Secondary 1 Science Scientific Inquiry Quiz

Secondary 1 Science Quiz - Scientific Inquiry (Answer Key)

Total Marks: 40

Section A: Multiple Choice Questions (10 marks)

1. Answer: B

Explanation: Parallax error occurs when the observer's eye is not positioned directly perpendicular to the scale marking, causing an apparent shift in the reading. This is a common error when using rulers, measuring cylinders, and other analog instruments.

2. Answer: B

Explanation: The independent variable is the variable that is deliberately changed by the experimenter. In this experiment, the temperature of water is being changed to observe its effect on the rate of dissolving.

3. Answer: A

Explanation: Average = (0.45 + 0.46 + 0.44 + 0.45 + 0.47) / 5 = 2.27 / 5 = 0.454 mm. Rounded to 2 decimal places (matching the precision of the readings), the average is 0.45 mm.

4. Answer: B

Explanation: A hypothesis is a testable prediction about the relationship between variables, often written as an "If... then..." statement. Option B predicts that increasing acid concentration will increase reaction rate. Option A is an observation, C is an observation, D is a procedural step.

5. Answer: B

Explanation: The uncertainty of an analog instrument is typically half of the smallest division. For a measuring cylinder with 1 cm³ graduations, the uncertainty is ±0.5 cm³.

6. Answer: C

Explanation: In a fair test, only the independent variable is changed, the dependent variable is measured, and all other variables (controlled variables) are kept constant to ensure that any change in the dependent variable is due only to the independent variable.

7. Answer: B

Explanation: Zero error = Observed reading - True value = (-1°C) - (0°C) = -1°C. The thermometer reads -1°C when it should read 0°C, so it has a negative zero error of -1°C. All readings will be 1°C lower than the true value.

8. Answer: C

Explanation: The dependent variable is the variable that is measured or observed in response to changes in the independent variable. Here, the speed of the toy car is measured as the ramp height is changed.

9. Answer: B

Explanation: Precision refers to how close repeated measurements are to each other. Accuracy refers to how close measurements are to the true value. Set B shows high precision (all values are 10.2, very close to each other) but low accuracy (true value is 9.8, readings are consistently 0.4 higher).

10. Answer: B

Explanation: A straight line graph passing through the origin indicates direct proportionality between the two variables. This means extension ∝ force, which is Hooke's Law.

Section B: Short Answer and Structured Questions (18 marks)

11. (a) Main scale reading: 2.4 cm [1]

(b) Vernier scale reading: 0.06 cm (6 × 0.01 cm) [1] (c) Diameter = 2.4 + 0.06 = 2.46 cm [1]

Explanation: The main scale reading is the value on the main scale just to the left of the vernier zero mark. The vernier reading is the number of the aligned vernier division multiplied by the least count (0.01 cm). Total reading = main scale + vernier scale.

12. (a) Independent variable: Distance of lamp from plant (or light intensity) [1]

(b) Dependent variable: Number of bubbles produced per minute (rate of photosynthesis) [1] (c) Two controlled variables (any two):

• Type/species of water plant
• Mass/length of water plant
• Temperature of water
• Concentration of CO₂ (e.g., same amount of sodium hydrogen carbonate)
• Time of day / ambient light conditions [2] (d) Repeating the experiment allows identification of anomalous results and calculation of an average, which reduces the effect of random errors and improves reliability. [1]

13. (a) Average time = (38.2 + 38.6 + 38.4) / 3 = 115.2 / 3 = 38.4 s [1]

(b) Period = 38.4 s / 20 = 1.92 s [1] (c) Measure the time for a larger number of oscillations (e.g., 50 or 100) and then divide by that number. This reduces the percentage error due to reaction time. [1]

Explanation: Reaction time error (typically ~0.2 s) is fixed regardless of how many oscillations are timed. By timing more oscillations, the absolute error stays the same but the calculated period becomes more accurate.

14. (a) Graph plotting [2 marks: 1 for correct plotting of all points, 1 for best-fit straight line through origin]

(b) Extension at 2.5 N = 5.25 cm (accept 5.2–5.3 cm from graph) [1] (c) Yes, the spring obeys Hooke's Law. The graph is a straight line passing through the origin, showing that extension is directly proportional to the force applied. [2]

Marking points for (c):

• Straight line graph [1]
• Passes through origin [1]
• Conclusion: extension ∝ force / obeys Hooke's Law [1] (Award 2 marks for any two correct points)

15. (a) Volume of stone = 58 cm³ - 45 cm³ = 13 cm³ [1]

(b) Parallax error [1] (c) Position the eye directly in line with the bottom of the meniscus (at eye level) when taking the reading. [1]

Explanation: The displacement method measures volume by the difference in water level before and after submerging an object. Reading the meniscus at eye level avoids parallax error.

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

16. (a) Graph plotting [3 marks: 1 for labeled axes with correct scales, 1 for correct plotting of both data series, 1 for smooth curves/best-fit lines with legend]

(b) Initial rate for 2.0 mol/dm³ HCl:

• Draw tangent to the curve at t = 0
• Gradient = (Volume at ~30 s - 0) / (30 - 0) = 28 cm³ / 30 s = 0.93 cm³/s (accept 0.9–1.0 cm³/s) [2]

Working: Rate = ΔVolume / ΔTime. Using first 30 s interval: (28 - 0) / (30 - 0) = 0.933 cm³/s.

(c) Higher concentration means more HCl particles per unit volume. This increases the frequency of effective collisions between HCl and Mg particles, increasing the rate of reaction. [2]

Marking points:

• More particles per unit volume / higher concentration [1]
• More frequent (effective) collisions [1]

(d) Wear safety goggles / gloves / lab coat. / Avoid skin contact with acid. / Clean up spills immediately. (Any one) [1]

17. (a) Procedure: [3]

1. Measure the mass of the empty measuring cylinder using the electronic balance.
2. Pour a known volume of the liquid into the measuring cylinder and record the volume (read at eye level, bottom of meniscus).
3. Measure the mass of the measuring cylinder with the liquid.
4. Calculate mass of liquid = (mass of cylinder + liquid) - (mass of empty cylinder).
5. Calculate density = mass of liquid / volume of liquid.

(b) Mass of liquid = 128.7 g - 45.2 g = 83.5 g Density = 83.5 g / 85 cm³ = 0.98 g/cm³ (0.98235... rounded to 2 d.p.) [2]

Working:

• Mass of liquid = 128.7 - 45.2 = 83.5 g [1]
• Density = 83.5 / 85 = 0.98235... = 0.98 g/cm³ [1]

(c) Percentage uncertainty = (Uncertainty / Measurement) × 100% = (1 / 85) × 100% = 1.18% (or 1.2%) [1]

18. (a) To ensure even/uniform heating of the naphthalene and to prevent localised overheating or cracking of the test tube. [1]

(b) During the plateau, naphthalene is changing state from liquid to solid (solidifying/freezing). The heat energy lost to the surroundings is balanced by the latent heat of fusion released during solidification, so the temperature remains constant until all the liquid has solidified. [2]

Marking points:

• Change of state / solidifying / freezing [1]
• Latent heat released compensates for heat loss / energy used to form bonds [1]

(c) Sketch of cooling curve [2 marks: 1 for correct shape with plateau, 1 for labeled axes and plateau label]

• Axes labeled: Time / s (x-axis), Temperature / °C (y-axis)
• Curve starts at ~90°C, decreases, plateaus at 80°C, then decreases to ~28°C
• Plateau region labeled "Solidifying at 80°C" or "Constant temperature during change of state"

19. Experimental Design [5 marks]

Independent variable: Surface area of calcium carbonate (e.g., powder vs. small chips vs. large chips) [1]

Dependent variable: Rate of reaction (measured by volume of CO₂ gas produced per unit time, or time taken for a fixed volume of gas, or mass loss per unit time) [1]

Controlled variables (any two):

• Concentration and volume of hydrochloric acid
• Mass of calcium carbonate
• Temperature of reactants
• Particle size of calcium carbonate (for each trial) [2]

Procedure:

1. Measure a fixed mass (e.g., 2 g) of calcium carbonate powder and place in a conical flask.
2. Add a fixed volume (e.g., 50 cm³) of HCl of fixed concentration (e.g., 1.0 mol/dm³).
3. Immediately connect to a gas syringe / inverted measuring cylinder / balance and start stopwatch.
4. Record volume of CO₂ produced every 10 seconds until reaction stops.
5. Repeat steps 1-4 using the same mass of small chips, then large chips.
6. Keep all other conditions constant. [1]

Analysis:

• Plot graphs of volume of CO₂ vs time for each surface area.
• Compare initial gradients (initial rates) or time taken to produce a fixed volume of gas.
• If the hypothesis is correct, the powder (largest surface area) will have the steepest gradient / shortest time, and large chips (smallest surface area) will have the shallowest gradient / longest time. [1]

20. (a) Resistance calculations: [2 marks: 1 for correct formula use, 1 for all correct values]

Working: R = V/I

• 20 cm: 1.8 / 0.45 = 4.0 Ω
• 40 cm: 1.8 / 0.23 = 7.83 ≈ 7.8 Ω
• 60 cm: 1.8 / 0.15 = 12.0 Ω
• 80 cm: 1.8 / 0.11 = 16.36 ≈ 16.4 Ω
• 100 cm: 1.8 / 0.09 = 20.0 Ω

(b) Graph plotting [2 marks: 1 for labeled axes with correct scales and plotted points, 1 for best-fit straight line through origin]

(c) Resistance is directly proportional to the length of the wire. (The graph is a straight line passing through the origin.) [1]

(d) Since R ∝ L, doubling length doubles resistance. Resistance at 100 cm = 20.0 Ω Resistance at 120 cm = 20.0 × (120/100) = 24.0 Ω [1]

Alternative: From graph, extend best-fit line to 120 cm and read off value ≈ 24 Ω.

End of Answer Key