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Question 1

A student investigates the effect of placing strips of potato in water and different concentrations of sugar solution. Table 1.1 shows the results.

Table 1.1

Concentration of sugar solution /mol dm^-3	Length of potato strip at the start of the investigation /mm	Length of the potato strip at the end of the investigation /mm	Change in length of potato strip /mm
0.0 (water)	49.5	52.5
0.2	50.0	52.0	+2.0
0.4	50.5	51.5	+1.0
0.6	50.0	50.5	+0.5
0.8	49.0	48.0	-1.0
1.0	49.5	47.5	-2.0

Question 1(a) (Subtopic – B3.2)

Calculate the change in length of the potato strip in water.

▶️Answer/Explanation

Answer: 3.0 mm

Solution:

The change in length is calculated by subtracting the initial length from the final length.

Change in length = Final length – Initial length

Change in length = 52.5 mm – 49.5 mm = 3.0 mm

Question 1(b) (Subtopic – B3.2)

Use Table 1.1 to suggest the concentration of sugar solution inside the cells of the potato.

▶️Answer/Explanation

Answer: Between 0.6 and 0.8 mol dm^-3

Solution:

The concentration of sugar solution inside the potato cells can be estimated by finding the concentration where there is no net change in length. From the table, the change in length is zero around 0.6 to 0.8 mol dm^-3. Therefore, the concentration inside the potato cells is likely between 0.6 and 0.8 mol dm^-3.

Question 1(c) (Subtopic – B3.2)

Explain why the potato strip immersed in a 0.2 mol dm^-3 sugar solution increased in length by completing the sentences.

The potato strip has a …… water potential than the sugar solution.

Water moves into the potato strip by ……

from an area of …… water potential to ……

water potential through the …… membrane.

▶️Answer/Explanation

Answer:

The potato strip has a higher water potential than the sugar solution.

Water moves into the potato strip by osmosis.

from an area of high water potential to low water potential through the partially permeable membrane.

Question 1(d)(i) (Subtopic – B3.2)

Describe and explain the appearance of the cell shown in Fig. 1.1.

▶️Answer/Explanation

Answer: The cell is plasmolyzed; the cell membrane has pulled away from the cell wall due to water loss by osmosis.

Solution:

The cell in Fig. 1.1 appears plasmolyzed. This means the cell membrane has pulled away from the cell wall due to water loss by osmosis. This occurs because the external solution has a lower water potential than the cell sap, causing water to move out of the cell.

Question 1(d)(ii) (Subtopic – B3.2)

Suggest which concentration of sugar solution in Table 1.1 this cell was immersed in.

▶️Answer/Explanation

Answer: 0.8 or 1.0 mol dm^-3

Solution:

Since the cell is plasmolyzed, it must have been immersed in a solution with a higher concentration than the cell sap. From Table 1.1, the concentrations that cause a decrease in length (plasmolysis) are 0.8 and 1.0 mol dm^-3.

Question 1(e) (Subtopic – B3.2)

State two uses of water in a plant.

▶️Answer/Explanation

Solution:

1. Photosynthesis: Water is a raw material in the process of photosynthesis, where it is split to produce oxygen and hydrogen.

2. Transport: Water is used to transport minerals and nutrients from the roots to other parts of the plant through the xylem.

Question 2

Chlorine and bromine are Group VII elements of the Periodic Table. Chlorine is more reactive than bromine.

Question 2(a) (Subtopic – C8.3)

State the names of the two products made when aqueous chlorine reacts with aqueous potassium bromide solution.

▶️Answer/Explanation

Solution:

Chlorine is more reactive than bromine, so it will displace bromine from potassium bromide. The reaction is:

Cl₂ + 2KBr → 2KCl + Br₂

The two products are potassium chloride and bromine.

Answer: Potassium chloride and bromine.

Question 2(b)(i) (Subtopic – C2.5)

Chlorine reacts with hydrogen to form hydrogen chloride. Hydrogen chloride is a covalent compound. Explain why hydrogen chloride is a gas at room temperature. Use ideas about structure and bonding.

▶️Answer/Explanation

Solution:

Hydrogen chloride (HCl) is a simple covalent molecule. It exists as a gas at room temperature because:

It has weak intermolecular forces (van der Waals forces) between molecules.
These weak forces require very little energy to overcome, so HCl molecules can easily separate and exist as a gas at room temperature.

Answer: Hydrogen chloride has weak intermolecular forces, which require little energy to overcome, allowing it to exist as a gas at room temperature.

Question 2(b)(ii) (Subtopic – C7.1)

Hydrogen chloride gas dissolves in water to form dilute hydrochloric acid. Describe the effect of dilute hydrochloric acid on litmus paper.

▶️Answer/Explanation

Solution:

Dilute hydrochloric acid is a strong acid. When it comes into contact with litmus paper:

Blue litmus paper turns red, indicating the presence of an acid.
Red litmus paper remains red, as acids do not change the color of red litmus paper.

Answer: Dilute hydrochloric acid turns blue litmus paper red.

Question 2(b)(iii) (Subtopic – C7.1)

State the formula of the ion present in all acids. Choose from the list:

Cl^–, H⁺, OH^–, O^2-

▶️Answer/Explanation

Solution:

All acids contain the H⁺ ion (hydrogen ion), which is responsible for their acidic properties.

Answer: H⁺

Question 2(c) (Subtopic – C3.3)

A solution of dilute hydrochloric acid has a concentration of 73 g/dm³. Calculate the mass of hydrogen chloride in 250 cm³ of the solution.

▶️Answer/Explanation

Solution:

First, convert 250 cm³ to dm³:

250 cm³ = 250 ÷ 1000 = 0.25 dm³

Now, calculate the mass of hydrogen chloride:

Mass = Concentration × Volume

Mass = 73 g/dm³ × 0.25 dm³ = 18.25 g

Answer: 18.25 g

Question 2(d)(i) (Subtopic – C11.5)

Bromine reacts with ethene. Fig. 2.1 shows the structures of the reactants and products in this reaction.

Put a circle around each of the bonds which are made when the reaction takes place.

▶️Answer/Explanation

Solution:

In the reaction between ethene (C₂H₄) and bromine (Br₂), the double bond in ethene breaks, and two new C-Br bonds are formed. The bonds made are the two C-Br bonds in the product, 1,2-dibromoethane.

Answer: The two C-Br bonds in the product are the bonds made during the reaction.

Question 2(d)(ii) (Subtopic – C5.1)

2(d)(ii) [C5.1 Exothermic and Endothermic Reactions]

When ethene reacts with bromine, the reaction is exothermic. Explain why the reaction of ethene and bromine is exothermic. Use ideas about bond breaking and bond making.

▶️Answer/Explanation

Solution:

The reaction is exothermic because:

Energy is required to break the C=C double bond in ethene and the Br-Br bond in bromine (endothermic process).
Energy is released when new C-Br bonds are formed (exothermic process).
The energy released during bond formation is greater than the energy required to break the bonds, so the overall reaction is exothermic.

Answer: The reaction is exothermic because more energy is released during bond formation than is absorbed during bond breaking.

Question 3

Carbon-14 is an unstable isotope which decays to produce nitrogen-14.

Question 3(a)

State what is meant by an isotope.

▶️Answer/Explanation

Answer: Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

Explanation: Isotopes have the same atomic number (same number of protons) but different mass numbers (different number of neutrons). For example, Carbon-12 and Carbon-14 are isotopes of carbon.

Question 3(b)

Use the correct nuclide notation to complete the symbol equation for this decay process.

\[ ^{14}C \rightarrow \underline{\hspace{2cm}} + \underline{\hspace{2cm}} \]

▶️Answer/Explanation

Answer: \[ ^{14}C \rightarrow ^{14}N + \beta^- \]

Explanation: Carbon-14 undergoes beta decay, where a neutron in the nucleus is converted into a proton, emitting a beta particle (electron) and an antineutrino. The resulting nucleus is Nitrogen-14.

Question 3(c)

Fig. 3.1 shows the percentage of carbon-14 in a sample.

Use Fig. 3.1 to determine the half-life of carbon-14.

▶️Answer/Explanation

Answer: 5700 years

Explanation: The half-life of carbon-14 is the time it takes for half of the carbon-14 atoms in a sample to decay. From the graph, the time taken for the percentage of carbon-14 to reduce from 100% to 50% is approximately 5700 years.

Question 3(d)(i)

On Fig. 3.2, write “gamma” in the correct position.

▶️Answer/Explanation

Answer: Gamma should be written in the leftmost box of the electromagnetic spectrum.

Explanation: Gamma rays have the highest frequency and shortest wavelength in the electromagnetic spectrum, so they belong to the leftmost position.

Question 3(d)(ii)

State the speed of the gamma rays produced by radioactive decay.

▶️Answer/Explanation

Answer: \(3 \times 10^8 \, \text{m/s}\)

Explanation: Gamma rays, like all electromagnetic waves, travel at the speed of light in a vacuum, which is approximately \(3 \times 10^8 \, \text{m/s}\).

Question 3(d)(iii)

A gamma ray has a wavelength of \(2.0 \times 10^{-11} \, \text{m}\). Use your answer to (d)(ii) to calculate the frequency of this gamma ray. State the unit for your answer.

▶️Answer/Explanation

Answer: \(1.5 \times 10^{19} \, \text{Hz}\)

Explanation: The frequency (\(f\)) of a wave is given by the equation \(f = \frac{c}{\lambda}\), where \(c\) is the speed of light and \(\lambda\) is the wavelength. Substituting the values, \(f = \frac{3 \times 10^8}{2.0 \times 10^{-11}} = 1.5 \times 10^{19} \, \text{Hz}\).

Question 3(d)(iv)

Draw lines to match each form of electromagnetic radiation to its use.

Form of electromagnetic radiation	Uses
Infrared	Remote controls and intruder alarms
Microwaves	Satellite television and telephones
Radiowaves	Radio and TV communications
X-rays	Medicine and security

▶️Answer/Explanation

Answer:

Infrared → Remote controls and intruder alarms
Microwaves → Satellite television and telephones
Radiowaves → Radio and TV communications
X-rays → Medicine and security

Explanation: Infrared radiation is used in remote controls and security systems. Microwaves are used in satellite communication and mobile phones. Radiowaves are used for broadcasting radio and TV signals. X-rays are used in medical imaging and security scanning.

Question 3(e)

All electromagnetic waves are transverse waves. Sound is an example of a longitudinal wave. Give one difference between transverse and longitudinal waves.

▶️Answer/Explanation

Answer: In transverse waves, the vibrations are perpendicular to the direction of energy transfer, whereas in longitudinal waves, the vibrations are parallel to the direction of energy transfer.

Explanation: Transverse waves, such as electromagnetic waves, have oscillations perpendicular to the direction of wave propagation. Longitudinal waves, such as sound waves, have oscillations parallel to the direction of wave propagation.

Sub Topic Codes

3(a): C2.3 Isotopes
3(b): P5.2 Radioactivity
3(c): P5.2.4 Half-life
3(d)(i): P3.3 Electromagnetic spectrum
3(d)(ii): P3.3 Electromagnetic spectrum
3(d)(iii): P3.3 Electromagnetic spectrum
3(d)(iv): P3.3 Electromagnetic spectrum
3(e): P3.1 General properties of waves

Question 4(Subtopic – B18.2)

Question4(a)

Complete the definition of the term ecosystem.

An ecosystem is defined as a unit containing all of the …… and their environment, …… together, in a given area.

▶️Answer/Explanation

Answer: organisms; interacting

Explanation: An ecosystem is a community of living organisms (plants, animals, and microbes) in conjunction with the non-living components of their environment (such as air, water, and mineral soil), interacting as a system. These biotic and abiotic components are linked together through nutrient cycles and energy flows.

Question4(b)

Fig. 4.1 is part of a food web. Use Fig. 4.1 to answer the following questions.

Question4(b)(i)

State the number of trophic levels in this food web.

▶️Answer/Explanation

Answer: 4

Explanation: The food web consists of four trophic levels: producers (plants), primary consumers (herbivores), secondary consumers (carnivores that eat herbivores), and tertiary consumers (carnivores that eat other carnivores).

Question4(b)(ii)

Name the general term given to the type of organisms that occupy the first trophic level.

▶️Answer/Explanation

Answer: producers

Explanation: The first trophic level in a food web is occupied by producers, which are organisms that produce their own food through photosynthesis, such as plants, algae, and some bacteria.

Question 4(b)(iii)

Name the organism that feeds at the 2nd and 3rd trophic level.

▶️Answer/Explanation

Answer: blackbirds

Explanation: Blackbirds are omnivores that feed on both primary consumers (herbivores) and secondary consumers (carnivores), placing them at both the 2nd and 3rd trophic levels.

Question 4(b)(iv)

Explain why there are fewer numbers of organisms in the 3rd trophic level than in the 2nd trophic level.

▶️Answer/Explanation

Answer: Any three from: energy is lost between the trophic levels; energy lost by respiration, movement, heat, or excretion; not all the organism is eaten or digested; not enough energy for larger numbers of organisms.

Explanation: As energy is transferred from one trophic level to the next, a significant amount of energy is lost as heat through respiration, movement, and other metabolic processes. Additionally, not all parts of an organism are consumed or digested, leading to further energy loss. This energy loss limits the number of organisms that can be supported at higher trophic levels, resulting in fewer organisms in the 3rd trophic level compared to the 2nd.

Question 4(c)

Wheat is a type of crop plant. The statements outline how artificial selection is used to improve yield of crop plants such as wheat. The yield is the amount of wheat crop produced in a given area. They are not in the correct order. Write numbers next to the statements to show the correct order. The first one has been done for you.

This process is repeated over many generations.
The offspring are observed and those that produce the highest yield are chosen and bred again.
Eventually the entire population of wheat plants will produce high yields.
Wheat plants are observed to see which produce the highest yield.	1
These wheat plants are crossed to produce offspring.

▶️Answer/Explanation

Answer: 4, 3, 5, 1, 2

Explanation: The correct order of steps in artificial selection is as follows:

Wheat plants are observed to see which produce the highest yield.
These wheat plants are crossed to produce offspring.
The offspring are observed and those that produce the highest yield are chosen and bred again.
This process is repeated over many generations.
Eventually the entire population of wheat plants will produce high yields.

Question 4(d)

State two ways that artificial selection is different from natural selection.

▶️Answer/Explanation

Answer: Any two from: traits are selected by humans in artificial selection; traits are selected by the environment in natural selection; artificial selection is faster; natural selection occurs over longer periods; artificial selection often reduces genetic diversity.

Explanation: Artificial selection involves humans selecting specific traits in organisms for breeding, often for economic or aesthetic reasons. In contrast, natural selection is driven by environmental pressures, where organisms with advantageous traits are more likely to survive and reproduce. Artificial selection can produce results more quickly than natural selection, which occurs over much longer timescales. Additionally, artificial selection often reduces genetic diversity as it focuses on specific traits, whereas natural selection can maintain or increase genetic diversity.

Question 5 (Subtopic – C9)

Question 5(a)

State two properties of transition metals that are not properties of all metals.

▶️Answer/Explanation

Answer: Any two from: high density; high melting point; form coloured compounds; act as catalysts.

Explanation: Transition metals have unique properties that distinguish them from other metals. They typically have high densities and high melting points. Additionally, they often form coloured compounds due to the presence of partially filled d-orbitals, which allow for the absorption of specific wavelengths of light. Many transition metals also act as catalysts in chemical reactions, speeding up the rate of reaction without being consumed.

Question 5(b)

Iron is extracted from iron(III) oxide, Fe₂O₃, in an industrial process. Two of the stages in the process are:

1. C + CO₂ → 2CO

2. Fe₂O₃ + 3CO → 2Fe + 3CO₂

Question 5(b)(i)

Suggest one hazard associated with stage 1.

▶️Answer/Explanation

Answer: Carbon monoxide is poisonous / toxic.

Explanation: In stage 1, carbon (C) reacts with carbon dioxide (CO₂) to produce carbon monoxide (CO). Carbon monoxide is a highly toxic gas that can cause serious health issues, including death, if inhaled in large quantities. It binds to hemoglobin in the blood, reducing the blood’s ability to carry oxygen.

Question 5(b)(ii)

In stage 2, iron(III) ions are reduced to iron atoms. Explain, in terms of electrons, why this is a reduction reaction.

▶️Answer/Explanation

Answer: Iron(III) ions gain electrons.

Explanation: Reduction is the gain of electrons. In stage 2, iron(III) ions (Fe³⁺) gain electrons to form iron atoms (Fe). This process is represented by the half-equation: Fe³⁺ + 3e^– → Fe. The gain of electrons by the iron(III) ions is what makes this a reduction reaction.

Question 5(b)(iii)

Complete and balance the half equation for the reaction in 5(b)(ii).

▶️Answer/Explanation

Answer: Fe³⁺ + 3e^– → Fe

Explanation: The half-equation for the reduction of iron(III) ions to iron atoms involves the gain of three electrons by each iron(III) ion. The balanced half-equation is: Fe³⁺ + 3e^– → Fe. This shows that each iron(III) ion gains three electrons to form a neutral iron atom.

Question 5(b)(iv)

In stage 2, 32 kg of iron(III) oxide, Fe₂O₃, is added to 17.5 kg of carbon monoxide, CO. The balanced symbol equation is shown.

Fe₂O₃ + 3CO → 2Fe + 3CO₂

Calculate the moles of iron(III) oxide and the number of moles of carbon monoxide. Use your answers to explain why iron(III) oxide is the limiting reactant. Show your working.

▶️Answer/Explanation

Answer: Moles of iron(III) oxide = 200; Moles of carbon monoxide = 625; Iron(III) oxide is the limiting reactant because there is less than 1/3 of the number of moles of CO.

Explanation:

Moles of Fe₂O₃: M_r of Fe₂O₃ = 160; Moles = mass / M_r = 32,000 g / 160 = 200 moles.
Moles of CO: M_r of CO = 28; Moles = mass / M_r = 17,500 g / 28 = 625 moles.
According to the balanced equation, 1 mole of Fe₂O₃ reacts with 3 moles of CO. Therefore, 200 moles of Fe₂O₃ would require 600 moles of CO. Since there are 625 moles of CO available, Fe₂O₃ is the limiting reactant because it will be completely consumed before all the CO is used up.

Question 6 (Subtopic – P1.6)

Question 6(a)

Draw a around each energy source which is non-renewable.

coal

hydroelectric

natural gas

solar

tidal

wind

▶️Answer/Explanation

Answer: coal; natural gas

Explanation: Non-renewable energy sources are those that cannot be replenished in a short period of time. Coal and natural gas are fossil fuels, which take millions of years to form and are therefore considered non-renewable. Hydroelectric, solar, tidal, and wind energy are renewable as they are derived from natural processes that are continuously replenished.

Question 6(b)

Fig. 6.1 shows a diagram of a geothermal power station. Cold water is heated by hot rocks to produce steam which drives a turbine that turns a generator. The geothermal power station can generate 0.72 kJ of electrical energy from 6.0 kJ of thermal energy.

Question 6(b)(i)

Calculate the efficiency of the geothermal power station.

▶️Answer/Explanation

Answer: 12%

Explanation: Efficiency is calculated using the formula: Efficiency = (useful output energy / total input energy) × 100%. Here, the useful output energy is 0.72 kJ, and the total input energy is 6.0 kJ. Therefore, Efficiency = (0.72 kJ / 6.0 kJ) × 100% = 12%.

Question 6(b)(ii)

Suggest an environmental advantage of using geothermal energy instead of coal to generate electricity.

▶️Answer/Explanation

Answer: Does not release greenhouse gases/carbon dioxide/cause global warming/climate change.

Explanation: Geothermal energy is a clean and sustainable energy source that does not emit greenhouse gases or contribute to global warming. In contrast, burning coal releases significant amounts of carbon dioxide and other pollutants, which contribute to climate change and air pollution.

Question 6(c)

The power station uses a large a.c. generator. Fig. 6.2 shows a simple a.c. generator.

Question 6(c)(i)

Define the term electromotive force (e.m.f.).

▶️Answer/Explanation

Answer: Energy supplied by a source in driving charge around a complete circuit.

Explanation: Electromotive force (e.m.f.) is the energy provided by a power source (such as a battery or generator) per unit charge that passes through it. It is the work done by the source in moving a unit charge around a complete circuit, measured in volts (V).

Question 6(c)(ii)

Describe how turning the coil produces an a.c. output from the coil.

▶️Answer/Explanation

Answer: Coil cuts magnetic field/experiences a changing magnetic field; direction of induced current/emf changes every half turn.

Explanation: When the coil is rotated in a magnetic field, it cuts through the magnetic field lines, inducing an electromotive force (emf) in the coil according to Faraday’s law of electromagnetic induction. As the coil rotates, the direction of the induced current changes every half turn, producing an alternating current (a.c.) output.

Question 6(c)(iii)

Name the component labelled X in Fig. 6.2. Describe two functions of component X in this generator.

▶️Answer/Explanation

Answer: slip-ring(s); to prevent wires tangling; to maintain electrical contact.

Explanation: The component labelled X is a slip-ring. Its functions include:

Preventing the wires from tangling as the coil rotates.
Maintaining electrical contact between the rotating coil and the external circuit, ensuring a continuous flow of current.

Question 7 (Subtopic – B15)

Question 7(a)

Fig. 7.1 is a drawing of a sperm cell.

Question 7(a)(i)

Identify the part labelled X in Fig. 7.1.

▶️Answer/Explanation

Answer: cell membrane

Explanation: The part labelled X in the sperm cell is the cell membrane, which is the outer layer that encloses the cell and controls the movement of substances in and out of the cell.

Question 7(a)(ii)

Table 7.1 compares some of the features of sperm and egg cells. Complete Table 7.1.

feature	sperm cell	egg cell
relative size
motility
relative number released

▶️Answer/Explanation

Answer: (relative size) small and large; (motility) motile and non-motile; (relative number released) many and few.

Explanation:

Relative size: Sperm cells are small, while egg cells are large.
Motility: Sperm cells are motile (can move), while egg cells are non-motile (cannot move).
Relative number released: Many sperm cells are released during ejaculation, while only one or a few egg cells are released during ovulation.

Question 7(a)(iii)

State one adaptive feature of egg cells.

▶️Answer/Explanation

Answer: jelly coat/energy stores

Explanation: Egg cells have a jelly coat that protects them and helps in the fertilization process. They also contain energy stores in the form of yolk, which provides nutrients for the developing embryo after fertilization.

Question 7(b)

The box on the left contains the beginning of a sentence about human sperm nuclei. The boxes on the right contain some sentence endings. Draw three lines from the box on the left to three boxes on the right to make three correct sentences.

are diploid.

are haploid.

are produced by mitosis.

contain unpaired chromosomes.

contain 23 chromosomes.

contain 2 sets of chromosomes.

contain 23 pairs of chromosomes.

▶️Answer/Explanation

Answer: are haploid; contain unpaired chromosomes; contain 23 chromosomes.

Explanation: Human sperm nuclei are haploid, meaning they contain half the number of chromosomes (23) compared to diploid cells. They contain unpaired chromosomes, as they are the result of meiosis, which reduces the chromosome number by half. Therefore, sperm cells contain 23 chromosomes, not 23 pairs.

Question 7(c)

State the name of the cell produced when fertilisation occurs.

Answer:

▶️Answer/Explanation

Answer: zygote

Explanation: When fertilization occurs, the sperm cell and egg cell fuse to form a zygote. The zygote is the initial cell formed when two gamete cells (sperm and egg) are joined by means of sexual reproduction.

Question 8 (Subtopic – C11)

Question 8(a)

Propene is an alkene. Put a tick (✓) in the box next to the statement which describes alkenes.

Alkenes are saturated polymers.
Alkenes are saturated hydrocarbons.
Alkenes are unsaturated polymers.
Alkenes are unsaturated hydrocarbons.

▶️Answer/Explanation

Answer: Alkenes are unsaturated hydrocarbons ticked.

Explanation: Alkenes are hydrocarbons that contain at least one carbon-carbon double bond, making them unsaturated. They are not polymers, as polymers are large molecules composed of repeating monomer units.

Question 8(b)

Propane is an alkane. Propane and propene are both gases. Describe a test to show which gas is propane.

▶️Answer/Explanation

Answer: test: aqueous bromine; result with propane: no change / aqueous bromine stays orange or yellow; result with propene: aqueous bromine is decolourised / aqueous bromine changes from orange or yellow to colourless.

Explanation:

Test: Add aqueous bromine to the gas.
Result with propane: Propane is a saturated hydrocarbon and does not react with bromine, so the bromine solution remains orange or yellow.
Result with propene: Propene is an unsaturated hydrocarbon and reacts with bromine, causing the bromine solution to decolourise (change from orange or yellow to colourless).

Question 8(c)

Propene is used to make poly(propene). Draw the bonds to complete the structures of propene and poly(propene) in Fig. 8.1.

H CH₃

n C C ⟶

H H

H CH₃

C C

H H ⁄ n

▶️Answer/Explanation

Answer: C=C in propene; C—C in poly(propene); all else correct.

Explanation:

Propene: The structure of propene includes a carbon-carbon double bond (C=C). The correct structure is CH₂=CH-CH₃.
Poly(propene): The structure of poly(propene) is formed by the polymerization of propene, resulting in a long chain of carbon atoms with single bonds (C—C). The correct structure is (CH₂-CH(CH₃))_n.

Question 8(d)

Poly(propene) is made by addition polymerisation. Nylon is made by condensation polymerisation. Describe two differences between addition and condensation polymerisation.

▶️Answer/Explanation

Answer: Any two from: addition polymerisation requires one monomer / condensation polymerisation requires two monomers; addition polymerisation produces a polymer only / condensation polymerisation produces a polymer molecule and a small molecule.

Explanation:

Addition polymerisation: This process involves the joining of monomers (usually containing a double bond) without the loss of any atoms or molecules. It typically requires only one type of monomer and produces only the polymer as the product.
Condensation polymerisation: This process involves the joining of monomers with the elimination of small molecules such as water or methanol. It usually requires two different types of monomers and produces both the polymer and a small molecule as by-products.

Question 9 (Subtopic – P1.2)

Question 9(a)

A car travels at 12 m/s for 15 seconds. The driver applies the brakes which brings the car to rest after 25 seconds of braking. The deceleration is constant.

Question 9(a)(i)

On the grid, draw a speed/time graph for this car’s journey.

▶️Answer/Explanation

Answer: Horizontal line drawn at 12 m/s for 15 s; straight line drawn from 12 m/s to 0 m/s taking 25 s.

Explanation:

The car travels at a constant speed of 12 m/s for the first 15 seconds, so the graph will show a horizontal line at 12 m/s from time 0 to 15 seconds.
After 15 seconds, the car decelerates uniformly to rest over the next 25 seconds. The graph will show a straight line decreasing from 12 m/s at 15 seconds to 0 m/s at 40 seconds (15 + 25).

Question 9(a)(ii)

Show that the deceleration of the car during the braking period is 0.48 m/s².

▶️Answer/Explanation

Answer: (a =) 12 / 25 (= 0.48 m/s²)

Explanation: Deceleration is calculated using the formula: a = (v – u) / t, where v is the final velocity (0 m/s), u is the initial velocity (12 m/s), and t is the time taken (25 s). Therefore, a = (0 – 12) / 25 = -0.48 m/s². The negative sign indicates deceleration, but the magnitude is 0.48 m/s².

Question 9(a)(iii)

The mass of the car is 1200 kg. Calculate the size of the braking force.

▶️Answer/Explanation

Answer: 576 N

Explanation: Force is calculated using Newton’s second law: F = ma, where m is the mass (1200 kg) and a is the deceleration (0.48 m/s²). Therefore, F = 1200 kg × 0.48 m/s² = 576 N.

Question 9(a)(iv)

The braking distance of the car is 150 m. Using your answer from 9(a)(iii) calculate the work done by the brakes.

▶️Answer/Explanation

Answer: 86,400 J

Explanation: Work done is calculated using the formula: W = F × d, where F is the force (576 N) and d is the distance (150 m). Therefore, W = 576 N × 150 m = 86,400 J.

Question 9(b)

Describe the main energy transfer that happens when the car brakes.

from …… energy to …… energy

▶️Answer/Explanation

Answer: kinetic; thermal

Explanation: When the car brakes, the kinetic energy of the car is converted into thermal energy due to friction between the brake pads and the wheels. This thermal energy is dissipated as heat into the surroundings.

Question 10

An athlete monitors their pulse rate at rest and during exercise. Fig. 10.1 shows the results.

Question 10(a)(i) (Subtopic – B9.2)

Explain the results shown in Fig. 10.1.

▶️Answer/Explanation

Answer: The pulse rate increases during exercise because the heart pumps more blood to deliver oxygen and glucose to the muscles, which are working harder.

Explanation: During exercise, the muscles require more oxygen and glucose to produce energy through respiration. The heart rate increases to pump more blood, which carries oxygen and nutrients, to the muscles. This also helps remove carbon dioxide and other waste products produced during exercise.

Question 10(a)(ii) (Subtopic – B9.2)

Describe the action of the different parts of the heart that make the heart pump blood.

▶️Answer/Explanation

Answer: The atria contract to push blood into the ventricles, and then the ventricles contract to pump blood out of the heart to the lungs and the rest of the body.

Explanation: The heart pumps blood through a series of coordinated contractions. First, the atria contract to fill the ventricles with blood. Then, the ventricles contract to pump blood out of the heart. The right ventricle pumps blood to the lungs for oxygenation, and the left ventricle pumps oxygenated blood to the rest of the body.

Question 10(a)(iii) (Subtopic – B9.2)

State the name of the structures in the heart that ensure the blood only flows one way.

▶️Answer/Explanation

Answer: Valves

Explanation: Valves in the heart, such as the atrioventricular (AV) valves and semilunar valves, ensure that blood flows in one direction, preventing backflow.

Question 10(b)(i) (Subtopic – B9.3)

Fig. 10.2 shows a blood vessel. State the name of the type of blood vessel shown in Fig. 10.2.

▶️Answer/Explanation

Answer: Artery

Explanation: The blood vessel shown has a thick wall and a narrow lumen, which are characteristic features of an artery. Arteries carry oxygenated blood away from the heart at high pressure.

Question 10(b)(ii) (Subtopic – B9.3)

Explain how each of the features adapt the blood vessel for its function.

Thick wall:

Narrow lumen:

▶️Answer/Explanation

Answer:

Thick wall: Withstands high pressure of blood.
Narrow lumen: Maintains high blood pressure.

Explanation: The thick wall of an artery contains elastic fibers and smooth muscle, which allow it to withstand and maintain the high pressure of blood pumped from the heart. The narrow lumen helps maintain this high pressure, ensuring efficient blood flow to tissues.

Question 11

A student investigates the reaction between zinc, Zn, and dilute hydrochloric acid, HCl. Zinc chloride, ZnCl₂, and hydrogen gas are made.

Question 11(a) (Subtopic – C6.2)

Write the balanced symbol equation for this reaction.

▶️Answer/Explanation

Answer: Zn + 2HCl → ZnCl₂ + H₂

Explanation: Zinc reacts with hydrochloric acid to produce zinc chloride and hydrogen gas. The equation is balanced by ensuring the number of atoms of each element is the same on both sides of the equation.

Question 11(b)(i) (Subtopic – C6.2)

The student does the experiment three times. The student uses dilute hydrochloric acid with the same concentration each time. Fig. 11.1 shows the student’s results. State which reaction took the longest to finish. Choose from experiments 1, 2 or 3.

▶️Answer/Explanation

Answer: Experiment 2

Explanation: Experiment 2 took the longest to finish because the volume of hydrogen gas produced over time increases more slowly compared to experiments 1 and 3, indicating a slower reaction rate.

Question 11(b)(ii) (Subtopic – C6.2)

In all three experiments, the student keeps the same: volume of dilute hydrochloric acid, concentration of dilute hydrochloric acid, size pieces of zinc. State one variable that could have been changed from experiment 1 to produce the results in experiment 2. Explain your answer.

▶️Answer/Explanation

Answer: Temperature

Explanation: A lower temperature in experiment 2 could have slowed down the reaction rate. Lower temperatures reduce the kinetic energy of the particles, leading to fewer effective collisions per unit time, which slows the reaction.

Question 11(b)(iii) (Subtopic – C6.2)

The student uses 1g of zinc in experiment 1. Suggest the mass of zinc used in experiment 3.

▶️Answer/Explanation

Answer: 0.5 g

Explanation: Experiment 3 likely used half the mass of zinc (0.5 g) compared to experiment 1 (1 g), as the volume of hydrogen gas produced in experiment 3 is approximately half that of experiment 1, indicating a proportional relationship between the mass of zinc and the volume of hydrogen gas produced.

Question 11(c) (Subtopic – C9.3)

Brass is an alloy made when zinc is mixed with copper. State which diagram shows the structure of brass.

▶️Answer/Explanation

Answer: Diagram D

Explanation: Brass is an alloy of zinc and copper, and Diagram D shows a mixture of two different types of atoms (zinc and copper) arranged in a regular pattern, which is characteristic of an alloy.

Question 11(d) (Subtopic – C9.1)

Copper metal is a good conductor of electricity. Explain why copper is a good conductor of electricity.

▶️Answer/Explanation

Answer: Copper has delocalized electrons that are free to move and carry electric charge.

Explanation: In copper, the outer electrons are not bound to any particular atom and are free to move throughout the metal lattice. These delocalized electrons can carry electric current, making copper an excellent conductor of electricity.

Question 12 (Subtopic – P2.1)

Fig. 12.1 shows a sealed glass jar filled with pure oxygen gas. Each oxygen molecule has a mass of \(5.34 \times 10^{-26} \, \text{kg}\).

Question 12(a)(i)

Describe how the motion of the oxygen molecules causes pressure inside the glass jar.

▶️Answer/Explanation

Answer: The oxygen molecules collide with the walls of the jar, exerting a force on the walls, which creates pressure.

Explanation: The oxygen molecules are in constant random motion. When they collide with the walls of the jar, they exert a force on the walls. The collective force of these collisions per unit area results in pressure inside the jar.

Question 12(a)(ii)

The average kinetic energy of a molecule of oxygen is \(2.67 \times 10^{-22} \, \text{J}\). Calculate the average speed of a molecule of oxygen.

▶️Answer/Explanation

Answer: \(100 \, \text{m/s}\)

Explanation: The kinetic energy (\(E_k\)) of a molecule is given by the equation \(E_k = \frac{1}{2}mv^2\), where \(m\) is the mass and \(v\) is the speed. Rearranging for \(v\), we get \(v = \sqrt{\frac{2E_k}{m}}\). Substituting the values, \(v = \sqrt{\frac{2 \times 2.67 \times 10^{-22}}{5.34 \times 10^{-26}}} = 100 \, \text{m/s}\).

Question 12(b)(i)

Fig. 12.2 shows a sample of gas in a sealed container attached to a pressure gauge. The temperature of the gas is increased and the pressure is measured. Fig. 12.3 shows how the pressure changes with temperature. Describe the results shown in Fig. 12.3.

▶️Answer/Explanation

Answer: The pressure increases as the temperature increases, and the relationship is linear.

Explanation: According to the ideal gas law, pressure is directly proportional to temperature (in Kelvin) when volume and the number of gas molecules are constant. Therefore, as the temperature increases, the pressure increases linearly.

Question 12(b)(ii)

A student suggests repeating the experiment with a non-flammable balloon filled with gas rather than a sealed container. Explain why this method would not produce the graph shown in Fig. 12.3.

▶️Answer/Explanation

Answer: The volume of the gas would not remain constant.

Explanation: In a sealed container, the volume of the gas is constant, allowing pressure to increase linearly with temperature. However, in a balloon, the volume can change as the gas expands or contracts, which would alter the relationship between pressure and temperature, making it non-linear.