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PAST PAPERS

QUESTION 6

Light travelling in air is incident on a diamond at an unknown angle of incidence.

The refractive index for diamond is 2,42 and the angle of refraction is 11o .

(refractive index for air = 1)

6.1 State Snell’s Law in words. (2)

6.2 Re-copy the diagram below in your answer book and complete it to show the

refraction for a light ray incident on a diamond until it passes into the

air again.

Label all relevant angles. (3)

6.3 Calculate the angle of incidence if the angle of refraction is 11. (3)

6.4 Calculate the speed of light in diamond. (3)

6.5 What is meant by “critical angle”? (2)

[13]

QUESTION 7

A grade 11 learner investigates the effect of slit width on the degree of diffraction.

She uses a monochromatic red light source and passes it through slits of different

widths.

7.1 State Huygens’ Principle as an explanation for diffraction. (2)

7.2 What property of light is demonstrated by diffraction? (1)

7.3 What is a wavefront? (2)

7.4 Draw two resultant diffraction patterns for a wide single slit and a narrow

single slit. (4)

7.5 What is the relationship between slit width and degree of diffraction? (2)

7.6 The monochromatic red light is now replaced with monochromatic blue light.

How will the diffraction pattern change? Explain. (3)

[14]

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QUESTION 3

An investigation to find the relationship between pressure and temperature of a given

mass of gas was done by a learner using 2,5 moles of an unknown diatomic gas under

normal temperature and pressure conditions and the following graph was plotted.

3.1 The graph is extrapolated to intersect the x-axis at X. What is the value of X

in degrees Celcius? (1)

3.2 What is point X referred to as? (1)

3.3 What physical quantity is kept constant during this experiment? (1)

3.4 Calculate the volume of the vessel in which the investigation was conducted. (4)

3.5 If 177, 5 g of this gas was used in the investigation, identify the gas. (3)

[10]

0 40 100 200 t( oC) -100 -200 -300

Y

120

P(kPa)

X

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QUESTION 4

4.1.1 State the two conditions under which real gases deviate from ideal gas

behaviour. (2)

4.1.2 Choose any one of these conditions and explain this deviation by referring to

the kinetic theory of gases. (2)

4.2 A fixed mass of gas occupies a volume of 1,5 cm3 in a gas syringe at 20oC.

The volume of the syringe is now increased to 2 cm3.

4.2.1 How does the average speed of the molecules in syringe now compare

with the average speed when the volume was 1,5 cm3?

Write down only INCREASE, DECREASE OR REMAINS THE SAME.

Explain. (3)

4.2.2 How will the pressure exerted by the gas now be affected? Write

down only INCREASE OR DECREASE. (1)

4.2.3 Name and state the law that explains this change in pressure. (3)

[11]

QUESTION 5

Butane is a compound used as a source of fuel. The boiling point of butane is -0,5o C.

It is composed of carbon and hydrogen atoms only. It is found that a 12,32 g sample

of butane contains 10,2 g of carbon.

5.1 Name the phase that butane exists in at room temperature. (1)

5.2 Calculate the mass of hydrogen atoms contained in the sample. (1)

5.3 Determine the empirical formula of butane. (5)

5.4 If the molar mass of butane is 58 g.mol-1, what is its molecular formula? (2)

[9]

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QUESTION 6

When 0,05 moles of CaCO3 (s) is placed in a reaction vessel containing 25,00 cm3

of a HCℓ solution of concentration 0,2 mol.dm-3, carbon dioxide gas is produced.

CaCO3(s) + 2HCℓ(aq) → CaCℓ2(aq) + CO2(g) + H2O(ℓ)

The gas is collected in a syringe.

6.1 What is a limiting reagent? (1)

6.2 How many moles of HCℓ were initially present in the reaction vessel? (3)

6.3 Calculate which reagent will be in excess. (3)

6.4 What is the maximum amount of CaCℓ2 that can be produced in this reaction

(theoretical yield). (3)

If the volume of the CO2(g) collected in the syringe was 0,023 dm3 at STP,

6.5 Calculate the percentage yield of the calcium chloride. (5)

[15]

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QUESTION 5

A layer of carbon tetrachloride (CCℓ4 ) (n = 1,46) is in contact with water (n = 1,33)

and air (n = 1) as shown in the diagram below. A ray of light from the water is

incident upon the CCℓ4 surface at an angle of incidence of 400 .

Air (n = 1)

CCℓ4 (n = 1,46)

Water (n = 1,33)

5.1 Define the terms:

5.1.1 refraction (2)

5.1.2 refractive index (2)

5.2 Will the ray of light experience total internal reflection at the water - CCℓ4

interface? Give a reason for the answer. (2)

5.3 Calculate the speed of light in CCℓ4. (3)

5.4 Calculate the critical angle of CCℓ4 , when light travels from CCℓ4 to air. (4)

5.5 In which direction does the ray of light refract if it enters the air?

(Choose from towards or away from normal) (2)

5.6 Determine whether the ray of light will experience total internal reflection

at the CCℓ4 – air interface. (6)

[21]

40O

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QUESTION 6

A learner uses a white light bulb, two pencils and a red filter to investigate a wave

phenomenon. He places the red filter in front of the light bulb and fastens two

pencils together with an elastic band. He then looks at the light bulb through the

small opening between the pencil from a distance of 2 m, as shown below.

6.1 Name the phenomenon that the learner is investigating. (2)

6.2 The learner makes notes of the following observations in his practical book:

Observation 1:

Red and dark bands of different widths are seen on both sides of the central

red band.

Observation 2:

When the two pencils are brought closer together, the red bands become broader.

Observation 3:

When the red filter is removed, spectral colours are seen on both sides of the

central band.

6.2.1 State Huygens’ principle. (3)

6.2.2 Use Huygens’ principle to explain the occurrence of red and dark

bands in observation 1. (4)

6.2.3 Give a reason for Observation 2. (3)

6.2.4 Explain the formation of spectral colours in Observation 3. (4)

[16]

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QUESTION 7

The vibrator in a ripple tank generates one wave every 0, 1 s. The wave is

propagated at a velocity of 400 mm.s-1 .

7.1 Calculate the frequency of the wave. (3)

7.2 Calculate the shortest distance between the two points on the wave which

are completely out of phase. (4)

7.3 What type of wave is generated by the vibrator? (2)

7.4 Name a property which is characteristic of the type of wave in 7.3 above. (2)

[11]

QUESTION 2

A compound consists of 32,45 % carbon, 3,64 % hydrogen and 63,91 % chlorine

by mass. The molar mass of the compound is 332,82 g.mol-1.

2.1 Distinguish between empirical formula and molecular formula. (4)

2.2 Calculate the empirical formula of the compound. (6)

2.3 Calculate its molecular formula. (2)

[12]

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QUESTION 3

Some potassium carbonate (K2CO3) is dissolved in water and the solution made up

to 700 cm3.

3.1 Write down the name of the bonds/forces occurring between the particles

of the:

3.1.1 solute (K2CO3). (1)

3.1.2 solvent (water). (1)

3.1.3 solute and the solvent (potassium carbonate solution). (1)

3.2 Calculate the mass of potassium carbonate that will be required to make this

solution with a concentration of 0,25 mol.dm-3. (4)

3.3 A learner now requires a potassium carbonate solution of concentration 0,01

mol.dm-3. What change must the learner make to the original solution

(in question 3.2)? Show using a calculation. (4)

3.4 Would the potassium carbonate dissolve more readily in carbon

tetrachloride? Explain your answer by referring to the types and strengths of the

intermolecular forces. (3)

[14]

QUESTION 4

In a chemical reaction 31,2 g of NH4 NO3 is allowed to react 32,8 g of Na3PO4.

The equation for the reaction is:

3NH4NO3(aq) + Na3PO4(aq) → (NH4)3 PO4(aq) + 3NaNO3

4.1 What is meant by a limiting reagent? (2)

4.2 Identify the limiting reagent. Show ALL calculations. (8)

4.3 How many moles of the reactant is in excess? (2)

[12]

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QUESTION 5

Iron (Fe) can be extracted from its ore by reacting it with carbon monoxide (CO)

in a furnace according to the equation:

Fe2O3 (s) + 3 CO (g) → 2 Fe (s) + 3 CO2 (g)

5.1 Calculate the percentage composition of iron in Fe2O3. (3)

5.2 Calculate the percentage of iron oxide in the ore if 15 g of an impure

sample of Fe2O3 is reacted with excess CO to produce 5 dm3 of CO2 at STP. (7)

[10]

QUESTION 6

An experiment was carried out to investigate the relationship between the pressure

exerted by a sample of air and the volume of the air.

The following graph of Pressure (kPa) versus Volume

1 (cm-3) for the air taken at

25 °C was drawn.

6.1 For this investigation, write down the following:

6.1.1 The TWO controlled variables (2)

Pre

ssu

re (

kPa)

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6.1.2 The dependent variable (1)

6.1.3 A conclusion that can be drawn from the results. (2)

6.1.4 The gas law that is being verified. (1)

6.2 Calculate the gradient of the graph. (3)

6.3 What does the gradient of the graph represent? (2)

6.4 State ONE precaution that must be taken when carrying out this investigation. (2)

6.5 Using data from the graph, calculate the number of moles of gas that was

used in this investigation. (5)

6.6 If this investigation was carried out at a higher temperature, describe what

would happen to the gradient of the graph. (2)

[20]

QUESTION 7

Sulphur dioxide is a gas at room temperature.

7.1 Draw the Lewis Dot diagram for the SO2 molecule. (2)

The following is a graph obtained for an ideal gas at different temperatures.

7.2 Redraw this graph in your answer book and on it draw the graph that would

be obtained to show the behaviour of sulphur dioxide. (2)

7.3 What happens to the sulphur dioxide gas at very low temperatures? (2)

7.4 Explain why this (in 7.3 above) happens to a gas like sulphur dioxide. (3)

[9]

T(K)

V Ideal gas

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QUESTION 8

Oxygen gas occupies a volume of 500 cm3 at a temperature of 27o C and a pressure

of 100 kPa. The gas is heated to 70o C and the pressure of the gas increases

to 200 kPa.

8.1 Explain, in terms of the kinetic molecular theory, how the volume of a gas varies

with changes in temperature. (3)

8.2 Calculate the new volume that the oxygen gas will occupy at a temperature

of 70o C. (6)

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QUESTION 4 (Start on a new page)

Two learners A and B, investigate the relationship between the temperature and

pressure of an enclosed mass of gas. The learners used different samples of SO2(g)

in two identical containers with a fixed volume of 1 dm3. The results obtained by

the learners A and B were plotted on the same set of axes as shown below:

4.1 Formulate an investigative question for this investigation. (2)

4.2 Write down the mathematical relationship between pressure and kelvin

temperature from the learners conclusion based on the graph they obtained. (2)

4.3 Which variable is kept constant during this investigation? (1)

4.4 Give an explanation for the relationship that you have written in

QUESTION 4.2 using the Kinetic Theory of gases. (3)

4.5 Calculate the value of temperature indicated by X (in °C) using the

information given on the graph. (6)

4.6 Calculate the mass of SO2(g) used by learner A. (7)

4.7 Write down the temperature which in degree celsius is equal to zero kelvin.

What is this temperature called? (2)

[23]

P

ressure

(kP

a)

150

100

298 X Temperature (K)

A

B

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QUESTION 5 (Start on a new page)

A dilute solution of ethanoic acid called vinegar is used daily in food industry and

households. The relative molecular mass of ethanoic acid is 60 g.mol-1. Ethanoic

acid consists of 39,9% carbon, 6,7% hydrogen and 53,4% oxygen.

5.1 Determine the molecular formula of ethanoic acid. (8)

5.2 A particular recipe for the baking of malva pudding requires 75 cm3 of

vinegar and 2,2g of baking soda (NaHCO3).

5.2.1 Calculate the number of moles of NaHCO3 in 2,2 g of baking soda. (3)

5.2.2 Is ethanoic acid a strong acid or a weak acid? Give a reason for

your answer. (3)

5.2.3 Calculate the concentration of the vinegar used if the 75 cm3

vinegar reacts completely with 60 cm3 of NaHCO3 solution of

concentration 0,1 mol.dm-3. The equation for the reaction that takes

place is given below:

CH3COOH + NaHCO3 → CH3COONa + H2O + CO2 (5)

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