Question 1
(a)(i)-(ii): Subtopic: B9.2 Heart
(b)(i): Subtopic: B7.1 Diet
(b)(ii): Subtopic: B16.1 Chromosomes and genes
(c): Subtopic: B16.2 Cell division
(a) A student monitors his pulse rate at rest and during exercise.
Table 1.1 shows the results.
| Activity | Pulse rate/beats per minute |
|---|---|
| At rest | 64 |
| During exercise | 122 |
(i) Calculate the difference between his pulse rate at rest and during exercise.
▶️Answer/Explanation
Answer: 58 beats per minute
Explanation: The difference is calculated by subtracting the pulse rate at rest from the pulse rate during exercise: 122 – 64 = 58 beats per minute.
(ii) Complete the sentences to explain the results in Table 1.1.
During exercise, the pulse rate increases because the heart is pumping blood ……
The pumping action is caused by contraction of the …… wall of the heart.
To provide the body with more energy, the process of …… increases.
This process requires increased blood flow to the cells to deliver more …… and ……
▶️Answer/Explanation
Answer:
During exercise, the pulse rate increases because the heart is pumping blood faster.
The pumping action is caused by contraction of the muscular wall of the heart.
To provide the body with more energy, the process of (aerobic) respiration increases.
This process requires increased blood flow to the cells to deliver more glucose and oxygen.
Explanation: During exercise, the body’s demand for energy increases, leading to faster heart rate and respiration to supply more oxygen and glucose to cells.
(b) Genetic predisposition and sex are both risk factors for coronary heart disease.
(i) Describe two dietary recommendations to follow to reduce the risk of developing coronary heart disease.
▶️Answer/Explanation
Answer: Any two of the following:
- Don’t consume too much fat.
- Don’t consume too much salt.
- Don’t consume excessive alcohol.
- Consume a balanced diet.
- Consume plenty of fibre.
Explanation: A healthy diet low in saturated fats, salt, and alcohol can help reduce the risk of coronary heart disease by maintaining healthy blood pressure and cholesterol levels.
(ii) Males are more likely to develop coronary heart disease than females. State the sex chromosomes in males.
▶️Answer/Explanation
Answer: XY
Explanation: Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).
(c) Male gametes are produced by meiosis.
Describe two ways in which the cells produced by meiosis are different from the cells produced by mitosis.
▶️Answer/Explanation
Answer: Any two of the following:
- Genetically different (to each other).
- Contain half the number of chromosomes (haploid).
Explanation: Meiosis produces gametes with genetic variation and half the chromosome number, while mitosis produces identical diploid cells for growth and repair.
Question 2
(a): Subtopic: C10.2 Air quality and climate
(b)(i)-(iii): Subtopic: C6.2 Rate of reaction
(c)(i)-(ii): Subtopic: C5.1 Exothermic and endothermic reactions
Clean air contains nitrogen gas and oxygen gas.
(a) State the percentage of nitrogen gas and oxygen gas in clean air.
▶️Answer/Explanation
Answer:
nitrogen gas = 78%
oxygen gas = 21%
Explanation:
Clean, dry air at Earth’s surface is approximately 78% nitrogen and 21% oxygen. The remaining 1% consists of other gases like argon, carbon dioxide, and trace gases.
(b) In a car engine, nitrogen gas and oxygen gas react together. Nitrogen monoxide, NO, is made.
(i) Construct the balanced symbol equation for this reaction.
▶️Answer/Explanation
Answer:
N2 + O2 → 2NO
Explanation:
The equation shows one nitrogen molecule (N2) reacting with one oxygen molecule (O2) to form two molecules of nitrogen monoxide (NO). The equation is balanced with equal numbers of each type of atom on both sides.
(ii) The rate of this reaction increases as the temperature inside the car engine increases. Explain why. Use ideas about collisions between particles.
▶️Answer/Explanation
Answer:
At higher temperatures, particles move faster and have more kinetic energy. More particles have sufficient energy (activation energy) to react when they collide, increasing the rate of successful collisions.
Explanation:
The collision theory states that for a reaction to occur, particles must collide with sufficient energy (activation energy) and proper orientation. Higher temperature increases both the frequency of collisions and the energy of collisions, making more collisions successful.
(iii) The rate of this reaction increases as the concentration of the oxygen gas increases. Explain why. Use ideas about collisions between particles.
▶️Answer/Explanation
Answer:
Higher concentration means more oxygen particles per unit volume. This increases the frequency of collisions between nitrogen and oxygen particles, leading to more successful collisions per unit time.
Explanation:
Concentration affects the number of particles in a given volume. More particles in the same space means they are closer together and collide more frequently, increasing the reaction rate.
(c) A catalytic converter removes nitrogen monoxide from the exhaust emissions of a car. Nitrogen monoxide reacts with carbon monoxide. Nitrogen and carbon dioxide are made.
Look at the equation for this reaction. It shows all the atoms and all the bonds.
2N = O + 2C ≡ O → N ≡ N + 2O = C = O
(i) Draw a circle around each set of bonds which are broken when the reaction takes place.
▶️Answer/Explanation
Answer:
Circle the triple bonds in 2N≡O and 2C≡O
Explanation:
In the reactants (left side), the triple bonds between N and O in NO and between C and O in CO are broken during the reaction. These are the N≡O and C≡O bonds.
(ii) When nitrogen monoxide reacts with carbon monoxide, the reaction is exothermic. Explain why. Use ideas about bond breaking and bond making.
▶️Answer/Explanation
Answer:
1. Breaking bonds requires energy (endothermic)
2. Making new bonds releases energy (exothermic)
3. More energy is released in bond making than absorbed in bond breaking
Explanation:
In an exothermic reaction, the energy released when new bonds form (N≡N and C=O) is greater than the energy required to break the original bonds (N≡O and C≡O). The net result is energy being released to the surroundings.
Question 3
(a)(i)-(ii): Subtopic: P1.6.1 Energy
(b)(i)-(iii): Subtopic: P1.5 Force
(c): Subtopic: P1.4 Density
(d)(i)-(ii): Subtopic: P1.5.1 Effects of forces
Fig. 3.1 shows a 35 kg child sliding down a long wire called a zipline.
(a) The child moves from point X to point Y.
Point X is 18 m vertically above point Y.
(i) Show that as the child moves from point X to point Y, the change in gravitational potential energy is 6300 J.
The gravitational field strength, g, is 10 N/kg.
▶️Answer/Explanation
GPE = mgh = 35 × 10 × 18 = 6300 J
(ii) As the child moves from point X to point Y, she gains kinetic energy before being slowed by a braking system.
The speed of the child at point Y is 14 m/s.
Calculate the kinetic energy of the child at point Y.
▶️Answer/Explanation
KE = ½mv² = ½ × 35 × 14² = 3430 J
(b) The zipline uses a thick cable made of steel. The zipline’s steel cable heats up as the child slides from point X to point Y.
(i) State the name of the force which causes the steel cable to heat up.
▶️Answer/Explanation
friction
(ii) State the name of the process that transfers thermal energy in steel.
▶️Answer/Explanation
conduction
(iii) Describe, in terms of particles, how energy is transferred by the process named in (b)(ii).
▶️Answer/Explanation
Vibrations pass from particle to particle. Free electrons gain kinetic energy and transfer it through collisions.
(c) Fig. 3.2 shows a section of the zipline’s steel cable.
The section of steel cable has a mass of 4.2 kg and a volume of 5.0 × 10⁻⁴ m³.
Calculate the density of the steel cable.
▶️Answer/Explanation
Density = mass/volume = 4.2/5.0×10⁻⁴ = 8400 kg/m³
(d) Fig. 3.3 shows an extension-load graph for the steel cable.
(i) On Fig. 3.3, label the limit of proportionality with a P.
▶️Answer/Explanation
Mark P where the graph stops being linear
(ii) Use Fig. 3.3 to calculate the spring constant of the steel cable in N/m.
▶️Answer/Explanation
k = F/x = 100,000/0.0005 = 200,000,000 N/m
Question 4
(a)(i)-(iv): Subtopic: B18.3 Carbon cycle
(b)(i): Subtopic: B7.1 Diet
(b)(ii): Subtopic: B4. Biological molecules
(a) Fig. 4.1 is a diagram of the carbon cycle.
(i) Identify process E in Fig. 4.1.
▶️Answer/Explanation
Answer: fossilisation
Explanation: Process E represents the long-term storage of carbon in fossil fuels, which occurs through the fossilisation of dead organisms over millions of years.
(ii) Draw one arrow on Fig. 4.1 to represent the process of feeding.
▶️Answer/Explanation
Answer: An arrow drawn from “carbon in plants” to “carbon in animals.”
Explanation: Feeding represents the transfer of carbon from plants (producers) to animals (consumers) when animals consume plants or other animals.
(iii) State the balanced chemical equation for the process occurring at A in Fig. 4.1.
▶️Answer/Explanation
Answer: \(6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2\)
Explanation: Process A is photosynthesis, where carbon dioxide and water are converted into glucose and oxygen using sunlight energy.
(iv) Name process D in Fig. 4.1 and describe its effect on the atmosphere.
▶️Answer/Explanation
Answer:
- Name: combustion (of fossil fuels)
- Effect: increases concentration of carbon dioxide in the atmosphere
Explanation: Process D represents the burning of fossil fuels, which releases stored carbon back into the atmosphere as CO₂, contributing to the greenhouse effect.
(b) The element carbon is found in proteins.
(i) Name one disease caused by protein-energy malnutrition.
▶️Answer/Explanation
Answer: kwashiorkor or marasmus
Explanation: These are conditions resulting from insufficient protein intake, common in areas with food scarcity.
(ii) Name the smaller molecules that proteins are made from.
▶️Answer/Explanation
Answer: amino acids
Explanation: Proteins are polymers composed of chains of amino acids linked by peptide bonds.
Question 5
(a): Subtopic: C2.2 Atomic structure and the Periodic Table
(b)(i)-(ii): Subtopic: C2.4 Ions and ionic bonds
(c): Subtopic: C8.3 Group VII properties
(d)(i)-(ii): Subtopic: C2.4 Ions and ionic bonds
(a) Table 5.1 shows some information about particles found in atoms.
Complete Table 5.1.
| Particle | Relative Mass | Charge |
|---|---|---|
| electron | …… | …… |
| proton | …… | +1 |
| neutron | 1 | …… |
▶️Answer/Explanation
Answer:
| Particle | Relative Mass | Charge |
|---|---|---|
| electron | almost 0 / negligible / 1/1836 | -1 |
| proton | 1 | +1 |
| neutron | 1 | 0 (no charge) |
Explanation:
- Electrons have a very small mass compared to protons and neutrons, often considered negligible.
- Protons have a relative mass of 1 and a charge of +1.
- Neutrons have a relative mass of 1 and no charge (neutral).
(b) Fig. 5.1 shows a sodium atom.
(i) A sodium atom, Na, can form a sodium ion, Na+. Describe how a sodium atom forms a sodium ion.
▶️Answer/Explanation
Answer: The sodium atom loses one electron.
Explanation: Sodium (Na) has 11 electrons, with 1 electron in its outermost shell. To achieve a stable electron configuration, it loses this single electron, forming a Na+ ion with a +1 charge.
(ii) Write a balanced ionic half-equation to show how a sodium atom forms a sodium ion. Use e– to represent an electron.
▶️Answer/Explanation
Answer: Na → Na+ + e–
Explanation: This half-equation shows the sodium atom (Na) losing one electron (e–) to form a sodium ion (Na+).
(c) Table 5.2 gives some information about three halogens.
Complete Table 5.2.
| Halogen | Atomic Number | Electronic Structure |
|---|---|---|
| fluorine | 9 | …… |
| chlorine | 17 | 2.8.7 |
| bromine | …… | 2.8.18.7 |
▶️Answer/Explanation
Answer:
| Halogen | Atomic Number | Electronic Structure |
|---|---|---|
| fluorine | 9 | 2.7 |
| chlorine | 17 | 2.8.7 |
| bromine | 35 | 2.8.18.7 |
Explanation:
- Fluorine (atomic number 9) has 9 electrons arranged as 2 in the first shell and 7 in the second shell (2.7).
- Bromine is in the same group as chlorine and has an atomic number of 35. Its electronic structure includes 2, 8, 18, and 7 electrons in successive shells.
(d) Sodium, Na, reacts with chlorine, Cl2, to make sodium chloride, NaCl.
(i) Construct the balanced symbol equation for this reaction.
▶️Answer/Explanation
Answer: 2Na + Cl2 → 2NaCl
Explanation: Sodium (Na) reacts with chlorine gas (Cl2) to form sodium chloride (NaCl). The equation is balanced with 2 sodium atoms reacting with 1 chlorine molecule to produce 2 sodium chloride units.
(ii) Sodium chloride, NaCl, is an ionic compound. Draw a dot-and-cross diagram to show the bonding in sodium chloride. Include the charges on the ions.
▶️Answer/Explanation
Answer:
Where:
- Na+ is represented with no outer electrons (lost 1 electron).
- Cl– is represented with 8 outer electrons (gained 1 electron).
Explanation: In NaCl, sodium donates one electron to chlorine, forming Na+ and Cl– ions. The dot-and-cross diagram shows the transfer of the electron and the resulting charges.
Question 6
(a): Subtopic: P1.3 Mass and weight
(b): Subtopic: P1.2 Motion
(c)(i)-(iii): Subtopic: P4.3.2 Series and parallel circuits
Fig. 6.1 shows a baby elephant born in a wildlife sanctuary. The elephant is undergoing a routine health check.
(a) Explain what is wrong with the statement “the weight of the elephant is 480 kg”.
▶️Answer/Explanation
480 kg is the mass / weight should be in Newtons.
(b) The top speed for a fully grown elephant is 11 m/s. Calculate the maximum distance that can be covered by an elephant in 120 seconds.
▶️Answer/Explanation
(d =) v×t or 11 × 120; 1320 (m).
(c) The wildlife sanctuary uses enclosures to keep the elephants safe. Fig. 6.2 shows an enclosure surrounded by four lamps.
The lamps are connected in parallel. A switch controls the a.c. power supply to the lamps.
(i) Complete the circuit diagram to show the lamps connected in parallel. Include the switch in your diagram. The a.c. power supply has been drawn for you.
▶️Answer/Explanation
Switch controls all lamps; 4 lamps in parallel and all else correct.
(ii) The current through the a.c. power supply is 16A. Draw a circle around the correct current through each lamp.
2A 4A 16A 32A 64A
▶️Answer/Explanation
4 A.
(iii) The potential difference across each lamp is 240V. Calculate the power output of each lamp.
▶️Answer/Explanation
(P =) IV / 4 × 240; 960 (W).
Question 7
(a)(i)-(ii): Subtopic: B8.3 Transpiration
(b)(i)-(ii): Subtopic: B8.1 Xylem and phloem
(c): Subtopic: B6.2 Leaf structure
(d): Subtopic: B8.4 Translocation
(a) A student investigates the effect of temperature on the rate of transpiration.
(i) Complete Fig. 7.1 by:
- labelling the x-axis
- drawing a line to predict the expected results.
▶️Answer/Explanation
X-axis labelled “temperature”. Line showing increasing rate of transpiration with temperature, possibly levelling off at higher temperatures.
(ii) The investigation is repeated at a greater humidity. Explain the effect of increasing humidity on the rate of transpiration.
▶️Answer/Explanation
Transpiration rate decreases because higher humidity reduces the water potential gradient between the leaf and air, resulting in less evaporation of water from stomata.
(b) Transpiration is the loss of water vapour from the leaves.
(i) Explain why transpiration causes a column of water to move upwards in the xylem.
▶️Answer/Explanation
Transpiration creates a pull (tension) that draws water up through the xylem, aided by cohesion between water molecules and adhesion to xylem walls.
(ii) State the term that describes how water molecules are held together.
▶️Answer/Explanation
Cohesion
(c) Name two cells in leaves that are adapted for gas exchange.
▶️Answer/Explanation
1. Guard cells 2. Spongy mesophyll cells
(d) The process of translocation is also used in plants. Draw three lines from the word translocation to the boxes on the right to make three correct sentences.
▶️Answer/Explanation
1. occurs in the phloem 2. involves the movement of amino acids 3. transports substances to regions of storage in a plant
Question 8
(a): Subtopic: C10.1 Water
(b): Subtopic: C3.3 The mole and the Avogadro constant
(c): Subtopic: C12.5 Identification of ions and gases
(d)(i)-(ii): Subtopic: C6.2 Rate of reaction
(e)(i)-(ii): Subtopic: C6.2 Rate of reaction
Plants need three essential elements: nitrogen, phosphorus and potassium. These elements are found in fertilisers.
(a) Describe why it is important that farmers use fertilisers containing nitrogen, phosphorus and potassium.
▶️Answer/Explanation
Fertilisers replenish essential nutrients (nitrogen, phosphorus, potassium) in the soil that are depleted by plant growth. These nutrients are crucial for:
- Nitrogen: Protein synthesis and chlorophyll production (for healthy leaf growth)
- Phosphorus: Root development and energy transfer in plants
- Potassium: Disease resistance and fruit quality
Without these nutrients, plants show stunted growth, discolored leaves, and reduced yields.
(b) Potassium sulfate, K2SO4, is a fertiliser that contains potassium. A student makes some potassium sulfate. He reacts potassium carbonate, K2CO3, with sulfuric acid. Look at the equation for this reaction:
K2CO3 + H2SO4 → K2SO4 + CO2 + H2O
The student uses 2.76 g of potassium carbonate. Calculate the mass of potassium sulfate the student makes. Show your working.
[Ar: C, 12; H, 1; K, 39; O, 16; S, 32]
▶️Answer/Explanation
3.48 g
Working:
1. Calculate relative formula masses:
K2CO3 = (2×39) + 12 + (3×16) = 138
K2SO4 = (2×39) + 32 + (4×16) = 174
2. Using the 1:1 mole ratio from the equation:
138 g K2CO3 → 174 g K2SO4
2.76 g K2CO3 → (174/138) × 2.76 = 3.48 g K2SO4
(c) Another student checks that a sample of fertiliser contains potassium. She uses a flame test. Describe how she will know if the fertiliser contains potassium.
▶️Answer/Explanation
The flame will turn lilac/purple if potassium is present.
(d) Ammonia is used to make some fertilisers. Ammonia is made from nitrogen and hydrogen.
N2 + 3H2 ⇌ 2NH3
(i) The use of a catalyst reduces the cost of making ammonia. Explain how.
▶️Answer/Explanation
The catalyst increases the reaction rate, allowing ammonia to be produced faster at lower temperatures, which reduces energy costs.
(ii) The reaction between nitrogen and hydrogen is reversible. Explain what is meant by a reversible reaction.
▶️Answer/Explanation
A reversible reaction can proceed in both directions (reactants → products and products → reactants) under the same conditions.
(e) Fig. 8.1 shows the percentage of ammonia made at different temperatures and pressures.
Look at Fig. 8.1.
(i) Describe how the percentage of ammonia made changes as the temperature increases.
▶️Answer/Explanation
The percentage of ammonia decreases as temperature increases (the reaction is exothermic, so lower temperatures favor the forward reaction).
(ii) State a temperature and pressure which would make 40% of ammonia.
▶️Answer/Explanation
Any one of these pairs:
- 350°C and 125 atm
- 400°C and 210 atm
- 450°C and 325 atm
Question 9
(a)(i)-(ii): Subtopic: P2.1.2 Particle model
(b)(i)-(ii): Subtopic: P3.2.3 Thin converging lens
(c)(i)-(ii): Subtopic: P3.3 Electromagnetic spectrum
A student investigates the motion of pollen grains in water seen through a microscope.
The student observes that the pollen grains constantly move short distances in random directions.
(a) Fig. 9.1 shows the pollen grains suspended in water.
(i) State the name given to the motion of these pollen grains.
▶️Answer/Explanation
Brownian (motion)
(ii) Explain why the pollen grains constantly move short distances in random directions.
▶️Answer/Explanation
ref to collisions (of pollen grains); with, light fast-moving particles / water particles or molecules
(b) The microscope uses a thin converging lens to produce an image. Fig. 9.2 shows a thin converging lens.
(i) Draw a ray diagram on Fig. 9.2 to show the formation of a real image. Label the image with the word image.
▶️Answer/Explanation
(ii) The image formed is a real image. Describe one difference between a real image and a virtual image.
▶️Answer/Explanation
real image can be projected on to a screen / is formed when rays of light actually meet / ORA
(c) The visible light that passes through the lens is part of the electromagnetic spectrum.
(i) State the speed of visible light in a vacuum.
▶️Answer/Explanation
3 × 10⁸ m / s
(ii) γ-rays and radio waves are also part of the electromagnetic spectrum. Place ticks (✓) in the boxes in Table 9.1 to show which statements are true for γ-rays and radio waves.
▶️Answer/Explanation
| | γ-rays | radio waves | |—|—|—| | is used in communication | ✓ | | | is used in medicine | ✓ | | | can cause cancer | ✓ | | | is higher frequency than visible light | ✓ | | | has a longer wavelength than visible light | ✓ | |
Question 10
Subtopic: B11. Gas exchange in humans
The percentage of the population of males and females in different age groups with chronic obstructive pulmonary disease (COPD) in one country is recorded.
Fig. 10.1 shows a graph of the results.
(a) Use evidence from Fig. 10.1 to suggest two risk factors associated with COPD in this country.
▶️Answer/Explanation
Answers:
1. Age (prevalence increases with age)
2. Sex (males have higher prevalence than females in most age groups)
Explanation:
The graph shows that COPD prevalence increases significantly with age, particularly after 45 years. Additionally, males consistently show higher percentages than females across most age groups, indicating sex is a risk factor. These are the two most evident risk factors visible from the graph data.
(b) The percentage of the population of males and females in different age groups with COPD in one other country is recorded. The country has a higher percentage of tobacco smokers across all age groups. Describe and explain the difference you would expect to see in the results.
▶️Answer/Explanation
Answer:
You would expect to see higher percentages of COPD across all age groups in the country with more smokers because smoking is a major cause of COPD.
Explanation:
Smoking damages lung tissue and is the primary cause of COPD. With more smokers in the population, the incidence of COPD would be higher in all age categories. The graph would show elevated percentages for both males and females at every age level compared to the original country’s data.
(c) Table 10.1 shows some components of tobacco smoke and their effects. Complete Table 10.1.
| Component of tobacco smoke | Effect |
|---|---|
| …… | causes addiction |
| carbon monoxide | …… |
| …… | causes cancer |
▶️Answer/Explanation
Completed Table:
| Component of tobacco smoke | Effect |
|---|---|
| nicotine | causes addiction |
| carbon monoxide | reduces oxygen carrying capacity of blood |
| tar | causes cancer |
Explanation:
1. Nicotine is the addictive substance in tobacco that causes dependence.
2. Carbon monoxide binds irreversibly to hemoglobin, reducing oxygen transport.
3. Tar contains carcinogens that can lead to lung and other cancers.
(d) Smoking also causes an increased concentration of carbon dioxide in the blood. State the effect of an increased concentration of carbon dioxide in the blood on the gas exchange system.
▶️Answer/Explanation
Answer:
Increased breathing rate
Explanation:
Higher CO₂ levels are detected by chemoreceptors, which stimulate the medulla to increase breathing rate. This is the body’s attempt to remove excess CO₂ and maintain proper blood pH.
(e) State the name of the specialised cells that protect the gas exchange system by removing mucus.
▶️Answer/Explanation
Answer:
Ciliated epithelial cells
Explanation:
These cells line the airways and have hair-like cilia that beat in coordinated waves to move mucus (containing trapped particles and pathogens) upward and out of the respiratory tract.
Question 11
(a): Subtopic: C11.4 Alkanes
(b): Subtopic: C11.3 Fuels
(c): Subtopic: C11.3 Fuels
(d): Subtopic: C11.4 Alkanes
(e): Subtopic: C3.3 The mole and the Avogadro constant
Fractional distillation of petroleum makes useful fractions. Three of these fractions are gasoline, gas oil and refinery gas.
(a) Refinery gas contains butane, \( C_4H_{10} \). Draw a diagram to show the structure of butane.
▶️Answer/Explanation
Butane is an alkane with the molecular formula \( C_4H_{10} \). Its structure can be represented as follows:
H H H H
| | | |
H-C-C-C-C-H
| | | |
H H H H
This is a straight-chain structure where each carbon atom is bonded to the maximum number of hydrogen atoms, fulfilling the tetravalency of carbon.
(b) Fractional distillation makes too much gas oil and not enough gasoline. Cracking breaks large hydrocarbon molecules into smaller molecules.
State two conditions needed for cracking.
▶️Answer/Explanation
The two conditions needed for cracking are:
- High temperature: Typically around 450–750°C to provide the energy required to break the covalent bonds in the large hydrocarbon molecules.
- Catalyst: Usually a zeolite catalyst is used to lower the activation energy and increase the rate of the reaction.
(c) Cracking involves the breaking of covalent bonds within molecules. Fig. 11.1 shows the structure of dodecane.
The cracking of dodecane makes a mixture of products. Explain why.
▶️Answer/Explanation
Dodecane (\( C_{12}H_{26} \)) is a large hydrocarbon molecule. During cracking, the covalent bonds within the molecule can break at various points along the carbon chain, leading to the formation of smaller hydrocarbon molecules. Since the breaking can occur randomly, a mixture of products such as alkanes (e.g., octane, \( C_8H_{18} \)) and alkenes (e.g., ethene, \( C_2H_4 \)) is produced. This randomness in bond breaking results in a variety of products rather than a single specific product.
(d) Dodecane has the formula \( C_{12}H_{26} \). During cracking, dodecane can make octane, \( C_8H_{18} \), and ethene, \( C_2H_4 \). Ethene is an alkene. Alkenes have the general formula \( C_nH_{2n} \). Dodecane and octane are alkanes. State the general formula of the alkanes.
▶️Answer/Explanation
The general formula for alkanes is \( C_nH_{2n+2} \), where \( n \) is the number of carbon atoms in the molecule. This formula indicates that alkanes are saturated hydrocarbons with single bonds between carbon atoms and the maximum number of hydrogen atoms attached.
(e) In an experiment, 114 g of octane react with oxygen. The mass of carbon dioxide gas made is 352 g. Calculate the volume occupied by 352 g of carbon dioxide gas. Show your working. The volume of one mole of any gas is 24 dm³ at room temperature and pressure (r.t.p.). [\( A_r \): C, 12; O, 16]
▶️Answer/Explanation
Step 1: Calculate the molar mass of \( CO_2 \).
\( CO_2 = 12 + (2 \times 16) = 44 \, \text{g/mol} \).
Step 2: Determine the number of moles of \( CO_2 \) produced.
\( \text{Moles of } CO_2 = \frac{352 \, \text{g}}{44 \, \text{g/mol}} = 8 \, \text{moles} \).
Step 3: Calculate the volume of \( CO_2 \) at r.t.p.
\( \text{Volume} = 8 \, \text{moles} \times 24 \, \text{dm}^3/\text{mole} = 192 \, \text{dm}^3 \).
Final Answer: The volume occupied by 352 g of \( CO_2 \) is \( \boxed{192 \, \text{dm}^3} \).
Question 12
(a)-(b): Subtopic: P4.5.6 The transformer
(c): Subtopic: P4.5.3 Magnetic effect of current
(d)(i)-(ii): Subtopic: P5.2.2 The three types of nuclear emission
(a) Fig. 12.1 shows a transformer.
(i) On Fig. 12.1, label the soft-iron core with an X.
▶️Answer/Explanation
The soft-iron core should be labeled with an X in the center of the transformer.
(ii) The transformer has 17 turns on the primary coil and 8 turns on the secondary coil. Calculate the output voltage when the a.c. power supply has an e.m.f. of 34,000 V.
Assume the transformer has an efficiency of 100%.
▶️Answer/Explanation
16,000 V
(b) Fig. 12.2 shows a current-carrying solenoid.
On Fig. 12.2, draw the magnetic field pattern, including direction, around the solenoid.
▶️Answer/Explanation
Draw parallel field lines inside the solenoid with arrows pointing from north to south pole, and curved field lines outside.
(c) The radioactive isotope uranium-238 decays into an isotope of thorium by emitting an α-particle.
(i) Use the correct nuclide notation to complete the decay equation for uranium-238.
▶️Answer/Explanation
²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂α
(ii) Suggest why an α-particle is deflected when moving through a magnetic field.
▶️Answer/Explanation
Because it is a charged particle (positive charge) and moving charges experience force in magnetic fields.