Cambridge IGCSE™

* 4 6 1 3 8 7 7 5 4 3 *

COMBINED SCIENCE 0653/62

Paper 6 Alternative to Practical October/November 2020

1 hour

You must answer on the question paper.

No additional materials are needed.

INSTRUCTIONS
● Answer all questions.
● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs.
● Write your name, centre number and candidate number in the boxes at the top of the page.
● Write your answer to each question in the space provided.
● Do not use an erasable pen or correction fluid.
● Do not write on any bar codes.
● You may use a calculator.
● You should show all your working and use appropriate units.

INFORMATION
● The total mark for this paper is 40.
● The number of marks for each question or part question is shown in brackets [ ].

This document has 16 pages. Blank pages are indicated.

DC (DH/FC) 194545/4
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1 (a) Diatoms are single-celled organisms that live in water.

Fig. 1.1 shows a diatom.

Fig. 1.1

In the box, make a large drawing of the diatom shown in Fig. 1.1.

[3]

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(b) Fig. 1.2 shows a different species of diatom. The photograph is magnified ×1500.

Fig. 1.2 (magnification ×1500)

(i) Measure the diameter of the photograph of the diatom in Fig. 1.2.

diameter of photograph = .................................................. mm [1]

(ii) Calculate the actual diameter of the diatom.

Use the equation shown.

diameter of photograph
actual diameter =
magnification

actual diameter = .................................................. mm [1]

(c) Describe one similarity and one difference between the diatom in Fig. 1.1 and the diatom in
Fig. 1.2.

similarity ....................................................................................................................................

...................................................................................................................................................

difference ..................................................................................................................................

...................................................................................................................................................
[2]

[Total: 7]

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2 A student wants to investigate two plant tissues to identify which plant tissue loses the most water
when placed in aqueous concentrated salt solution.

The student is provided with a potato, a carrot and aqueous concentrated salt solution.

Plan an investigation to compare the loss of water in pieces of potato and carrot placed in aqueous
concentrated salt solution.

In your answer, include:

• the apparatus you will need, including a labelled diagram if you wish
• a brief description of the method and the measurements you will make
• the variables you will control
• how you will process and use the results to draw a conclusion.

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3 A student investigates the changes in temperature that occur when dilute acid is added to aqueous
sodium hydroxide. The student investigates two dilute acids, dilute hydrochloric acid and dilute
sulfuric acid.

The student uses methyl orange as an indicator. Methyl orange is yellow in alkaline solutions and
red in acidic solutions.

(a) Procedure

The student:

step 1 measures 20 cm3 aqueous sodium hydroxide in a measuring cylinder and pours it
into a conical flask
step 2 adds 6 drops of methyl orange to the aqueous sodium hydroxide in the conical flask
step 3 measures the temperature of the aqueous sodium hydroxide in the conical flask and
records the value in Table 3.1
step 4 uses a burette to add 5.0 cm3 dilute hydrochloric acid to the aqueous sodium
hydroxide in the conical flask and swirls the mixture
step 5 measures the temperature of the mixture in the conical flask and records the value
in Table 3.1
step 6 records the colour of the methyl orange in the mixture in Table 3.1
step 7 repeats steps 4–6 until a total of 40.0 cm3 dilute hydrochloric acid has been added.

(i) Fig. 3.1 shows the thermometer readings for 0.0 cm3, 30.0 cm3 and 35.0 cm3 of dilute
hydrochloric acid added.

°C °C °C

30 40 40

20 30 30

10 20 20

0.0 cm3 30.0 cm3 35.0 cm3

dilute hydrochloric acid dilute hydrochloric acid dilute hydrochloric acid
added added added

Fig. 3.1

Record these values in Table 3.1.

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Table 3.1

volume of dilute hydrochloric temperature of colour of methyl

acid added / cm3 mixture / °C orange
0.0 yellow
5.0 25.5 yellow
10.0 29.5 yellow
15.0 34.5 yellow
20.0 38.0 yellow
25.0 38.5 red
30.0 red
35.0 red
40.0 37.0 red
[3]

(ii) Using the data in Table 3.1, plot on the grid the points for temperature of mixture against
volume of dilute hydrochloric acid added.

temperature
of mixture
/ °C

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0

volume of dilute acid added / cm3

[2]

(iii) Draw a straight best-fit line for the first five points.
Draw a straight best-fit line for the last four points.
Extend both lines until they cross.
The point where the two lines cross is the maximum temperature reached.
Label these two lines hydrochloric acid. [1]
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(b) The student repeats the procedure in (a) using dilute sulfuric acid instead of dilute hydrochloric
acid.

The results are shown in Table 3.2.

Table 3.2

volume of dilute sulfuric temperature of colour of

acid added / cm3 mixture / °C methyl orange
0.0 21.5 yellow
5.0 28.0 yellow
10.0 35.5 yellow
15.0 39.0 red
20.0 38.0 red
25.0 37.0 red
30.0 36.5 red
35.0 35.0 red
40.0 33.5 red

On the grid in (a)(ii), plot the points for temperature against volume of dilute sulfuric acid
added.

Draw a straight best-fit line for the first three points.

Draw a straight best-fit line for the last six points.
Extend both lines until they cross.
The point where the two lines cross is the maximum temperature reached.
Label these two lines sulfuric acid. [2]

(c) State the maximum temperature reached for each acid.

dilute hydrochloric acid = .......................................................... °C

dilute sulfuric acid = .......................................................... °C

[1]

(d) Suggest what happens to the colour of the methyl orange when the mixture is near the
maximum temperature.

...................................................................................................................................................

............................................................................................................................................. [1]

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(e) The concentrations of the dilute hydrochloric acid and the dilute sulfuric acid are the same.

(i) State which dilute acid neutralises the aqueous sodium hydroxide using a smaller volume
of acid.
Use data from your graph to explain your answer.

acid .................................................................

explanation ........................................................................................................................

..................................................................................................................................... [1]

(ii) Hydrochloric acid has the formula HCl.

Sulfuric acid has the formula H2SO4.

Suggest why the dilute acid chosen in (e)(i) uses a smaller volume to neutralise the
sodium hydroxide.

...........................................................................................................................................

..................................................................................................................................... [1]

(iii) Suggest a change to the apparatus which would give you greater confidence in your
answer to (e)(i).

..................................................................................................................................... [1]

[Total: 13]

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4 The ‘internal resistance’ of a cell is the resistance inside the cell.

A student investigates the internal resistance of a cell.

(a) The student uses a series circuit containing:

• a cell
• a switch
• a variable resistor to control the current in the circuit
• an ammeter to measure the current in the circuit
• a voltmeter to measure the potential difference (p.d.) across the cell.

Complete the circuit diagram in Fig. 4.1 to show how the student measures the current in the
circuit and the potential difference across the cell.

Fig. 4.1
[2]

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(b) Procedure

The student:

• uses the variable resistor to change the current in the circuit

• measures the current in the circuit
• measures the potential difference (p.d.) across the cell
• plots the graph of p.d. against current shown in Fig. 4.2.

2.5

2.0

p.d.
/V

1.5

1.0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

current / A

Fig. 4.2

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(i) Use Fig. 4.2 to find the p.d. when the current is 0.44 A.

p.d. = ...................................................... V [1]

(ii) Fig. 4.3 shows the voltmeter used by the student.

On Fig. 4.3, draw the pointer to show the p.d. in (b)(i).

2.0 3.0
1.0 4.0

0 5.0

Fig. 4.3
[1]

(iii) The electromotive force (e.m.f.) of the cell is the p.d. when the current = 0 A.

Extend the straight best-fit line on Fig. 4.2 to determine the e.m.f. of the cell.

e.m.f. = ...................................................... V [2]

(iv) The internal resistance of the cell is found from the gradient of the straight best-fit line in
Fig. 4.2.

Determine the gradient of the straight best-fit line in Fig. 4.2.

Show on Fig. 4.2 the values you use to calculate the gradient.
Show your working.

gradient = ..................................................... Ω [3]

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(c) The student identifies the point circled on Fig. 4.2 as an anomalous result.

The student repeats the measurements for this point.

Fig. 4.4 shows the repeated ammeter and voltmeter readings.

2.0 3.0
0.4 0.5 0.6 1.0 4.0
0.3 0.7
0.2 0.8
0.1 0.9 0 5.0
0.0 1.0

A V

Fig. 4.4

Record the readings of current and potential difference shown in Fig. 4.4.

current = ............................................................ A

potential difference = ........................................................... V

[2]

(d) A second student predicts that the graph will not be straight at higher values of current.

Explain how the first student can extend the investigation to find out if this prediction is correct.

...................................................................................................................................................

...................................................................................................................................................

............................................................................................................................................. [2]

[Total: 13]

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© UCLES 2020 0653/62/O/N/20