Question 1
(a) (i) Subtopic: B5 Enzymes
(a) (ii) Subtopic: B5 Enzymes
(b) Subtopic: B5 Enzymes
(c) (i) Subtopic: B4 Biological molecules
(c) (ii) Subtopic: B4 Biological molecules
(a) Fig. 1.1 is a graph showing the effect of pH on an enzyme’s activity at 20 °C.
(i) State the optimum pH of this enzyme.
▶️Answer/Explanation
Answer: 9
Explanation: The optimum pH is where the enzyme shows maximum activity. From the graph, this occurs at pH 9, which is the peak of the curve.
(ii) Explain why this enzyme is inactive at pH 12.
▶️Answer/Explanation
Answer: The enzyme denatures at pH 12. The shape of the active site changes. The substrate no longer fits into the enzyme/active site.
Explanation:
- At extreme pH (like pH 12), the enzyme’s tertiary structure is disrupted, causing it to denature.
- This changes the shape of the active site.
- Since enzymes work via the lock-and-key mechanism, the substrate can no longer bind to the altered active site, making the enzyme inactive.
(b) The investigation was repeated at a temperature of 30 °C. There was an increase in enzyme activity recorded across the pH range. Explain why there is an increase in enzyme activity at 30 °C.
▶️Answer/Explanation
Answer: Particles move faster/have increased kinetic energy. At higher temperature there’s greater frequency of collisions. More successful collisions occur.
Explanation:
- Higher temperature (30°C vs 20°C) gives molecules more kinetic energy, making them move faster.
- This increases the frequency of collisions between enzyme and substrate molecules.
- More collisions have sufficient energy to overcome the activation energy barrier, leading to more successful reactions.
Note: The temperature increase is within the enzyme’s tolerance range (not causing denaturation).
(c) Enzymes are proteins.
(i) List the chemical elements that make up proteins.
▶️Answer/Explanation
Answer: carbon, hydrogen, oxygen, nitrogen
Explanation: These are the four fundamental elements found in all amino acids, which are the building blocks of proteins. Some proteins may also contain sulfur (in cysteine and methionine) but the question asks for the basic elements.
(ii) State the test for the protein and the positive result.
▶️Answer/Explanation
Answer: Test: Add Biuret solution Positive result: Solution turns purple/violet
Explanation:
- The Biuret test detects peptide bonds in proteins.
- When Biuret reagent (blue) is added to a protein solution, the copper ions in the reagent form a complex with the peptide bonds.
- This complex has a distinctive purple/violet color, indicating the presence of protein.
Question 2
(a) Subtopic: C11.7 Polymers
(b) Subtopic: C1.1 Solids, liquids and gases
(c) Subtopic: C5.1 Exothermic and endothermic reactions
(d) Subtopic: C6.2 Rate of reaction
(e) (i) Subtopic: C11.7 Polymers
(e) (ii) Subtopic: C11.5 Alkenes
Fig. 2.1 shows industrial processes carried out to make some useful materials from petroleum.
(a) Use words and phrases from the list below to name the processes A to D in Fig. 2.1.
Each word or phrase may be used once, more than once or not at all.
Process C has been named for you.
| Process | Name |
|---|---|
| A | …… |
| B | …… |
| C | catalytic addition |
| D | …… |
Word list: addition polymerisation, catalytic addition, condensation polymerisation, cracking, dehydration, electrolysis, fractional distillation, oxidation, reduction
▶️Answer/Explanation
Answer:
A: fractional distillation
B: cracking
D: addition polymerisation
Explanation:
- Process A (fractional distillation): Petroleum is separated into fractions based on boiling points.
- Process B (cracking): Large hydrocarbon molecules are broken down into smaller ones like ethene.
- Process D (addition polymerisation): Ethene monomers join to form poly(ethene) polymer.
Note: Process C is correctly given as catalytic addition (ethene + steam → ethanol).
(b) In process A petroleum is separated into mixtures of hydrocarbons, such as naphtha.
State the physical property of naphtha that enables it to be separated from the other hydrocarbon mixtures in process A.
▶️Answer/Explanation
Answer: boiling point (range)
Explanation: Fractional distillation separates hydrocarbons based on differences in their boiling points. Naphtha has a specific boiling range (30-200°C) that allows it to be collected at a particular level in the fractionating column.
(c) In process B, larger molecules are changed into smaller molecules.
The energy level diagram for this reaction is shown in Fig. 2.2.
State the type of chemical reaction that causes the type of energy change shown in Fig. 2.2. Explain your answer in terms of bond breaking and bond making.
▶️Answer/Explanation
Answer:
Type of reaction: endothermic
Explanation: Bond breaking takes in energy (endothermic) and bond formation releases energy (exothermic). More energy is taken in than given out.
Explanation:
- The diagram shows products at higher energy than reactants, indicating net energy absorption.
- Breaking C-C bonds in large hydrocarbons requires energy input (endothermic).
- While forming new bonds in smaller molecules releases energy, the overall process absorbs more energy than it releases.
(d) In process C ethene reacts with steam to produce ethanol, C2H5OH. A catalyst is used to increase the rate of reaction. State two other conditions necessary for this reaction.
▶️Answer/Explanation
Answer:
1: high temperature (~300°C)
2: high pressure (~60 atm)
Explanation: These conditions are needed because:
- High temperature provides sufficient activation energy for the reaction.
- High pressure increases collision frequency between ethene and steam molecules.
- The catalyst (phosphoric acid) works optimally under these conditions.
(e) (i) In process D poly(ethene) is formed.
The structure of poly(ethene) is shown.
(n is a large number)
Describe the formation of poly(ethene) using the terms monomer and polymer.
▶️Answer/Explanation
Answer:
Ethene is the monomer. Many ethene molecules join together to form a long-chain polymer (polyethene).
Explanation:
- Monomers are small reactive molecules (here: ethene, C2H4).
- Under addition polymerization conditions, the double bond breaks allowing monomers to link together.
- The process forms a polymer – a long molecular chain of repeating units (-CH2-CH2-).
(ii) Ethene is reactive and reacts with bromine.
Poly(ethene) is less reactive and does not react with bromine. Explain this difference.
▶️Answer/Explanation
Answer: Poly(ethene) is not an alkene/does not have double bonds/is saturated.
Explanation: Ethene has a reactive C=C double bond that undergoes addition reactions with bromine. In poly(ethene), all carbon atoms are saturated (single bonds only), making it chemically inert to bromine under normal conditions.
Question 3
(a) (i) Subtopic: P1.5 Force
(a) (ii) Subtopic: P1.3 Mass and weight
(a) (iii) Subtopic: P1.3 Mass and weight
(b) Subtopic: P1.2 Motion
(c) Subtopic: P1.6.1 Energy
(d) (i) Subtopic: P3.4 Sound
(d) (ii) Subtopic: P3.4 Sound
(a) Fig. 3.1 shows the forces acting on an aircraft.
Four forces P, Q, R and S are shown.
(i) Compare the sizes of forces Q and S when the aircraft is accelerating.
▶️Answer/Explanation
Answer: Q is greater than S
Explanation: For an aircraft to accelerate forward (Newton’s Second Law), there must be a net forward force. Q (thrust) must exceed S (drag) to produce this acceleration. The difference between these forces causes the aircraft to speed up.
(ii) State which force is the weight of the aircraft.
▶️Answer/Explanation
Answer: R
Explanation: Weight always acts vertically downward toward the center of the Earth. In the diagram, R is shown as the downward vertical force, while P is lift (upward), Q is thrust (forward), and S is drag (backward).
(iii) Complete the sentence below to describe the relationship between the mass and the weight of an object.
Weight is the effect of a ………. field on a mass.
▶️Answer/Explanation
Answer: gravitational
Explanation: Weight is the force exerted on a mass by a gravitational field (W=mg). This distinguishes it from mass, which is an intrinsic property of matter measured in kilograms.
(b) Fig. 3.2 is the speed-time graph for an aircraft during take-off.
Calculate the acceleration between 5s and 45s. Show your working. State the units of your answer.
▶️Answer/Explanation
Answer: 1.25 m/s²
Working:
1. Change in velocity = Final speed – Initial speed = 50 m/s – 0 m/s = 50 m/s
2. Time interval = 45s – 5s = 40s
3. Acceleration = Δv/Δt = 50/40 = 1.25 m/s²
Explanation: The gradient of a speed-time graph gives acceleration. Here we calculate the steepness of the linear portion between 5-45 seconds. The units are meters per second squared (m/s²), the standard unit for acceleration.
(c) State the two types of energy gained as the aircraft continues to accelerate and gain height after take-off.
▶️Answer/Explanation
Answer:
1: kinetic
2: gravitational potential
Explanation:
- Kinetic energy: Increases as velocity increases (KE=½mv²)
- Gravitational potential energy: Increases with altitude (GPE=mgh)
The aircraft gains both forms of energy simultaneously during climb.
(d) The aircraft engines are noisy. Sound waves from the engines pass through the air as a series of compressions and rarefactions.
(i) State what is meant by a compression.
▶️Answer/Explanation
Answer: A region of high pressure where particles are closer together
Explanation: In sound waves, compressions are areas where air molecules are temporarily pushed together, creating localized high pressure. This contrasts with rarefactions where molecules are spread farther apart (low pressure).
(ii) Describe the wavelength of a sound wave in terms of compressions.
▶️Answer/Explanation
Answer: The distance between two successive compressions
Explanation: Wavelength (λ) can be measured either:
- Between consecutive compressions (peak-to-peak)
- Between consecutive rarefactions (trough-to-trough)
- Or any two identical points on successive waves
This represents one complete wave cycle.
Question 4
(a) (i) Subtopic: B18.2 Food chains and food webs
(a) (ii) Subtopic: B18.2 Food chains and food webs
(a) (iii) Subtopic: B18.2 Food chains and food webs
(b) Subtopic: B18.2 Food chains and food webs
(c) Subtopic: B12 Respiration
(a) Fig. 4.1 is a diagram of a food web.
Use the food web in Fig. 4.1 to answer these questions.
(i) State the number of trophic levels in this food web.
▶️Answer/Explanation
Answer: 4
Explanation: Trophic levels represent feeding positions:
- 1st level: Producers (green algae/phytoplankton)
- 2nd level: Primary consumers (limpets/mussels)
- 3rd level: Secondary consumers (crab)
- 4th level: Tertiary consumer (herring gull)
Each step in the food chain represents a different trophic level.
(ii) Name one organism that occupies the first trophic level.
▶️Answer/Explanation
Answer: green algae / phytoplankton
Explanation: The first trophic level always consists of autotrophic producers that convert sunlight into chemical energy via photosynthesis. In aquatic ecosystems, these are typically phytoplankton or algae.
(iii) Construct a food chain that includes one tertiary consumer.
▶️Answer/Explanation
Answer: green algae → limpets → crab → herring gull
OR
phytoplankton → mussels → crab → herring gull
Explanation:
- Tertiary consumer: Herring gull (top predator)
- Correct order: Producer → Primary consumer → Secondary consumer → Tertiary consumer
- Direction: Energy flows from prey to predator (arrows should point right if drawn)
Both possible chains score full marks as they include four trophic levels with the herring gull as tertiary consumer.
(b) A disease causes a decrease in the population of mussels. Explain the effect of a decrease in mussel population on the limpet population.
▶️Answer/Explanation
Answer:
Crabs lose a source of food (mussels).
Increased predation pressure on limpets by crabs.
Explanation:
- Mussels and limpets are both primary consumers that crabs feed on.
- With fewer mussels available, crabs will consume more limpets to compensate.
- This increased predation pressure will cause the limpet population to decrease.
This demonstrates competitive exclusion and predator-prey dynamics in ecosystems.
(c) Organisms in the food web respire.
Complete the sentence to define the term respiration.
Respiration is the …… reactions in cells that break down …… molecules and release …… for metabolism.
▶️Answer/Explanation
Answer:
Respiration is the chemical reactions in cells that break
down nutrient molecules and release
energy for metabolism.
Explanation:
- Chemical: Respiration involves enzyme-controlled reactions
- Nutrient: Typically glucose but can include lipids and amino acids
- Energy: Released as ATP for cellular processes
Respiration can be aerobic (with oxygen) or anaerobic (without oxygen), but both types release energy from organic molecules.
Question 5
(a) (i) Subtopic: C6.2 Rate of reaction
(a) (ii) Subtopic: C6.2 Rate of reaction
(b) (i) Subtopic: C3.3 The mole and the Avogadro constant
(b) (ii) Subtopic: C3.3 The mole and the Avogadro constant
(c) Subtopic: C3.3 The mole and the Avogadro constant
(a) A teacher investigates the rate at which carbon dioxide is produced when dilute hydrochloric acid reacts with excess calcium carbonate powder. She uses the apparatus shown in Fig. 5.1.
The temperature of the acid is 20°C.
She measures the volume of carbon dioxide collected in the measuring cylinder every minute for 10 minutes.
Fig. 5.2 shows a graph of her results.
(i) Use ideas about colliding particles to explain the shape of the graph.
▶️Answer/Explanation
Answer:
Rate decreases over time
Acid particles are used up/concentration decreases
Frequency of collisions decreases
Explanation:
- The curve flattens because the reaction slows as reactants are consumed
- With fewer HCl particles available, collision frequency decreases (lower concentration)
- Fewer successful collisions occur per unit time, reducing CO₂ production rate
The plateau indicates reaction completion when all acid has reacted.
(ii) The teacher repeats the experiment, adding dilute hydrochloric acid at 30°C to excess calcium carbonate powder.
Sketch the graph she obtains on Fig. 5.2.
▶️Answer/Explanation
Answer:
– Steeper initial gradient
– Earlier plateau (same final volume)
Explanation:
- Steeper curve: Higher temperature increases particle kinetic energy → more frequent collisions with sufficient activation energy
- Same final volume: Total CO₂ depends on limiting reagent (HCl) quantity, not temperature
- Faster completion: Reaction reaches completion sooner at higher temperature
(b) The symbol equation for the reaction between calcium carbonate and dilute hydrochloric acid is shown.
CaCO3 + 2HCl → CaCl2 + CO2 + H2O
(i) State the volume of gas produced in 10 minutes when dilute hydrochloric acid at 20°C is added to excess calcium carbonate powder.
▶️Answer/Explanation
Answer: 0.070
Explanation: Read directly from the graph’s y-axis at t=10 minutes. The plateau shows maximum CO₂ volume collected.
(ii) Use your answer to (b)(i) to calculate the volume of dilute hydrochloric acid added to the excess calcium carbonate. Complete steps 1 to 3. Show your working.
The concentration of the dilute hydrochloric acid is 0.50 mol/dm³. The volume of 1 mole of any gas is 24 dm³ at room temperature and pressure.
Step 1
Calculate the number of moles of carbon dioxide produced.
Step 2
Calculate the number of moles of HCl reacting.
Step 3
Calculate the volume of dilute acid added.
▶️Answer/Explanation
Answer:
Step 1: 0.0029 mol
Step 2: 0.0058 mol
Step 3: 0.012 dm³
Working:
- Moles of CO₂: 0.070 dm³ ÷ 24 dm³/mol = 0.002916… mol ≈ 0.0029 mol
- Moles of HCl: From equation, 2HCl:1CO₂ ratio → 0.0029 × 2 = 0.0058 mol
- Volume of HCl: moles ÷ concentration = 0.0058 mol ÷ 0.50 mol/dm³ = 0.0116 dm³ ≈ 0.012 dm³
(c) State the ratio of the number of molecules in 1 mole of carbon dioxide to the number of molecules in 1 mole of water.
▶️Answer/Explanation
Answer: 1:1
Explanation: By definition:
- 1 mole of any substance contains Avogadro’s number of particles (6.02×10²³)
- Thus 1 mole CO₂ : 1 mole H₂O = 1:1 molecule ratio
- This holds regardless of the substances’ molecular masses
Question 6
(a) Subtopic: P1.7 Pressure
(b) Subtopic: P3.2.2 Refraction of light
(c) (i) Subtopic: P3.1 General properties of waves
(c) (ii) Subtopic: P3.1 General properties of waves
(d) (i) Subtopic: P5.2.5 Applications and safety precautions
(d) (ii) Subtopic: P5.2.2 The three types of nuclear emission
(d) (iii) Subtopic: P5.2.3 Radioactive decay
(a) Fig 6.1 shows a penguin walking on the ice in Antarctica.
The penguin has a weight of 25 N and its feet have a total area of 22 cm².
Calculate the pressure in N/m² exerted by the penguin on the ice when it is standing on both feet. Show your working.
▶️Answer/Explanation
Answer: 11,000 N/m²
Working:
1. Convert area: 22 cm² → 0.0022 m² (22 ÷ 10,000)
2. Pressure = Force ÷ Area = 25 N ÷ 0.0022 m²
3. Calculation: 25 ÷ 0.0022 = 11,363.636… ≈ 11,000 N/m²
Explanation:
- Pressure is force per unit area (P=F/A)
- SI unit conversion essential (1 m² = 10,000 cm²)
- Final answer given to 2 significant figures matching the input data precision
(b) The penguin observes a fish swimming in a pool.
Fig. 6.2 shows a ray of light going from the fish to the penguin. The ray is refracted at the surface. The angles of incidence and refraction are shown.
Calculate the refractive index of water. Show your working.
▶️Answer/Explanation
Answer: 1.3
Working:
Using Snell’s Law: n = sin(i) ÷ sin(r)
Given: i = 40°, r = 30° (example values – actual angles would be in the diagram)
Calculation: sin(40°) ÷ sin(30°) ≈ 0.6428 ÷ 0.5 ≈ 1.2856 ≈ 1.3
Explanation:
- Refractive index (n) = ratio of light speeds in two media
- Calculated using sine of angles from the normal
- Typical water refractive index ≈1.33 (experimental value may vary slightly)
(c) The penguin jumps into the pool of water and produces water waves. A 3-metre section of the pool is shown in Fig. 6.3.
(i) Show that the wavelength of the waves is 0.5 m.
▶️Answer/Explanation
Answer: 6 waves in 3 m → 3 ÷ 6 = 0.5 m per wave
Explanation: Wavelength (λ) is the distance between consecutive wave crests. The diagram likely shows 6 complete waves in the 3m section, giving λ = 3m ÷ 6 = 0.5m.
(ii) The speed of the waves produced in the pool is 1.5 m/s.
Calculate the frequency of the waves. Show your working.
▶️Answer/Explanation
Answer: 3 Hz
Working:
Wave equation: v = fλ → f = v/λ
Given: v = 1.5 m/s, λ = 0.5 m
Calculation: f = 1.5 ÷ 0.5 = 3 Hz
Explanation:
- Frequency (f) = number of waves passing a point per second
- Derived from the fundamental wave relationship
- Units in Hertz (Hz) equivalent to waves/second
(d) In the Antarctic, harmful ultraviolet radiation reaches the Earth’s surface.
(i) State one danger to living things of being exposed to large quantities of ionising radiation.
▶️Answer/Explanation
Answer: cancer / mutation
Explanation: Ionising radiation can:
- Damage DNA in cells leading to uncontrolled growth (cancer)
- Cause mutations in reproductive cells affecting offspring
- Kill cells causing radiation burns or organ failure
(ii) α-particles and β-particles are both types of ionising radiation.
State two differences between an α-particle and a β-particle.
▶️Answer/Explanation
Answer: (Any two)
1. α heavier (4 amu) vs β light (1/1840 amu)
2. α +2 charge vs β -1 charge
3. α less penetrating vs β more penetrating
4. α more ionising vs β less ionising
Explanation:
| Property | α-particle | β-particle |
|---|---|---|
| Nature | Helium nucleus (2p+2n) | High-speed electron |
| Mass | 4 atomic mass units | 1/1840 amu |
| Charge | +2e | -1e |
| Penetration | Stopped by paper | Stopped by few mm aluminum |
(iii) An isotope of an unknown element decays by β-emission to produce an isotope of silicon, which has a nucleon number of 28.
Identify the unknown element and give its full nuclide notation.
▶️Answer/Explanation
Answer: 28Al13
Explanation:
- β-decay increases atomic number by 1 while keeping same mass number
- Silicon (product) has Z=14, so parent must be Z=13 (Aluminum)
- Nuclide notation shows:
- Mass number (A=28) as superscript
- Atomic number (Z=13) as subscript
- Element symbol (Al)
Question 7
(a) Subtopic: B6.1 Photosynthesis
(b) Subtopic: B6.1 Photosynthesis
(c) Subtopic: B8.4 Translocation
(d) Subtopic: B6.1 Photosynthesis
(e) Subtopic: B8.2 Water uptake
A student investigates the need for chlorophyll in photosynthesis. He uses a variegated leaf.
Fig. 7.1 shows a variegated leaf.
The student prepares the leaf by boiling it in ethanol. He then tests the leaf for the presence of starch using iodine solution.
Table 7.1 shows his results.
| part of leaf | colour when tested with iodine solution |
|---|---|
| green part | blue-black |
| white part | orange-brown |
(a) Explain the result for the green part of the leaf.
▶️Answer/Explanation
Answer:
Green parts photosynthesize
Photosynthesis produces glucose
Glucose converted to starch
Starch turns iodine blue-black
Explanation:
- Chlorophyll in green areas absorbs light for photosynthesis
- Photosynthesis produces glucose as an immediate product
- Excess glucose is polymerized into starch for storage
- Iodine forms a blue-black complex with starch (positive test)
This confirms chlorophyll is essential for starch production via photosynthesis.
(b) Name the mineral ion needed to make chlorophyll.
▶️Answer/Explanation
Answer: magnesium
Explanation:
- Magnesium ions (Mg²⁺) form the central atom in chlorophyll molecules
- Deficiency causes chlorosis (yellowing between leaf veins)
- Other components (C,H,O,N) come from CO₂, H₂O, and NO₃⁻
(c) Starch is one carbohydrate found in plants.
Describe how carbohydrates are transported around the plant.
▶️Answer/Explanation
Answer:
Process called translocation
As sucrose solution
In phloem tissue
From source to sink
Explanation:
- Translocation: Active transport process requiring ATP
- Sucrose form: Converted from glucose for transport (less reactive)
- Phloem vessels: Living sieve tube cells with companion cells
- Source-sink: From photosynthesizing leaves (source) to growing roots/fruits (sink)
This is mass flow hypothesis demonstrated by ringing experiments.
(d) Water is one of the raw materials needed for photosynthesis.
State the chemical formula of one other raw material needed for photosynthesis.
▶️Answer/Explanation
Answer: CO₂
Explanation:
- Carbon dioxide provides carbon atoms for glucose synthesis
- Obtained through stomata from the atmosphere
- Overall equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
- Light energy and chlorophyll are requirements but not raw materials
(e) State the term used for the property of water molecules that enables them to be drawn up the xylem during transpiration.
▶️Answer/Explanation
Answer: cohesion
Explanation:
- Hydrogen bonding between water molecules creates continuous columns
- Cohesion-tension theory explains water movement:
- Transpiration pull creates tension
- Cohesive forces maintain water column
- Adhesion to xylem walls provides support
- Enables transport against gravity to heights >100m in tall trees
Question 8
(a) (i) Subtopic: C2.2 Atomic structure and the Periodic Table
(a) (ii) Subtopic: C8.2 Group I properties
(b) (i) Subtopic: C7.1 The characteristic properties of acids and bases
(b) (ii) Subtopic: C8.2 Group I properties
(c) Subtopic: C2.4 Ions and ionic bonds
Fig. 8.1 shows part of Group I of the Periodic Table.
(a) (i) State the electronic structure of a sodium atom.
▶️Answer/Explanation
Answer: 2,8,1
Explanation:
- Sodium (Na) has atomic number 11 (11 protons and 11 electrons)
- Electron configuration: 2 electrons in first shell, 8 in second shell, 1 in outer shell
- Written as K2L8M1 in some notation systems
(ii) Describe how the electronic structure of sodium is related to its group number.
▶️Answer/Explanation
Answer: Number of valence/outer shell electrons equals group number (1 for Group I)
Explanation:
- Group number indicates valence electrons (outer shell electrons available for bonding)
- All Group I elements have 1 valence electron (ns1 configuration)
- This determines chemical properties (e.g., forming +1 ions)
(b) A teacher adds Universal Indicator solution to water in a large bowl. She places a piece of sodium onto the surface of the water.
Fig. 8.2 shows the apparatus she uses.
Students notice that gas forms around the sodium and the indicator changes colour.
(i) The teacher informs her students that hydrogen and sodium hydroxide are formed by the reaction.
State and explain the change in colour of the indicator.
▶️Answer/Explanation
Answer:
Change: Green to blue/violet
Explanation: Sodium hydroxide is alkaline (pH >7)
Explanation:
- Universal Indicator color scheme:
- Green = neutral (pH7)
- Blue/violet = alkaline (pH8-14)
- Reaction: 2Na + 2H2O → 2NaOH + H2
- NaOH is a strong base that increases pH
(ii) Suggest one similarity and one difference between rubidium and sodium in their reaction with water containing Universal Indicator.
Explain your answers.
▶️Answer/Explanation
Answer:
Similarity: Both produce hydrogen/hydroxide/alkali
Explanation: Same group → same valence electron configuration
Difference: Rubidium reacts more vigorously
Explanation: Outer electron more easily lost (further from nucleus)
Explanation:
| Aspect | Sodium | Rubidium |
|---|---|---|
| Reaction speed | Moderate (melts, moves) | Violent (may ignite hydrogen) |
| Indicator change | Same color change | Same but faster |
| Reason | Increased reactivity down Group I due to:
| |
(c) Fig. 8.3 shows an incomplete diagram of part of the structure of a sodium chloride crystal.
Complete the diagram by showing the arrangement of sodium ions, Na+, and chloride ions, Cl–.
▶️Answer/Explanation
Answer: Alternating Na+ and Cl– ions in 3D cubic arrangement
Explanation:
- NaCl forms ionic lattice with:
- Each Na+ surrounded by 6 Cl–
- Each Cl– surrounded by 6 Na+
- 1:1 ratio maintained throughout
- Key features to show:
- Alternating positive and negative ions
- Regular repeating pattern
- Equal numbers of each ion
Question 9
(a) Subtopic: P2.1.2 Particle model
(b) Subtopic: P2.2 Thermal properties and temperature
(c) (i) Subtopic: P4.2.4 Resistance
(c) (ii) Subtopic: P4.2.5 Electrical energy and electrical power
(c) (iii) Subtopic: P2.1.1 States of matter
Fig. 9.1 shows a potato being baked in the oven of an electric cooker.
(a) The potato has a steel skewer (a long metal pin) pushed through it. When heated the metal skewer expands.
Explain in terms of the motion and arrangement of molecules why a solid expands less than a gas when heated.
▶️Answer/Explanation
Answer:
Particles in solids vibrate more but maintain fixed positions
Particles in gases move freely and spread further apart
Explanation:
| Property | Solid | Gas |
|---|---|---|
| Particle motion | Vibrations about fixed points | Random, high-speed movement |
| Expansion mechanism | Increased vibration amplitude slightly increases average separation | Particles overcome intermolecular forces and occupy more space |
| Expansion magnitude | Small (typically <1% per 100°C) | Large (can be several hundred percent) |
(b) A thermocouple is used to measure the temperature inside the oven.
Describe the structure of a thermocouple.
▶️Answer/Explanation
Answer: Two different metals joined together at two junctions
Explanation:
- Consists of two dissimilar metal wires (e.g., copper-constantan)
- Junctions formed at:
- Measurement junction (hot end in oven)
- Reference junction (cold end at known temperature)
- Working principle: Seebeck effect produces voltage proportional to temperature difference
(c) The cooker has one electrically heated hotplate. The hotplate uses a current of 2.0A when used with a mains voltage of 230V.
(i) Calculate the resistance of the hotplate. Show your working.
▶️Answer/Explanation
Answer: 115 Ω
Working:
Using Ohm’s Law: R = V/I
= 230V ÷ 2.0A
= 115 Ω
Explanation:
- Ohm’s Law relates voltage (V), current (I), and resistance (R)
- Standard UK mains voltage is 230V AC
- Resistance calculated to 3 significant figures matching given values
(ii) Calculate the energy supplied to the hotplate in 1200 seconds. Show your working.
▶️Answer/Explanation
Answer: 552,000 J
Working:
Using E = VIt
= 230V × 2.0A × 1200s
= 552,000 J
Explanation:
- Electrical energy formula combines power (VI) and time
- 1 Joule = 1 watt-second
- Equivalent to 0.153 kWh (kilowatt-hours)
(iii) Some water is heated in a saucepan and turns to steam. Describe the differences between water and steam in terms of the forces and distances between the molecules and the motion of the molecules.
▶️Answer/Explanation
Answer:
Water: Strong intermolecular forces, molecules closer, move around each other
Steam: Weak forces, molecules far apart, move rapidly in straight lines
Explanation:
| Property | Liquid Water | Steam (Water Vapor) |
|---|---|---|
| Intermolecular forces | Strong hydrogen bonds | Negligible (except during collisions) |
| Molecular spacing | Close together (~0.3 nm) | Far apart (several nm) |
| Molecular motion | Vibrate, rotate, and slide past neighbors | High-speed linear motion with random collisions |
| Density | 1000 kg/m³ | ~0.6 kg/m³ at 100°C |
Question 10
(a) (i) Subtopic: B9.1 Circulatory systems
(a) (ii) Subtopic: B9.2 Heart
(b) Subtopic: B11 Gas exchange in humans
(c) Subtopic: B13.3 Homeostasis
(a) Fig. 10.1 shows the circulatory system of a fish and a human.
(i) Use Fig. 10.1 to describe three ways the circulatory system of a human is different from the circulatory system of a fish.
▶️Answer/Explanation
Answer: (Any three)
1. Double circulation (blood passes heart twice per circuit) vs single circulation
2. 4-chambered heart (2 atria/2 ventricles) vs 2-chambered heart (1 atrium/1 ventricle)
3. Separated oxygenated/deoxygenated blood vs mixed blood in heart
4. Lungs vs gills as respiratory organs
Explanation:
| Feature | Human | Fish |
|---|---|---|
| Circulation type | Double (pulmonary + systemic) | Single (heart→gills→body→heart) |
| Heart chambers | 4 (complete septum) | 2 (no septum) |
| Blood mixing | None (fully separated) | Occurs in heart |
| Efficiency | Higher pressure systemic circulation | Lower pressure after gill capillaries |
(ii) State the name of the structure in the human heart that separates the left ventricle from the right ventricle.
▶️Answer/Explanation
Answer: septum
Explanation:
- Muscular wall dividing heart longitudinally
- Prevents mixing of oxygenated (left side) and deoxygenated blood (right side)
- Thicker in left ventricle to withstand higher pressures
- Defects cause conditions like ventricular septal defect (VSD)
(b) Gills are the gas exchange surface in fish.
Suggest two features that gills have that allow efficient gas exchange.
▶️Answer/Explanation
Answer: (Any two)
1. Large surface area (from gill filaments/lamellae)
2. Thin epithelium (short diffusion distance)
3. Rich blood supply (maintains concentration gradient)
4. Countercurrent flow mechanism
Explanation:
- Surface area: Folded lamellae provide ≈10× body surface area
- Thinness: Typically 1-2 cell layers thick (≈3µm)
- Vascularization: Dense capillary networks extract 80-90% of oxygen
- Countercurrent: Blood flows opposite to water maximizing O2 uptake
(c) The human circulatory system contains arterioles. Arterioles are used in the regulation of body temperature.
Describe the role of arterioles in reducing body temperature.
▶️Answer/Explanation
Answer:
Arterioles near skin surface dilate (vasodilation)
Increased blood flow to skin capillaries
More heat lost by radiation/convection
Explanation:
- Vasodilation: Smooth muscles in arteriole walls relax, increasing lumen diameter
- Blood redistribution: Up to 30% cardiac output directed to skin
- Heat transfer:
- Warmer blood reaches superficial capillaries
- Heat conducted through skin layers
- Lost to environment via infrared radiation/convection
- Controlled by hypothalamus through sympathetic nerves
Question 11
(a) Subtopic: C9.6 Extraction of metals
(b) (i) Subtopic: C9.6 Extraction of metals
(b) (ii) Subtopic: C6.3 Redox
(c) Subtopic: C9.6 Extraction of metals
(d) (i) Subtopic: C9.6 Extraction of metals
(d) (ii) Subtopic: C9.5 Corrosion of metals
Fig. 11.1 shows a blast furnace used to extract iron from iron oxide.
(a) State the substance that reacts with oxygen in the blast furnace.
▶️Answer/Explanation
Answer: carbon / coke
Explanation:
- Coke (impure carbon) burns to produce heat and carbon monoxide
- Primary reaction: 2C + O2 → 2CO (exothermic)
- Also forms carbon dioxide: C + O2 → CO2
- Reaches temperatures up to 1500°C in the furnace
(b) (i) Identify the reducing agent that is formed in the blast furnace.
▶️Answer/Explanation
Answer: carbon monoxide
Explanation:
- CO is the active reducing agent for iron oxide
- Formed by: CO2 + C → 2CO (Boudouard reaction)
- Reduces Fe2O3 stepwise to Fe
(ii) Iron(III) oxide consists of iron ions, Fe3+, and oxide ions, O2-.
Use ideas about atoms, ions and electron transfer to explain how iron (III) oxide is reduced to iron.
▶️Answer/Explanation
Answer:
Fe3+ ions gain electrons
Forming Fe atoms
Explanation:
- Reduction is gain of electrons (OIL RIG)
- Overall reaction: Fe2O3 + 3CO → 2Fe + 3CO2
- Half-reactions:
- Reduction: Fe3+ + 3e– → Fe
- Oxidation: CO + O2- → CO2 + 2e–
(c) Complete the sentences, using words from the list below, to describe how acidic impurities are removed in the blast furnace. Each word or phrase may be used once, more than once or not at all.
Calcium carbonate decomposes to …… and …… …… at the high temperature in the blast furnace.
Acidic impurities such as …… react with …… to form molten …… .
Word list: air, calcium carbonate, calcium oxide, carbon, carbon dioxide, iron, silicon dioxide, slag
▶️Answer/Explanation
Answer:
Calcium carbonate decomposes to calcium oxide and carbon dioxide
Acidic impurities such as silicon dioxide react with calcium oxide
to form molten slag
Explanation:
- Decomposition: CaCO3 → CaO + CO2 (endothermic, ≈900°C)
- Neutralization: CaO + SiO2 → CaSiO3 (calcium silicate)
- Slag:
- Melts at furnace temperatures
- Floats on molten iron for easy separation
- Used in road construction/cement
(d) (i) Explain why a blast furnace cannot be used to extract aluminium from aluminium oxide.
▶️Answer/Explanation
Answer: aluminium is too reactive
Explanation:
- Al is higher in reactivity series than C
- Carbon cannot reduce Al2O3 (E° = -1.66V vs Fe3+/Fe = -0.04V)
- Requires electrolysis (Hall-Héroult process) with cryolite
(ii) Explain why aluminium appears to be resistant to corrosion.
▶️Answer/Explanation
Answer: oxide layer on surface
Explanation:
- Forms thin, adherent Al2O3 layer (2-3nm thick)
- Self-healing – reforms instantly if scratched
- Impermeable to oxygen/water
- Unlike iron oxide (rust) which is porous and flakes off
Question 12
(a) Subtopic: P1.6.4 Power
(b) Subtopic: P4.2.2 Electric current
(c) (i) Subtopic: P4.5.5 The d.c. motor
(c) (ii) Subtopic: P4.5.3 Magnetic effect of current
(c) (iii) Subtopic: P4.5.4 Force on a current-carrying conductor
(a) Fig. 12.1 shows a gardener using a leaf-blower.
Fig. 12.2 shows the energy input and outputs for the leaf-blower.
Calculate the efficiency of the leaf-blower as a percentage. Show your working.
▶️Answer/Explanation
Answer: 37.5%
Working:
Efficiency = (useful energy output ÷ total energy input) × 100
= (3 ÷ 8) × 100
= 37.5%
Explanation:
- Efficiency measures how much input energy is converted to useful output
- Always expressed as percentage (0-100%)
- Typical leaf blowers are 30-40% efficient due to:
- Air resistance
- Motor heat losses
- Sound energy
- Vibration
(b) When used the leaf-blower takes a current of 3.0A.
Calculate the charge that flows through the leaf-blower when it is used for 180 seconds. Show your working.
▶️Answer/Explanation
Answer: 540 C
Working:
Charge (Q) = Current (I) × Time (t)
= 3.0 A × 180 s
= 540 C
Explanation:
- 1 Coulomb = 1 Amp × 1 second
- This equals ≈3.36×10²¹ electrons flowing
- Practical implications:
- Higher current or longer use → more charge transferred
- Battery capacity often rated in Amp-hours (1 Ah = 3600 C)
(c) The leaf-blower contains a small electric motor powered by a battery.
Fig. 12.3 shows a simple electric motor powered by a battery.
(i) State the name of the component labelled Q on Fig. 12.3.
▶️Answer/Explanation
Answer: split ring commutator
Explanation:
- Function:
- Reverses current direction every half-rotation
- Maintains unidirectional torque
- Construction:
- Two semicircular copper segments
- Insulated from each other
- Connects to coil via brushes
- Differs from slip rings (AC motors)
(ii) Draw an arrow on Fig. 12.3 to show the direction of the magnetic field.
▶️Answer/Explanation
Answer: Arrow from N pole to S pole of permanent magnet
Explanation:
- Magnetic field lines:
- Exit North pole, enter South pole
- Continuous loops through magnet
- Right-hand rule:
- Thumb points N→S outside magnet
- Fingers show field direction
- Affects motor rotation direction (Fleming’s Left Hand Rule)
(iii) Explain why the coil moves when an electric current passes through it.
▶️Answer/Explanation
Answer:
Current creates magnetic field around coil
Interaction with permanent magnet’s field
Force acts on current-carrying conductor (Fleming’s Left Hand Rule)
Explanation:
- Motor effect: Charged particles moving in magnetic field experience force
- Field interaction:
- Coil field is circular (right-hand grip rule)
- Permanent magnet field is N→S
- Resultant field causes attraction/repulsion
- Force calculation: F = BILsinθ
- B = magnetic flux density
- I = current
- L = conductor length
Question 13
(a) Subtopic: P2.1.2 Particle model
(b) Subtopic: P2.1.2 Particle model
A student investigates the effect of temperature on the movement of red dye through water.
She adds one drop of red dye to the centre of the water in a Petri dish. She measures the time taken for the dye to move to the edge of the Petri dish. She repeats this with water at different temperatures.
Fig. 13.1 shows the apparatus used.
Table 13.1 shows her results.
| temperature/°C | time taken for dye to move to the edge/s |
|---|---|
| 5 | 321 |
| 40 | 98 |
| 80 | 55 |
(a) Use the results in Table 13.1 to describe the relationship between temperature and the time taken for the dye to move to the edge.
▶️Answer/Explanation
Answer: As temperature increases, the time decreases
Explanation:
- Inverse relationship shown quantitatively:
- 5°C → 321s
- 40°C → 98s (≈3.3× faster)
- 80°C → 55s (≈5.8× faster than 5°C)
- Non-linear relationship – greater effect at higher temperatures
- Consistent with kinetic theory predictions
(b) Explain, in terms of particles, the movement of the red dye through the water.
▶️Answer/Explanation
Answer:
Dye particles move randomly (Brownian motion)
From high to low concentration (down gradient)
Until evenly distributed
Explanation:
- Diffusion mechanism:
- Dye molecules collide with water molecules
- Gain kinetic energy from water molecules
- Move in random directions (zig-zag path)
- Temperature effect:
- Higher temperature → faster water molecules
- More energetic collisions with dye particles
- Increased particle speed (KE=½mv²)
- Net movement:
- Initially high concentration at center
- Random motion causes net movement outward
- Equilibrium reached when uniform concentration