Question 1
(a) Fig. 1.1 is a diagram of the female reproductive system. (Sub-topic – B15.4)
(i) State the letter from Fig. 1.1 that shows the part where:
- fertilisation occurs
- gametes are produced.
▶️Answer/Explanation
- Fertilisation occurs: A
- Gametes are produced: E
Explanation: Fertilisation typically occurs in the oviduct (fallopian tube), which is labelled as A in the diagram. Gametes (eggs) are produced in the ovaries, labelled as E.
(ii) Identify the part labelled B in Fig. 1.1. (Sub-topic – B15.4)
▶️Answer/Explanation
The part labelled B is the uterus.
Explanation: The uterus is the organ where the fertilised egg implants and develops during pregnancy.
(b) Below information shows a student’s description of fertilisation in humans. (Sub-topic – B15.4)
The description of fertilisation in humans is incorrect.
Circle the two incorrect words in the description in Fig. 1.2.
| Fertilisation is the separation of the nuclei from a sperm cell and an ovary cell. |
▶️Answer/Explanation
The two incorrect words are separation and ovary.
Explanation: Fertilisation is the fusion (not separation) of the nuclei from a sperm cell and an egg cell (not ovary cell).
(c) Fig. 1.3 shows how the thickness of the uterus lining changes during the menstrual cycle. (Sub-topic – B15.4)
Table 1.1 represents the days during an average menstrual cycle.
Use Fig. 1.3 and your own knowledge to:
(i) Place ticks (✓) in Table 1.1 to show the days when the uterus lining is shed.
▶️Answer/Explanation
Ticks should be placed under days 1–4.
Explanation: The uterus lining is shed during the menstrual phase, which typically occurs in the first few days of the menstrual cycle.
(ii) Place crosses (×) in Table 1.1 to show the days when the uterus lining is at its thickest.
▶️Answer/Explanation
Crosses should be placed under days 24–26.
Explanation: The uterus lining is at its thickest just before menstruation begins, typically around days 24–26 of the menstrual cycle.
(d) Complete the sentence to define the term reproduction. (Sub-topic – B15.1)
Reproduction is the processes that make …… of the same …… of organism.
▶️Answer/Explanation
Reproduction is the processes that make more of the same kind of organism.
Explanation: Reproduction is the biological process by which new individuals of the same species are produced, ensuring the continuation of the species.
Question 2
(a) Magnesium is in Period 3 of the Periodic Table. (Sub-topic – C2.2)
(i) Use the Periodic Table to name the noble gas in Period 3 of the Periodic Table.
▶️Answer/Explanation
Answer: Argon
Explanation: The noble gases are found in Group 18 of the Periodic Table. In Period 3, the noble gas is Argon (Ar).
(ii) Describe the change in metallic character across Period 3.
▶️Answer/Explanation
Answer: The metallic character decreases across Period 3.
Explanation: As you move from left to right across Period 3, the elements become less metallic and more non-metallic. This is because the tendency to lose electrons decreases, and the tendency to gain electrons increases.
(b) Magnesium reacts with carbon dioxide. Magnesium oxide and carbon are made.
(i) Write the word equation for this reaction.
▶️Answer/Explanation
Answer: Magnesium + Carbon dioxide → Magnesium oxide + Carbon
Explanation: The reaction between magnesium and carbon dioxide produces magnesium oxide and carbon. The word equation represents the reactants and products involved in the reaction.
(ii) The reaction between magnesium and carbon dioxide is exothermic. Explain what is meant by an exothermic reaction.
▶️Answer/Explanation
Answer: An exothermic reaction is a reaction that releases thermal energy to the surroundings.
Explanation: In an exothermic reaction, energy is released in the form of heat, causing the temperature of the surroundings to increase.
(c) An atom of magnesium has a proton number (atomic number) of 12 and a nucleon number (mass number) of 24.
Complete Table 2.1 to show the names and numbers of the two particles contained in the nucleus of this magnesium atom.
| Name of particle | Number of particles |
|---|---|
▶️Answer/Explanation
Answer: Protons: 12, Neutrons: 12
Explanation: The proton number (atomic number) is 12, which means there are 12 protons in the nucleus. The nucleon number (mass number) is 24, which is the sum of protons and neutrons. Therefore, the number of neutrons is 24 – 12 = 12.
(d) Magnesium carbonate reacts with dilute hydrochloric acid to make aqueous magnesium chloride.
(i) Magnesium carbonate is insoluble in water. State the separation technique used to remove magnesium carbonate from a mixture of magnesium carbonate and water.
▶️Answer/Explanation
Answer: Filtration
Explanation: Filtration is used to separate an insoluble solid (magnesium carbonate) from a liquid (water). The solid remains on the filter paper, while the liquid passes through.
(ii) Magnesium chloride dissolves in water. State the separation technique used to obtain solid magnesium chloride from a solution of magnesium chloride.
▶️Answer/Explanation
Answer: Crystallization
Explanation: Crystallization is used to obtain a solid (magnesium chloride) from a solution by evaporating the water, leaving behind the solid crystals.
(iii) Magnesium carbonate reacts with dilute hydrochloric acid. Complete the balanced symbol equation for this reaction.
MgCO3 + …..HCl → MgCl2 + CO2 + H2O
▶️Answer/Explanation
Answer: MgCO3 + 2HCl → MgCl2 + CO2 + H2O
Explanation: The balanced equation shows that one mole of magnesium carbonate reacts with two moles of hydrochloric acid to produce one mole of magnesium chloride, one mole of carbon dioxide, and one mole of water.
(iv) Dilute hydrochloric acid contains aqueous chloride ions. State the test for aqueous chloride ions and give the observation for a positive result.
▶️Answer/Explanation
Answer: Test: Add acidified silver nitrate solution. Observation: A white precipitate forms.
Explanation: Chloride ions react with silver nitrate in the presence of nitric acid to form a white precipitate of silver chloride.
(e) Table 2.2 shows the composition of a magnesium alloy.
| Element | % by mass |
|---|---|
| Magnesium | 94 |
| Neodymium | 2 |
| Yttrium | 4 |
(i) Calculate the mass of magnesium in 500 kg of the alloy.
▶️Answer/Explanation
Answer: 470 kg
Explanation: The mass of magnesium in the alloy is 94% of 500 kg. Therefore, 0.94 × 500 kg = 470 kg.
(ii) The alloy is used in aircraft bodies. Suggest why the alloy of magnesium is used rather than pure magnesium for aircraft bodies.
▶️Answer/Explanation
Answer: The alloy is stronger and less dense than pure magnesium.
Explanation: Alloys are generally stronger and more durable than pure metals. In the case of magnesium alloys, they are also lighter, making them ideal for use in aircraft bodies where strength and low weight are crucial.
Question 3
(a) A torch (flashlight) contains four cells, a lamp, and a switch connected in series.
(i) Draw a circuit diagram for the torch using standard electrical symbols. (Sub-topic – P4.3.1)
▶️Answer/Explanation
The circuit diagram should include:
- Four cells connected in series.
- A lamp connected in series with the cells.
- A switch connected in series with the lamp and cells.
The standard symbols for cells, lamp, and switch should be used.
(ii) The potential difference (p.d.) across the lamp is 6.0 V when the switch is closed. The resistance of the lamp is 5.0 Ω when lit. Calculate the current in the lamp. (Sub-topic – P4.2.4)
▶️Answer/Explanation
Using Ohm’s Law: \( V = IR \), where \( V \) is the potential difference, \( I \) is the current, and \( R \) is the resistance.
Given: \( V = 6.0 \, \text{V} \), \( R = 5.0 \, \Omega \)
\( I = \frac{V}{R} = \frac{6.0}{5.0} = 1.2 \, \text{A} \)
The current in the lamp is 1.2 A.
(iii) Two lamps each of resistance 5.0 Ω are connected together in a series circuit. Calculate the combined resistance of the two lamps in series. (Sub-topic – P4.3.2)
▶️Answer/Explanation
In a series circuit, the total resistance \( R_{\text{total}} \) is the sum of the individual resistances.
Given: \( R_1 = 5.0 \, \Omega \), \( R_2 = 5.0 \, \Omega \)
\( R_{\text{total}} = R_1 + R_2 = 5.0 + 5.0 = 10.0 \, \Omega \)
The combined resistance of the two lamps in series is 10.0 Ω.
(b) Choose words from the list to complete the sentences to describe the energy transfers that occur when the torch is switched on. (Sub-topic – P1.6.1)
You may use each word once, more than once, or not at all.
- chemical
- elastic
- electrical
- gravitational
- light
- nuclear
- sound
- thermal
The energy stored in the cells is …… potential energy. This energy is transferred into …… energy which passes through the lamp. The useful energy from the lamp is …… energy. Some energy is wasted as …… energy.
▶️Answer/Explanation
The energy stored in the cells is chemical potential energy. This energy is transferred into electrical energy which passes through the lamp. The useful energy from the lamp is light energy. Some energy is wasted as thermal energy.
(c) Solar energy is sometimes used to power torches. Solar energy is a renewable energy resource. State two other renewable energy resources. (Sub-topic – P1.6.3)
▶️Answer/Explanation
Two other renewable energy resources are:
- Wind energy – Energy harnessed from the wind using wind turbines.
- Hydropower – Energy generated from the movement of water, typically in dams or rivers.
(d) Fig. 3.1 shows a ray of light from a torch shining on a mirror. (Sub-topic – P3.2.1)
(i) State the name of line XZ.
▶️Answer/Explanation
Line XZ is called the normal. The normal is an imaginary line perpendicular to the surface of the mirror at the point where the light ray strikes the mirror.
(ii) State what happens to the ray of light at point X on Fig. 3.1.
▶️Answer/Explanation
At point X, the ray of light undergoes reflection. According to the law of reflection, the angle of incidence is equal to the angle of reflection, and both angles are measured relative to the normal.
Question 4
(a) Fig. 4.1 is a diagram of the heart. (Sub-topic – B9.2)
(i) Identify the parts labelled B, C and D in Fig. 4.1.
(ii) Describe the function of the structure labelled E.
(iii) The blood vessel labelled A is an artery. Describe the role of arteries in the circulatory system.
▶️Answer/Explanation
(i) B: septum, C: muscle / muscle wall, D: ventricles
(ii) Ensure one-way flow of blood.
(iii) Transport blood away from the heart.
(b) Name two of the main components of blood.
▶️Answer/Explanation
1: Red blood cells
2: White blood cells
(Other possible answers: platelets, plasma)
(c) A student measures their heart rate over a 24-hour period. Fig. 4.2 shows a graph of the results.
(i) Calculate the difference in heart rate between the minimum and maximum heart rate seen in Fig. 4.2.
(ii) At 10:00 hours the student attends a fitness class. Estimate the length of time of the fitness class.
(iii) At 18:00 hours the student was scared by a snake. Describe and explain the result seen at 18:00 hours in Fig. 4.2. Use ideas about hormones in your answer.
▶️Answer/Explanation
(i) 110 bpm
(ii) 4 hours
(iii) There is a rapid increase in heart rate (increase by 70 bpm or increase to 140 bpm) due to the release of adrenaline, which prepares the body for a “fight or flight” response.
Question 5
(a) Potassium is a very reactive metal. Potassium is stored under oil as shown in Fig. 5.1. (Sub-topic – C9.1)
Suggest two reasons why potassium is stored under oil.
▶️Answer/Explanation
1. To prevent potassium from reacting with air or oxygen.
2. To prevent potassium from reacting with water vapor.
(b) Potassium has a proton number of 19. Complete Fig. 5.2 to show the electronic structure of a potassium atom. The inner shell electrons have been drawn for you. (Sub-topic – C2.2)
▶️Answer/Explanation
The electronic structure of a potassium atom is 2, 8, 8, 1.
(c) Solid potassium reacts with chlorine gas to make solid potassium chloride.
(i) Describe the differences between the structures of a solid and a gas in terms of particle separation and particle arrangement. (Sub-topic – C1.1)
▶️Answer/Explanation
Particle separation: In a solid, particles are closely packed together, while in a gas, particles are far apart.
Particle arrangement: In a solid, particles are arranged in a regular pattern, while in a gas, particles are arranged randomly.
(ii) When potassium reacts with chlorine, potassium atoms become potassium ions. Describe what happens to a potassium atom when it becomes a potassium ion. (Sub-topic – C2.4)
▶️Answer/Explanation
A potassium atom loses one electron to become a potassium ion (K⁺).
(iii) Potassium and chlorine are elements. Potassium chloride is a compound. Describe the difference between an element and a compound. (Sub-topic – C2.1)
▶️Answer/Explanation
An element is a substance made up of only one type of atom, while a compound is a substance made up of two or more different types of atoms chemically combined.
(d) The maximum mass of potassium chloride that dissolves in 100 cm³ of water is called the solubility of potassium chloride. Fig. 5.3 shows the solubility of potassium chloride in water at different temperatures. (Sub-topic – C12.4)
(i) Describe the trend in solubility shown in Fig. 5.3.
▶️Answer/Explanation
The solubility of potassium chloride increases as the temperature increases.
(ii) State the mass of potassium chloride that dissolves in 100 cm³ of water at 45 °C.
▶️Answer/Explanation
41 g (±1)
Question 6 (Sub-topic – P1.2)
(a) Fig. 6.1 shows the speed-time graph for the journey of a train travelling between two stations.
(i) Use letters from the graph in Fig. 6.1 to identify the two stations on the train’s journey.
▶️Answer/Explanation
Answer: A and D
Explanation: The graph shows the train starting at station A (where the speed is zero) and ending at station D (where the speed returns to zero).
(ii) On Fig. 6.1, label with a cross \(X\) a part of the journey when the train is accelerating.
▶️Answer/Explanation
Answer: X anywhere between A and B or between C and D
Explanation: The train is accelerating when the speed is increasing, which occurs between A and B and between C and D.
(iii) Use Fig. 6.1 to calculate the total distance travelled by the train on this journey.
▶️Answer/Explanation
Answer: 2500 m
Explanation: The total distance travelled can be calculated by finding the area under the speed-time graph. The graph can be divided into three sections: a triangle, a rectangle, and another triangle. The area of the first triangle (A to B) is \( \frac{1}{2} \times 1000 \times 10 = 5000 \) m, the area of the rectangle (B to C) is \( 1000 \times 10 = 10000 \) m, and the area of the second triangle (C to D) is \( \frac{1}{2} \times 1000 \times 10 = 5000 \) m. Adding these areas together gives a total distance of 2500 m.
(b) Fig. 6.2 shows the forces acting on the train when it travels at a constant speed.
(i) State which force, P, Q, R or S, is the weight of the train.
▶️Answer/Explanation
Answer: R
Explanation: The weight of the train acts vertically downward, which is represented by force R in the diagram.
(ii) Compare the magnitude and the direction of forces Q and S when the train is travelling at a constant speed.
▶️Answer/Explanation
Answer: Equal (magnitude); opposite directions
Explanation: When the train is travelling at a constant speed, the forces acting on it are balanced. Therefore, the magnitude of force Q (driving force) is equal to the magnitude of force S (frictional force), but they act in opposite directions.
Question 7 (Sub-topic – B3.2, B8.1, B6.1, B19.1)
(a) A scientist investigates the effect of immersion of plant cells in different concentrations of sugar solution. Fig. 7.1 shows the appearance of the plant cells before immersion.
Beakers A–D contain different concentrations of sugar solution. Some plant cells are placed in each solution and left for an hour. Table 7.1 shows the results.
(i) Describe the change seen to the plant cells placed in beaker A in Table 7.1.
▶️Answer/Explanation
The cells swell or increase in size due to water entering the cells by osmosis.
(ii) Suggest which beaker contains the solution with the same concentration as the plant cells. Give a reason for your answer.
▶️Answer/Explanation
Beaker B; the cells have not changed, indicating that the concentration of the solution is the same as inside the cells, so there is no net movement of water.
(b) Water enters the plant through the root hair cells. Complete the flow chart to show the pathway of water through the cells of a plant.
root hair cell → …… → xylem → ……
▶️Answer/Explanation
root hair cell → root cortex cell → xylem → mesophyll cell
(c) Xylem transports water through the plant stem. Name the tissue that transports sugars through the plant stem.
▶️Answer/Explanation
Phloem
(d) Water and carbon dioxide are raw materials required for photosynthesis. Name two other requirements for photosynthesis.
▶️Answer/Explanation
1. Light
2. Chlorophyll
(e) Protecting land from deforestation helps stop the loss of soil. This is because tree roots hold the soil together, stopping it being washed away. Suggest two other benefits of protecting land from deforestation.
▶️Answer/Explanation
1. Prevents extinction of animals
2. Maintains biodiversity
Question 8
(a) Fig. 8.1 shows the electrolysis of molten lead(II) bromide. (Sub Topic – C4.1)
(i) State the name of the electrode where lead is made.
▶️Answer/Explanation
Answer: cathode
Explanation: During the electrolysis of molten lead(II) bromide, lead ions (Pb2+) gain electrons at the cathode to form lead metal. Therefore, lead is made at the cathode.
(ii) Explain why an orange gas is seen above the molten lead(II) bromide.
▶️Answer/Explanation
Answer: Bromine (vapour) is released.
Explanation: During the electrolysis, bromide ions (Br–) lose electrons at the anode to form bromine gas (Br2). Bromine gas is orange in color, which is why an orange gas is seen above the molten lead(II) bromide.
(b) Lead is extracted from lead oxide by reaction with carbon. The equation for the reaction is shown. (Sub Topic – C9.4)
lead oxide + carbon → lead + carbon dioxide
Name the substance that is oxidised and the substance that is reduced in this reaction.
▶️Answer/Explanation
Answer: Oxidised: carbon; Reduced: lead oxide
Explanation: In this reaction, carbon is oxidised because it gains oxygen to form carbon dioxide. Lead oxide is reduced because it loses oxygen to form lead metal.
(c) Lead is a metal. Suggest one test to show that lead is a metal. (Sub Topic – C4.1)
▶️Answer/Explanation
Answer: Test for electrical conductivity.
Explanation: Metals are good conductors of electricity. A simple test to show that lead is a metal is to check if it conducts electricity. If it does, it confirms that lead is a metal.
(d) Lead reacts very slowly with dilute sulfuric acid. State two ways of increasing the rate of reaction between lead and dilute sulfuric acid. (Sub Topic – C9.4)
▶️Answer/Explanation
Answer: Increase temperature; Increase surface area of lead.
Explanation: The rate of reaction can be increased by increasing the temperature, which provides more energy for the particles to collide more frequently and with greater energy. Additionally, increasing the surface area of the lead (e.g., by using lead powder instead of a solid block) allows more particles to be exposed to the acid, increasing the rate of reaction.
Question 9 (Sub-topic – P2.2.2)
Fig. 9.1 shows a tumble dryer.
In a tumble dryer, wet clothes are warmed and dried. Water on the clothes evaporates.
(a) (i) Describe the process of evaporation. Use ideas about molecules in your answer.
▶️Answer/Explanation
Evaporation is the process by which molecules at the surface of a liquid gain enough energy to escape into the gas phase. In the case of water, faster-moving or more energetic molecules at the surface can overcome the intermolecular forces holding them in the liquid and escape as water vapour. This process occurs even below the boiling point of the liquid.
(ii) During evaporation, the water does not boil. State the boiling point of water.
▶️Answer/Explanation
The boiling point of water is 100°C at standard atmospheric pressure.
(iii) Inside the tumble dryer, water vapour changes into liquid water. State the term used to describe a gas changing into a liquid.
▶️Answer/Explanation
The term used to describe a gas changing into a liquid is condensation.
(iv) Thermal energy passes through the metal casing of the tumble dryer. State the method of thermal energy transfer through metals.
▶️Answer/Explanation
The method of thermal energy transfer through metals is conduction.
(b) The tumble dryer is noisy and emits loud sound waves with a low pitch.
(i) Describe the sound waves in terms of their amplitude and frequency.
▶️Answer/Explanation
Loud sound waves have a large amplitude, which corresponds to the volume or loudness of the sound. A low pitch indicates that the sound waves have a low frequency, meaning fewer wave cycles per second.
(ii) State the lowest audible frequency for a healthy human ear. State the unit of your answer.
▶️Answer/Explanation
The lowest audible frequency for a healthy human ear is 20 Hz (Hertz).
(iii) The speed of sound in air is 340 m/s. Calculate the time taken for a sound wave to travel 85 m.
▶️Answer/Explanation
To calculate the time taken for a sound wave to travel 85 m, we use the formula:
\[ \text{Time} = \frac{\text{Distance}}{\text{Speed}} = \frac{85 \, \text{m}}{340 \, \text{m/s}} = 0.25 \, \text{s} \]
Therefore, the time taken is 0.25 seconds.
Question 10 (Sub-topic – B7.2)
(a) Fig. 10.1 is a diagram of the human alimentary canal and associated organs.
(i) Label Fig. 10.1 on the answer lines provided.
Choose words from the list:
- anus
- large intestine
- mouth
- pancreas
- small intestine
- stomach
(ii) Different processes occur in the alimentary canal. Complete Table 10.1 using words from the list in (a)(i).
| Process | One part of the alimentary canal where process occurs |
|---|---|
| ingestion | |
| egestion | |
| mechanical digestion |
▶️Answer/Explanation
(i) Labels for Fig. 10.1:
- mouth
- stomach
- pancreas
- small intestine
(ii) Table 10.1:
| Process | One part of the alimentary canal where process occurs |
|---|---|
| ingestion | mouth |
| egestion | anus |
| mechanical digestion | mouth / stomach |
(b) Describe the role of chemical digestion in the alimentary canal.
▶️Answer/Explanation
Chemical digestion is the process by which large, insoluble food molecules are broken down into smaller, soluble molecules that can be absorbed into the bloodstream. This process is facilitated by enzymes, which are biological catalysts that speed up chemical reactions without being consumed in the process. For example, amylase breaks down starch into simple sugars, proteases break down proteins into amino acids, and lipases break down fats into fatty acids and glycerol. These smaller molecules can then be absorbed through the walls of the small intestine and transported to cells throughout the body for use as energy or building blocks.
(c) The boxes contain the beginnings and the endings of some sentences. Join one sentence beginning to one sentence ending to define the term assimilation.
▶️Answer/Explanation
Assimilation is the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells.
Question 11 (Sub-topic – C11.1, C11.2, C11.3, C11.5)
Fig. 11.1 shows the structures of five compounds A, B, C, D, and E.
(a) Use the letters A–E to identify all the hydrocarbon molecules.
▶️Answer/Explanation
Answer: B, C, and D
Explanation: Hydrocarbons are compounds that contain only hydrogen and carbon atoms. From the structures shown in Fig. 11.1, compounds B, C, and D consist solely of hydrogen and carbon atoms, making them hydrocarbons.
(b) Use the letters A–E to identify the two products of the complete combustion of a hydrocarbon.
▶️Answer/Explanation
Answer: A and E
Explanation: The complete combustion of a hydrocarbon produces carbon dioxide (CO₂) and water (H₂O). From the structures shown in Fig. 11.1, compound A represents carbon dioxide (CO₂), and compound E represents water (H₂O).
(c) Use Fig. 11.1 to name one greenhouse gas.
▶️Answer/Explanation
Answer: Carbon dioxide (CO₂) or methane (CH₄)
Explanation: Greenhouse gases trap heat in the Earth’s atmosphere. From the structures shown in Fig. 11.1, compound A is carbon dioxide (CO₂), which is a well-known greenhouse gas. Additionally, compound D could represent methane (CH₄), another potent greenhouse gas.
(d) Draw a dot-and-cross diagram to show the bonding in molecule E.
Only show the outer shell electrons.
▶️Answer/Explanation
Answer:
Explanation: Molecule E is water (H₂O). In the dot-and-cross diagram, oxygen has six outer shell electrons, and each hydrogen atom has one. Oxygen shares one electron with each hydrogen atom, forming two covalent bonds. The remaining four electrons on oxygen are lone pairs.
(e) Compound D is an unsaturated compound.
- State what is meant by the term unsaturated compound.
- Name the process that produces smaller unsaturated hydrocarbon molecules from large saturated hydrocarbon molecules.
- State the chemical test for an unsaturated hydrocarbon and give the observation for a positive result.
▶️Answer/Explanation
Answer:
- An unsaturated compound contains at least one carbon-carbon double or triple bond.
- The process is called cracking.
- The chemical test is the addition of aqueous bromine (bromine water). A positive result is indicated by the bromine water changing from orange to colorless.
Explanation:
- Unsaturated compounds have double or triple bonds between carbon atoms, which allow them to undergo addition reactions.
- Cracking is a process where large hydrocarbon molecules are broken down into smaller, more useful molecules, often producing unsaturated hydrocarbons.
- Bromine water reacts with the double bonds in unsaturated hydrocarbons, causing the orange color of bromine to disappear, indicating the presence of an unsaturated compound.
Question 12
(a) Electricity is generated in a nuclear power station by the nuclear fission of plutonium-239. Describe what happens to a nucleus of plutonium-239 during nuclear fission. (Sub-topic –P5.1)
▶️Answer/Explanation
During nuclear fission, the nucleus of plutonium-239 splits into two smaller nuclei, releasing a large amount of energy and several neutrons. This process is typically initiated by the absorption of a neutron by the plutonium-239 nucleus.
(b) Plutonium-239 is an isotope of plutonium.
(i) State the meaning of isotope. (Sub-topic code: C2.3)
▶️Answer/Explanation
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This results in isotopes having the same atomic number but different mass numbers.
(ii) Plutonium-239 emits β-radiation. Suggest how a small sample of plutonium-239 can be stored safely. (Sub-topic – P5.2.5)
▶️Answer/Explanation
A small sample of plutonium-239 can be stored safely in a lead-lined container to shield against β-radiation. The container should be kept in a secure, controlled environment to prevent any leakage or exposure.
(iii) Plutonium-239 has a half-life of 24000 years. A sample of plutonium-239 has a mass of 800 g. Calculate the mass of plutonium-239 remaining after 48000 years. (Sub-topic – P5.2.4)
▶️Answer/Explanation
After 48000 years, which is 2 half-lives, the mass of plutonium-239 remaining would be:
Initial mass = 800 g
After 1 half-life (24000 years): 800 g / 2 = 400 g
After 2 half-lives (48000 years): 400 g / 2 = 200 g
Therefore, the mass remaining after 48000 years is 200 g.
(iv) State two differences between β-radiation and γ-radiation. (Sub-topic – P5.2.2)
▶️Answer/Explanation
1. Nature: β-radiation consists of high-energy electrons (or positrons), while γ-radiation consists of high-energy photons (electromagnetic waves).
2. Penetration: β-radiation is less penetrating than γ-radiation. β-particles can be stopped by a few millimeters of aluminum, whereas γ-rays require several centimeters of lead or concrete to be effectively shielded.
(v) Fig. 12.1 shows an incomplete electromagnetic spectrum. Place γ-radiation in its correct place in Fig. 12.1. (Sub-topic – P3.3)
▶️Answer/Explanation
γ-radiation should be placed at the far right end of the electromagnetic spectrum, as it has the highest frequency and shortest wavelength among the types of electromagnetic radiation.