2024 Cambridge IGCSE Science - Combined (0653) Practice Paper with Answers

(a) (i) Fractional distillation separates petroleum into fractions with different boiling point ranges. (ii) By balancing carbon and hydrogen atoms, the remaining product has 2 carbons and 4 hydrogens, which is \(C_2H_4\). (b) Ethene has a double covalent bond between the two carbon atoms (sharing 4 electrons) and single covalent bonds between each carbon and two hydrogen atoms (each sharing 2 electrons). (c) Saturated hydrocarbons like octane do not react with bromine water, so it remains orange-brown. Unsaturated alkenes like ethene readily react via addition, decolourising the bromine water. (d) Addition polymerisation occurs when unsaturated monomers join together without forming any by-products.

(a) (i) fractional distillation [1] (ii) \(C_2H_4\) [1] (b) 4 shared electrons in C=C double bond [1], 2 shared electrons in each of the four C-H single bonds [1], no extra electrons shown on hydrogen or carbon [1] (c) Test: add bromine water / aqueous bromine [1], Octane: remains orange / yellow / brown [1], Ethene: decolourises / turns colourless [1] (d) addition (polymerisation) [1]

(a) (i) The pulmonary artery carries deoxygenated blood to the lungs. (ii) The left ventricle must pump blood throughout the entire systemic circulation to all body organs, requiring high force and pressure. The right ventricle only pumps blood a short distance to the lungs. (b) In double circulation, blood flows through the pulmonary circuit (lungs) and the systemic circuit (rest of the body), returning to the heart after each loop. (c) (i) Plaque/cholesterol builds up inside the coronary artery walls, narrowing the lumen. This deprives the heart muscle cells of the oxygen and glucose they need for aerobic respiration, leading to cell dysfunction or death. (ii) Eating foods low in saturated fats reduces cholesterol levels, and regular exercise improves cardiovascular strength.

(a) (i) pulmonary artery [1] (ii) left ventricle pumps blood to the whole body / further distance (at higher pressure) [1], right ventricle only pumps blood to the lungs / shorter distance [1] (b) blood passes through the heart twice [1], for one complete circuit / loop of the body [1] (c) (i) buildup of fatty deposits / cholesterol / plaque in the coronary arteries [1], reduces oxygen / glucose supply to heart muscle cells [1] (ii) Any two from: regular exercise [1], reducing saturated fat intake [1], avoiding smoking [1], reducing stress [1]

(a) (i) Sound waves travel as longitudinal waves where particles vibrate back and forth parallel to the energy transfer, creating high-pressure regions (compressions) and low-pressure regions (rarefactions). (ii) The speed of light is extremely high (\(3.0 \times 10^8\text{ m/s}\)) compared to the speed of sound in air (about \(340\text{ m/s}\)). (b) (i) Using \(v = f \lambda\), the frequency is \(f = v / \lambda = (3.0 \times 10^8) / (5.32 \times 10^{-7}) = 5.64 \times 10^{14}\text{ Hz}\). (ii) Infrared radiation lies just beyond the red end of the visible spectrum. (c) The light ray bends towards the normal because glass has a higher optical density than air, causing the light wave to slow down.

(a) (i) air particles vibrate / oscillate parallel to the direction of wave travel [1], creating compressions and rarefactions [1] (ii) speed of light is much greater than speed of sound [1] (b) (i) formula: \(f = v / \lambda\) or \(v = f \lambda\) [1], substitution: \((3.0 \times 10^8) / (5.32 \times 10^{-7})\) [1], correct answer with unit: \(5.6 \times 10^{14}\text{ Hz}\) or \(5.64 \times 10^{14}\text{ Hz}\) [1] (ii) infrared [1] (c) bends towards the normal [1], because light slows down / speed decreases as it enters the glass [1]

(a) (i) Weight of the container is \(W = m \times g = 400\text{ kg} \times 10\text{ N/kg} = 4000\text{ N}\). Work done is \(\text{Work} = \text{Force} \times \text{distance} = 4000\text{ N} \times 12\text{ m} = 48000\text{ J}\). (ii) Time taken is \(t = \text{distance} / \text{speed} = 12\text{ m} / 1.5\text{ m/s} = 8.0\text{ s}\). Useful power is \(P = \text{Work} / t = 48000\text{ J} / 8.0\text{ s} = 6000\text{ W}\). (b) (i) Since mechanical energy is conserved, all gravitational potential energy converts to kinetic energy just before hitting the ground: \(48000\text{ J}\). (ii) The only force acting on the falling object is gravity (weight), which is constant. This constant unbalanced force causes a constant downward acceleration, meaning its speed increases at a constant rate of \(10\text{ m/s}^2\).

(a) (i) formula: \(\text{Force} = mg\) [1], calculation of weight: \(4000\text{ N}\) [1], calculation of work done: \(4000 \times 12 = 48000\text{ J}\) (or \(48\text{ kJ}\)) [1] (ii) formula: \(\text{Power} = \text{Work} / t\) or \(\text{Power} = F \times v\) [1], calculation: \(4000 \times 1.5 = 6000\) [1], correct unit: \(W\) or \(\text{Watts}\) or \(\text{J/s}\) [1] (b) (i) \(48000\text{ J}\) [1] (ii) there is a constant downward force / weight [1], which causes a constant acceleration / speed increases at a constant rate [1]

(a) (i) Photosynthesis combines carbon dioxide and water to produce glucose and oxygen: \(6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2\). (ii) Chlorophyll absorbs the light energy required to drive this endothermic reaction. (b) (i) Iodine solution turns from orange-brown to blue-black in the presence of starch. (ii) Moving the light source closer increases light intensity. Because light intensity was a limiting factor, this increases the rate of photosynthesis, releasing more oxygen bubbles. (iii) Temperature is a key factor because the process is controlled by enzymes. (c) Magnesium is the central ion in the chlorophyll molecule; without it, the plant cannot synthesise chlorophyll and cannot absorb light.

(a) (i) correct chemical formulas for reactants and products [1], correct balanced equation [2] (ii) to absorb / trap light energy [1] (b) (i) add iodine solution [1], positive result: turns blue-black [1] (ii) increased light intensity increases the rate of photosynthesis [1] (iii) temperature [1] (c) magnesium is required to produce chlorophyll [1]

(a) (i) Positive zinc ions gain electrons at the negative cathode to form zinc metal. (ii) At the positive anode, chloride ions lose electrons: \(2Cl^- \rightarrow Cl_2 + 2e^-\). (iii) Chlorine is a pale yellow-green gas, seen as effervescence. (b) (i) Hydrogen gas forms because water dissociates into \(H^+\) and \(OH^-\) ions. (ii) Highly reactive metals like sodium remain as ions in solution; hydrogen ions are more easily reduced. (c) Solid zinc chloride has ions locked in a giant ionic lattice. Melting breaks these bonds, allowing the ions to become mobile charge carriers.

(a) (i) zinc [1] (ii) reactant \(2Cl^-\), product \(Cl_2\) [1], balanced with \(2e^-\) on product side [1] (iii) bubbles / effervescence of a pale green / yellow-green gas [1] (b) (i) hydrogen [1] (ii) sodium is more reactive than hydrogen [1], hydrogen ions / \(H^+\) are discharged preferentially [1] (c) in solid, ions are fixed in a lattice / cannot move [1], in liquid/molten state, ions are free to move [1]

(a) (i) Using Ohm's law: \(I = V_1 / R_1 = 4.5\text{ V} / 6.0\ \Omega = 0.75\text{ A}\). In a series circuit, current is identical everywhere. (ii) For resistor \(R_2\): \(V_2 = I \times R_2 = 0.75\text{ A} \times 3.0\ \Omega = 2.25\text{ V}\). (iii) Power \(P = I \times V = 0.75\text{ A} \times 4.5\text{ V} = 3.375\text{ W}\). (b) When components are added in parallel, the total resistance of the circuit decreases. Because \(I = V / R\) and voltage remains constant, a decrease in total resistance causes an increase in total current.

(a) (i) formula: \(I = V / R\) [1], calculation: \(4.5 / 6.0 = 0.75\text{ A}\) [1] (ii) recall that current is same in series [1], calculation: \(0.75 \times 3.0 = 2.25\text{ V}\) [1] (iii) formula: \(P = VI\) or \(P = I^2 R\) [1], calculation: \(4.5 \times 0.75 = 3.375\) [1], correct unit: \(W\) / \(\text{Watts}\) / \(\text{J/s}\) [1] (b) ammeter reading increases [1], because connecting resistors in parallel decreases the total resistance [1]

(a) (i) High concentration means more reacting particles in the same volume, raising collision frequency. (ii) Higher temperature increases the speed of particles (kinetic energy), so they collide more frequently. Crucially, a larger fraction of these collisions have energy \(\ge\) activation energy, so more collisions are successful. (b) (i) Powder has a larger surface-area-to-volume ratio, leaving more metal atoms available to react at any one time, raising collision rate. (ii) The total volume of gas depends only on the moles of limiting reactant. Since the quantities of acid and magnesium are identical, the maximum yield of hydrogen is unchanged.

(a) (i) more particles per unit volume [1], more frequent collisions [1] (ii) particles have more kinetic energy / move faster [1], more frequent collisions [1], a greater proportion of collisions have energy equal to or greater than the activation energy [1] (b) (i) initial rate increases [1], powder has a larger surface area / more frequent collisions [1] (ii) no change in total volume of gas [1], same mass of magnesium / same amount of acid used [1]

(a)(i)
Using the formula for acceleration:
\(a = \frac{v - u}{t}\)
\(a = \frac{5.0\text{ m/s} - 0\text{ m/s}}{4.0\text{ s}} = 1.25\text{ m/s}^2\)

(a)(ii)
The distance travelled can be calculated using the average speed:
\(\text{average speed} = \frac{u + v}{2} = \frac{0 + 5.0}{2} = 2.5\text{ m/s}\)
\(d = \text{average speed} \times t = 2.5\text{ m/s} \times 4.0\text{ s} = 10\text{ m}\)
(Alternatively, \(\text{Area under speed-time graph} = \frac{1}{2} \times 4.0 \times 5.0 = 10\text{ m}\).)

(b)
First, find the height gained (\(\Delta h\)) during the \(6.0\text{ s}\) at constant speed:
\(\Delta h = v \times t = 5.0\text{ m/s} \times 6.0\text{ s} = 30\text{ m}\)
Now calculate the increase in gravitational potential energy (\(\Delta E_p\)):
\(\Delta E_p = m g \Delta h\)
\(\Delta E_p = 1.2\text{ kg} \times 10\text{ N/kg} \times 30\text{ m} = 360\text{ J}\)

(c)
Since the drone is rising at a constant velocity, its acceleration is zero, which means the resultant force acting on it is zero.
Therefore, the upward thrust force must exactly balance the downward weight of the drone:
\(\text{Thrust} = \text{Weight} = m \times g = 1.2\text{ kg} \times 10\text{ N/kg} = 12\text{ N}\)

(a)(i) [2 marks]
• \(1.25\text{ m/s}^2\) (or \(1.3\text{ m/s}^2\)) [1]
• Correct unit: \(\text{m/s}^2\) [1]

(a)(ii) [2 marks]
• Correct method shown: e.g., \(\text{average speed} \times t\) OR \(\frac{1}{2} \times 4.0 \times 5.0\) [1]
• \(10\text{ m}\) [1]

(b) [3 marks]
• Height gained = \(30\text{ m}\) [1]
• \(\text{GPE} = mgh\) OR substitution: \(1.2 \times 10 \times 30\) [1]
• \(360\text{ J}\) [1]

(c) [2 marks]
• State \(12\text{ N}\) [1]
• Explanation: constant velocity means zero acceleration / zero resultant force, so upward thrust equals downward weight / gravity force [1]