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13+ · Science

CE.S-W2 Science: Working Scientifically and Practical Skills Set 2

ISEB CE ISEB Common Entrance 13+ Science · Calculator allowed · about 90 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

A student measures the volume of gas produced by a reaction every 10 seconds. Which type of graph is most suitable for displaying this data?

A) Bar chart
B) Pie chart
C) Line graph
D) Scatter graph with no line of best fit

(Total for Question 1 is 1 mark)

A student records the mean height of three different varieties of pea plant: Kelvedon Wonder, Meteor and Alderman. Which type of graph is most suitable for displaying this data?

A) Line graph
B) Bar chart
C) Scatter graph
D) Pie chart

(Total for Question 2 is 1 mark)

In a school investigation, which variable is measured or observed as the outcome of the experiment?

A) Independent variable
B) Dependent variable
C) Control variable
D) Categoric variable

(Total for Question 3 is 1 mark)

A student uses a forcemeter (spring balance) with graduations every 0.2 N to measure the weight of a rock sample. The pointer lines up exactly halfway between the 4.2 N and 4.4 N graduation marks.

(a)State the reading shown on the forcemeter.(1)

(b)Give one reason why the student should make sure the forcemeter is held still and vertical before taking the reading.(1)

(Total for Question 4 is 2 marks)

Priya is investigating how the temperature of hydrogen peroxide solution affects the rate at which oxygen gas is produced when a piece of potato (which contains the enzyme catalase) is added to it.

(a)State the independent variable.(1)

(b)State the dependent variable.(1)

(Total for Question 5 is 2 marks)

State three variables, other than temperature, that Priya should control to make this a fair test.

(Total for Question 6 is 3 marks)

Match each term to its correct definition by writing the correct letter next to each term.
Terms: 1. Validity 2. Precision
Definitions:
A. How close together repeated measurements are to each other, shown by how little they are spread out.
B. Whether an investigation is designed so that it truly answers the question being asked, including whether all relevant variables were controlled.

(Total for Question 7 is 2 marks)

A student investigates how the temperature of water affects the time taken for a sugar cube to completely dissolve. As the temperature of the water increases from 20 degC to 80 degC, the time taken for the sugar cube to dissolve decreases.

(a)State the type of correlation shown by this data.(1)

(b)Explain, in terms of particles, why increasing the temperature of the water decreases the time taken for the sugar to dissolve.(2)

(Total for Question 8 is 3 marks)

Priya carries out her investigation from Question 5. She measures the volume of oxygen gas collected in the first 30 seconds after adding a potato cube to hydrogen peroxide solution, at six different temperatures, with three repeats at each temperature.

Temperature (degC): 10	20	30	40	50	60
Trial 1 (cm³): 4	9	15	24	12	3
Trial 2 (cm³): 5	10	16	23	11	2
Trial 3 (cm³): 3	8	14	25	25	4
Mean (cm³): ___	9	___	24	___	3

(a)Identify the anomalous result in the table, stating its value and the temperature at which it occurs.(1)

(b)Suggest one possible cause of this anomalous result.(1)

(c)Calculate the mean volume of gas at 50 degC, using only the two consistent (non-anomalous) readings.(2)

(d)Complete the table by calculating the mean volumes of gas produced at 10 degC and at 30 degC.(2)

(e)State one variable that Priya must control in this investigation, and explain why it must be kept the same at every temperature.(2)

(f)Plot a graph of the mean volume of gas produced (y-axis) against temperature (x-axis), using the corrected mean at 50 degC found in part (c). Draw a suitable curve of best fit through your points.(3)

(g)Describe the trend in the volume of gas produced as the temperature increases from 10 degC to 40 degC.(1)

(h)Explain, in terms of the enzyme and its substrate, why the volume of gas produced decreases sharply as the temperature increases from 40 degC to 60 degC.(3)

(i)State the optimum temperature for this enzyme shown by these results, and explain how you know this from the data.(2)

(j)Priya wants to estimate the volume of gas that would be produced at 35 degC. Use the table to estimate this value. State whether this is an example of interpolation or extrapolation, and explain your answer.(3)

(Total for Question 9 is 20 marks)

A student investigates how the extension of a spring depends on the mass hung from it. She hangs increasing masses on the spring and measures its extension from its natural (unstretched) length.

Mass added (g): 0	20	40	60	80	100	120
Extension (mm): 0	8	16	24	32	40	58

(a)State the independent variable and the dependent variable in this investigation.(2)

(b)State one variable that should be kept the same to make this a fair test.(1)

(c)Plot a graph of extension (y-axis, mm) against mass added (x-axis, g). Draw a straight line of best fit through the points that follow a linear pattern.(3)

(d)Describe the relationship between mass added and extension for masses from 0 g to 100 g.(1)

(e)Calculate the force, in newtons, applied to the spring when a mass of 100 g is hung from it. (Use gravitational field strength g = 10 N/kg.)(2)

(f)Using your answer to part (e) and the extension at 100 g, calculate the spring constant of the spring in N/m. Give your answer to 2 significant figures.(3)

(g)The extension recorded at 120 g was 58 mm. Explain what this result shows about the spring, compared with the pattern for masses up to 100 g.(2)

(h)Suggest one improvement, other than repeating the readings, that would increase the accuracy of the extension measurements taken with a metre ruler.(1)

(Total for Question 10 is 15 marks)

A student investigates the rate of reaction between marble chips (calcium carbonate) and dilute hydrochloric acid. She uses an excess of dilute hydrochloric acid, so that all of a fixed mass of marble chips reacts completely. She repeats the experiment using two different concentrations of acid and measures the total volume of carbon dioxide gas produced using a gas syringe.

Time (s): 0	20	40	60	80	100	120
Volume of CO2, 1.0 mol/dm³ acid (cm³): 0	18	32	42	48	50	50
Volume of CO2, 2.0 mol/dm³ acid (cm³): 0	30	46	50	50	50	50

(a)Write the balanced symbol equation, including state symbols, for the reaction between calcium carbonate and hydrochloric acid.(3)

(b)State the independent variable in this investigation.(1)

(c)State one variable that must be kept the same for this to be a fair comparison between the two concentrations.(1)

(d)Explain, in terms of particles, why the reaction with 2.0 mol/dm³ acid produces gas more quickly than the reaction with 1.0 mol/dm³ acid.(2)

(e)Both reactions eventually produce the same total volume of gas (50 cm³). Explain why.(2)

(f)Calculate the mean rate of reaction between 0 s and 40 s for the reaction using 2.0 mol/dm³ acid. Give the correct unit.(3)

(g)A student says: "Using a more concentrated acid means more gas is produced overall." Use the results in the table to evaluate whether this statement is correct.(2)

(Total for Question 11 is 14 marks)

A student is investigating a pendulum. Instead of measuring the time for one complete swing (oscillation), she measures the time for 10 complete oscillations and then divides this time by 10 to find the time for one oscillation. Explain why this method gives a more accurate value for the time of one oscillation than timing a single oscillation.

(Total for Question 12 is 2 marks)

A student measures the extension of a spring using a metre ruler with a resolution (smallest division) of 1 mm. She records an extension of 32 mm. Calculate the percentage uncertainty in this measurement, giving your answer to 1 decimal place. (Uncertainty = half of the smallest division.)

(Total for Question 13 is 3 marks)

A thermometer was not fully immersed in the liquid during an experiment. As a result, every temperature reading taken with it was 2 degC lower than the true temperature.

(a)State the type of error this represents.(1)

(b)Explain how repeating the temperature reading several times and calculating a mean would affect this error.(2)

(Total for Question 14 is 3 marks)

Using the corrected mean results from Question 9, write a conclusion for Priya's investigation into how temperature affects the rate of reaction of catalase. Your conclusion should refer to specific data values and use scientific knowledge of enzymes.

(Total for Question 15 is 3 marks)

A student tests only one concentration of hydrogen peroxide solution and takes a single reading of the volume of gas produced in 30 seconds. She concludes that this concentration produces the fastest rate of reaction out of all possible concentrations of hydrogen peroxide. Give two reasons why her conclusion is not justified.

(Total for Question 16 is 2 marks)

Priya's teacher asks her to plan a new investigation into how the concentration of hydrogen peroxide solution affects the rate of the reaction with a fixed piece of potato (which contains the enzyme catalase). Plan a method she could use, including how she would make it a fair test and how she would ensure her results are reliable.

(Total for Question 17 is 6 marks)

Evaluate the method used in Question 10 to investigate how the extension of a spring depends on the mass added to it. In your answer, comment on the reliability and accuracy of the results and suggest improvements that could be made.

(Total for Question 18 is 6 marks)

Mark scheme · CE.S-W2 Science: Working Scientifically and Practical Skills Set 2

Question 1

B1 C cao
Answer: C) Line graph

Question 2

B1 B cao
Answer: B) Bar chart

Question 3

B1 B cao
Answer: B) Dependent variable

Question 4

(a) B1 4.3 N cao
(a) Answer: 4.3 N
(b) B1 if it is moving or held at an angle, the pointer will not settle at the position that shows the true weight, giving an inaccurate reading oe
(b) Answer: So the pointer settles at the position that shows the true weight; if the forcemeter is swinging or at an angle, the reading will not be accurate.

Question 5

(a) B1 temperature of the hydrogen peroxide solution oe
(a) Answer: Temperature of the hydrogen peroxide solution.
(b) B1 rate of oxygen gas production, e.g. volume of gas produced in a fixed time oe
(b) Answer: The rate at which oxygen gas is produced (e.g. volume of gas collected in a fixed time).

Question 6

B1 same size (surface area) of potato cube used each time
B1 same volume and concentration of hydrogen peroxide solution used each time
B1 any other valid control, e.g. same variety/type of potato, same time allowed before adding the potato, same apparatus
Answer: Any three of: same size (surface area) of potato cube, same volume and concentration of hydrogen peroxide, same variety of potato, same apparatus, same time period over which gas is collected.

Question 7

B1 1-B cao
B1 2-A cao
Answer: 1-B, 2-A

Question 8

(a) B1 negative correlation oe
(a) Answer: A negative correlation.
(b) B1 particles in warmer water have more kinetic energy and move faster oe
(b) B1 so water particles collide with (and break apart) the sugar particles more frequently, making it dissolve more quickly oe
(b) Answer: Water particles in warmer water have more kinetic energy and move faster, so they collide with the sugar particles more often, making the sugar dissolve more quickly.

Question 9

(a) B1 25 cm³ (trial 3, at 50 degC) cao
(a) Answer: 25 cm³, trial 3, at 50 degC.
(b) B1 a plausible cause, e.g. an air bubble entered the gas-collecting tube, the potato cube used was larger than the others, or a timing/reading error oe
(b) Answer: For example, an air bubble entered the gas syringe, a larger piece of potato was accidentally used, or the volume was misread.
(c) M1 (12 + 11) / 2
(c) A1 11.5 cm³ cao
(c) Answer: 11.5 cm³
(d) B1 4 cm³ at 10 degC cao
(d) B1 15 cm³ at 30 degC cao
(d) Answer: 4 cm³ at 10 degC; 15 cm³ at 30 degC.
(e) B1 a valid control variable, e.g. size/surface area of the potato cube, or volume and concentration of hydrogen peroxide
(e) B1 explanation: if it changed, differences in results could be caused by this rather than by temperature, making the comparison unfair oe
(e) Answer: For example, the size of the potato cube must be kept the same; otherwise a larger piece (more surface area) would produce more gas regardless of temperature, making the comparison unfair.
(f) B1 sensible linear scales on both axes, with axes correctly labelled including units
(f) B1 all six points plotted accurately: (10, 4), (20, 9), (30, 15), (40, 24), (50, 11.5), (60, 3)
(f) B1 a single smooth curve of best fit drawn through (or close to) the points, rising to a peak and then falling
(f) Answer: A curve that rises from (10, 4) up to a peak at (40, 24), then falls steeply to (60, 3).
(g) B1 the volume of gas produced (rate of reaction) increases as temperature increases oe
(g) Answer: The volume of gas produced (the rate of reaction) increases as the temperature increases, from 4 cm³ at 10 degC to 24 cm³ at 40 degC.
(h) B1 above the optimum temperature, the enzyme (catalase) becomes denatured oe
(h) B1 the shape of its active site changes (is destroyed) oe
(h) B1 so the substrate (hydrogen peroxide) can no longer bind to (fit) the active site, so fewer successful reactions occur and the rate decreases oe
(h) Answer: Above 40 degC the enzyme catalase becomes denatured, so the shape of its active site changes and the hydrogen peroxide substrate can no longer fit it; fewer successful reactions occur, so the rate of gas production falls sharply.
(i) B1 40 degC cao
(i) B1 because the highest (corrected) mean volume of gas, 24 cm³, is produced at this temperature oe
(i) Answer: 40 degC, because this is the temperature at which the highest mean volume of gas (24 cm³) was produced.
(j) B1 a sensible estimate between the values at 30 degC and 40 degC, e.g. any value in the range 15-24 cm³
(j) B1 interpolation cao
(j) B1 because 35 degC lies between two temperatures that were actually tested (30 degC and 40 degC) oe
(j) Answer: Approximately 19-20 cm³ (accept any sensible value between 15 and 24 cm³); this is interpolation, because 35 degC lies between two temperatures (30 degC and 40 degC) that were actually tested.

Question 10

(a) B1 independent variable: mass added (g)
(a) B1 dependent variable: extension of the spring (mm)
(a) Answer: Independent variable: mass added. Dependent variable: extension of the spring.
(b) B1 a valid control, e.g. the same spring is used throughout, the starting (unstretched) length is measured the same way each time, or temperature is kept constant oe
(b) Answer: The same spring must be used for every mass (its unstretched length measured the same way each time).
(c) B1 sensible linear scales on both axes, with axes correctly labelled including units
(c) B1 all seven points plotted accurately
(c) B1 a straight line of best fit drawn through the origin and the points up to 100 g, without being forced through the point at 120 g
(c) Answer: A straight line through the origin fitting the points up to 100 g; the point at 120 g lies clearly above this line and should not be used to draw the line of best fit.
(d) B1 directly proportional (a straight line through the origin) oe
(d) Answer: The extension is directly proportional to the mass added (a straight line through the origin).
(e) M1 F = mass (kg) x g = 0.1 x 10
(e) A1 1 N cao
(e) Answer: 1 N
(f) M1 k = F / extension
(f) M1 1 / 0.040 (extension = 40 mm = 0.040 m)
(f) A1 25 N/m cao
(f) Answer: 25 N/m
(g) B1 the extension is greater than the proportional pattern predicts (0.4 mm per gram would give 48 mm, not 58 mm) oe
(g) B1 this shows the spring has been stretched beyond its limit of proportionality (elastic limit), so it no longer obeys Hooke's law oe
(g) Answer: The extension (58 mm) is greater than the proportional pattern predicts (48 mm), showing the spring has passed its limit of proportionality and no longer obeys Hooke's law.
(h) B1 use a set square to check the ruler is vertical, take the reading at eye level to avoid parallax error, or use a fixed reference (fiducial) marker oe
(h) Answer: Use a set square to keep the ruler vertical and take the reading at eye level, to avoid parallax error.

Question 11

(a) B1 correct formulae: CaCO3 + HCl -> CaCl2 + H2O + CO2
(a) B1 correctly balanced: CaCO3 + 2HCl -> CaCl2 + H2O + CO2
(a) B1 correct state symbols: (s), (aq), (aq), (l), (g) in the right places
(a) Answer: CaCO3(s) + 2HCl(aq) -> CaCl2(aq) + H2O(l) + CO2(g)
(b) B1 concentration of hydrochloric acid oe
(b) Answer: Concentration of the hydrochloric acid.
(c) B1 a valid control, e.g. mass (and size/surface area) of marble chips, volume of acid, or temperature oe
(c) Answer: The mass and size of the marble chips used must be the same each time.
(d) B1 the more concentrated acid has more acid particles in the same volume, so they are more crowded together oe
(d) B1 this increases the frequency of collisions between acid and marble chip particles, so more successful collisions happen each second, increasing the rate oe
(d) Answer: The more concentrated acid has more acid particles in the same volume, so collisions between acid particles and the marble chips happen more often, increasing the rate of reaction.
(e) B1 the same mass of marble chips (calcium carbonate) is used in both experiments, and there is enough acid to react with all of it in each case oe
(e) B1 so the same amount (number of moles) of carbon dioxide gas is produced in total, regardless of the acid's concentration oe
(e) Answer: The same mass of marble chips is used each time and there is enough acid to react with all of it in both cases, so the same total amount of carbon dioxide is produced; concentration changes only how quickly this happens, not the total amount.
(f) M1 change in volume = 46 - 0 = 46 cm³
(f) M1 rate = change in volume / change in time = 46 / 40
(f) A1 1.15 cm³/s cao
(f) Answer: 1.15 cm³/s
(g) B1 the statement is incorrect, because both concentrations produce the same total (final) volume of gas, 50 cm³ oe
(g) B1 concentration affects the rate (how quickly the gas is produced), not the total amount of gas produced, since the same mass of marble chips (the limiting reactant) reacts in both cases oe
(g) Answer: The statement is incorrect: both concentrations produce the same total volume of gas (50 cm³). Concentration affects only the rate at which the gas is produced, not the total amount, because the same mass of marble chips reacts fully in both experiments.

Question 12

B1 a single oscillation happens quickly, so any error in starting/stopping the stopwatch (e.g. due to human reaction time) makes up a large fraction of the time being measured oe
B1 timing 10 oscillations spreads this same fixed timing error over a much longer total time, so once divided by 10 it makes up a much smaller fraction of the time for one oscillation oe
Answer: Timing 10 oscillations and dividing by 10 spreads the fixed reaction-time error over a longer total time, so it has a much smaller effect on the calculated time for a single oscillation.

Question 13

M1 uncertainty = 1 / 2 = 0.5 mm
M1 percentage uncertainty = (0.5 / 32) x 100
A1 1.6% (1 d.p.) awrt
Answer: 1.6%

Question 14

(a) B1 systematic error oe
(a) Answer: A systematic error.
(b) B1 repeating and taking a mean would not correct or reduce this error oe
(b) B1 because the error affects every reading by the same fixed amount (2 degC too low), so the mean would also be 2 degC too low oe
(b) Answer: Taking a mean would not fix this error, because it shifts every single reading by the same 2 degC, so the mean would still be 2 degC lower than the true temperature.

Question 15

B1 correctly refers to data showing the volume of gas (rate) increasing as temperature rises from 10 degC to 40 degC, e.g. from 4 cm³ to 24 cm³ oe
B1 correctly refers to data showing the volume of gas (rate) decreasing sharply above 40 degC, e.g. falling to 11.5 cm³ at 50 degC and 3 cm³ at 60 degC oe
B1 links this pattern to scientific explanation: catalase has an optimum temperature (40 degC) at which it works fastest, and becomes denatured above this temperature, reducing the rate oe
Answer: As temperature increased from 10 degC to 40 degC, the mean volume of oxygen produced increased from 4 cm³ to 24 cm³, but above 40 degC it fell sharply, to 11.5 cm³ at 50 degC and 3 cm³ at 60 degC. This shows that catalase has an optimum temperature of around 40 degC, above which the enzyme becomes denatured and the rate of reaction falls.

Question 16

B1 she has not tested or compared any other concentrations, so she has no data to compare this result against and cannot claim it is the fastest oe
B1 she has taken only one reading with no repeats, so she cannot be sure this result is reliable and not an anomaly oe
Answer: She has not tested any other concentrations, so there is nothing to compare this result with; and she has taken only a single reading, with no repeats, so she cannot be sure the result is reliable rather than an anomaly.

Question 17

Level 0 (0): No relevant content, or the answer does not address planning an investigation.
Level 1 (1-2): A basic method is given. The independent and/or dependent variable may be named, but there is little or no reference to controlling other variables, apparatus, or improving reliability.
Level 2 (3-4): A clear method is given describing suitable apparatus and key steps. Some relevant variables to control are stated and/or repeats are mentioned, but detail is incomplete or not fully linked together.
Level 3 (5-6): A detailed, logically ordered method is given. It states a suitable range of concentrations, clearly controlled variables, an appropriate method for measuring the dependent variable, and explains how repeats and means will be used to improve reliability. Relevant safety precautions are included.
Indicative content:
- Use potato cubes of the same size (surface area) each time, e.g. 1 cm cubes, cut from the same potato.
- Vary the concentration of hydrogen peroxide across a suitable range, e.g. by diluting a stock solution to give concentrations such as 20%, 15%, 10% and 5%.
- Use the same volume of hydrogen peroxide solution each time, e.g. 20 cm^3.
- Keep the temperature constant throughout, e.g. by carrying out the investigation at room temperature or using a water bath.
- Measure the volume of oxygen gas produced using a gas syringe, or by collecting gas over water in an inverted measuring cylinder.
- Start a stopwatch as soon as the potato is added to the hydrogen peroxide.
- Record the volume of gas produced after a fixed time (e.g. 60 seconds), or record the time taken to collect a fixed volume of gas.
- Repeat each concentration at least three times and calculate a mean.
- Identify and exclude any anomalous results before calculating the mean.
- Wear eye protection, since hydrogen peroxide can irritate the skin and eyes.
- Plot a graph of rate (or volume of gas) against concentration to identify the pattern.

Question 18

Level 0 (0): No relevant content, or the answer does not evaluate the method.
Level 1 (1-2): A simple weakness or improvement is identified with little or no explanation, e.g. 'she should repeat it'.
Level 2 (3-4): More than one weakness in the method is identified (e.g. no repeats, ruler resolution, the anomalous point at 120 g), with some explanation of the effect on the results.
Level 3 (5-6): A well-reasoned evaluation covering both reliability (repeats, means, range of masses tested) and accuracy (ruler resolution, parallax error, checking the spring's behaviour) is given, with clearly justified and specific improvements linked to each weakness identified.
Indicative content:
- Only one reading was taken at each mass; repeating each mass at least three times and calculating a mean would help identify anomalies and improve reliability.
- The extension was measured with a metre ruler with millimetre graduations; using a fiducial marker with a set square to keep the ruler vertical would reduce parallax error and improve accuracy.
- It is not stated whether the spring returned to its original (unstretched) length after each mass was removed; checking this would confirm whether the spring had passed its elastic limit and whether earlier results were still valid.
- Only seven masses were tested, 20 g apart, and the limit of proportionality falls somewhere between 100 g and 120 g; testing smaller intervals (e.g. every 5-10 g) in this region would more precisely locate the limit of proportionality.
- The masses were not stated to be calibrated or checked before use; using calibrated slotted masses would reduce systematic error in the applied force.
- The temperature of the room was not recorded or controlled, and temperature can slightly affect a spring's stiffness; keeping this constant and recording it would make the investigation more valid.

Science: Working Scientifically and Practical Skills Set 2 - Worksheets, Questions and Revision