quiz - Scientific Inquiry (Answer Key)

Total Marks: 40

Section A: Multiple Choice Questions (10 marks)

1. C — Precise but not accurate
   Explanation: The readings (15.2, 15.3, 15.2) are close to each other (precise) but far from the true value of 15.0 cm (not accurate).
   Marking: 1 mark for correct choice.

2. B — Temperature of water
   Explanation: The independent variable is the one deliberately changed by the experimenter. Here, temperature is being changed to see its effect on dissolving rate.
   Marking: 1 mark for correct choice.

3. B — Parallax error
   Explanation: Parallax error occurs when the eye is not perpendicular to the scale reading. Viewing from above the meniscus causes the reading to appear lower than the true value.
   Marking: 1 mark for correct choice.

4. B — 3
   Explanation: In 0.00450 kg, the leading zeros are not significant. The digits 4, 5, and the trailing zero after the decimal are significant (3 s.f.).
   Marking: 1 mark for correct choice.

5. C — 3
   Explanation: For multiplication/division, the result should have the same number of significant figures as the measurement with the fewest significant figures. Both mass (45.0 g) and volume (15.0 cm³) have 3 s.f., so density = 3.00 g/cm³ (3 s.f.).
   Marking: 1 mark for correct choice.

6. D — Height from which parachute is dropped
   Explanation: In a fair test, only the independent variable (surface area) and dependent variable (time to fall) change. All other variables (mass, drop height, shape, etc.) must be controlled.
   Marking: 1 mark for correct choice.

7. C — Line graph
   Explanation: Line graphs are used for continuous data showing how one variable changes over time or against another continuous variable. Temperature vs. time is continuous.
   Marking: 1 mark for correct choice.

8. A — 2.86 mm
   Explanation: Observed reading = main scale + thimble scale = 2.5 mm + 0.38 mm = 2.88 mm. Corrected reading = observed reading − zero error = 2.88 mm − (+0.02 mm) = 2.86 mm.
   Marking: 1 mark for correct choice.

9. C — "If the concentration of acid increases, the rate of reaction will increase."
   Explanation: A hypothesis is a testable prediction stating a relationship between variables, often in "If... then..." form. Option C predicts how changing the independent variable (acid concentration) affects the dependent variable (reaction rate).
   Marking: 1 mark for correct choice.

10. B — Multiple experiments dropping objects of different masses in a vacuum
    Explanation: To test the conclusion scientifically, controlled experiments are needed. A vacuum removes air resistance (a confounding variable), and testing multiple masses provides reliable evidence.
    Marking: 1 mark for correct choice.

Section B: Structured Questions (18 marks)

11. (a) Average time = 28.5 s
    Working: (28.4 + 28.6 + 28.5 + 28.7 + 28.4) / 5 = 142.6 / 5 = 28.52 s ≈ 28.5 s (to 1 d.p. or 3 s.f.)
    Marking: 1 mark for correct calculation and answer.

    (b) Period = 1.43 s (or 1.425 s)
    Working: Period = Average time for 20 oscillations / 20 = 28.52 s / 20 = 1.426 s ≈ 1.43 s (3 s.f.)
    Marking: 1 mark for correct calculation using answer from (a).

    (c) Random errors fluctuate randomly above and below the true value. Taking multiple readings and averaging them causes positive and negative errors to cancel out, bringing the average closer to the true value.
    Marking: 1 mark for mentioning random errors fluctuate/cancel out; 1 mark for explaining average reduces effect.

12. (a) Independent variable: Distance of lamp from pondweed (or light intensity)
    Dependent variable: Number of bubbles produced per minute (rate of photosynthesis)
    Marking: 1 mark each for correct identification.

    (b) Any two of:

    • Type/species of pondweed
    • Length/mass of pondweed
    • Volume of water
    • Temperature of water (initially)
    • Concentration of CO₂ (e.g., NaHCO₃ concentration)
    • Time allowed for equilibration
      Marking: 1 mark each for any two valid controlled variables.

    (c) When the lamp is closer, it emits more heat, raising the water temperature. Temperature also affects the rate of photosynthesis (enzyme activity). Since temperature changes with distance, it becomes a confounding variable — the student cannot tell if changes in bubble rate are due to light intensity or temperature.
    Marking: 1 mark for identifying temperature increases; 1 mark for explaining it acts as a confounding variable/unfair test.

13. (a) Mass of salt = 17.5 g
    Working: 62.8 g − 45.3 g = 17.5 g
    Marking: 1 mark for correct subtraction and answer with unit.

    (b) Uncertainty = ±0.5 cm³
    Explanation: For an analogue measuring instrument, the uncertainty is typically half the smallest division. Smallest division = 1 cm³, so uncertainty = ±0.5 cm³.
    Marking: 1 mark for correct value with unit.

    (c) Density = 1.54 g/cm³ (3 s.f.)
    Working: Total mass = 62.8 g (beaker + salt + water). Wait — the question says "total volume of the solution is 52.0 cm³". The mass of the solution = mass of salt + mass of water. Mass of water = 50.0 g (assuming density 1 g/cm³). Mass of solution = 17.5 g + 50.0 g = 67.5 g. Density = 67.5 g / 52.0 cm³ = 1.298... g/cm³ ≈ 1.30 g/cm³ (3 s.f.).
    Correction: Let me recalculate carefully.
    Mass of salt = 17.5 g. Volume of water = 50.0 cm³ → mass of water ≈ 50.0 g. Total mass of solution = 67.5 g. Total volume = 52.0 cm³. Density = 67.5 / 52.0 = 1.298... = 1.30 g/cm³ (3 s.f.).
    Marking: 1 mark for correct mass of solution; 1 mark for correct density calculation to 3 s.f. with unit.

14. (a) Main scale reading = 2.5 mm; Thimble scale reading = 0.38 mm
    Marking: 1 mark for both correct.

    (b) Observed reading = 2.88 mm
    Working: 2.5 mm + 0.38 mm = 2.88 mm
    Marking: 1 mark for correct addition.

    (c) Corrected reading = 2.86 mm
    Working: Corrected = Observed − Zero error = 2.88 mm − (+0.02 mm) = 2.86 mm
    Marking: 1 mark for correct subtraction of zero error.

15. (a) Graph requirements:

    • Axes labelled with units: "Length of wire / cm" and "Resistance / Ω"
    • Appropriate scales (e.g., 1 cm = 5 cm on x-axis, 1 cm = 1 Ω on y-axis)
    • All 5 points plotted correctly
    • Best-fit straight line passing through origin (0,0) and points
      Marking: 1 mark for correct axes, scales, and points; 1 mark for best-fit line through origin.

    (b) Resistance is directly proportional to the length of the wire. (Or: As length increases, resistance increases linearly/proportionally.)
    Marking: 1 mark for "directly proportional" or equivalent description.

    (c) Resistance at 65 cm = 7.8 Ω
    Working: From graph, gradient = 0.12 Ω/cm. At 65 cm, R = 0.12 × 65 = 7.8 Ω. Or by extrapolation of best-fit line.
    Marking: 1 mark for correct value from graph (accept 7.7–7.9 Ω).

    (d) Any one of:

    • Temperature of wire changes due to heating (resistance increases with temperature)
    • Wire not uniform in thickness/material
    • Contact resistance at connections
    • Measurement errors in length or resistance
      Marking: 1 mark for any valid reason.

Section C: Data Analysis and Experimental Design (12 marks)

16. (a) Density = 2.7 g/cm³ (2 s.f.)
    Working: Volume of stone = Final volume − Initial volume = 48 cm³ − 30 cm³ = 18 cm³. Density = Mass / Volume = 48.5 g / 18 cm³ = 2.694... g/cm³ ≈ 2.7 g/cm³ (2 s.f.)
    Marking: 1 mark for correct volume; 1 mark for correct density to 2 s.f. with unit.

    (b) Uncertainty = ±0.5 cm³
    Explanation: Half the smallest division (1 cm³).
    Marking: 1 mark for correct value with unit.

    (c) Average density = 2.7 g/cm³
    Working: (2.7 + 2.8 + 2.6) / 3 = 8.1 / 3 = 2.7 g/cm³
    Marking: 1 mark for correct calculation.

    (d) Percentage error = 0%
    Working: % error = |(Experimental − Accepted) / Accepted| × 100% = |(2.7 − 2.7) / 2.7| × 100% = 0%
    Marking: 1 mark for correct formula/substitution; 1 mark for correct answer with % sign.

17. (a) Hypothesis: "As the angle of the ramp increases, the speed of the toy car at the bottom increases." (Or equivalent testable prediction linking angle and speed.)
    Marking: 1 mark for a clear, testable hypothesis mentioning both variables and direction of effect.

    (b) Independent variable: Angle of ramp
    Dependent variable: Speed of toy car at bottom of ramp
    Controlled variable: Mass of car / height of ramp / surface of ramp / length of ramp / starting position (any one)
    Marking: 1 mark each for correct identification.

    (c) Apparatus: Metre rule, stopwatch, ramp, protractor, toy car.
    Method:

    1. Set up ramp at chosen angle (measure with protractor).
    2. Mark a fixed distance (e.g., last 50 cm) at the bottom of the ramp.
    3. Release car from rest at top of ramp.
    4. Use stopwatch to measure time taken to travel the marked distance at the bottom.
    5. Speed = Distance / Time.
    6. Repeat 3 times and average.
       Alternative: Use light gates and data logger for more accurate speed measurement.
       Marking: 1 mark for apparatus; 1 mark for method (distance/time); 1 mark for repetition/averaging or use of light gates.

    (d) Any one of:

    • Ensure ramp is stable and won't slip
    • Keep fingers away from moving car
    • Use a barrier at the end to stop the car safely
    • Wear safety goggles if car might fly off
      Marking: 1 mark for any valid safety precaution.

18. (a) Graph requirements:

    • Axes labelled: "Time / min" (x-axis, 0–12) and "Temperature / °C" (y-axis, 30–85)
    • Appropriate scales
    • Points for metal container plotted and joined with smooth solid curve
    • Points for plastic container plotted and joined with smooth dashed curve
    • Key/legend identifying which line is which
      Marking: 1 mark for axes and scales; 1 mark for both sets of points plotted correctly; 1 mark for smooth curves with key.

    (b) Time ≈ 3.5–4.0 minutes (accept range based on graph reading)
    Working: From graph, find time at 70°C (~1.5 min) and 50°C (~5.5 min). Difference = 4.0 min. Or read directly: cooling from 70 to 50 takes about 4 minutes.
    Marking: 1 mark for correct reading from graph (accept 3.5–4.5 min).

    (c) Metal is a good thermal conductor, so heat transfers quickly from the hot water through the container walls to the surroundings. Plastic is a poor thermal conductor (insulator), so heat transfer is slower.
    Marking: 1 mark for identifying metal as good conductor/plastic as poor conductor; 1 mark for linking to faster heat loss.

19. (a) Corrected diameter = 1.26 cm
    Working: Observed reading = Main scale + Vernier scale = 1.2 cm + 0.04 cm = 1.24 cm. Zero error = −0.02 cm (negative zero error means the reading is smaller than true value). Corrected = Observed − Zero error = 1.24 cm − (−0.02 cm) = 1.24 cm + 0.02 cm = 1.26 cm.
    Marking: 1 mark for observed reading; 1 mark for correct zero error correction.

    (b) Volume should be given to 3 significant figures.
    Explanation: The diameter is measured to 3 s.f. (1.26 cm). The radius is half the diameter, so also 3 s.f. In the formula $V = \frac{4}{3}\pi r^3$, the radius is cubed. For multiplication/powers, the result should have the same number of significant figures as the least precise measurement. Since radius has 3 s.f., volume should be given to 3 s.f. Constants like $\frac{4}{3}$ and $\pi$ are exact and do not limit significant figures.
    Marking: 1 mark for stating 3 s.f.; 1 mark for correct explanation linking to radius cubed and rules for significant figures in multiplication/powers.

20. (a) Bubble wrap is the best insulator.
    Explanation: It has the smallest temperature drop (15°C) among the insulating materials tested, meaning it reduces heat loss most effectively. (Note: "No insulation" has the largest drop, 30°C.)
    Marking: 1 mark for identifying bubble wrap; 1 mark for using data (smallest temperature drop) to justify.

    (b) The conclusion is not fully supported. While aluminium foil is a metal and metals are generally good thermal conductors, the foil may trap air (a good insulator) if wrapped loosely, or reflect radiant heat back. The experiment only tests one configuration. Also, the foil might be in direct contact with the beaker, conducting heat well. A better conclusion would reference the specific experimental setup.
    Marking: 1 mark for evaluating the conclusion (not fully supported/oversimplified); 1 mark for explaining why (trapped air, radiation reflection, contact conduction).

    (c) Any two of:

    • Repeat the experiment multiple times and average the results
    • Use a lid on the beakers to reduce heat loss by convection/evaporation
    • Ensure the same thickness of each insulating material
    • Use a digital thermometer/data logger for more accurate temperature readings
    • Control initial temperature more precisely
    • Use more beakers per material to account for variations
      Marking: 1 mark each for any two valid improvements.

End of Answer Key