Question 1 (Sub-topic: B9.2)
(a) An athlete monitors her pulse rate during different types of activity.
Fig. 1.1 shows the results.
Use Fig. 1.1 to complete these sentences.
The activity with the highest pulse rate is ………………….
Two activities have the same pulse rate. They are …………………. and ………………….
The athlete’s pulse rate was 54 beats per minute when the activity is ………………….
▶️Answer/Explanation
The activity with the highest pulse rate is running.
Two activities have the same pulse rate. They are cycling and walking.
The athlete’s pulse rate was 54 beats per minute when the activity is sleeping.
(b) Fig. 1.2 is a diagram of the heart.
(i) Draw an X on Fig. 1.2 to identify the position of one ventricle.
▶️Answer/Explanation
X should be drawn on one of the ventricles in the diagram.
(ii) State the function of the part labelled Y in Fig. 1.2.
▶️Answer/Explanation
The function of the part labelled Y is to ensure one-way flow of the blood.
(iii) Identify the part labelled Z in Fig. 1.2.
▶️Answer/Explanation
The part labelled Z is the septum.
(iv) Name the type of tissue the wall of the heart is made from.
▶️Answer/Explanation
The wall of the heart is made from muscle tissue.
(v) State the function of the heart.
▶️Answer/Explanation
The function of the heart is to pump blood around the body.
(c) Name one of the main blood vessels to or from the:
Lungs ………………….
Kidney ………………….
▶️Answer/Explanation
Lungs: pulmonary artery/vein
Kidney: renal artery/vein
Question 2 (Sub-topic: C2.1)
2(a) Petroleum is a fossil fuel. Name two other fossil fuels.
▶️Answer/Explanation
1. Coal
2. Natural gas
Fossil fuels are formed from the remains of ancient plants and animals that have been subjected to heat and pressure over millions of years. The two most common fossil fuels, apart from petroleum, are coal and natural gas. Coal is primarily composed of carbon and is used extensively in electricity generation, while natural gas, mainly methane, is used for heating and cooking.
2(b) Complete the sentences using words or phrases from the list. Each word or phrase may be used once, more than once or not at all.
bitumen chromatography filtration fractional distillation
gases hydrocarbons naphtha refinery gas solids
Petroleum is a mixture of …… .
The fractions in petroleum are separated using …… .
The fraction used as a feedstock for making chemicals is the …… fraction.
▶️Answer/Explanation
Petroleum is a mixture of hydrocarbons.
The fractions in petroleum are separated using fractional distillation.
The fraction used as a feedstock for making chemicals is the naphtha fraction.
Petroleum is a complex mixture of hydrocarbons, which are compounds made up of hydrogen and carbon atoms. The process of fractional distillation is used to separate these hydrocarbons based on their boiling points. The naphtha fraction, which is obtained during this process, is particularly important as it serves as a feedstock for the production of various chemicals, including plastics and synthetic fibers.
2(c) Octane, \( C_{8}H_{18} \), is a hydrocarbon fuel.
(i) State the number of different elements in one molecule of octane.
▶️Answer/Explanation
Two elements: Carbon (C) and Hydrogen (H).
Octane (\( C_8H_{18} \)) is a hydrocarbon, meaning it is composed solely of carbon and hydrogen atoms. Therefore, there are two different elements in one molecule of octane.
(ii) State the total number of atoms in one molecule of octane.
▶️Answer/Explanation
26 atoms (8 carbon atoms + 18 hydrogen atoms).
The molecular formula of octane (\( C_8H_{18} \)) indicates that each molecule contains 8 carbon atoms and 18 hydrogen atoms, totaling 26 atoms.
(iii) When fuels burn, the reaction produces a temperature increase. State the name given to all reactions that produce a temperature increase.
▶️Answer/Explanation
Exothermic reactions.
Exothermic reactions are chemical reactions that release energy in the form of heat, resulting in a temperature increase. Combustion reactions, such as the burning of fuels, are classic examples of exothermic reactions.
(iv) State the chemical test for carbon dioxide and the observation for a positive result.
▶️Answer/Explanation
Test: Bubble the gas through limewater.
Observation: Limewater turns milky.
Carbon dioxide (\( CO_2 \)) can be detected using limewater. When \( CO_2 \) is bubbled through limewater, it reacts to form calcium carbonate, which is insoluble and causes the limewater to turn milky. This is a standard test for the presence of carbon dioxide.
Question 3
A student uses her laptop computer.
(a) The laptop screen acts as a plane mirror.
Fig. 3.1 shows a ray of light reflected by the laptop screen. (Sub-topic: P3.2.1 Reflection of light)
(i) Name the line labelled XY.
▶️Answer/Explanation
Answer: normal
Explanation: The line labelled XY is the normal, which is an imaginary line perpendicular to the surface of the mirror at the point where the light ray strikes the mirror.
(ii) Label the angle of incidence with the letter \(i\).
▶️Answer/Explanation
Answer: The angle of incidence should be labelled with the letter \(i\) between the incident ray and the normal.
Explanation: The angle of incidence is the angle between the incident ray and the normal to the surface at the point of incidence.
(iii) The angle of incidence is \(40^\circ\). State the angle of reflection.
▶️Answer/Explanation
Answer: \(40^\circ\)
Explanation: According to the law of reflection, the angle of incidence is equal to the angle of reflection. Therefore, if the angle of incidence is \(40^\circ\), the angle of reflection is also \(40^\circ\).
(b) The laptop contains two speakers each with a resistance of \(8 \Omega\). (Sub-topic: P4.2.4 Resistance)
(i) The current in one speaker is \(3A\). Calculate the potential difference (p.d.) across this speaker.
▶️Answer/Explanation
Answer: \(24V\)
Explanation: Using Ohm’s Law, \(V = IR\), where \(V\) is the potential difference, \(I\) is the current, and \(R\) is the resistance. Substituting the given values, \(V = 3A \times 8\Omega = 24V\).
(ii) The two speakers are connected in parallel. The combined resistance of the two speakers is one of the following values.
4Ω 8Ω 16Ω 64Ω
State the correct value of the combined resistance and explain your answer.
▶️Answer/Explanation
Answer: \(4 \Omega\)
Explanation: When resistors are connected in parallel, the combined resistance is given by the formula \(\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2}\). Substituting the given values, \(\frac{1}{R_{total}} = \frac{1}{8\Omega} + \frac{1}{8\Omega} = \frac{2}{8\Omega} = \frac{1}{4\Omega}\). Therefore, \(R_{total} = 4\Omega\).
(iii) Fig. 3.2 shows circuit symbols for four electrical components found in the laptop.
Identify the four electrical components.
▶️Answer/Explanation
Answer: cell, variable resistor, lamp, switch
Explanation: The circuit symbols typically represent a cell (power source), a variable resistor (to adjust resistance), a lamp (light source), and a switch (to control the circuit).
(c) Fig. 3.3 shows the laptop being closed.
Calculate the moment of the force about the pivot in Nm. (Sub-topic: P1.5.2 Turning effect of forces)
▶️Answer/Explanation
Answer: \(2.9 Nm\)
Explanation: The moment of a force is calculated using the formula \(moment = force \times distance\). Given the force is \(12N\) and the distance is \(0.24m\) (converted from \(24cm\)), the moment is \(12N \times 0.24m = 2.88 Nm\), which rounds to \(2.9 Nm\).
Question 4 (Sub-topic: B16.1)
4(a) The inheritance of smooth or wrinkled skin in pea plants is controlled by a single gene.
- The allele for smooth skin is R.
- The allele for wrinkled skin is r.
Fig. 4.1 is a photograph of two peas:
- Pea A has wrinkled skin.
- Pea B has smooth skin.
4(a)(i) Table 4.1 shows the genotypes and genotype descriptions of the peas shown in Fig. 4.1.
Complete Table 4.1.
| pea | genotype | description of genotype |
|---|---|---|
| A | homozygous recessive | |
| B | Rr |
▶️Answer/Explanation
Answer:
Pea A: genotype = rr, description = homozygous recessive
Pea B: genotype = Rr, description = heterozygous
4(a)(ii) A scientist crossed two pea plants and observed the results. Complete the genetic diagram in Fig. 4.2 to identify the parental gametes.
▶️Answer/Explanation
Answer:
Parental gametes: R and r
4(a)(iii) State the ratio of smooth peas to wrinkled peas from Fig. 4.2.
smooth …… : wrinkled ……
▶️Answer/Explanation
Answer:
smooth 3 : wrinkled 1
4(b) Fertilisation in plants occurs when the nuclei of the male and female gametes fuse. Name these two gametes.
▶️Answer/Explanation
Answer:
1. pollen
2. ovule
4(c) State the name of the female gamete in humans.
▶️Answer/Explanation
Answer:
egg / ovum
4(d) Table 4.2 contains one term and two definitions linked to inheritance. Complete Table 4.2.
| term | definition |
|---|---|
| A thread-like structure of DNA, carrying genetic information in the form of genes. | |
| gene | |
| A version of a gene. |
▶️Answer/Explanation
Answer:
term: chromosome, gene, allele
definition: A thread-like structure of DNA, carrying genetic information in the form of genes; A length of DNA that codes for a protein; A version of a gene.
Question 5 (Sub-topic: C9.3)
5 (a) Aluminium is a metal.
Two physical properties of metals are that they are good thermal conductors and good electrical conductors.
State two other physical properties of metals.
▶️Answer/Explanation
1. High melting point
2. Malleable
5 (b) Duralumin is an alloy of 95% aluminium and 5% copper.
(i) Calculate the mass of aluminium used in 1000 kg of duralumin.
▶️Answer/Explanation
950 kg
(ii) State why aluminium alloys are used in aircraft parts.
▶️Answer/Explanation
Low density / high tensile strength
5 (c) Aluminium is extracted from its ore by electrolysis.
(i) State the name of the ore of aluminium used.
▶️Answer/Explanation
Bauxite
(ii) Define electrolysis.
▶️Answer/Explanation
Breakdown of an ionic compound when molten or in aqueous solution by the passage of an electric current.
(iii) Aluminium cannot be extracted from its ore by heating with carbon. Name one metal which can be extracted from its ore by heating with carbon.
▶️Answer/Explanation
Iron
5 (d) Aluminium ores must be conserved.
(i) State why aluminium ores must be conserved.
▶️Answer/Explanation
Finite resource / material being used at a faster rate than it can be replaced.
(ii) Suggest how aluminium ores may be conserved.
▶️Answer/Explanation
Recycling
Question 6 (Sub-topic: P3.3)
Many types of radiation are used in hospitals.
(a) Fig. 6.1 shows an infrared thermometer used to measure body temperature.
(i) Place infrared radiation in the correct place in the incomplete electromagnetic spectrum shown in Fig. 6.2.
(ii) Electromagnetic radiation is used in hospitals.
On Fig. 6.3, draw one straight line from each radiation to its correct medical use. One line has been drawn for you.
(b) Ionising radiation from radioactive sources is used in hospitals.
(i) Place α-radiation, β-radiation and γ-radiation in order of their relative ionising effect.
(ii) State one harmful effect of ionising radiation on the human body.
(c) The isotope iodine-131 is used in hospitals.
(i) State the meaning of the term isotope.
(ii) The half-life of iodine-131 is 8 days. A sample of iodine-131 is left for 16 days. The mass of iodine-131 remaining is 0.05g.
Calculate the mass of iodine-131 in the sample at the start.
(d) In the hospital, the audible frequency range of a patient’s hearing is measured. The result is a range from 100 Hz to 15 000 Hz.
State how this compares to the average range of audible frequencies for a healthy human ear.
(e) A power station supplies electricity to the hospital. The power station uses petroleum as a fuel.
Complete Fig. 6.4 to show the energy transformations that occur in the power station.
▶️Answer/Explanation
(a)(i) Infrared radiation should be placed in the third box from the right in the electromagnetic spectrum.
(a)(ii) γ-radiation should be linked to treating cancer, and X-rays should be linked to diagnosing broken bones.
(b)(i) The order of ionising effect from greatest to least is: α-radiation, β-radiation, γ-radiation.
(b)(ii) One harmful effect of ionising radiation on the human body is that it can cause cancer or mutations in cells.
(c)(i) Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.
(c)(ii) The mass of iodine-131 at the start can be calculated as follows:
Since the half-life is 8 days, 16 days correspond to 2 half-lives. The mass remaining after 2 half-lives is 0.05g, so the initial mass is:
Initial mass = 0.05g × 22 = 0.05g × 4 = 0.2g.
(d) The average range of audible frequencies for a healthy human ear is typically from 20 Hz to 20,000 Hz. The patient’s range of 100 Hz to 15,000 Hz is narrower, indicating some hearing loss, especially at the lower and higher frequencies.
(e) The energy transformations in the power station are:
Chemical energy (from petroleum) → Thermal energy → Kinetic energy → Electrical energy.
Question 7
Fig. 7.1 is a diagram of the male reproductive system.
(a) The boxes on the left show the letters of some of the parts in Fig. 7.1. The boxes on the right show the functions of these parts. Draw lines to link each letter to its correct function. (Sub-topic: B15.4)
▶️Answer/Explanation
Answer:
A – production of male gametes
B – secretes fluid for sperm to swim in
C – transfers sperm to urethra
D – transfers urine and semen
(b) Sperm need a high rate of respiration for movement. State the word equation for aerobic respiration. (Sub-topic: B12.1)
▶️Answer/Explanation
Answer:
glucose + oxygen → carbon dioxide + water
(c) Sperm is an example of a type of animal cell. The list shows some components of cells. Circle two components that you would expect to find in a sperm cell. (Sub-topic: B2.1)
- cell membrane
- cell wall
- chloroplast
- cytoplasm
- vacuole
▶️Answer/Explanation
Answer:
cell membrane and cytoplasm
(d) State the name of the cell that is formed when gametes fuse. (Sub-topic: B15.2)
▶️Answer/Explanation
Answer:
zygote
(e) Name the part of the cell that contains the genetic material. (Sub-topic: B2.1)
▶️Answer/Explanation
Answer:
nucleus
Question 8
8(a) Table 8.1 shows the names of eight gases.
| Name of Gas |
|---|
| ammonia |
| carbon monoxide |
| chlorine |
| helium |
| hydrogen |
| methane |
| nitrogen |
| oxygen |
(i) One of the gases in Table 8.1 has molecules with the formula \( C_2 \). State the name of this gas. (Sub-topic: C11.3)
▶️Answer/Explanation
Answer: chlorine
Explanation: Chlorine exists as a diatomic molecule with the formula \( Cl_2 \), which fits the description of a molecule with the formula \( C_2 \).
(ii) State the name of the gas from Table 8.1 that is a product of the incomplete combustion of carbon-containing substances. (Sub-topic: C10.2)
▶️Answer/Explanation
Answer: carbon monoxide
Explanation: Incomplete combustion of carbon-containing substances produces carbon monoxide (CO) instead of carbon dioxide (CO₂).
(iii) State the name of the gas from Table 8.1 that is 78% of clean air. (Sub-topic: C10.2)
▶️Answer/Explanation
Answer: nitrogen
Explanation: Nitrogen makes up approximately 78% of the Earth’s atmosphere, making it the most abundant gas in clean air.
(iv) State the name of the gas from Table 8.1 that is a greenhouse gas. (Sub-topic: C10.2)
▶️Answer/Explanation
Answer: methane
Explanation: Methane (CH₄) is a potent greenhouse gas that contributes to global warming by trapping heat in the atmosphere.
(v) State the name of the gas from Table 8.1 that is a noble gas. (Sub-topic: C8.5)
▶️Answer/Explanation
Answer: helium
Explanation: Helium is a noble gas, which means it is inert and does not readily react with other elements.
8(b) Fig. 8.1 shows apparatus a student uses to investigate the rate of reaction between calcium carbonate and dilute hydrochloric acid.
(i) State the name of the gas collected in the measuring cylinder. (Sub-topic: C6.2)
▶️Answer/Explanation
Answer: carbon dioxide
Explanation: When calcium carbonate reacts with hydrochloric acid, carbon dioxide gas is produced, which is collected in the measuring cylinder.
(ii) Predict how the pH of the water changes as the gas bubbles through it. Explain your answer. (Sub-topic: C7.1)
▶️Answer/Explanation
Answer: The pH decreases.
Explanation: Carbon dioxide dissolves in water to form carbonic acid (H₂CO₃), which lowers the pH of the water, making it more acidic.
(iii) The student repeats the experiment using the same mass of calcium carbonate and the same volume of dilute hydrochloric acid. Suggest two changes the student can make to their experiment to increase the rate of reaction. (Sub-topic: C6.2)
▶️Answer/Explanation
Answer:
- Increase the concentration of the hydrochloric acid.
- Increase the temperature of the acid.
Explanation:
- Increasing the concentration of the acid increases the number of acid particles available to react with the calcium carbonate, speeding up the reaction.
- Increasing the temperature provides more energy to the particles, increasing the frequency of collisions and thus the rate of reaction.
Question 9 (Sub-topic: P1.5 )
9(a) Fig. 9.1 shows a wind surfer on a surfboard, driven by the wind, sailing at a constant speed across the water.
Four forces J, K, L and M acting on the surfboard are shown.
(i) Explain why force K and force M must be equal and opposite.
▶️Answer/Explanation
The surfboard is moving at a constant speed, which means there is no acceleration. According to Newton’s first law of motion, if an object is moving at a constant speed, the net force acting on it must be zero. Therefore, force K (the force of the wind pushing the surfboard forward) and force M (the force of water resistance opposing the motion) must be equal in magnitude and opposite in direction to balance each other out.
(ii) Identify force L.
▶️Answer/Explanation
Force L is the gravitational force or weight acting downward on the surfboard.
(iii) Work is done by the wind to move the surfboard across the water. State the two quantities needed to calculate the work done by the wind.
▶️Answer/Explanation
The two quantities needed to calculate the work done by the wind are:
- The force exerted by the wind (force K).
- The distance over which the force is applied (the distance the surfboard moves).
9(b) Fig. 9.2 represents a water wave.
(i) On Fig. 9.2, label the amplitude of the wave with a double-headed arrow (↔ or ↓).
▶️Answer/Explanation
The amplitude of the wave should be labeled as the vertical distance from the equilibrium position to the crest or trough of the wave.
(ii) The waves have a frequency of 0.1 Hz. Explain what is meant by a frequency of 0.1 Hz.
▶️Answer/Explanation
A frequency of 0.1 Hz means that one wave passes a fixed point every 10 seconds. Frequency is the number of complete waves that pass a point per second, so 0.1 Hz corresponds to one wave every 10 seconds.
9(c) Water molecules in the sea are able to form water vapour above the sea. During this process, the more energetic molecules escape from the surface of the sea.
(i) Suggest the effect this will have on the energy of the water molecules remaining in the seawater.
▶️Answer/Explanation
The water molecules remaining in the seawater will have less energy on average because the more energetic molecules have escaped as water vapour. This results in a decrease in the average kinetic energy of the remaining molecules.
(ii) Suggest the effect this will have on the temperature of the seawater.
▶️Answer/Explanation
The temperature of the seawater will decrease because the average kinetic energy of the remaining water molecules has decreased. Temperature is a measure of the average kinetic energy of the molecules, so a decrease in kinetic energy leads to a decrease in temperature.
9(d) Some seawater has a volume of 5.0 m3 and a mass of 5120 kg. Calculate the density of the seawater.
▶️Answer/Explanation
Density is calculated using the formula:
\[ \text{Density} = \frac{\text{Mass}}{\text{Volume}} \]
Given:
Mass = 5120 kg
Volume = 5.0 m3
\[ \text{Density} = \frac{5120 \, \text{kg}}{5.0 \, \text{m}^3} = 1024 \, \text{kg/m}^3 \]
Therefore, the density of the seawater is 1024 kg/m3.
Question 10 (Sub-topic: B8.3)
(a) Water is lost from leaves by transpiration. This causes a loss in mass. A student records the mass of leaves from a plant. He places the leaves under a heat lamp. He records the mass of the leaves every 24 hours for 5 days. The results are shown in Table 10.1.
| Day | Mass of leaves/g |
|---|---|
| 1 | 115 |
| 2 | 100 |
| 3 | 85 |
| 4 | 65 |
| 5 | 58 |
(i) Calculate the total decrease in mass between day 1 and day 5.
▶️Answer/Explanation
Answer: 57 g
Explanation: The total decrease in mass is calculated by subtracting the mass on day 5 from the mass on day 1: 115 g – 58 g = 57 g.
(ii) The investigation is repeated at a lower temperature. The statements show some predictions. Tick (✓) one box to show the correct prediction.
| Statement | Tick |
|---|---|
| The decrease in mass will be less than in the first investigation. | ✓ |
| The decrease in mass will be more than in the first investigation. | |
| The mass will increase not decrease. | |
| The decrease in mass will be the same as in the first investigation. |
▶️Answer/Explanation
Answer: The decrease in mass will be less than in the first investigation.
Explanation: At a lower temperature, the rate of transpiration decreases, leading to less water loss and therefore a smaller decrease in mass.
(b) State the process by which water is lost from the surfaces of the mesophyll cells during transpiration.
▶️Answer/Explanation
Answer: Evaporation
Explanation: Water evaporates from the surfaces of the mesophyll cells into the air spaces within the leaf and then diffuses out through the stomata.
(c) State the name of the part of the leaf where water exits the plant.
▶️Answer/Explanation
Answer: Stomata
Explanation: Stomata are small openings on the underside of leaves that allow water vapor to exit the plant during transpiration.
(d) A plant obtains water from the soil. Describe how water enters the plant and is transported to the mesophyll cells in the leaves.
▶️Answer/Explanation
Answer: Water enters the plant through the root hair cells by osmosis. It then moves through the root cortex cells and into the xylem vessels. The xylem transports water up the stem to the leaves. In the leaves, water moves from the xylem into the mesophyll cells.
Explanation: Water is absorbed by the root hairs due to the higher concentration of water in the soil compared to the root cells. The water then travels through the root cortex and into the xylem, which carries it upwards due to transpiration pull. Once in the leaves, water moves into the mesophyll cells where it can be used for photosynthesis or lost through transpiration.
(e) One use of water in a plant is for photosynthesis. (i) State one other use of water in a plant.
▶️Answer/Explanation
Answer: Support (turgor pressure)
Explanation: Water helps maintain the turgor pressure in plant cells, which keeps the plant upright and provides structural support.
(ii) State two other requirements of photosynthesis.
▶️Answer/Explanation
Answer: Light and carbon dioxide
Explanation: Photosynthesis requires light energy to drive the process and carbon dioxide as a source of carbon for the production of glucose.
Question 11 (Subtopic: C8.2)
Fig. 11.1 shows part of Group I of the Periodic Table.
(i) State the electronic structure of a potassium atom.
▶️Answer/Explanation
Answer: 2.8.8.1
Explanation: The electronic structure of a potassium atom (K) is 2.8.8.1. Potassium has 19 electrons, which are arranged in shells as follows: 2 electrons in the first shell, 8 electrons in the second shell, 8 electrons in the third shell, and 1 electron in the fourth shell.
(ii) Describe how the electronic structure of potassium is related to its group number.
▶️Answer/Explanation
Answer: The number of outer shell electrons is the same as the group number.
Explanation: Potassium is in Group I of the Periodic Table, which means it has 1 electron in its outermost shell. The group number indicates the number of electrons in the outermost shell of the elements in that group.
(iii) The proton number of a potassium atom is 19. The nucleon number of this potassium atom is 39. State the numbers of electrons and neutrons in this potassium atom.
▶️Answer/Explanation
Answer: Electrons = 19; Neutrons = 20
Explanation: The number of electrons in a neutral atom is equal to the number of protons, which is 19. The number of neutrons is calculated by subtracting the proton number from the nucleon number: 39 – 19 = 20.
(iv) Complete Table 11.1 to show the charges and approximate relative masses of an electron and a neutron.
| Particle | Charge | Relative Mass |
|---|---|---|
| Proton | +1 | 1 |
| Electron | ||
| Neutron |
▶️Answer/Explanation
Answer: See table below.
Explanation: The electron has a charge of -1 and a relative mass of approximately 1/2000 (or 0 for practical purposes). The neutron has no charge (0) and a relative mass of 1.
(b) Potassium, K, is an element. Potassium hydroxide, KOH, is a compound. Explain the difference between an element and a compound.
▶️Answer/Explanation
Answer: An element contains only one type of atom, while a compound contains two or more elements chemically combined.
Explanation: Potassium (K) is an element because it consists of only one type of atom, which is potassium. Potassium hydroxide (KOH) is a compound because it is made up of potassium (K), oxygen (O), and hydrogen (H) atoms chemically bonded together.
(c) Balance the symbol equation for the reaction between potassium and water.
▶️Answer/Explanation
Answer: 2K + 2H2O → 2KOH + H2
Explanation: The balanced equation for the reaction between potassium and water is 2K + 2H2O → 2KOH + H2. This equation shows that 2 potassium atoms react with 2 water molecules to produce 2 potassium hydroxide molecules and 1 hydrogen molecule.
Question 12
(a) Fig. 12.1 shows a large snow tractor used in Antarctica. (Sub-topic: P1.5.1)
The snow tractor has large continuous tracks. These tracks allow the snow tractor to move across the snow without sinking.
Explain why a tractor with normal wheels would sink into the snow.
▶️Answer/Explanation
Answer: A tractor with normal wheels would sink into the snow because the weight of the tractor is distributed over a smaller surface area, leading to higher pressure on the snow. The large continuous tracks of the snow tractor distribute the weight over a larger surface area, reducing the pressure on the snow and preventing the tractor from sinking.
(b) When gasoline (petrol) burns in the engine of the snow tractor, carbon dioxide gas and water vapour are produced. State which of the diagrams, X, Y or Z in Fig. 12.2, shows the arrangement of gaseous carbon dioxide molecules. Give a reason for your answer. (Sub-topic: C1.1)
▶️Answer/Explanation
Answer: Diagram Z shows the arrangement of gaseous carbon dioxide molecules. The reason is that in the gaseous state, molecules are far apart and move freely, which is represented by the widely spaced and randomly arranged molecules in Diagram Z.
12(c)(i) The snow tractor accelerates. State the form of energy gained as the tractor accelerates. (Sub-topic: P1.6.1)
▶️Answer/Explanation
Answer: The form of energy gained as the tractor accelerates is kinetic energy.
12(c)(ii) The snow tractor moves up a hill at constant speed. State the form of energy gained as the tractor moves up the hill. (Sub-topic: P1.6.1)
▶️Answer/Explanation
Answer: The form of energy gained as the tractor moves up the hill is gravitational potential energy.
12(d) Fig. 12.3 shows a distance-time graph for the snow tractor moving at constant speed.
Calculate this constant speed. (Sub-topic: P1.2)
▶️Answer/Explanation
Answer: The constant speed can be calculated using the formula: \[ \text{speed} = \frac{\text{distance}}{\text{time}} \] From the graph, the distance covered is 8 meters in 16 seconds. Therefore: \[ \text{speed} = \frac{8 \, \text{m}}{16 \, \text{s}} = 0.5 \, \text{m/s} \]