Question 1 (Sub-topic – B15.3)
(a) Fig. 1.1 is a photograph of an insect-pollinated flower.
(i) Identify the parts labelled A, B and C in Fig. 1.1.
▶️Answer/Explanation
A: Stigma
B: Petal
C: Anther
(ii) Describe two visible pieces of evidence from Fig. 1.1 that suggest this is an insect-pollinated flower.
▶️Answer/Explanation
1: The presence of large, brightly colored petals to attract insects.
2: The stigma and anther are positioned inside the flower, making it easier for insects to transfer pollen.
(iii) Describe two ways the pollen from the flower in Fig. 1.1 would be different from pollen in a wind-pollinated flower.
▶️Answer/Explanation
1: Pollen grains in insect-pollinated flowers are larger and heavier compared to wind-pollinated flowers.
2: Pollen grains in insect-pollinated flowers are often sticky or spiky to adhere to insects, whereas wind-pollinated pollen is smooth and light.
(b) Pollen contains the male gametes.
State one way the chromosome number in the nuclei of a gamete is different from that of a zygote.
▶️Answer/Explanation
The chromosome number in the nuclei of a gamete is haploid (half the number of chromosomes), whereas the zygote is diploid (full set of chromosomes).
(c) A zygote is produced after fertilisation.
State where fertilisation occurs in a plant.
▶️Answer/Explanation
Fertilisation occurs in the ovary of the plant.
(d) Many plants are capable of both asexual and sexual reproduction.
Complete Table 1.1 to show the disadvantages of asexual and sexual reproduction in plants by placing ticks (✓) in the correct boxes.
| less genetic diversity | more energy is used finding a partner | no or less evolution | usually takes a longer length of time | |
|---|---|---|---|---|
| asexual | ✓ | |||
| sexual |
▶️Answer/Explanation
Asexual reproduction leads to less genetic diversity, while sexual reproduction requires more energy to find a partner and usually takes a longer time.
| less genetic diversity | more energy is used finding a partner | no or less evolution | usually takes a longer length of time | |
|---|---|---|---|---|
| asexual | ✓ | ✓ | ||
| sexual | ✓ | ✓ |
Question 2
Hydrogen peroxide solution slowly decomposes to make water and oxygen gas.
(a) (i) Write the word equation for this reaction. (Sub-topic – C6.2)
▶️Answer/Explanation
hydrogen peroxide → water + oxygen
(ii) Manganese(IV) oxide is a catalyst for this reaction. Describe what is meant by a catalyst.
▶️Answer/Explanation
A catalyst is a substance that speeds up a reaction without being used up in the reaction. It is not included in the chemical equation and remains unchanged at the end of the reaction.
(b) A student investigates the decomposition of hydrogen peroxide solution. Fig. 2.1 shows the student’s experiment.
Fig. 2.2 shows a graph of the student’s results.
(i) State the loss in mass after 2 minutes.
▶️Answer/Explanation
0.4 g
(ii) State what happens to the rate of the reaction between 1 and 4 minutes.
▶️Answer/Explanation
The rate of the reaction decreases.
(c) The student wants to increase the rate of the decomposition of the hydrogen peroxide solution. He does not want to change the catalyst or the volume of the hydrogen peroxide solution. Describe and explain one way that the student can use to increase the rate of the reaction. Explain your answer in terms of collisions between particles. (Sub-topic – C6.2)
▶️Answer/Explanation
The student can increase the temperature of the hydrogen peroxide solution. Increasing the temperature increases the kinetic energy of the particles, causing them to move faster. This results in more frequent collisions between the particles, leading to a higher rate of reaction. Additionally, more particles will have energy greater than the activation energy, increasing the number of successful collisions.
Question 3
Fig. 3.1 shows a kettle and the label on the bottom of the kettle. The kettle contains a heating element inside its base. The kettle is made of white plastic. (Subtopics: P1.6.1, P1.6.2)
(a) Explain, in terms of thermal energy transfer, why the kettle is:
- made of plastic.
- white.
▶️Answer/Explanation
(i) Made of plastic:
Plastic is a poor conductor of thermal energy, meaning it does not easily transfer heat. This property makes it a good insulator, preventing heat from escaping the kettle and reducing the risk of burns when touching the kettle’s exterior.
(ii) White:
White objects emit less thermal radiation compared to darker colors. This means that the kettle loses less heat through radiation, making it more energy-efficient.
(b) The kettle is filled with cold water and switched on. (Subtopics: P1.5.1, P1.6.1, P1.6.2)
Question:
- Describe, in terms of density changes, how the heating element heats up all of the water.
- Calculate the current in the heating element. State the unit for your answer.
- Show that the resistance of the heating element is 24 Ω.
- The heating element is connected in parallel with a 12 Ω resistor. Calculate the combined resistance of the heating element and the resistor.
▶️Answer/Explanation
(i) Heating the water:
When the heating element heats the water at the bottom of the kettle, the water’s density decreases as it gets warmer. The less dense, warmer water rises, and the cooler, denser water sinks to the bottom. This creates a convection current, which circulates the water and ensures that all of it is heated evenly.
(ii) Current calculation:
The current \( I \) can be calculated using the formula: \[ I = \frac{P}{V} \] Where \( P = 2400 \, \text{W} \) (power) and \( V = 240 \, \text{V} \) (voltage). Substituting the values: \[ I = \frac{2400}{240} = 10 \, \text{A} \] The unit for current is amperes (A).
(iii) Resistance calculation:
The resistance \( R \) can be calculated using Ohm’s Law: \[ R = \frac{V}{I} \] Substituting the values: \[ R = \frac{240}{10} = 24 \, \Omega \] Thus, the resistance of the heating element is 24 Ω.
(iv) Combined resistance:
When resistors are connected in parallel, the combined resistance \( R_{\text{total}} \) is given by: \[ \frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2} \] Where \( R_1 = 24 \, \Omega \) and \( R_2 = 12 \, \Omega \). Substituting the values: \[ \frac{1}{R_{\text{total}}} = \frac{1}{24} + \frac{1}{12} = \frac{1}{24} + \frac{2}{24} = \frac{3}{24} = \frac{1}{8} \] Therefore: \[ R_{\text{total}} = 8 \, \Omega \] The combined resistance of the heating element and the resistor is 8 Ω.
Question 4
(a) Table 4.1 shows the forest area in two different continents, A and B, in 1990 and 2010. (Subtopics: B19.1)
| Continent | Total forest area / thousand km² (1990) | Total forest area / thousand km² (2010) |
|---|---|---|
| A | 9460 | 8640 |
| B | 9890 | 10050 |
(i) Compare the total forest area for continents A and B between the years 1990 and 2010. Use comparative data from Table 4.1 in your answer.
▶️Answer/Explanation
Answer:
The forest area in continent A decreased from 9460 thousand km² in 1990 to 8640 thousand km² in 2010, indicating a loss of forest area.
The forest area in continent B increased from 9890 thousand km² in 1990 to 10050 thousand km² in 2010, indicating a gain in forest area.
Continent B consistently had more forest area than continent A in both years.
Explanation:
The data shows a clear trend of deforestation in continent A and afforestation in continent B over the 20-year period.
(ii) The change to the total forest area for continent A may affect the animals living in the forest. Describe three ways the animals may be affected.
▶️Answer/Explanation
Answer:
1. Loss of habitat: Animals may lose their natural habitat due to deforestation, leading to displacement.
2. Disruption of food chains: Deforestation can disrupt the availability of food sources, affecting the survival of animals.
3. Increased risk of extinction: Some species may face extinction due to the loss of their natural environment.
Explanation:
Deforestation directly impacts the ecosystem, leading to habitat loss, food scarcity, and potential extinction of species.
(iii) Explain two ways that deforestation causes the carbon dioxide concentration in the atmosphere to increase.
▶️Answer/Explanation
Answer:
1. Reduced photosynthesis: Trees absorb CO₂ during photosynthesis. Deforestation reduces the number of trees, leading to less CO₂ being absorbed.
2. Combustion of trees: When trees are cut down and burned, the carbon stored in them is released as CO₂ into the atmosphere.
Explanation:
Deforestation contributes to higher CO₂ levels by reducing the number of trees that can absorb CO₂ and by releasing stored carbon when trees are burned.
(b) Plants in a forest will compete for light. Auxin is a hormone that is responsible for the chemical control of shoot growth. Complete the sentences to describe how auxin causes shoots to grow towards the light. Subtopics: B19.2 (Conservation)
Auxin is made in the shoot ……………………………………….. and moves and spreads through the plant.
It collects on the ……………………………………….. side of the shoot.
Auxin stimulates cell ………………………………………..so this side will grow more.
This results in the shoot bending towards the light. This growth response to light is called ……………………………………….. .
▶️Answer/Explanation
Answer:
Auxin is made in the shoot tip(s) and moves and spreads through the plant. It collects on the shaded side of the shoot. Auxin stimulates cell elongation so this side will grow more. This results in the shoot bending towards the light. This growth response to light is called phototropism.
Explanation:
Auxin is a plant hormone that promotes cell elongation. It accumulates on the shaded side of the shoot, causing cells on that side to grow longer, which results in the shoot bending towards the light. This process is known as phototropism.
Question 5
Different methods can be used to extract metals from their ores. The method used depends on how reactive each metal is.
(a) Draw a line to link the reactivity of each metal to the method of extracting it from the ore. Use each method only once. (Sub-topic – C9.4)
▶️Answer/Explanation
Answer:
Reactive metal e.g. aluminium → Electrolysis
Less reactive metal e.g. copper → Heating with carbon
Very unreactive metal e.g. gold → Extracted from the ground as the metal
Explanation:
The method of extracting a metal from its ore depends on its reactivity. Highly reactive metals like aluminium require electrolysis because they cannot be reduced by carbon. Less reactive metals like copper can be reduced by heating with carbon. Very unreactive metals like gold are found in their native state and can be extracted directly from the ground.
(b) Fig. 5.1 shows a blast furnace. It is used to extract iron from iron ore.
Three raw materials:
- Iron ore
- Limestone
- Substance A
(i) State the name of an ore that contains iron. Choose from the list:
- bauxite
- hematite
- malachite
- marble
▶️Answer/Explanation
Answer: Hematite
Explanation: Hematite (Fe2O3) is an iron ore commonly used in the extraction of iron in a blast furnace.
(ii) State the name of substance A.
▶️Answer/Explanation
Answer: Carbon (coke)
Explanation: Substance A is carbon, usually in the form of coke, which acts as a reducing agent in the blast furnace.
(iii) Inside the blast furnace, iron ore, Fe2O3, reacts with carbon monoxide, CO. Iron, Fe, and carbon dioxide, CO2, are made. Write the balanced symbol equation for this reaction.
▶️Answer/Explanation
Answer: Fe2O3 + 3CO → 2Fe + 3CO2
Explanation: In the blast furnace, iron(III) oxide reacts with carbon monoxide to produce iron and carbon dioxide. The equation is balanced with 2 iron atoms and 3 CO2 molecules.
(iv) In the blast furnace, iron(III) ions, Fe3+, are changed into iron.
The balanced half-equation is shown.
Fe3+ + 3e– → Fe.
State the name of the process when electrons are gained.
▶️Answer/Explanation
Answer: Reduction
Explanation: The process of gaining electrons is called reduction. In this case, iron(III) ions gain electrons to form iron atoms.
(v) Iron(III) ions, Fe3+, react with sulfate ions, SO42-, to make iron(III) sulfate. Determine the formula of iron(III) sulfate.
▶️Answer/Explanation
Answer: Fe2(SO4)3
Explanation: Iron(III) sulfate is formed by combining 2 iron(III) ions (Fe3+) with 3 sulfate ions (SO42-), resulting in the formula Fe2(SO4)3.
(c) Calcium carbonate, CaCO3, is used to remove acidic impurities in the blast furnace. Calcium carbonate thermally decomposes to make calcium oxide and carbon dioxide.
The balanced symbol equation for the reaction is shown:
CaCO3 → CaO + CO2.
1000 kg of calcium carbonate are heated. Calculate the mass of carbon dioxide gas made. Show your working. [Ar: C, 12; Ca, 40; O, 16]
▶️Answer/Explanation
Answer: 440 kg
Explanation:
The molar mass of CaCO3 is 40 + 12 + (3 × 16) = 100 g/mol.
The molar mass of CO2 is 12 + (2 × 16) = 44 g/mol.
From the balanced equation, 1 mole of CaCO3 produces 1 mole of CO2.
Therefore, 1000 kg of CaCO3 will produce (44/100) × 1000 = 440 kg of CO2.
Question 6
(a) A sprinter runs a 200 m race in 25 seconds.
(i) Calculate the average speed of the sprinter. (Sub-topic – P1.2.1)
▶️Answer/Explanation
Average speed = 8 m/s
Solution:
Average speed is calculated using the formula:
\[ \text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} \]
Given:
Total distance = 200 m
Total time = 25 s
\[ \text{Average speed} = \frac{200 \, \text{m}}{25 \, \text{s}} = 8 \, \text{m/s} \]
Therefore, the average speed of the sprinter is 8 m/s.
(ii) The sprinter has a mass of 90 kg. Calculate the average kinetic energy of the sprinter. (Sub-topic – P1.6.1)
▶️Answer/Explanation
Average kinetic energy = 2880 J
Solution:
Kinetic energy is calculated using the formula:
\[ \text{Kinetic energy} = \frac{1}{2} m v^2 \]
Given:
Mass (m) = 90 kg
Speed (v) = 8 m/s (from part (i))
\[ \text{Kinetic energy} = \frac{1}{2} \times 90 \, \text{kg} \times (8 \, \text{m/s})^2 \]
\[ \text{Kinetic energy} = \frac{1}{2} \times 90 \times 64 = 2880 \, \text{J} \]
Therefore, the average kinetic energy of the sprinter is 2880 J.
(b) Fig. 6.1 shows the forces acting on the sprinter during the race.
(i) Calculate the resultant force acting on the sprinter. (Sub-topic – P1.5.1)
▶️Answer/Explanation
Resultant force = 130 N
Solution:
The resultant force is calculated by subtracting the opposing force from the forward force:
\[ \text{Resultant force} = \text{Forward force} – \text{Opposing force} \]
Given:
Forward force = 240 N
Opposing force = 110 N
\[ \text{Resultant force} = 240 \, \text{N} – 110 \, \text{N} = 130 \, \text{N} \]
Therefore, the resultant force acting on the sprinter is 130 N.
(ii) Describe how these forces would change the motion of the sprinter. (Sub-topic – P1.5.1)
▶️Answer/Explanation
The sprinter will accelerate forward due to the resultant force acting in the forward direction.
Solution:
The resultant force of 130 N acts in the forward direction. According to Newton’s second law of motion, a resultant force causes acceleration in the direction of the force. Therefore, the sprinter will accelerate forward, increasing their speed over time.
Question 7
Fig. 7.1 is a diagram of a cross-section through human skin. (Subtopics: B13.1)
(a)The boxes on the left show the letters in Fig. 7.1. The boxes on the right show the names of some of the parts of the skin. Draw lines to link each letter in Fig. 7.1 to its correct name.
▶️Answer/Explanation
Answer:
- A – fatty tissue
- B – hair erector muscle
- C – receptor
- D – sweat gland
Explanation: The diagram shows a cross-section of human skin, and the labels correspond to the different structures within the skin. Fatty tissue is found beneath the dermis, hair erector muscles are attached to hair follicles, receptors are sensory structures, and sweat glands are responsible for producing sweat.
(b) Fig. 7.2 shows blood vessels in the skin during warm conditions. (Subtopics: B13.3)
(i) Describe the role of arterioles and capillaries in temperature control when the body gets too hot. Include the name of the process in your answer.
(ii) State one response by the body to a decrease in internal body temperature.
(iii) Name the term used to describe the mechanism used to return internal body temperature to a normal level.
▶️Answer/Explanation
Answer:
(i) Arterioles dilate (vasodilation) to increase blood flow to the skin’s surface, allowing more heat to be lost through radiation. Capillaries also widen, increasing blood flow near the skin surface, which helps in heat loss.
(ii) One response to a decrease in internal body temperature is shivering, which generates heat through muscle activity.
(iii) The term used to describe the mechanism is negative feedback.
Explanation: When the body gets too hot, vasodilation occurs, increasing blood flow to the skin to release heat. When the body gets too cold, shivering generates heat. Negative feedback is the process that helps maintain homeostasis by reversing any changes in internal conditions.
(c) Adrenaline is a hormone that can also affect the skin and blood flow. (Subtopics: B13.2)
Describe two ways that adrenaline affects the blood.
▶️Answer/Explanation
Answer:
1. Adrenaline increases blood flow to muscles by dilating blood vessels in muscles, preparing the body for “fight or flight.”
2. Adrenaline increases the heart rate, which increases blood pressure and ensures more oxygen and glucose are delivered to tissues.
Explanation: Adrenaline is a hormone released during stress or danger. It prepares the body for action by increasing blood flow to muscles and raising heart rate, ensuring that the body has enough energy and oxygen to respond to the situation.
Question 8
The fractional distillation of petroleum makes useful fractions. Three of the fractions made are petrol, fuel oil and refinery gas.
Refinery gas contains ethane, C2H6.
(a) Draw the structure of an ethane molecule. Show all the covalent bonds. [Subtopic: C11.2]
▶️Answer/Explanation
The structure of ethane (C2H6) is as follows:
H H
| |
H-C-C-H
| |
H H
Each carbon atom forms single covalent bonds with three hydrogen atoms and one carbon atom.
(b) Ethane burns in oxygen to make carbon dioxide and water. The balanced symbol equation is shown: [Subtopic: C5.1]
2C2H6 + 7O2 → 4CO2 + 6H2O
The reaction is exothermic.
Use the axes shown in Fig. 8.1 to draw and label the energy level diagram for this reaction.
Label:
- the energy of the reactants and the products
- the energy change in the reaction
- the activation energy of the reaction.
▶️Answer/Explanation
The energy level diagram for the exothermic reaction of ethane burning in oxygen:
The reactants (2C2H6 + 7O2) are at a higher energy level.
The products (4CO2 + 6H2O) are at a lower energy level.
The energy change (ΔH) is negative, indicating an exothermic reaction.
The activation energy (Ea) is the energy required to start the reaction.
(c) Fractional distillation makes too much fuel oil and not enough petrol.
Cracking is a process that breaks large molecules into smaller molecules.
Some fractions are cracked.
Suggest why cracking is useful. [Subtopic: C11.3]
▶️Answer/Explanation
Cracking is useful because:
It converts large, less useful hydrocarbon molecules (like fuel oil) into smaller, more useful molecules (like petrol).
It helps balance the supply and demand for different fractions.
It produces alkenes, which are valuable for making plastics and other chemicals.
(d) During cracking, dodecane, C12H26, can make octane, C8H18, and ethene, C2H4.
Write the balanced symbol equation for this reaction. [Subtopic: C11.5]
▶️Answer/Explanation
The balanced symbol equation for the cracking of dodecane is:
C12H26 → C8H18 + 2C2H4
(e) Ethene is changed into poly(ethene) in a polymerisation reaction.
Polymerisation changes many small molecules into larger long chain molecules.
State the name of the small molecules used in polymerisation. Choose from the list: [Subtopic: C11.7]
- alkane
- monomer
- nylon
- polymer
▶️Answer/Explanation
The small molecules used in polymerisation are called monomers.;
(f) Fig. 8.2 shows the structure of a small molecule called propene.
Propene is an alkene. It is unsaturated.
Explain why propene is unsaturated. [Subtopic: C11.5]
▶️Answer/Explanation
Propene is unsaturated because it contains a carbon-carbon double bond (C=C). Unsaturated hydrocarbons have at least one double or triple bond between carbon atoms, allowing them to undergo addition reactions.
(g) Table 8.1 shows the structures of some small molecules and long chain molecules.
Complete Table 8.1. [Subtopic: C11.7]
▶️Answer/Explanation
The completed table is as follows:
Question 9
(a) Fig. 9.1 represents a straight piece of wire carrying a current passing through a sheet of paper. (Sub-topic – P4.5.3)
(i) On Fig. 9.1, draw two field lines to show the shape and direction of the magnetic field around the wire.
▶️Answer/Explanation
The magnetic field lines should be concentric circles around the wire, with the direction of the field determined by the right-hand rule (thumb points in the direction of current, fingers curl in the direction of the magnetic field).
(ii) State what effect reversing the direction of the current would have on the magnetic field.
▶️Answer/Explanation
Reversing the direction of the current would reverse the direction of the magnetic field lines. The field lines would still be concentric circles, but their direction would be opposite to the original.
(b) Fig. 9.2 shows the wire placed into the magnetic field of a permanent magnet. (Sub-topic – P4.5.4)
(i) State the direction of the force acting on the wire.
▶️Answer/Explanation
The force acting on the wire is perpendicular to both the direction of the current and the magnetic field. Using Fleming’s Left-Hand Rule, the force would be directed upwards.
(ii) Suggest two changes that would increase the size of the force acting on the wire.
▶️Answer/Explanation
1. Increasing the current flowing through the wire.
2. Increasing the strength of the magnetic field.
(c) Fig. 9.3 shows an electric motor. (Sub-topic – P4.5.5)
(i) The following statements explain what causes the coil in Fig. 9.3 to rotate.
The statements are in the wrong order.
A A current flows through the coil.
B The coil experiences a force and starts to spin.
C The power supply applies a potential difference across the coil.
D This causes a magnetic field to be induced around the coil.
E This interacts with the permanent magnetic field.
Arrange the statements into the correct order.
▶️Answer/Explanation
The correct order is:
C → A → D → E → B
C: The power supply applies a potential difference across the coil.
A: A current flows through the coil.
D: This causes a magnetic field to be induced around the coil.
E: This interacts with the permanent magnetic field.
B: The coil experiences a force and starts to spin.
(ii) On Fig 9.3, label the split-ring commutator with a cross (X).
▶️Answer/Explanation
The split-ring commutator should be labeled with a cross (X) at the point where the coil connects to the external circuit.
(iii) Describe how the split-ring commutator allows the coil to keep on turning.
▶️Answer/Explanation
The split-ring commutator reverses the direction of the current in the coil every half turn, ensuring that the force acting on the coil always remains in the same direction, allowing the coil to continue rotating.
(d) A simple a.c. generator produces an alternating voltage. (Sub-topic – P4.5.2)
Fig 9.4 shows how the voltage from the generator varies with time in the form of a wave.
(i) On Fig. 9.4, draw a double-headed arrow (↔) to show the time taken for the coil in the generator to complete one full rotation.
▶️Answer/Explanation
The double-headed arrow should span the time period of one complete cycle of the wave, indicating the time taken for the coil to complete one full rotation.
(ii) The size of the voltage from the generator is indicated by the amplitude of the wave in Fig. 9.4. On Fig. 9.4, draw the voltage output of the generator with a smaller voltage.
▶️Answer/Explanation
Draw a sine wave with a smaller amplitude (height) compared to the original wave, indicating a smaller voltage output.
Question 10
(a) The percentage of oxygen in inspired air, in expired air when resting and in expired air during exercise is different. Table 10.1 shows these differences.
The percentage of oxygen in expired air when resting and expired air during exercise is different.
(i) Calculate the difference in the percentage of oxygen between expired air when resting and expired air during exercise. (Subtopic – B11.1)
▶️Answer/Explanation
The difference in the percentage of oxygen between expired air when resting and expired air during exercise is:
16% – 14% = 2%
(ii) Explain this difference. (Subtopic – B11.1)
▶️Answer/Explanation
During exercise, the body’s demand for oxygen increases to meet the higher energy requirements. As a result, more oxygen is extracted from the inspired air by the muscles, leading to a lower percentage of oxygen in the expired air during exercise compared to when at rest.
(b) Exercise increases the rate of breathing. Describe one other effect of exercise on the pattern of breathing. (Subtopic – B11.1)
▶️Answer/Explanation
Another effect of exercise on the pattern of breathing is an increase in the depth of breathing. This means that each breath taken during exercise is deeper, allowing more air to enter and exit the lungs, which helps to meet the increased oxygen demand and remove more carbon dioxide.
(c) An increase in the concentration levels of one gas in the blood causes the increase in breathing rate. Name this gas. (Subtopic – B11.1)
▶️Answer/Explanation
The gas that causes an increase in breathing rate when its concentration levels in the blood rise is carbon dioxide (CO2).
(d) Alveoli is the gas exchange surface in humans. Name two structures that air must pass through before it reaches the alveoli during inspiration. (Subtopic – B11.1)
▶️Answer/Explanation
Two structures that air must pass through before it reaches the alveoli during inspiration are:
- Trachea
- Bronchi
Question 11
Fig. 11.1 shows an outline of the Periodic Table.
(a) Draw a line to link each element to its correct description. (Subtopic – C8.1)
Use each description only once.
▶️Answer/Explanation
He – an element with an electronic structure of 2
Al – an element in Group 3 and Period 3
Ar – an element with 8 electrons in its outer shell
(b) Argon is a gas used in lamps. Explain why. (Subtopic – C8.5)
▶️Answer/Explanation
Argon is a noble gas, which means it is chemically inert and does not react with other substances. This makes it ideal for use in lamps, as it prevents the filament from oxidizing and burning out quickly.
(c) The nucleus of a carbon atom contains six protons. State the charge on a proton. (Subtopic – C2.2)
▶️Answer/Explanation
The charge on a proton is +1.
(d) Potassium metal reacts with the non-metal bromine to form potassium bromide. Potassium bromide is an ionic compound. Describe how metallic and non-metallic elements form ionic bonds.
(Subtopic – C2.4)
▶️Answer/Explanation
Metallic elements lose electrons to form positively charged ions (cations), while non-metallic elements gain electrons to form negatively charged ions (anions). These oppositely charged ions are held together by strong electrostatic forces, forming an ionic bond. In the case of potassium bromide, potassium (K) loses one electron to form K⁺, and bromine (Br) gains one electron to form Br⁻, resulting in the ionic compound KBr.
(e) The electronic structure of carbon is 2.4. The electronic structure of oxygen is 2.6. The atoms in a molecule of carbon dioxide, CO₂, are held together by covalent bonds. Draw the dot-and-cross diagram to show the bonding in carbon dioxide. You only need to include the outer shell electrons. (Subtopic – C2.5)
▶️Answer/Explanation
In the dot-and-cross diagram for CO₂:
Carbon has 4 outer electrons and forms double bonds with each oxygen atom.
Each oxygen atom has 6 outer electrons and shares 2 electrons with carbon to complete its octet.
The structure is linear, with carbon in the center and oxygen atoms on either side.
Question 12
Fig. 12.1 shows the arrangement of molecules in samples of a solid, a liquid and a gas.
(a) Some statements about the structure and properties of matter are given. Place a tick (✓) next to all of the statements that describe the structure or properties of a solid. (Sub-topic: P1.5.1)
▶️Answer/Explanation
Answer:
Forces between molecules are strong.
It has a fixed volume.
Molecules can only vibrate.
(b) Fig. 12.2 shows a syringe filled with a gas similar to the sample shown in Fig. 12.1.
The syringe is attached to a pressure gauge which measures the pressure of the gas.
Describe what causes the pressure in the sample of gas in terms of molecular motion. (Sub-topic: P1.5.1)
▶️Answer/Explanation
Answer:
The pressure in the gas is caused by the collisions of gas molecules with the walls of the syringe. As the molecules move randomly and collide with the walls, they exert a force on the walls, which results in pressure. The more frequent and forceful the collisions, the higher the pressure.
(c) A student conducts an investigation into how the pressure of the gas changes with volume. The temperature of the gas remains constant.
Fig. 12.3 shows the results of the student’s investigation. (Sub-topic: P1.5.1)
(i) Use Fig. 12.3 to determine the volume of the sample of gas when the pressure is 500 kPa.
▶️Answer/Explanation
Answer:
The volume of the gas when the pressure is 500 kPa is 10 cm3.
(ii) The mass of the sample of gas is 2.45 g. Calculate the density of the sample of gas when the pressure is 500 kPa.
▶️Answer/Explanation
Answer:
Density = Mass / Volume
Density = 2.45 g / 10 cm3 = 0.245 g/cm3.
(d) Explain why increasing the temperature of a sample of gas, while keeping the volume constant, causes an increase in pressure. (Sub-topic: P1.5.1)
▶️Answer/Explanation
Answer:
Increasing the temperature of a gas while keeping the volume constant causes the gas molecules to move faster. This increases the frequency and force of collisions with the walls of the container, resulting in an increase in pressure. According to the kinetic theory of gases, pressure is directly proportional to temperature when volume is constant.