Question 1
(a) Fig. 1.1 is a photograph of blood as seen under a microscope. (Sub-topic: B9.4)
(i) Use a label and a label line on Fig. 1.1 to identify a white blood cell.
▶️Answer/Explanation
White blood cell labelled correctly on Fig. 1.1.
(ii) Name one other type of cell visible in Fig. 1.1. (Sub-topic: B9.4)
▶️Answer/Explanation
Red blood cell.
(b) White blood cells produce antibodies that fight infection in the body. The graph in Fig. 1.2 shows how the number of antibodies in the blood changes for 15 days after a person is infected by a pathogen. (Sub-topic: B10.1)
(i) Use Fig. 1.2 to identify on which day there are the most antibodies in the blood.
▶️Answer/Explanation
Day 12.
(ii) Suggest one reason why there is a decrease in the number of antibodies in the blood as shown in Fig. 1.2. [1]
▶️Answer/Explanation
The pathogen was destroyed, so fewer antibodies are needed.
(c) Twenty days after the first infection, the same person is infected with a different pathogen. Draw a line on Fig. 1.2 to suggest how the number of antibodies in the blood changes from day 15. (Sub-topic: B10.1)
▶️Answer/Explanation
Line decreasing or flat from 15–20 days, then increasing and decreasing again.
(d) Platelets are also found in the blood. State the function of platelets. (Sub-topic: B9.4)
▶️Answer/Explanation
Blood clotting.
Question 2 (Sub-topic: C2.2)
Fig. 2.1 is a diagram of an atom of element Q.
(a)(i) Explain why the mass of an atom is almost the same as the mass of its nucleus.
▶️Answer/Explanation
The mass of an atom is almost the same as the mass of its nucleus because the electrons, which orbit the nucleus, have a very small mass compared to the protons and neutrons in the nucleus. The mass of an electron is approximately 1/1836 of the mass of a proton or neutron, so the contribution of electrons to the total mass of the atom is negligible.
(ii) Use Fig. 2.1 to identify element Q. A copy of the Periodic Table is shown on page 32. Explain your answer.
▶️Answer/Explanation
Element Q is argon (Ar). The diagram shows that the atom has 18 electrons, which means it has 18 protons in the nucleus. The number of protons defines the atomic number, and in the Periodic Table, the element with atomic number 18 is argon.
(iii) State why element Q does not easily combine with other elements.
▶️Answer/Explanation
Element Q (argon) does not easily combine with other elements because it has a full outer electron shell. This makes it chemically inert, meaning it does not need to gain, lose, or share electrons to achieve stability.
(b) A teacher investigates the change in mass when calcium burns in air to form calcium oxide.
(i) The mass of calcium oxide produced is greater than the mass of calcium the teacher used. Explain this result.
▶️Answer/Explanation
The mass of calcium oxide produced is greater than the mass of calcium used because the calcium reacts with oxygen from the air to form calcium oxide. The additional mass comes from the oxygen atoms that combine with the calcium during the reaction.
(ii) The teacher mixes calcium oxide with water to form a solution. Predict the pH of the solution. Explain your answer.
▶️Answer/Explanation
The pH of the solution will be alkaline (pH > 7). Calcium oxide is a basic oxide, and when it reacts with water, it forms calcium hydroxide, which is an alkaline solution.
Question 3 (Sub-topic: P1.2)
(a) A girl runs around a 400 m athletics track. State a device she could use to measure precisely the time this takes.
▶️Answer/Explanation
Answer: stopwatch
Explanation: A stopwatch is a precise device used to measure time intervals, making it suitable for timing the girl’s run around the track.
(b) Fig. 3.1 shows the speed-time graph for her run around the track.
(i) Label with the letter X a point on the graph when the girl is running at constant speed.
▶️Answer/Explanation
Answer: X anywhere on the horizontal section of the graph.
Explanation: A horizontal line on a speed-time graph indicates constant speed, so any point on this section can be labeled as X.
(ii) Label with the letter Y a point on the graph when the girl is at rest.
▶️Answer/Explanation
Answer: Y at t = 0 s or t = 110 s.
Explanation: The girl is at rest when her speed is zero, which occurs at the start (t = 0 s) and the end (t = 110 s) of the run.
(iii) The girl’s deceleration is greater than her acceleration. Describe the evidence for this from the graph.
▶️Answer/Explanation
Answer: The gradient of the graph is steeper during deceleration than during acceleration.
Explanation: A steeper gradient indicates a greater change in speed over a shorter time, meaning the girl decelerates more quickly than she accelerates.
(iv) Calculate the distance travelled by the girl in the first 15 seconds of her run.
▶️Answer/Explanation
Answer: 30 m
Explanation: The distance travelled can be calculated using the area under the speed-time graph. For the first 15 seconds, the graph forms a triangle with a base of 15 s and a height of 4 m/s. The area (distance) is given by:
\[ \text{Distance} = \frac{1}{2} \times \text{base} \times \text{height} = \frac{1}{2} \times 15 \times 4 = 30 \, \text{m} \]
(c) When she returns home, the girl rings the doorbell. The electric circuit for the doorbell contains a cell, a switch, and an electric bell all connected in series.
is the symbol for an electric bell.
(i) Complete the circuit diagram for the doorbell.
▶️Answer/Explanation
Answer: The circuit diagram should show a cell, a switch, and an electric bell connected in series.
Explanation: In a series circuit, all components are connected end-to-end, so the current flows through each component in turn. The cell provides the energy, the switch controls the flow of current, and the electric bell produces the sound.
(ii) The potential difference across the electric bell is 6 V. The resistance of the electric bell is 2 Ω. Calculate the current in the circuit.
▶️Answer/Explanation
Answer: 3 A
Explanation: Using Ohm’s Law, \( V = IR \), the current \( I \) can be calculated as:
\[ I = \frac{V}{R} = \frac{6}{2} = 3 \, \text{A} \]
(iii) The girl hears the bell clearly. State the approximate range of audible frequencies that the girl is able to hear with healthy hearing.
▶️Answer/Explanation
Answer: 20 Hz to 20,000 Hz
Explanation: The human ear can typically detect sound frequencies in the range of 20 Hz to 20,000 Hz, which is considered the audible range for healthy hearing.
Question 4 (Sub-topic: B12.1)
(a) Respiration is a process that is part of the carbon cycle. Use words from the list to complete the definition of the term respiration. Each word may be used once, more than once or not at all.
cells DNA elements energy
enzymes molecules
Respiration is the chemical reactions in …………….. that break down nutrient …………….. and release …………….. .
▶️Answer/Explanation
Respiration is the chemical reactions in cells that break down nutrient molecules and release energy.
(b) Fig. 4.1 is a simplified diagram of the carbon cycle. Some of the processes that take place in the carbon cycle are represented with the letters A, B, C and D.
(i) Identify all the letters that represent respiration in Fig. 4.1.
▶️Answer/Explanation
B and C
(ii) Add an arrow to Fig. 4.1 to represent photosynthesis.
▶️Answer/Explanation
An arrow should be drawn from carbon dioxide in the atmosphere to carbon in plants, indicating the process of photosynthesis.
(c) Deforestation can cause an increase of carbon dioxide in the atmosphere. Animal species living in areas where deforestation occurs are also affected. Describe two effects of deforestation on animal species.
▶️Answer/Explanation
1 Loss of habitat
2 Extinction
Question 5
Impurities are unwanted substances in mixtures. Impurities can be removed using purification techniques.
(a) Some gaseous oxides are impurities which pollute air. (Sub-topic: C10.2)
(i) Name the gaseous oxide that forms when sulfur burns.
▶️Answer/Explanation
Sulfur dioxide (SO2)
(ii) Describe how this gaseous oxide can damage the environment.
▶️Answer/Explanation
Sulfur dioxide can cause acid rain, which damages buildings, statues, and vegetation. It can also lead to respiratory problems in humans and harm aquatic life in rivers and lakes.
(iii) Identify two gaseous oxides, other than water vapour or carbon dioxide, that can form during the combustion of hydrocarbons in air.
▶️Answer/Explanation
1. Carbon monoxide (CO)
2. Oxides of nitrogen (NOx)
(b) A scientist uses the apparatus shown in Fig. 5.1 to test four food dyes, P, Q, R and S. (Sub-topic: C12.3)
Fig. 5.2 shows her results for food dyes Q, R and S.
(i) Name this method the scientist uses to test the food dyes.
▶️Answer/Explanation
Chromatography
(ii) Describe what happens inside the container that produces the results shown in Fig. 5.2.
▶️Answer/Explanation
Water moves up the paper by capillary action. The dyes dissolve in the water and are carried along with it. Different dyes move at different speeds, causing them to separate and form distinct spots at different heights on the paper.
(iii) Food dye P is made by mixing together food dyes Q, R and S. Complete Fig. 5.2 by drawing the result for food dye P.
▶️Answer/Explanation
Food dye P will show three spots vertically in a line above the letter P, corresponding to the positions of the spots for dyes Q, R, and S.
(iv) Suggest why impurities in food dyes must be removed before the dyes are used to colour food.
▶️Answer/Explanation
Impurities in food dyes may be harmful or toxic, and their presence could affect the safety and quality of the food. Removing impurities ensures that the food dyes are safe for consumption and provide the desired color without adverse effects.
Question 6
(a) A team of students enter a competition to see who can build the highest tower from identical wooden cubes. One cube has a mass of 200 g. One cube has a volume of 250 cm3.
(i) Calculate the density of one wooden cube. (Sub-topic: P1.4)
▶️Answer/Explanation
Solution:
Density is calculated using the formula:
\[ \text{Density} = \frac{\text{Mass}}{\text{Volume}} \]
Given:
Mass = 200 g
Volume = 250 cm3
\[ \text{Density} = \frac{200 \, \text{g}}{250 \, \text{cm}^3} = 0.8 \, \text{g/cm}^3 \]
Therefore, the density of one wooden cube is 0.8 g/cm3.
Answer: 0.8 g/cm3
(ii) Calculate the weight of each wooden cube. Gravitational field strength = 10 N/kg. (Sub-topic: P1.3)
▶️Answer/Explanation
Solution:
Weight is calculated using the formula:
\[ \text{Weight} = \text{Mass} \times \text{Gravitational Field Strength} \]
Given:
Mass = 200 g = 0.2 kg
Gravitational Field Strength = 10 N/kg
\[ \text{Weight} = 0.2 \, \text{kg} \times 10 \, \text{N/kg} = 2 \, \text{N} \]
Therefore, the weight of each wooden cube is 2 N.
Answer: 2 N
(b) Fig. 6.1 shows the towers of cubes built by two teams. Team A’s tower is only 6 cubes tall before it falls over. Team B’s tower reaches 10 cubes tall and stays standing.
(i) Use ideas about stability and centre of mass to suggest why team A’s tower falls over. (Sub-topic: P1.5.3)
▶️Answer/Explanation
Solution:
The stability of an object depends on the position of its centre of mass. If the centre of mass is not directly above the base of the object, it becomes unstable and may topple over. In the case of Team A’s tower, the centre of mass is likely not aligned over the base, causing the tower to fall. Team B’s tower, on the other hand, has a centre of mass that is aligned over the base, making it more stable and able to stand taller.
Answer: Team A’s tower falls over because the centre of mass is not directly above the base, making it unstable.
(ii) Explain why more work is done to lift a cube to the top of the tower as the tower gets taller. (Sub-topic: P1.6.2)
▶️Answer/Explanation
Solution:
Work is done against gravity to lift a cube to a certain height. The work done is calculated using the formula:
\[ \text{Work} = \text{Force} \times \text{Distance} \]
As the tower gets taller, the distance (height) that each cube needs to be lifted increases. Therefore, more work is required to lift each cube to the top of the tower as the tower grows taller.
Answer: More work is done because the height (distance) increases as the tower gets taller, requiring more energy to lift each cube.
(iii) State the type of energy that is greater for a cube at the top of the tower compared with a cube lower down the tower. (Sub-topic: P1.6.1)
▶️Answer/Explanation
Solution:
The type of energy that is greater for a cube at the top of the tower is gravitational potential energy. This is because gravitational potential energy depends on the height of the object above the ground. The higher the cube is, the more gravitational potential energy it possesses.
Answer: Gravitational potential energy
(c) One student hits two cubes together. He hears the sound echo from the back wall of the room. The time interval from the student hitting the cubes to the student hearing the echo is 0.25 seconds. The distance to the wall is 39 m.
Calculate the speed of sound through the air. (Sub-topic: P3.4)
▶️Answer/Explanation
Solution:
The speed of sound can be calculated using the formula:
\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \]
Given:
Distance to the wall = 39 m
Time for the sound to travel to the wall and back = 0.25 s
Since the sound travels to the wall and back, the total distance is twice the distance to the wall:
\[ \text{Total Distance} = 2 \times 39 \, \text{m} = 78 \, \text{m} \]
\[ \text{Speed of Sound} = \frac{78 \, \text{m}}{0.25 \, \text{s}} = 312 \, \text{m/s} \]
Therefore, the speed of sound through the air is 312 m/s.
Answer: 312 m/s
Question 7
(a) In plants, glucose produced by photosynthesis is stored in leaves as starch. (Sub-topic: B6.1)
A student investigates one factor that affects photosynthesis by testing for the presence of starch in the leaves of two plants, A and B.
- Plant A is kept next to a window for two days.
- Plant B is kept in the dark for two days.
The student uses iodine solution to test leaves from plants A and B for the presence of starch.
(i) Predict the colour of the iodine solution after testing a leaf from each plant for starch.
colour of iodine solution after testing a leaf from plant A
colour of iodine solution after testing a leaf from plant B
▶️Answer/Explanation
Answer:
– Colour of iodine solution after testing a leaf from plant A: blue-black
– Colour of iodine solution after testing a leaf from plant B: orange/yellow/brown
Explanation:
Plant A, which was kept next to a window, received light and was able to carry out photosynthesis, producing glucose that was stored as starch. When iodine solution is added to the leaf, it turns blue-black, indicating the presence of starch. Plant B, which was kept in the dark, could not carry out photosynthesis and therefore did not produce starch. The iodine solution remains orange/yellow/brown, indicating the absence of starch.
(ii) State the factor needed for photosynthesis which the student is investigating.
▶️Answer/Explanation
Answer:
Light
Explanation:
The student is investigating the effect of light on photosynthesis. Plant A was exposed to light, while Plant B was kept in the dark. The presence or absence of starch in the leaves indicates whether photosynthesis occurred, which is directly influenced by the availability of light.
(b) Soil provides mineral ions to plants for healthy growth. (Sub-topic: B6.1)
Explain the importance of magnesium ions for healthy plant growth.
▶️Answer/Explanation
Answer:
Magnesium ions are needed for the production of chlorophyll, which is necessary for photosynthesis.
Explanation:
Magnesium is a central component of the chlorophyll molecule, which is essential for photosynthesis. Without magnesium, plants cannot produce chlorophyll, and therefore cannot capture light energy to convert carbon dioxide and water into glucose. This would severely limit the plant’s ability to grow and produce energy.
(c) Water is another substance needed by plants.
(i) Describe how water enters a plant. (Sub-topic: B8.2)
▶️Answer/Explanation
Answer:
Water enters a plant through the root hair cells by osmosis.
Explanation:
Water enters the plant through the root hair cells, which are specialized for absorption. The process of osmosis allows water to move from an area of higher water potential (the soil) to an area of lower water potential (the root hair cells) across a partially permeable membrane.
(ii) Describe how water is lost from a plant. (Sub-topic: B8.3)
▶️Answer/Explanation
Answer:
Water is lost from a plant through transpiration, which involves the evaporation of water from the surfaces of mesophyll cells into the air spaces and then diffusion out of the leaves through the stomata as water vapour.
Explanation:
Transpiration is the process by which water is lost from the plant through the stomata in the leaves. Water evaporates from the surfaces of mesophyll cells into the air spaces within the leaf. This water vapour then diffuses out of the leaf through the stomata, which are small openings on the underside of the leaf. This process helps to cool the plant and transport nutrients from the roots to the leaves.
Question 8
Sodium is a very reactive metallic element.
(a) Sodium chloride is a raw material that occurs in nature. Fig. 8.1 shows a process that is used to extract useful products from concentrated aqueous sodium chloride. (Sub-topic: C4.1)
(i) Name this process.
▶️Answer/Explanation
Answer: Electrolysis
Explanation: The process shown in Fig. 8.1 is electrolysis, which is used to extract useful products from concentrated aqueous sodium chloride.
(ii) On Fig. 8.1, use the letter E to label the electrolyte and the letter C to label the cathode.
▶️Answer/Explanation
Answer: The electrolyte should be labelled with the letter E, and the cathode should be labelled with the letter C.
Explanation: In the electrolysis process, the electrolyte is the substance that undergoes electrolysis, and the cathode is the negative electrode where reduction occurs.
(iii) State one useful gaseous element produced by this process.
▶️Answer/Explanation
Answer: Chlorine or Hydrogen
Explanation: During the electrolysis of concentrated aqueous sodium chloride, chlorine gas is produced at the anode, and hydrogen gas is produced at the cathode.
(b) Fig. 8.2 shows how sodium is stored so that it does not react with air. (Sub-topic: C9.1)
(i) Suggest one compound that forms when sodium reacts in air.
▶️Answer/Explanation
Answer: Sodium oxide, sodium hydroxide, or sodium carbonate
Explanation: Sodium reacts with oxygen in the air to form sodium oxide (Na2O), with water vapor to form sodium hydroxide (NaOH), and with carbon dioxide to form sodium carbonate (Na2CO3).
(ii) Suggest one reason why oil containing alkanes is a suitable liquid to use to protect sodium from contact with air.
▶️Answer/Explanation
Answer: Alkanes are relatively unreactive and do not react with sodium.
Explanation: Alkanes are saturated hydrocarbons that are chemically stable and do not react with sodium, making them suitable for protecting sodium from air and moisture.
(c) Fig. 8.3 shows apparatus a teacher uses to show the reaction between sodium and cold water. The water contains a solution of full-range universal indicator. The gas that is given off collects in the test-tube.
(Sub-topic: C7.1)
(i) Before the sodium is added the water is neutral. State the pH of the water and the colour of the full-range universal indicator before any sodium is added.
▶️Answer/Explanation
Answer: pH 7; green
Explanation: Neutral water has a pH of 7, and the full-range universal indicator shows green at this pH.
(ii) The teacher tests the gas in the test-tube using a lighted splint. She obtains a positive result. Describe the positive result and identify the gas.
▶️Answer/Explanation
Answer: Squeaky pop; hydrogen
Explanation: The gas produced is hydrogen, which burns with a squeaky pop sound when a lighted splint is brought near it.
(d) Sodium combines with bromine to form sodium bromide.
(i) State the type of chemical bonding in sodium bromide. (Sub-topic: C2.4)
▶️Answer/Explanation
Answer: Ionic or electrovalent bonding
Explanation: Sodium bromide is formed by the transfer of electrons from sodium to bromine, resulting in ionic bonding.
(ii) Balance the symbol equation for this reaction. (Sub-topic: C3.1)
▶️Answer/Explanation
Answer: 2 Na + Br2 → 2 NaBr
Explanation: The balanced equation shows that two sodium atoms react with one bromine molecule to form two sodium bromide molecules.
Question 9
(a) A battery from a mobile phone (cell phone) is analysed to see what it contains. One of the materials is the metal lithium. The sample taken from the battery consists of two types of lithium atom, lithium-6 and lithium-7.
(i) Name the two types of particle in the nucleus of an atom. (Sub-topic: C2.2)
▶️Answer/Explanation
Proton and neutron.
(ii) The nuclide notation for lithium-6 is written as \(\frac{6}{3}\)Li. State what each of the numbers in the nuclide notation represents. (Sub-topic: C2.2)
▶️Answer/Explanation
6 represents the nucleon number (mass number), which is the total number of protons and neutrons in the nucleus. 3 represents the proton number (atomic number), which is the number of protons in the nucleus.
(iii) The nuclide notation for lithium-7 is written as \(\frac{7}{3}\)Li. Explain why this is an isotope of lithium. (Sub-topic: C2.3)
▶️Answer/Explanation
Lithium-7 is an isotope of lithium because it has the same number of protons (3) as lithium-6 but a different number of neutrons (4 instead of 3). Isotopes are atoms of the same element with different numbers of neutrons.
(b) The lithium battery is connected to a lamp to produce visible light.
(i) Write visible light in the correct position in the incomplete electromagnetic spectrum in Fig. 9.1. (Sub-topic: P3.3)
▶️Answer/Explanation
Visible light should be placed in the centre box of the electromagnetic spectrum, between infrared and ultraviolet.
(ii) The lithium battery produces an electromotive force (e.m.f.). State the unit of e.m.f. (Sub-topic: P4.2.3)
▶️Answer/Explanation
Volts (V).
(c) Fig. 9.2 shows the arrangement of lithium atoms in three different states of matter. Label Fig. 9.2 to identify the state represented in each diagram. (Sub-topic: C1.1)
▶️Answer/Explanation
Solid, gas, liquid.
Question 10
(a) Fig. 10.1 is a diagram showing a simple reflex arc. (Sub-topic: B13.1)
(i) If a neurone is cut, impulses cannot pass along the neurone. Place only two ticks (✓) in Table 10.1 to show the correct effect of cutting each neurone in the reflex arc shown in Fig. 10.1.
| sensory neurone cut | motor neurone cut | |
|---|---|---|
| CNS does not receive impulses from the receptor and effector does not receive impulses from CNS. | ||
| CNS receives impulses from the receptor and effector receives impulses from CNS. | ||
| CNS receives impulses from the receptor but effector does not receive impulses from CNS. |
▶️Answer/Explanation
Answer:
The correct ticks should be placed as follows:
- CNS does not receive impulses from the receptor and effector does not receive impulses from CNS. – Tick under sensory neurone cut.
- CNS receives impulses from the receptor but effector does not receive impulses from CNS. – Tick under motor neurone cut.
Explanation:
If the sensory neurone is cut, the CNS will not receive impulses from the receptor, and the effector will not receive impulses from the CNS. If the motor neurone is cut, the CNS will still receive impulses from the receptor, but the effector will not receive impulses from the CNS.
(ii) Circle all the words that can be used to describe a reflex action.
automatic chemical conscious rapid slow
▶️Answer/Explanation
Answer:
The words to be circled are: automatic and rapid.
Explanation:
Reflex actions are automatic and rapid responses to stimuli, which do not involve conscious thought.
(b) State how impulses are passed along a neurone. (Sub-topic: B13.1)
▶️Answer/Explanation
Answer:
Impulses are passed along a neurone in the form of electrical signals.
Explanation:
Neurones transmit electrical impulses, which are generated by changes in the electrical potential across the neurone’s membrane. These impulses travel along the neurone from the dendrites, through the cell body, and down the axon to the axon terminals.
(c) Name the two parts of the central nervous system. (Sub-topic: B13.1)
▶️Answer/Explanation
Answer:
The two parts of the central nervous system are the brain and the spinal cord.
Explanation:
The central nervous system (CNS) consists of the brain and the spinal cord, which are responsible for processing and coordinating sensory information and motor responses.
(d) Muscles are one example of an effector. Name another example of an effector. (Sub-topic: B13.1)
▶️Answer/Explanation
Answer:
Another example of an effector is a gland.
Explanation:
Effectors are organs or cells that respond to stimuli by producing a response. Muscles and glands are both examples of effectors. Glands respond by secreting hormones or other substances.
Question 11
Useful hydrocarbons are obtained from petroleum.
(a) Fig. 11.1 shows the industrial process used to separate useful hydrocarbons from petroleum. (Sub-topic: C11.3)
(i) Name this process shown in Fig. 11.1.
(ii) State if chemical changes or physical changes are involved when useful hydrocarbons are obtained from petroleum in this process. Explain your answer.
(iii) Refinery gas and bitumen are obtained from petroleum. State one use of refinery gas and one use of bitumen.
(b) Explain why the measurement of boiling temperature can be used to find out whether a liquid is a pure alkane or a mixture of alkanes. (Sub-topic: C11.4)
(c) Methane and ethane are gaseous alkanes.
(i) Complete the dot-and-cross diagram of a molecule of methane. In your diagram, show: (Sub-topic: C2.5)
- the chemical symbols of the elements
- the arrangement of the outer shell electrons.
(ii) State why ethane is a saturated hydrocarbon. (Sub-topic: C11.4)
(iii) State the name of the unsaturated hydrocarbon that has only two carbon atoms in each of its molecules. (Sub-topic: C11.5)
▶️Answer/Explanation
11 (a) (i) The process shown in Fig. 11.1 is fractional distillation.
11 (a) (ii) Physical changes are involved in this process. This is because the separation of hydrocarbons is based on their different boiling points, which is a physical property. No new substances are formed during fractional distillation.
11 (a) (iii)
- Refinery gas is used for heating and cooking.
- Bitumen is used for surfacing roads and waterproofing.
11 (b) The measurement of boiling temperature can be used to determine whether a liquid is a pure alkane or a mixture of alkanes because a pure substance has a single, sharp boiling point, whereas a mixture of alkanes will have a range of boiling points due to the different boiling points of the individual components.
11 (c) (i) The dot-and-cross diagram for methane (CH4) should show:
- One carbon atom with four outer shell electrons (dots or crosses).
- Four hydrogen atoms, each with one outer shell electron (dots or crosses).
- Each hydrogen atom shares one electron with the carbon atom, forming four single covalent bonds.
11 (c) (ii) Ethane is a saturated hydrocarbon because it contains only single covalent bonds between carbon atoms, meaning it has the maximum number of hydrogen atoms bonded to the carbon atoms.
11 (c) (iii) The unsaturated hydrocarbon with only two carbon atoms in each molecule is ethene (C2H4).
Question 12
A boy swims in a heated swimming pool.
(a) Water molecules with enough energy escape from the surface of the swimming pool. Name the process in which more-energetic molecules escape from the surface of a liquid. (Sub-topic: P2.2.2)
▶️Answer/Explanation
Evaporation
(b) Fig. 12.1 shows a boy looking at an object at the bottom of the pool. A ray of light is shown from the object to the boy’s eye. The ray of light is refracted as it leaves the water. (Sub-topic: P3.2.2)
(i) Describe why the light is refracted.
▶️Answer/Explanation
The light is refracted because it changes speed as it passes from one medium (water) to another (air). This change in speed causes the light to bend at the boundary between the two media.
(ii) On Fig. 12.1, mark the angle of incidence and label with the letter \( I \).
▶️Answer/Explanation
The angle of incidence is the angle between the incident ray and the normal (a line perpendicular to the surface at the point of incidence). It should be marked and labeled with the letter \( I \).
(c) The boy stands in the swimming pool and repeatedly splashes his hand on the surface of the water to create a regular set of waves. Place the terms relating to wave properties into the correct sentence. Each word may be used once, more than once, or not at all. (Sub-topic: P3.1)
amplitude frequency speed wavefront wavelength
By splashing his hand more times per second, he will increase the …… of the waves.
By splashing his hand harder, the height of the waves increases, which means the …… has increased.
By splashing his hand more slowly, he notices that the distance between each crest of the wave has increased, which means the …… has increased.
▶️Answer/Explanation
By splashing his hand more times per second, he will increase the frequency of the waves.
By splashing his hand harder, the height of the waves increases, which means the amplitude has increased.
By splashing his hand more slowly, he notices that the distance between each crest of the wave has increased, which means the wavelength has increased.
(d) Fig. 12.2 shows the boy swimming. (Sub-topic: P1.5.1)
(i) State what happens to the swimming speed of the boy if his driving force becomes less than the frictional force.
▶️Answer/Explanation
If the driving force becomes less than the frictional force, the boy’s swimming speed will decrease (slow down).
(ii) State what happens to the swimming speed of the boy if his driving force is equal to the frictional force.
▶️Answer/Explanation
If the driving force is equal to the frictional force, the boy’s swimming speed will remain constant (no acceleration).
(e) The temperature of the water in the swimming pool is measured using a liquid-in-glass thermometer. Before the water temperature is measured, the thermometer has a reading of \(20^\circ C\). When used to measure the temperature of the water, the thermometer reading rises to \(28^\circ C\). Explain why the liquid inside the thermometer rises when the thermometer is put into the water. (Sub-topic: P2.2.2)
▶️Answer/Explanation
The liquid inside the thermometer rises because the liquid expands when it is heated. As the temperature of the water is higher than the initial temperature of the thermometer, the liquid absorbs heat and expands, causing it to rise in the thermometer’s narrow tube.
Question 13 (Subtopic: 15.3)
(a) Fig. 13.1 is a diagram of a flower.
Table 13.1 shows some of the parts labelled in Fig. 13.1.
Use Fig. 13.1 to complete Table 13.1.
▶️Answer/Explanation
(b) Describe fertilisation in plants.
▶️Answer/Explanation
13(b) ref to pollen and ovule ;
fusion of nuclei ;
(c) Name the cell formed by the fusion of the nuclei of gametes.
▶️Answer/Explanation
13(c) zygote ;
(d) State the number of parents needed for: asexual reproduction & sexual reproduction
▶️Answer/Explanation
13(d) 1 and 2 ;