Question 1
(a) The total number of new HIV infections in the world is monitored. The results are shown in Fig. 1.1. (Sub-topic – B10.1)
(i) Calculate the percentage decrease in the number of new HIV infections between 2000 and 2010 as shown in Fig. 1.1.
▶️Answer/Explanation
Answer: 31%
Explanation: The number of new HIV infections in 2000 was 3.2 million, and in 2010, it was 2.2 million. The decrease is 3.2 – 2.2 = 1.0 million. The percentage decrease is calculated as (1.0 / 3.2) × 100 = 31.25%, which rounds to 31%.
(ii) Suggest three reasons for the decrease in the number of new HIV infections.
▶️Answer/Explanation
Answer: 1. Discovery of routes of transmission
2. Increased use of barrier contraception
3. Screening of blood transfusions
Explanation: The decrease in HIV infections can be attributed to better understanding of how the virus spreads, increased use of protective measures like condoms, and improved screening of blood donations to prevent transmission.
(b) HIV is a virus that targets white blood cells. (Sub-topic – B9.4)
(i) State two functions of white blood cells.
▶️Answer/Explanation
Answer: 1. Phagocytosis
2. Antibody production
Explanation: White blood cells play a crucial role in the immune system by engulfing and destroying pathogens (phagocytosis) and producing antibodies to neutralize harmful substances.
(ii) White blood cells are one component of blood. State two other main components of blood.
▶️Answer/Explanation
Answer:
1. Red blood cells
2. Plasma
Explanation: Blood is composed of red blood cells, which transport oxygen, and plasma, the liquid component that carries cells and nutrients throughout the body.
(c) State the name of the barrier that protects the fetus from toxins in the mother’s blood. (Sub-topic – B15.4)
▶️Answer/Explanation
Answer: Placenta
Explanation: The placenta acts as a barrier between the mother and fetus, allowing the exchange of nutrients and oxygen while protecting the fetus from harmful substances in the mother’s blood.
Question 2
(a) Fig. 2.1 shows the atoms of some elements. The letters do not represent the symbols of the elements. (Sub-topic – C2.2)
(i) State the evidence from Fig. 2.1 that shows that element C is in Group III of the Periodic Table.
(ii) Identify which of the elements in Fig. 2.1 forms an ion with a charge of –3. Choose from A, B, C, D or E.
(iii) Write the electronic structure of element E.
(iv) Identify which of the elements in Fig. 2.1 has a proton number (atomic number) of 9. Choose from A, B, C, D or E.
(v) State the evidence from Fig. 2.1 that shows that element A is unreactive.
(vi) Elements B and D react together to form an ionic compound. Draw a dot-and-cross diagram to show the ions formed when elements B and D react together.
Include the charges on the ions.
(vii) Ionic compounds have a lattice structure. Describe the lattice structure of ionic compounds.
▶️Answer/Explanation
(i) Element C has 3 electrons in the outer shell.
(ii) Element E forms an ion with a charge of –3.
(iii) The electronic structure of element E is 2.8.5.
(iv) Element D has a proton number (atomic number) of 9.
(v) Element A has a full outer shell, making it unreactive.
(vi) 
(vii) regular / alternating, arrangement ;
of positive and negative ions ;
(b) The nucleus of an atom contains protons and neutrons. Table 2.1 shows the relative charge and relative mass of a proton. Complete the table to show the relative charge and relative mass of a neutron.
(Sub-topic – C2.2)
Table 2.1
| relative charge | relative mass | |
|---|---|---|
| proton | +1 | 1 |
| neutron |
▶️Answer/Explanation
The completed table is as follows:
| relative charge | relative mass | |
|---|---|---|
| proton | +1 | 1 |
| neutron | 0 | 1 |
Question 3
(a) Fig. 3.2 shows a distance-time graph for part of the journey of a man transporting luggage in a small boat. (Sub-topic – P1.2)
(i) Using data from the graph, describe the journey shown in Fig. 3.2.
(ii) Show that the speed of the boat, 20 seconds after the start of the journey, is \(4.0 \, \text{m/s}\).
(iii) The combined mass of the man, his luggage, and the small boat is 100 kg. Calculate the total kinetic energy of the man, his luggage, and the small boat when their speed reaches \(4.0 \, \text{m/s}\).
▶️Answer/Explanation
(i) The journey shown in the graph can be described as follows:
- From 0 to 50 seconds, the boat travels at a constant speed, covering 200 meters.
- From 50 to 100 seconds, the boat is stationary, as the distance does not change.
(ii) To calculate the speed at 20 seconds: \[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} = \frac{80 \, \text{m}}{20 \, \text{s}} = 4.0 \, \text{m/s} \]
(iii) The kinetic energy (KE) is calculated using the formula: \[ KE = \frac{1}{2}mv^2 = \frac{1}{2} \times 100 \, \text{kg} \times (4.0 \, \text{m/s})^2 = 800 \, \text{J} \]
(b) The man lifts the boat off the water and attaches it to a trolley. The man exerts a downward force \( F \) which keeps the boat in equilibrium as shown in Fig. 3.3. The wheels of the trolley act as a pivot.
Use the principle of moments to calculate the size of the force \( F \). (Sub-topic – P1.5.2)
▶️Answer/Explanation
To calculate the force \( F \), we use the principle of moments. The moment of a force is given by: \[ \text{Moment} = \text{Force} \times \text{Distance from pivot} \] For equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments: \[ 600 \, \text{N} \times 40 \, \text{cm} = F \times 100 \, \text{cm} \] Solving for \( F \): \[ F = \frac{600 \, \text{N} \times 40 \, \text{cm}}{100 \, \text{cm}} = 240 \, \text{N} \]
Question 4
(a) A scientist tests the resistance of one strain of bacteria to four different antibiotics, A, B, C, and D. Four paper discs, each soaked with a different antibiotic, are placed on an agar plate containing the bacteria. The shaded areas show where the bacteria grow. The clear areas show where no bacteria grow. Fig. 4.1 shows the results. (Sub-topic – B10.1)
(i) Use Fig. 4.1 to identify the antibiotic that is the most effective against this strain of bacteria.
▶️Answer/Explanation
Answer: B
Explanation: The antibiotic that is most effective will have the largest clear area around the disc, indicating that it has inhibited bacterial growth the most. In Fig. 4.1, antibiotic B has the largest clear area, showing it is the most effective against the bacteria.
(ii) Strains of bacteria develop antibiotic resistance due to natural selection. Complete the sentences to describe how strains with antibiotic resistance develop.
Different strains of bacteria will show …… in their ability to resist antibiotics. When antibiotics are used, some of the bacteria will survive and some will …… Those that survive will pass on their …… to the next generation. The next generation will also show …… to antibiotics. Eventually, the whole population will have this feature.
▶️Answer/Explanation
Answer: variation, die, alleles, resistance
Explanation: Natural selection leads to the development of antibiotic resistance in bacteria. Different strains of bacteria show variation in their ability to resist antibiotics. When antibiotics are used, some bacteria survive while others die. The surviving bacteria pass on their resistant alleles to the next generation, which will also show resistance to antibiotics. Over time, the entire population may become resistant.
(b) Natural selection results in evolution. The box on the left contains the term evolution. The boxes on the right show some sentence endings. Draw two lines from the box on the left to make two correct sentences. (Sub-topic – B17.2)
▶️Answer/Explanation
Answer: Evolution increases suitability to the environment. Evolution is a change of adaptive features.
Explanation: Evolution is a process that leads to changes in the adaptive features of organisms, making them more suited to their environment. It does not occur in a single generation or only in bacteria, and it does not cause changes in individual organisms within their lifetime.
(c) Antibiotic resistance originates due to mutation. (Sub-topic – B17.1)
(i) Define the term mutation.
▶️Answer/Explanation
Answer: Mutation is a change in the gene or chromosome.
Explanation: A mutation is a change in the DNA sequence of a gene or chromosome. This change can lead to variations in traits, some of which may provide an advantage, such as antibiotic resistance in bacteria.
(ii) State the name of the type of radiation that increases the rate of mutation.
▶️Answer/Explanation
Answer: Ionising radiation
Explanation: Ionising radiation, such as X-rays or gamma rays, can cause mutations by damaging the DNA in cells, leading to changes in the genetic material.
Question 5
(a) A scientist investigates a food colouring, X, using chromatography. The scientist also analyses four known food colourings, A, B, C, and D. Fig. 5.1 shows the chromatogram produced. The result for food colouring D is not shown. (Sub-topic – C12.3)
The Rf value of a food colouring is calculated using the formula:
\[ Rf = \frac{\text{distance travelled by substance}}{\text{distance travelled by solvent}} \]
Calculate the Rf value of food colouring B.
Show your working.
▶️Answer/Explanation
Answer: 0.90
Explanation: The distance travelled by substance B is 4.5 cm, and the distance travelled by the solvent is 5.0 cm. Using the formula: \[ Rf = \frac{4.5}{5.0} = 0.90 \]
(b) Food colouring D has an Rf value of 0.56. Calculate the distance travelled by food colouring D. (Sub-topic – C12.3)
▶️Answer/Explanation
Answer: 2.8 cm
Explanation: The Rf value is given as 0.56, and the distance travelled by the solvent is 5.0 cm. Using the formula: \[ \text{Distance travelled by D} = Rf \times \text{distance travelled by solvent} = 0.56 \times 5.0 = 2.8 \, \text{cm} \]
(c) State which food colouring, A, B, or C, is not in food colouring X. (Sub-topic – C12.3)
▶️Answer/Explanation
Answer: A
Explanation: Food colouring A does not match any of the spots in food colouring X on the chromatogram, indicating that it is not present in X.
(d) The scientist also investigates the purity of four substances, V, W, Y, and Z. Table 5.1 shows the melting point of each substance. (Sub-topic – C12.4)
| Substance | Melting Point/°C |
|---|---|
| V | 98 |
| W | 92 – 95 |
| Y | 82 |
| Z | 102 – 104 |
State which of the substances are pure.
Explain your answer.
▶️Answer/Explanation
Answer: V and Y
Explanation: Pure substances have a specific melting point, whereas impure substances melt over a range of temperatures. Substances V and Y have specific melting points (98°C and 82°C, respectively), indicating they are pure. Substances W and Z melt over a range, indicating they are impure.
(e) The scientist dissolves 4.8 g of a substance in 250 cm3 of distilled water. The relative molecular mass, \( M_r \), of the substance is 192. Calculate the concentration of the solution in mol/dm3.
(Sub-topic – C3.3)
▶️Answer/Explanation
Answer: 0.10 mol/dm3
Explanation: First, calculate the number of moles of the substance: \[ \text{Moles} = \frac{\text{Mass}}{\text{Relative Molecular Mass}} = \frac{4.8}{192} = 0.025 \, \text{mol} \] Next, convert the volume from cm3 to dm3: \[ 250 \, \text{cm}^3 = 0.25 \, \text{dm}^3 \] Finally, calculate the concentration: \[ \text{Concentration} = \frac{\text{Moles}}{\text{Volume}} = \frac{0.025}{0.25} = 0.10 \, \text{mol/dm}^3 \]
Question 6
(a) The fence is powered by an e.m.f. of 2000V and carries a current of 80mA. (Sub-topic – P4.2.4)
(i) Calculate the total resistance of the fence.
▶️Answer/Explanation
Solution:
Given:
E.m.f. (V) = 2000 V
Current (I) = 80 mA = 0.08 A
Using Ohm’s Law: \( R = \frac{V}{I} \)
\( R = \frac{2000}{0.08} = 25000 \, \Omega \)
Answer: 25000 Ω
(ii) The fence is made of two identical cables connected in parallel. The cables act as resistors. Use your answer to 6(a)(i) to calculate the resistance of one of the cables.
▶️Answer/Explanation
Solution:
For resistors in parallel, the total resistance \( R_{total} \) is given by:
\( \frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} \)
Since the two cables are identical, \( R_1 = R_2 = R \).
\( \frac{1}{25000} = \frac{1}{R} + \frac{1}{R} = \frac{2}{R} \)
\( R = 2 \times 25000 = 50000 \, \Omega \)
Answer: 50000 Ω
(iii) A different enclosure uses a fence made of cables that are the same thickness but twice the length of those shown in Fig. 6.1. State the effect of doubling the cable length on the resistance of the fence.
▶️Answer/Explanation
Solution:
Resistance is directly proportional to the length of the cable. Therefore, doubling the length of the cable will double the resistance.
Answer: The resistance doubles.
(b) One of the zebras is startled by a loud sound. (Sub-topic – P3.4)
(i) Describe how sound waves are transmitted in air.
▶️Answer/Explanation
Solution:
Sound waves are transmitted in air through the vibration of air molecules. These vibrations create compressions and rarefactions, which propagate as a longitudinal wave through the air.
Answer: Sound waves are transmitted through compressions and rarefactions in the air.
(ii) After hearing the sound, the zebra runs across the enclosure in 7.5s. The average speed of the zebra is 16 m/s. Calculate the distance the zebra runs.
▶️Answer/Explanation
Solution:
Given:
Speed (v) = 16 m/s
Time (t) = 7.5 s
Using the formula: \( \text{Distance} = \text{Speed} \times \text{Time} \)
\( \text{Distance} = 16 \times 7.5 = 120 \, \text{m} \)
Answer: 120 m
(c) Fig. 6.3 shows one of the zebras in the enclosure. The zebra has black and white stripes. A vet uses an infrared camera to measure the temperature of the zebra. The infrared camera shows that the black stripes are a different temperature to the white parts of the zebra. Describe and explain the difference in temperature recorded. (Sub-topic – P2.3.3)
▶️Answer/Explanation
Solution:
Black surfaces absorb more infrared radiation than white surfaces, which reflect more radiation. Therefore, the black stripes will absorb more heat and show a higher temperature on the infrared camera compared to the white stripes.
Answer: The black stripes will show a higher temperature because they absorb more infrared radiation, while the white stripes reflect more radiation and show a lower temperature.
Question 7
(a) Discarded rubbish pollutes ecosystems such as oceans and rivers. (Sub-topic – B19.1)
A student has written a definition of an ecosystem. Their definition is not correct. Circle the two words in their definition that are not correct.
‘An ecosystem is a unit containing all of the organisms and their offspring, interacting together, in a given time.’
▶️Answer/Explanation
The two incorrect words are offspring and time. An ecosystem includes all living organisms and their physical environment, not just their offspring, and it is not limited to a specific time period.
(b) Several countries estimate the average mass of discarded rubbish per person per day. Fig. 7.1 shows the results. (Sub-topic – B19.1)
(i) Which country discards the most rubbish per person per day?
(ii) State the average mass of discarded rubbish per person per day in country E.
▶️Answer/Explanation
(i) Country C discards the most rubbish per person per day.
(ii) The average mass of discarded rubbish per person per day in country E is 0.75 kg.
(c) Pollution from excess use of fertilisers may cause eutrophication in rivers and lakes. Part of the process of eutrophication is an increase in the number of surface producers and the death of underwater producers. (Sub-topic – B19.1)
(i) Describe how an increase in the number of surface producers causes underwater producers to die.
(ii) Explain how the death of underwater producers causes the death of aquatic animals.
▶️Answer/Explanation
(i) An increase in the number of surface producers blocks light from reaching underwater producers, preventing them from photosynthesizing and eventually causing them to die.
(ii) The death of underwater producers leads to their decomposition by aerobic bacteria, which consume oxygen in the water. This reduces the oxygen levels in the water, leading to the death of aquatic animals due to lack of oxygen.
Question 8
(a)(i) The student tests the pH of dilute sulfuric acid, \( H_2SO_4 \), using Universal Indicator. Suggest the pH of the dilute sulfuric acid. (Sub-topic: C7.1)
▶️Answer/Explanation
Answer: Any pH below 7.
Explanation: Sulfuric acid is a strong acid, and strong acids typically have a pH value below 7. Universal Indicator turns red in the presence of strong acids, indicating a low pH.
(a)(ii) The student tests aqueous sodium hydroxide, NaOH, with red litmus paper. State what the student observes. (Sub-topic: C7.1)
▶️Answer/Explanation
Answer: The red litmus paper turns blue.
Explanation: Sodium hydroxide is a strong base (alkali). Red litmus paper turns blue in the presence of a base, indicating that the solution is alkaline.
(a)(iii) The student reacts dilute sulfuric acid with aqueous sodium hydroxide. Sodium sulfate, \( Na_2SO_4 \), and water are made. Construct the balanced symbol equation for this reaction. (Sub-topic: C7.1)
▶️Answer/Explanation
Answer: \( H_2SO_4 + 2NaOH \rightarrow Na_2SO_4 + 2H_2O \)
Explanation: This is a neutralization reaction between an acid (sulfuric acid) and a base (sodium hydroxide). The products are a salt (sodium sulfate) and water. The equation is balanced with 2 moles of NaOH reacting with 1 mole of \( H_2SO_4 \) to produce 1 mole of \( Na_2SO_4 \) and 2 moles of \( H_2O \).
(b) When acids and bases react, protons, \( H^+ \), are transferred. Define an acid in terms of proton transfer. (Sub-topic: C7.1)
▶️Answer/Explanation
Answer: An acid is a proton donor.
Explanation: According to the Brønsted-Lowry theory, an acid is a substance that donates a proton (\( H^+ \)) during a chemical reaction. In the reaction between an acid and a base, the acid donates a proton to the base.
(c) The student makes up a solution of dilute sulfuric acid, \( H_2SO_4 \), with a concentration of 0.2 mol/dm\(^3\). Calculate the concentration of the solution in \( g/dm^3 \). (Sub-topic: C3.3)
▶️Answer/Explanation
Answer: 19.6 \( g/dm^3 \)
Explanation:
Step 1: Calculate the molar mass of \( H_2SO_4 \).
\( H_2SO_4 \) = (2 × 1) + 32 + (4 × 16) = 2 + 32 + 64 = 98 g/mol.
Step 2: Use the formula for concentration in \( g/dm^3 \):
Concentration (\( g/dm^3 \)) = Molarity (mol/dm\(^3\)) × Molar mass (g/mol).
Concentration = 0.2 mol/dm\(^3\) × 98 g/mol = 19.6 \( g/dm^3 \).
(d)(i) Sulfuric acid is made by the Contact process. The equations for the stages in the Contact process are shown. Write the balanced symbol equation for the reaction in stage 2. (Sub-topic: C6.3)
▶️Answer/Explanation
Answer: \( 2SO_2 + O_2 \rightleftharpoons 2SO_3 \)
Explanation: In stage 2 of the Contact process, sulfur dioxide (\( SO_2 \)) reacts with oxygen (\( O_2 \)) to form sulfur trioxide (\( SO_3 \)). The reaction is reversible, and the equation is balanced with 2 moles of \( SO_2 \) reacting with 1 mole of \( O_2 \) to produce 2 moles of \( SO_3 \).
(d)(ii) A pressure of 2 atmospheres is one of the conditions chosen for stage 2. State two other conditions chosen for stage 2. (Sub-topic: C6.3)
▶️Answer/Explanation
Answer:
1. Temperature of 450°C.
2. Use of a vanadium(V) oxide (\( V_2O_5 \)) catalyst.
Explanation: The Contact process requires specific conditions to maximize the yield of sulfur trioxide. A temperature of 450°C is optimal for the reaction, and a vanadium(V) oxide catalyst is used to increase the reaction rate without being consumed in the process.
Question 9
(a) State one advantage and one disadvantage of using coal to generate electricity. (Sub-topic – P1.6.3)
▶️Answer/Explanation
Advantage: Coal has a high energy density, meaning it can produce a large amount of energy per unit of mass. It is also relatively abundant and easy to transport and store.
Disadvantage: Burning coal releases carbon dioxide (CO₂), which contributes to global warming and climate change. It also releases sulfur dioxide (SO₂), which can cause acid rain, and particulates, which can lead to respiratory problems.
(b)(i) Compare the:
- forces between molecules
- distances between molecules
- motions of molecules
in a liquid at 100°C and a gas at 100°C. (Sub-topic – P2.1.1)
▶️Answer/Explanation
Forces between molecules: In a liquid, the forces between molecules are stronger compared to a gas. In a gas, the intermolecular forces are much weaker, allowing molecules to move more freely.
Distances between molecules: In a liquid, the molecules are closer together, whereas in a gas, the molecules are much farther apart.
Motions of molecules: In a liquid, the molecules have less freedom of movement and vibrate and slide past each other. In a gas, the molecules move rapidly and randomly in all directions.
(b)(ii) Complete Table 9.1 to describe what happens to the pressure in a sample of steam under different conditions. Assume the steam remains as a gas under each set of conditions.
Use the words increases, decreases or remains constant. (Sub-topic – P2.1.3)
| Temperature | Volume | Pressure |
|---|---|---|
| increases | remains constant | increases |
| decreases | remains constant | decreases |
| remains constant | increases | decreases |
| remains constant | decreases | increases |
▶️Answer/Explanation
The pressure of a gas is directly proportional to its temperature when the volume is constant (Gay-Lussac’s Law). Therefore, if the temperature increases, the pressure increases, and if the temperature decreases, the pressure decreases. When the volume increases at constant temperature, the pressure decreases (Boyle’s Law), and when the volume decreases, the pressure increases.
(c)(i) The potential difference across the primary coil is 20 kV. The primary coil contains 120 turns. The potential difference across the secondary coil is 400 kV. Calculate the number of turns on the secondary coil. (Sub-topic – P4.5.6)
▶️Answer/Explanation
Using the transformer equation: \[ \frac{V_p}{V_s} = \frac{N_p}{N_s} \] Where:
- \( V_p = 20 \, \text{kV} \) (primary voltage)
- \( V_s = 400 \, \text{kV} \) (secondary voltage)
- \( N_p = 120 \) (number of turns in the primary coil)
- \( N_s \) = number of turns in the secondary coil (to be calculated)
Rearranging the equation to solve for \( N_s \): \[ N_s = \frac{V_s \times N_p}{V_p} = \frac{400 \, \text{kV} \times 120}{20 \, \text{kV}} = 2400 \] Therefore, the number of turns on the secondary coil is 2400.
(c)(ii) The electric power is transported from the power station over large distances at 400 kV. This is a very high potential difference. Explain why a very high potential difference is used. (Sub-topic – P4.5.6)
▶️Answer/Explanation
A very high potential difference is used to transport electric power over large distances because it reduces the current in the transmission lines. According to the equation \( P = IV \), for a given power \( P \), increasing the voltage \( V \) reduces the current \( I \). Lower current reduces the energy lost as heat in the transmission lines (since power loss \( P_{\text{loss}} = I^2R \)), making the transmission more efficient.
Question 10
(a) Fig. 10.1 is a diagram of a cross-section through a leaf. (Subtopic – B6.2)
(i) Use Fig. 10.1 to identify the letter that represents the part:
- that provides structural support for the leaf: B
- that transports mineral ions: B
- where most photosynthesis occurs: A
- that controls gas exchange: D
(ii) Draw a circle around the vascular bundle in Fig. 10.1.
▶️Answer/Explanation
Explanation:
(i) The parts of the leaf are identified as follows:
- B represents the vascular bundle, which provides structural support and transports mineral ions.
- A represents the palisade mesophyll, where most photosynthesis occurs.
- D represents the stomata, which control gas exchange.
(ii) The vascular bundle should be circled in the diagram.
(b) Phloem is responsible for translocation. (Subtopic – B8.4)
(i) Circle the two main substances transported by phloem:
- amino acids
- fatty acids
- glucose
- glycogen
- starch
- sucrose
(ii) Translocation occurs from source to sink. State which of these regions in a plant acts as a source and which as a sink:
- region of growth: sink
- region of production: source
- region of storage: sink
▶️Answer/Explanation
Explanation:
(i) The two main substances transported by phloem are amino acids and sucrose.
(ii) In translocation:
- Source refers to the region of production, where sugars are produced (e.g., leaves).
- Sink refers to the regions of growth and storage, where sugars are used or stored (e.g., roots, fruits).
(c) Gas exchange occurs in both plants and animals. (Subtopic – B11.1)
(i) State the chemical formula of the gas that is required for photosynthesis: CO2
(ii) State two features of gas exchange surfaces in humans:
- 1: large surface area
- 2: thin surface
▶️Answer/Explanation
Explanation:
(i) The gas required for photosynthesis is carbon dioxide, with the chemical formula CO2.
(ii) Two features of gas exchange surfaces in humans are:
- Large surface area to maximize the amount of gas that can be exchanged.
- Thin surface to allow for efficient diffusion of gases.
Question 11
(a) Ethane and ethene are members of two different homologous series. Fig. 11.1 shows the structure of ethene.
Draw the structure of ethane. (Sub-topic – C11.2)
▶️Answer/Explanation
The structure of ethane is:
H H
| |
H-C-C-H
| |
H H
Ethane is a saturated hydrocarbon with the molecular formula C2H6. It consists of two carbon atoms single-bonded to each other, with each carbon atom bonded to three hydrogen atoms.
(b) Ethene is a member of the homologous series called the alkenes. The alkenes are all hydrocarbons. State two other features that the alkenes in the homologous series have in common. (Sub-topic – C11.2)
▶️Answer/Explanation
Two other features that alkenes in the homologous series have in common are:
- They contain at least one carbon-carbon double bond (C=C).
- They have the general formula CnH2n.
Alkenes are unsaturated hydrocarbons, meaning they have fewer hydrogen atoms compared to alkanes with the same number of carbon atoms due to the presence of the double bond.
(c) Ethene undergoes an addition reaction with steam. Fig. 11.2 shows the equation for the reaction. Complete the equation, by drawing the structure of the compound formed. (Sub-topic – C11.5)
▶️Answer/Explanation
The structure of the compound formed when ethene reacts with steam is ethanol:
H H
| |
H-C-C-OH
| |
H H
Ethene (C2H4) reacts with steam (H2O) in the presence of a catalyst to form ethanol (C2H5OH). This is an example of an addition reaction where the double bond in ethene is broken, and a hydroxyl group (-OH) is added to one of the carbon atoms.
(d) Propene is another alkene. Fig. 11.3 shows the structure of propene. The polymer poly(propene) can be made from propene. Complete the structure of poly(propene) in Fig. 11.4. Include all the atoms and bonds of the repeating unit. (Sub-topic – C11.7)
▶️Answer/Explanation
The repeating unit of poly(propene) is:
H H
| |
-C-C-
| |
CH3 H
Poly(propene) is formed through the polymerization of propene (C3H6). The double bond in propene breaks, and the monomers link together to form a long chain polymer. The repeating unit has a methyl group (CH3) attached to every other carbon atom in the chain.
(e) Poly(propene) is made from propene in an addition polymerisation reaction. Polyesters are a group of polymers made in a condensation polymerisation reaction. Describe the differences between addition polymerisation and condensation polymerisation. (Sub-topic – C11.7)
▶️Answer/Explanation
The differences between addition polymerisation and condensation polymerisation are:
- Addition Polymerisation: Involves the joining of monomers with double or triple bonds (e.g., alkenes) to form a polymer without the loss of any small molecules. The polymer formed has the same empirical formula as the monomer.
- Condensation Polymerisation: Involves the joining of monomers with the loss of small molecules such as water or methanol. The polymer formed has a different empirical formula from the monomers.
For example, in addition polymerisation, ethene monomers join to form polyethene, while in condensation polymerisation, a dicarboxylic acid and a diol react to form a polyester, releasing water as a byproduct.
Question 12
(a) Fig. 12.1 shows the equipment used by a teacher to demonstrate the properties of ionising radiation. The teacher uses a source which emits α-particles and a thick lead shield placed between the radioactive source and the radiation detector. (Sub-topic – P5.2.1)
(i) Explain why the count rate recorded by the laptop is low but not zero.
▶️Answer/Explanation
The count rate is low because the thick lead shield absorbs most of the α-particles, which have low penetrating power. However, the count rate is not zero because some background radiation, such as cosmic rays and natural radioactive materials in the environment, can still reach the detector.
(ii) The teacher replaces the source emitting α-particles with a source that emits γ-rays. The count rate recorded by the laptop increases. Suggest why the count rate recorded by the laptop increases.
▶️Answer/Explanation
The count rate increases because γ-rays have much higher penetrating power than α-particles. The thick lead shield is less effective at blocking γ-rays, allowing more radiation to reach the detector.
(b) Before performing the investigation, the teacher uses a plane mirror to inspect the condition of the radioactive source. (Sub-topic – P3.2.1)
(i) Complete Fig. 12.2, with a ray diagram, to show how the mirror allows the teacher to see the radioactive source.
▶️Answer/Explanation
The ray diagram should show the radioactive source emitting light rays that reflect off the mirror and enter the teacher’s eye. The angle of incidence should equal the angle of reflection.
(ii) Visible light is an example of a transverse wave. State what is meant by a transverse wave.
▶️Answer/Explanation
A transverse wave is a wave in which the oscillations are perpendicular to the direction of energy transfer. In the case of visible light, the electric and magnetic fields oscillate perpendicular to the direction of propagation.
(iii) A visible light wave travels at \(3.0 \times 10^8 \, \text{m/s}\) and has a frequency of \(5.0 \times 10^{14} \, \text{Hz}\). Calculate the wavelength of the visible light wave.
▶️Answer/Explanation
The wavelength (\(\lambda\)) can be calculated using the formula: \[ \lambda = \frac{v}{f} \] where \(v\) is the speed of light and \(f\) is the frequency. Substituting the given values: \[ \lambda = \frac{3.0 \times 10^8 \, \text{m/s}}{5.0 \times 10^{14} \, \text{Hz}} = 6.0 \times 10^{-7} \, \text{m} \] Therefore, the wavelength of the visible light wave is \(6.0 \times 10^{-7} \, \text{m}\).