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Question 1 Report
A company makes flexible electrical contacts from a mixture of copper and silver. Fig. 1 shows particles in the solid alloy. Both metals form positive ions, and their outer electrons become delocalised. The company tests whether the material can carry current after being bent 1000 times. The contact remains intact and its resistance changes only slightly.
(a) Name the bonding in the copper-silver alloy. [1]
(b) Describe what happens to electrons when copper and silver atoms form the alloy structure. [2]
(c) Explain why the alloy conducts electricity after it has been bent. [2]
(d) What is the term for a mixture of metals? [1]
(a) The alloy has metallic bonding. [1 mark]
(b) Outer electrons are released from the copper and silver atoms. They become delocalised, meaning they are free to move through the metal structure. [2 marks]
(c) When bent, layers of metal ions can move without breaking the metallic attraction. The delocalised electrons remain mobile and continue to carry charge, so the alloy still conducts. [2 marks]
(d) A mixture of metals is an alloy. [1 mark]
(a) The alloy has metallic bonding. [1 mark]
(b) Outer electrons are released from the copper and silver atoms. They become delocalised, meaning they are free to move through the metal structure. [2 marks]
(c) When bent, layers of metal ions can move without breaking the metallic attraction. The delocalised electrons remain mobile and continue to carry charge, so the alloy still conducts. [2 marks]
(d) A mixture of metals is an alloy. [1 mark]
Question 2 Report
The diagram shows a swimming-pool controller adding a small amount of acid to pool water. The controller keeps the pH within a safe range so that chlorine disinfectant works well without irritating swimmers' eyes.
The diagram shows a student using red cabbage indicator to compare household liquids. Cabbage indicator is purple before it is mixed with a solution. The student is investigating lemon juice, washing-up liquid and distilled water.
pH, acids, and alkalis
For pool water: (a) A neutral solution at room temperature has pH 7. [1] (b) Pool water of pH 8.2 is alkaline. [1] (c) Acid adds hydrogen ions to the water. This increases hydrogen-ion concentration, so pH falls. [2]
For cabbage indicator: (a) An acid turns cabbage indicator red or pink. [1] (b) Distilled water is neutral, so the indicator remains purple. [1] (c) Washing-up liquid is likely to be alkaline, or a base. Alkaline solutions have pH values greater than 7. [2] (d) An alkali is a base that dissolves in water. [1]
pH, acids, and alkalis
For pool water: (a) A neutral solution at room temperature has pH 7. [1] (b) Pool water of pH 8.2 is alkaline. [1] (c) Acid adds hydrogen ions to the water. This increases hydrogen-ion concentration, so pH falls. [2]
For cabbage indicator: (a) An acid turns cabbage indicator red or pink. [1] (b) Distilled water is neutral, so the indicator remains purple. [1] (c) Washing-up liquid is likely to be alkaline, or a base. Alkaline solutions have pH values greater than 7. [2] (d) An alkali is a base that dissolves in water. [1]
Question 3 Report
Fig. 1 shows a school investigation into decomposition in a freshwater pond. Students place equal masses of dead reed leaves in two mesh bags. One bag is held in flowing, oxygen-rich water near a fountain. The other rests in still mud at the pond edge. Both bags are recovered after three weeks and dried before their masses are compared. The mesh allows bacteria, fungi and small invertebrates to enter but prevents leaves washing away. The students also notice that the mud is darker and has a sour smell, suggesting little oxygen is present.
(a) Describe one reason for using mesh bags in this investigation. [2]
(b) Name two types of organism that may cause the leaves to decay. [3]
(c) Use Fig. 1 to predict which bag will have the smaller dry mass after three weeks. Explain your prediction. [4]
(d) Explain why drying the leaves before measuring mass improves the validity of the comparison. [4]
(e) What conclusion about oxygen and decay could the students make if bag A has a much smaller dry mass than bag B? [5]
(a) [2] Mesh bags allow decomposers and small invertebrates to enter, while preventing leaves being washed away and keeping them together for recovery.
(b) [3] Two organisms that may cause decay are bacteria and fungi. Detritivores or small invertebrates, such as freshwater shrimp, are also acceptable. These organisms act as decomposers. A third correct example gains the additional marking point.
(c) [4] Bag A should have the smaller dry mass. It is in flowing water near the fountain, where more dissolved oxygen is available. Aerobic microorganisms can respire and decay the leaves faster, leaving less leaf material after three weeks.
(d) [4] Leaves can hold different amounts of water. Wet mass would include this water, which is not leaf material. Drying means the measured mass is mainly the remaining leaf material. Therefore a mass difference is more validly attributed to decay rather than unequal water content.
(e) [5] If bag A has a much smaller dry mass, decay was faster in the oxygen-rich condition. Its smaller dry mass shows less leaf material remained. Oxygen allows decomposers to carry out aerobic respiration, releasing energy for growth and enzyme-controlled breakdown. Therefore the lack of oxygen in still mud slows decomposition.
(a) [2] Mesh bags allow decomposers and small invertebrates to enter, while preventing leaves being washed away and keeping them together for recovery.
(b) [3] Two organisms that may cause decay are bacteria and fungi. Detritivores or small invertebrates, such as freshwater shrimp, are also acceptable. These organisms act as decomposers. A third correct example gains the additional marking point.
(c) [4] Bag A should have the smaller dry mass. It is in flowing water near the fountain, where more dissolved oxygen is available. Aerobic microorganisms can respire and decay the leaves faster, leaving less leaf material after three weeks.
(d) [4] Leaves can hold different amounts of water. Wet mass would include this water, which is not leaf material. Drying means the measured mass is mainly the remaining leaf material. Therefore a mass difference is more validly attributed to decay rather than unequal water content.
(e) [5] If bag A has a much smaller dry mass, decay was faster in the oxygen-rich condition. Its smaller dry mass shows less leaf material remained. Oxygen allows decomposers to carry out aerobic respiration, releasing energy for growth and enzyme-controlled breakdown. Therefore the lack of oxygen in still mud slows decomposition.
Question 4 Report
Sodium chloride is heated in a laboratory furnace to investigate changes of state. A sample of the ionic compound is given energy until it melts. The student notes that the temperature remains constant for a short time while melting occurs, although the heater continues to transfer energy. The solid structure contains positive sodium ions and negative chloride ions in a regular lattice. This investigation is carried out with a very small sample because the melting temperature is high.
(a) Name the change of state taking place at the constant temperature. [1]
(b) Describe what happens to the energy transferred to sodium chloride while it melts. [2]
(c) Explain why sodium chloride needs much more energy to melt than a simple molecular substance. [2]
Fig. 1 is a Sankey diagram for a small petrol engine driving a water pump on a farm. The chemical energy supplied by the fuel in one minute is 1000 kJ. Some energy is transferred usefully to the moving pump. The rest is wasted, mainly as thermal energy to the engine, water and surrounding air, with a small amount as sound. The engine uses an oil lubricant to reduce friction, but it cannot stop all unwanted energy transfers.
(a) Name the useful energy store increased by the moving pump. [1]
(b) Use the diagram to calculate the percentage efficiency if 280 kJ is transferred usefully. [2]
(c) Describe two ways in which energy is wasted by the engine. [2]
Sodium chloride melting
Petrol engine
Sodium chloride melting
Petrol engine
Question 5 Report
A museum conservator finds a woollen glove in a dry storage box. Fig. 1 shows pieces of the same wool fabric placed in three different storage conditions for a trial. One piece is damp, one is dry, and one is dry but treated with a fungicide. The conservator observes each piece after fourteen days. The glove is made from animal fibres, which are carbon compounds. She must choose a method that prevents decay without damaging the historic object or adding ethanol-based chemicals to the fabric.
(a) Name the microorganism most likely to grow as visible mould on the damp fabric. [1]
(b) Describe three control variables the conservator should keep the same for all three pieces of fabric. [3]
(c) Explain why the damp fabric is likely to decay faster than the dry fabric. [4]
(a) Fungus, or mould, [1] is the microorganism most likely to grow visibly on damp fabric.
(b) [3] Any three appropriate control variables are: the same type of wool fabric; the same mass or surface area of fabric; the same temperature; the same storage time; the same size of box; or the same light level. Keeping these constant ensures that moisture and fungicide are the meaningful differences.
(c) [4] Microorganisms need water for growth and decay. Water allows substances to dissolve and move into microorganisms. Their enzymes can then catalyse breakdown reactions more effectively. Therefore more of the carbon-containing wool is broken down in the damp condition, so it decays faster.
(a) Fungus, or mould, [1] is the microorganism most likely to grow visibly on damp fabric.
(b) [3] Any three appropriate control variables are: the same type of wool fabric; the same mass or surface area of fabric; the same temperature; the same storage time; the same size of box; or the same light level. Keeping these constant ensures that moisture and fungicide are the meaningful differences.
(c) [4] Microorganisms need water for growth and decay. Water allows substances to dissolve and move into microorganisms. Their enzymes can then catalyse breakdown reactions more effectively. Therefore more of the carbon-containing wool is broken down in the damp condition, so it decays faster.
Question 6 Report
Fig. 1 is a simplified energy-level diagram for a sodium atom in a flame test. A flame supplies energy to the atom. One outer electron can move to a higher energy level, but this state is unstable. When the electron falls back, energy is released as yellow light. Students compare this effect with potassium compounds, which give a different flame colour because their electron energy levels are different. The same sample also contains sodium chloride dissolved in water.
(a) Describe what happens to the electron when it moves upwards in Fig. 1. [2]
(b) Explain why light is emitted when the electron returns to the lower level. [2]
(c) Use the idea of electron energy levels to explain why potassium gives a different flame colour from sodium. [3]
(d) What is the charge on a sodium ion in the sodium chloride solution? [3]
(a) [2] The electron absorbs or gains energy from the flame, then moves to a higher energy level.
(b) [2] The electron falls back to a lower energy level. The energy difference between the levels is released as light.
(c) [3] Potassium has different electron energy levels, so the gaps between its levels differ from those in sodium. Its electrons release a different amount of energy when they fall to lower levels. Therefore the light has a different wavelength and colour.
(d) [3] A sodium ion has charge +1. Sodium loses one electron, so it has one more proton than electrons.
(a) [2] The electron absorbs or gains energy from the flame, then moves to a higher energy level.
(b) [2] The electron falls back to a lower energy level. The energy difference between the levels is released as light.
(c) [3] Potassium has different electron energy levels, so the gaps between its levels differ from those in sodium. Its electrons release a different amount of energy when they fall to lower levels. Therefore the light has a different wavelength and colour.
(d) [3] A sodium ion has charge +1. Sodium loses one electron, so it has one more proton than electrons.
Question 7 Report
Fig. 1 shows a simplified diagram of an electrolytic cell used by a recycling company. Molten sodium chloride is placed in the heated container. The company wants to calculate the mass of sodium metal that could be obtained from a pure 11.7 g sample of sodium chloride. The relative atomic masses are Na = 23 and Cl = 35.5.
(a) Name the metal made at the negative electrode. [1]
(b) Explain why sodium chloride must be molten rather than solid. [1]
(c) Use the formula NaCl to calculate its relative formula mass. [1]
(d) Use 11.7 g of NaCl to calculate the mass of sodium that can be made. [2]
The table below shows data from a water-treatment company. The company neutralises a pure sample of hydrochloric acid using sodium hydroxide. The equation is HCl + NaOH → NaCl + H2O. The relative formula mass of sodium hydroxide is 40.0. A fixed volume of acid is used each time, and the sodium hydroxide is weighed as a dry solid before making a solution.
| trial | mass of NaOH used / g | amount of NaOH / mol |
|---|---|---|
| 1 | 1.00 | 0.0250 |
| 2 | 2.00 | 0.0500 |
| 3 | 3.00 | 0.0750 |
In trial 2, exactly 0.0500 mol of acid reacts.
(a) Name the salt made in this reaction. [1]
(b) Use the equation to state the amount of HCl reacting in trial 2. [1]
(c) Complete this calculation for trial 3: amount = mass ÷ Mr. [1]
(d) Explain why 2.00 g of NaOH is needed when 0.0500 mol of HCl reacts. [2]
Electrolysis of molten sodium chloride
(a) The metal made at the negative electrode is sodium. Positive sodium ions gain electrons at the negative electrode. [1]
(b) Sodium chloride must be molten because its ions can move when molten. Moving ions carry charge, so the molten liquid conducts electricity. In solid sodium chloride, the ions are fixed in a lattice. [1]
(c) \[M_r(\mathrm{NaCl})=23+35.5=58.5\]
The relative formula mass is 58.5. [1]
(d) Calculate the amount of sodium chloride:
\[\text{amount of NaCl}=\frac{11.7\text{ g}}{58.5\text{ g mol}^{-1}}=0.200\text{ mol}\]
Each formula unit of NaCl contains one sodium ion, so 0.200 mol of NaCl can produce 0.200 mol of sodium.
\[\text{mass of Na}=0.200\text{ mol}\times23\text{ g mol}^{-1}=4.60\text{ g}\]
The mass of sodium is 4.60 g. [2]
Neutralisation with sodium hydroxide
(a) The salt made is sodium chloride. [1]
(b) The equation \(\mathrm{HCl+NaOH\rightarrow NaCl+H_2O}\) has a 1:1 mole ratio between HCl and NaOH. Thus, in trial 2, the amount of HCl reacting is 0.0500 mol. [1]
(c) \[\text{amount of NaOH}=\frac{3.00\text{ g}}{40.0\text{ g mol}^{-1}}=0.0750\text{ mol}\]
The calculation for trial 3 gives 0.0750 mol. [1]
(d) The equation shows a 1:1 mole ratio, so 0.0500 mol of HCl requires 0.0500 mol of NaOH for complete neutralisation. The corresponding mass is:
\[\text{mass of NaOH}=0.0500\text{ mol}\times40.0\text{ g mol}^{-1}=2.00\text{ g}\]
Therefore, 2.00 g of NaOH is needed. [2]
Electrolysis of molten sodium chloride
(a) The metal made at the negative electrode is sodium. Positive sodium ions gain electrons at the negative electrode. [1]
(b) Sodium chloride must be molten because its ions can move when molten. Moving ions carry charge, so the molten liquid conducts electricity. In solid sodium chloride, the ions are fixed in a lattice. [1]
(c) \[M_r(\mathrm{NaCl})=23+35.5=58.5\]
The relative formula mass is 58.5. [1]
(d) Calculate the amount of sodium chloride:
\[\text{amount of NaCl}=\frac{11.7\text{ g}}{58.5\text{ g mol}^{-1}}=0.200\text{ mol}\]
Each formula unit of NaCl contains one sodium ion, so 0.200 mol of NaCl can produce 0.200 mol of sodium.
\[\text{mass of Na}=0.200\text{ mol}\times23\text{ g mol}^{-1}=4.60\text{ g}\]
The mass of sodium is 4.60 g. [2]
Neutralisation with sodium hydroxide
(a) The salt made is sodium chloride. [1]
(b) The equation \(\mathrm{HCl+NaOH\rightarrow NaCl+H_2O}\) has a 1:1 mole ratio between HCl and NaOH. Thus, in trial 2, the amount of HCl reacting is 0.0500 mol. [1]
(c) \[\text{amount of NaOH}=\frac{3.00\text{ g}}{40.0\text{ g mol}^{-1}}=0.0750\text{ mol}\]
The calculation for trial 3 gives 0.0750 mol. [1]
(d) The equation shows a 1:1 mole ratio, so 0.0500 mol of HCl requires 0.0500 mol of NaOH for complete neutralisation. The corresponding mass is:
\[\text{mass of NaOH}=0.0500\text{ mol}\times40.0\text{ g mol}^{-1}=2.00\text{ g}\]
Therefore, 2.00 g of NaOH is needed. [2]
Question 8 Report
Fig. 1 shows a car battery technician measuring the pH of a spill after it has been diluted with water. The battery contains sulfuric acid. The technician must decide whether sodium hydrogencarbonate powder can be used to make the spill safer.
This solution is prepared by a student who needs 1000 cm3 of dilute hydrochloric acid for a reaction-rate investigation. Fig. 1 shows concentrated acid being transferred into a measuring cylinder already containing water. The student must use the correct order of mixing.
Safe dilution and neutralisation
For the battery spill: (a) The ion responsible for acidic properties is the hydrogen ion, \(\mathrm{H^+}\). [1] (b) As sodium hydrogencarbonate neutralises the acid, pH increases towards 7. [1] (c) Dilution can release heat. Adding water slowly reduces rapid heating and splashing. [2]
For preparing dilute acid: (a) A measuring cylinder or volumetric flask can measure 1000 cm3 accurately. [1] (b) Add acid slowly to water. [1] (c) Mixing releases heat. The larger amount of water absorbs the heat, reducing boiling and dangerous acid splashes. [2]
Safe dilution and neutralisation
For the battery spill: (a) The ion responsible for acidic properties is the hydrogen ion, \(\mathrm{H^+}\). [1] (b) As sodium hydrogencarbonate neutralises the acid, pH increases towards 7. [1] (c) Dilution can release heat. Adding water slowly reduces rapid heating and splashing. [2]
For preparing dilute acid: (a) A measuring cylinder or volumetric flask can measure 1000 cm3 accurately. [1] (b) Add acid slowly to water. [1] (c) Mixing releases heat. The larger amount of water absorbs the heat, reducing boiling and dangerous acid splashes. [2]
Question 9 Report
A shipyard produces sodium metal from molten sodium chloride. Fig. 1 shows a protected industrial cell. The sodium is kept away from water because it reacts violently with water. Table 1 compares the melting points of two substances used at the site.
| Substance | Melting point / degrees C |
|---|---|
| Sodium chloride | 801 |
| Sodium metal | 98 |
(a) Name the particles that move to the negative electrode in molten sodium chloride. [1]
(b) Describe what happens to chloride ions at the positive electrode. [1]
(c) Explain why solid sodium chloride cannot be electrolysed. [2]
(d) Use Table 1 to state why the cell is operated above 801 degrees C. [1]
(a) Sodium ions, \(\text{Na}^+\), move to the negative electrode. [1]
(b) Chloride ions lose electrons at the positive electrode. They are oxidised to form chlorine molecules. [1]
(c) In solid sodium chloride, ions are fixed in a lattice. They cannot move to carry charge, so electrolysis cannot occur. [2]
(d) The cell is operated above 801 degrees C to melt the sodium chloride. [1]
(a) Sodium ions, \(\text{Na}^+\), move to the negative electrode. [1]
(b) Chloride ions lose electrons at the positive electrode. They are oxidised to form chlorine molecules. [1]
(c) In solid sodium chloride, ions are fixed in a lattice. They cannot move to carry charge, so electrolysis cannot occur. [2]
(d) The cell is operated above 801 degrees C to melt the sodium chloride. [1]
Question 10 Report
Fig. 1 is a lattice model used by an engineer selecting a material for a reusable heat pack. The model represents calcium chloride, which dissolves in water and releases energy. Calcium ions and chloride ions are held together by strong attractions. The engineer compares it with paraffin wax, a molecular substance, before deciding which material can be stored safely as a solid.
(a) Name the type of structure represented in Fig. 1. [1]
(b) Use the charges in Fig. 1 to complete the formula: CaCl__. [1]
(c) Describe the force holding calcium ions and chloride ions together. [2]
(d) Explain why calcium chloride has a higher melting point than paraffin wax. [2]
(a) The model is a giant ionic lattice, also called an ionic lattice. [1 mark]
(b) The formula is \(\mathrm{CaCl_2}\), so the missing number is \(2\). [1 mark]
(c) Calcium and chloride ions are held together by strong electrostatic attraction between oppositely charged ions. [2 marks]
(d) Calcium chloride has strong ionic attractions throughout its lattice. Paraffin wax is molecular and has weaker forces between its molecules, so less energy is needed to melt it. [2 marks]
(a) The model is a giant ionic lattice, also called an ionic lattice. [1 mark]
(b) The formula is \(\mathrm{CaCl_2}\), so the missing number is \(2\). [1 mark]
(c) Calcium and chloride ions are held together by strong electrostatic attraction between oppositely charged ions. [2 marks]
(d) Calcium chloride has strong ionic attractions throughout its lattice. Paraffin wax is molecular and has weaker forces between its molecules, so less energy is needed to melt it. [2 marks]
Question 11 Report
A science museum displays an old filament lamp beside a modern LED lamp. Fig. 1 shows a simplified section of the filament lamp. The filament is tungsten, a metal with a very high melting temperature. It is enclosed in a glass bulb containing a small amount of inert gas. When current flows, energy is transferred to the tungsten and its temperature rises until it glows. The glass is a covalent network solid and the copper wires are metallic.
(a) Name the type of bonding in tungsten. [1]
(b) Explain why tungsten is suitable for a hot filament. [2]
(c) What particles carry charge in the copper wires? [1]
(d) Describe why the glass bulb does not conduct electricity. [1]
A jeweller compares a gold ring with a brittle crystal of copper chloride. Fig. 1 shows part of the metallic structure of gold. The positive gold ions are arranged in rows and a cloud of electrons moves between them. The jeweller reshapes the ring by tapping it, without heating it. Gold is also chosen for electrical connectors because it carries charge and does not react easily with air or water.
(a) Name the bonding in gold. [1]
(b) Use Fig. 1 to explain why gold conducts electricity. [2]
(c) Describe what happens to layers of gold ions when the ring is hammered. [1]
Filament lamp
(a) Tungsten has metallic bonding. [1]
(b) Tungsten has strong metallic bonds, or strong attractions, in its structure. Much energy is needed to melt it, so it can withstand the very high temperature of a glowing filament. [2]
(c) Charge in the copper wires is carried by delocalised electrons. [1]
(d) Glass does not conduct because it has no mobile charged particles: its electrons are not free to move. [1]
Gold ring
(a) Gold has metallic bonding. [1]
(b) The delocalised electrons shown can move through the gold structure. These moving electrons carry charge, so gold conducts electricity. [2]
(c) When the ring is hammered, layers or rows of gold ions slide past one another. [1]
Filament lamp
(a) Tungsten has metallic bonding. [1]
(b) Tungsten has strong metallic bonds, or strong attractions, in its structure. Much energy is needed to melt it, so it can withstand the very high temperature of a glowing filament. [2]
(c) Charge in the copper wires is carried by delocalised electrons. [1]
(d) Glass does not conduct because it has no mobile charged particles: its electrons are not free to move. [1]
Gold ring
(a) Gold has metallic bonding. [1]
(b) The delocalised electrons shown can move through the gold structure. These moving electrons carry charge, so gold conducts electricity. [2]
(c) When the ring is hammered, layers or rows of gold ions slide past one another. [1]
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