Combined Science Double Award 9204 | Paper 2 Mock 01 | Chemistry
Question 1 Report
This reaction is used by a jewellery workshop to recover copper from a solution containing copper sulfate. A strip of magnesium is placed in the blue solution. Fig. 1 shows the observations after several minutes. The workshop records the mass of copper collected, rather than throwing the metal-containing waste away. Magnesium is higher than copper in the reactivity series.
(a) Name the type of reaction taking place. [1]
(b) Describe two visible changes expected in the beaker. [2]
(c) Use the reactivity series to explain why magnesium, but not gold, could remove copper from this solution. [2]
A university archive has a sample of gold leaf used to decorate an old book cover. Fig. 1 compares the arrangement of particles in gold metal with particles in diamond, a form of carbon. Gold can be hammered into thin sheets, but diamond is extremely hard. The archive conservator needs a scientific explanation for these different properties.
(a) Name the type of structure in diamond. [1]
(b) Describe the bonding between carbon atoms in diamond. [2]
(c) Explain why gold can be shaped into leaf. [2]
Magnesium in copper sulfate
(a) This is a displacement reaction. [1]
(b) Two visible changes are that the blue solution becomes paler or colourless [1] and brown or pink copper forms, usually as a coating. [1] The magnesium strip becoming smaller is also acceptable.
(c) Magnesium is more reactive than copper, so it displaces copper from copper sulfate solution. [1] Gold is less reactive than copper, so it cannot displace copper ions. [1]
Gold and diamond
(a) Diamond has a giant covalent structure, or giant covalent lattice. [1]
(b) Each carbon atom forms strong covalent bonds [1] with other carbon atoms in a repeating network. [1]
(c) In gold, layers of atoms can slide over one another [1] while metallic bonding continues to hold the metal together. This makes gold malleable enough to form leaf. [1]
Answer Details
Magnesium in copper sulfate
(a) This is a displacement reaction. [1]
(b) Two visible changes are that the blue solution becomes paler or colourless [1] and brown or pink copper forms, usually as a coating. [1] The magnesium strip becoming smaller is also acceptable.
(c) Magnesium is more reactive than copper, so it displaces copper from copper sulfate solution. [1] Gold is less reactive than copper, so it cannot displace copper ions. [1]
Gold and diamond
(a) Diamond has a giant covalent structure, or giant covalent lattice. [1]
(b) Each carbon atom forms strong covalent bonds [1] with other carbon atoms in a repeating network. [1]
(c) In gold, layers of atoms can slide over one another [1] while metallic bonding continues to hold the metal together. This makes gold malleable enough to form leaf. [1]
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.
(a) Name the pH of a neutral solution at room temperature. [1]
(b) Use the term alkaline to describe pool water with pH 8.2. [1]
(c) Explain why adding acid decreases the pH of the pool water. [2]
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.
(a) Name the type of substance that turns cabbage indicator red or pink. [1]
(b) Describe the expected indicator colour in distilled water. [1]
(c) Explain why washing-up liquid is likely to have a pH above 7. [2]
(d) Use the term alkali to describe a soluble base. [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]
Answer Details
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
The diagram in Fig. 1 shows a water-treatment worker checking the concentration of a chlorine compound in a storage tank. A sample contains 0.0150 mol of sodium hypochlorite in 2.50 dm3 of water. Sodium hypochlorite is used to kill microorganisms, but a solution that is too concentrated could irritate skin. The worker has also written the formula for concentration on the clipboard.
(a) Write the unit for molar concentration. [1]
(b) Use the information to calculate the concentration of sodium hypochlorite. [2]
(c) Explain why a fixed volume of water is needed when preparing this disinfectant. [2]
(a) The unit of molar concentration is mol/dm3, also written as mol dm-3. [1]
(b) Use \(c=\frac{n}{V}\): \[c=\frac{0.0150\text{ mol}}{2.50\text{ dm}^3}=0.00600\text{ mol/dm}^3\] [2]
(c) Concentration depends on volume as well as amount of solute. Using a fixed volume of water ensures the stated amount of sodium hypochlorite gives a safe, repeatable concentration of active disinfectant. [2]
Answer Details
(a) The unit of molar concentration is mol/dm3, also written as mol dm-3. [1]
(b) Use \(c=\frac{n}{V}\): \[c=\frac{0.0150\text{ mol}}{2.50\text{ dm}^3}=0.00600\text{ mol/dm}^3\] [2]
(c) Concentration depends on volume as well as amount of solute. Using a fixed volume of water ensures the stated amount of sodium hypochlorite gives a safe, repeatable concentration of active disinfectant. [2]
Question 4 Report
Fig. 1 shows a simplified protein polymer in a wool fibre. The chain is folded, and links between parts of the chain help the fibre keep its shape. A textile company investigates whether wool can replace some acrylic fibre in hats. Acrylic is a synthetic addition polymer. Wool is obtained from sheep and is made mainly from protein. The company needs hats that trap air and remain warm, but it also needs to consider washing and the source of each material.
(a) Name the naturally occurring polymer in wool. [1]
(b) Describe one difference between wool and acrylic in terms of source. [1]
(c) Explain why trapped air in a wool hat helps keep a person's head warm. [2]
(d) What type of small molecules join together to make a protein polymer? [1]
(e) Use the information to give one reason a company might blend wool with acrylic rather than use only wool. [2]
Natural and synthetic polymers
(a) The naturally occurring polymer in wool is protein. [1]
(b) Wool comes from sheep, a living organism, whereas acrylic is made synthetically from chemicals. [1]
(c) Trapped air is a poor conductor of thermal energy. Therefore less energy is transferred from the head to the cooler surroundings, helping the head stay warm. [2]
(d) Protein polymers are made from small molecules called amino acids. [1]
(e) Acrylic may improve durability, reduce cost, or reduce the need for animal fibre. Consequently, blending it with wool can make the hats more practical while retaining some useful wool properties. [2]
Answer Details
Natural and synthetic polymers
(a) The naturally occurring polymer in wool is protein. [1]
(b) Wool comes from sheep, a living organism, whereas acrylic is made synthetically from chemicals. [1]
(c) Trapped air is a poor conductor of thermal energy. Therefore less energy is transferred from the head to the cooler surroundings, helping the head stay warm. [2]
(d) Protein polymers are made from small molecules called amino acids. [1]
(e) Acrylic may improve durability, reduce cost, or reduce the need for animal fibre. Consequently, blending it with wool can make the hats more practical while retaining some useful wool properties. [2]
Question 5 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.
(a) Name the ion responsible for the acidic properties of the spill. [1]
(b) Describe what happens to pH when sodium hydrogencarbonate neutralises the acid. [1]
(c) Explain why water should be added slowly to a concentrated acid spill. [2]
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.
(a) Name the piece of equipment used to measure 1000 cm3 accurately in a laboratory. [1]
(b) Describe the correct order for mixing acid and water. [1]
(c) Explain why acid is added to water rather than water to acid. [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]
Answer Details
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 6 Report
Fig. 1 is part of a safety poster for a laboratory that stores gases in sealed cylinders. The poster compares chlorine with argon. Chlorine is used to disinfect water, while argon is used to protect hot metal during welding. Both substances are elements, but their position in the periodic table is different.
(a) Name the group containing argon. [1]
(b) Describe the difference between the outer electron shells of chlorine and argon. [2]
(c) Explain why argon can protect hot metal from reacting with oxygen. [2]
Fig. 1 shows part of a periodic table display used in a museum. The coloured boxes have been replaced by letters so that visitors can focus on the pattern of the elements. Element R is a shiny solid which is stored under oil because it reacts quickly with water. Element T is a pale gas used in some lamps. The museum guide says that elements in the same vertical group have related chemical properties.
(a) Name the group containing R. [1]
(b) Use the information about R to explain why oil is placed above the metal. [2]
(c) What property makes T suitable for a lamp? [1]
Chlorine and argon
(a) Argon is in Group 0, the noble gases. [1]
(b) Chlorine has seven outer-shell electrons [1], whereas argon has a full outer shell, containing eight outer-shell electrons. [1]
(c) Argon is unreactive. [1] It does not react with hot metal and excludes oxygen from the metal surface, reducing oxidation. [1]
R and T in the periodic-table display
(a) R is in Group 1, the alkali metals. [1]
(b) Oil prevents water reaching the metal. [1] Therefore the vigorous reaction with water that produces hydrogen does not occur. [1]
(c) T is suitable for a lamp because it is unreactive, or chemically inert. [1]
Answer Details
Chlorine and argon
(a) Argon is in Group 0, the noble gases. [1]
(b) Chlorine has seven outer-shell electrons [1], whereas argon has a full outer shell, containing eight outer-shell electrons. [1]
(c) Argon is unreactive. [1] It does not react with hot metal and excludes oxygen from the metal surface, reducing oxidation. [1]
R and T in the periodic-table display
(a) R is in Group 1, the alkali metals. [1]
(b) Oil prevents water reaching the metal. [1] Therefore the vigorous reaction with water that produces hydrogen does not occur. [1]
(c) T is suitable for a lamp because it is unreactive, or chemically inert. [1]
Question 7 Report
A technician prepared two solid compounds for a water-treatment plant. Fig. 1 shows particles in molten potassium chloride and molten silicon carbide. The plant melts potassium chloride in a furnace, then uses the liquid in an electrolysis process. Silicon carbide is used as a hard lining because it remains solid at the furnace temperature. In the first box, ions can move. In the second box, atoms are held in a network by covalent bonds.
(a) Name the particles that carry charge in molten potassium chloride. [1]
(b) Use Fig. 1 to describe one difference between the structures. [1]
(c) Explain why silicon carbide has a high melting temperature. [2]
(d) What happens to the potassium and chloride ions when the potassium chloride cools and solidifies? [1]
Table 1 shows data collected while a student compares substances used in electrical equipment. The student measures the mass of equal-sized pieces before testing them. Copper is used in cables, graphite is used in some electrodes, and sulfur is stored as a molecular solid. The results help the student relate bonding and structure to conductivity and melting temperature. All tests are carried out at room temperature except the melting temperature measurement.
| substance | mass of piece in g | melting temperature in degrees C | conductivity as a solid |
|---|---|---|---|
| copper | 8.9 | 1085 | high |
| graphite | 2.2 | 3650 | medium |
| sulfur | 2.1 | 115 | zero |
(a) Name the substance with metallic bonding. [1]
(b) Use Table 1 to state the melting temperature difference between copper and sulfur. [1]
(c) Explain why graphite conducts but sulfur does not. [2]
(d) Describe why sulfur has the lowest melting temperature. [1]
Potassium chloride and silicon carbide
(a) Charge in molten potassium chloride is carried by potassium ions and chloride ions. [1]
(b) Potassium chloride contains oppositely charged ions, whereas silicon carbide contains atoms joined in a covalent network. [1]
(c) Silicon carbide contains many strong covalent bonds. A large amount of energy is needed to break these bonds, giving it a high melting temperature. [2]
(d) As potassium chloride cools and solidifies, its ions become fixed in position in a lattice and can no longer move freely. [1]
Copper, graphite and sulfur
(a) The substance with metallic bonding is copper. [1]
(b) \[1085-115=970\text{ °C}\] [1]
(c) Graphite conducts because it has delocalised electrons that can move through its structure. Sulfur has no mobile charged particles or electrons, so it does not conduct. [2]
(d) Sulfur has weak intermolecular forces between its molecules, so little energy is needed to overcome them. [1]
Answer Details
Potassium chloride and silicon carbide
(a) Charge in molten potassium chloride is carried by potassium ions and chloride ions. [1]
(b) Potassium chloride contains oppositely charged ions, whereas silicon carbide contains atoms joined in a covalent network. [1]
(c) Silicon carbide contains many strong covalent bonds. A large amount of energy is needed to break these bonds, giving it a high melting temperature. [2]
(d) As potassium chloride cools and solidifies, its ions become fixed in position in a lattice and can no longer move freely. [1]
Copper, graphite and sulfur
(a) The substance with metallic bonding is copper. [1]
(b) \[1085-115=970\text{ °C}\] [1]
(c) Graphite conducts because it has delocalised electrons that can move through its structure. Sulfur has no mobile charged particles or electrons, so it does not conduct. [2]
(d) Sulfur has weak intermolecular forces between its molecules, so little energy is needed to overcome them. [1]
Question 8 Report
Fig. 1 represents particles in two sealed reaction vessels used to make a harmless chloride compound from a toxic gas. Vessel A has a lower temperature than vessel B. The same number of particles is present in each vessel. The diagram includes arrows of different lengths to show particle speeds. A reaction occurs only when particles collide with enough energy and in a suitable arrangement.
(a) Name the vessel with the higher temperature. Use evidence from Fig. 1. [3]
(b) Describe what is meant by activation energy. [3]
(c) Explain why vessel B has a faster reaction rate. [4]
(d) Use the diagram to explain why increasing pressure would increase rate for gaseous reactants but would have little effect on a reaction between solids. [4]
(a) Vessel B has the higher temperature. Its particles have longer arrows, showing greater speed; faster particles have greater kinetic energy. [3]
(b) Activation energy is the minimum energy that reacting particles need during a collision in order to react. This energy is needed to break bonds or start the reaction. [3]
(c) In vessel B, particles move faster, so collisions occur more frequently. Also, a greater fraction of collisions have energy equal to or greater than the activation energy. There are therefore more successful collisions per second, giving a faster rate. [4]
(d) Increasing pressure pushes gas particles closer together. They collide more often, so the gas reaction rate rises. In a solid, particles are already fixed very close together, so pressure has little effect on their collision frequency or exposed surface area. [4]
Answer Details
(a) Vessel B has the higher temperature. Its particles have longer arrows, showing greater speed; faster particles have greater kinetic energy. [3]
(b) Activation energy is the minimum energy that reacting particles need during a collision in order to react. This energy is needed to break bonds or start the reaction. [3]
(c) In vessel B, particles move faster, so collisions occur more frequently. Also, a greater fraction of collisions have energy equal to or greater than the activation energy. There are therefore more successful collisions per second, giving a faster rate. [4]
(d) Increasing pressure pushes gas particles closer together. They collide more often, so the gas reaction rate rises. In a solid, particles are already fixed very close together, so pressure has little effect on their collision frequency or exposed surface area. [4]
Question 9 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.
Answer Details
(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 10 Report
A forensic team finds Fig. 1 on a label from a damaged solvent container. It shows the displayed formula of but-2-ene and a note that the liquid reacted with hydrogen in the presence of a nickel catalyst. The team must identify the product before deciding how to store the recovered liquid. Hydrogen is added across the double bond, producing a saturated hydrocarbon. This reaction is also used on some plant oils to alter their physical properties.
(a) Name the type of reaction between but-2-ene and hydrogen. [1]
(b) Complete the molecular formula of but-2-ene: C4H___. [1]
(c) Use the displayed formula to explain why the product has the formula C4H10. [5]
(a) The reaction is addition, also called hydrogenation. Hydrogen adds across the carbon-carbon double bond. [1]
(b) But-2-ene has formula \(\text{C}_4\text{H}_8\), so the missing number is 8. [1]
(c) But-2-ene contains four carbon atoms and eight hydrogen atoms, giving \(\text{C}_4\text{H}_8\). It has one carbon-carbon double bond. Hydrogen adds across this double bond, with one hydrogen atom bonding to each of the two carbon atoms. This adds two hydrogen atoms, giving \(\text{C}_4\text{H}_{10}\). [5]
Answer Details
(a) The reaction is addition, also called hydrogenation. Hydrogen adds across the carbon-carbon double bond. [1]
(b) But-2-ene has formula \(\text{C}_4\text{H}_8\), so the missing number is 8. [1]
(c) But-2-ene contains four carbon atoms and eight hydrogen atoms, giving \(\text{C}_4\text{H}_8\). It has one carbon-carbon double bond. Hydrogen adds across this double bond, with one hydrogen atom bonding to each of the two carbon atoms. This adds two hydrogen atoms, giving \(\text{C}_4\text{H}_{10}\). [5]
Question 11 Report
Fig. 1 shows a sealed respirometer used by students to investigate decay of leaf litter. The flask contains damp leaves and soil bacteria. A small tube of potassium hydroxide solution absorbs carbon dioxide made by the bacteria. As the bacteria respire, oxygen is used and the coloured drop moves along the capillary tube. The students place a second, identical apparatus in a refrigerator. They plan to compare the distance moved in 20 minutes. The apparatus is checked carefully because potassium hydroxide is corrosive and must not touch the leaf litter.
(a) Name the chemical in Fig. 1 that absorbs carbon dioxide. [2]
(b) Use Fig. 1 to describe why the coloured drop moves when the bacteria respire. [3]
(c) Explain why the students should use the same mass of leaves in each apparatus. [3]
(d) Complete the prediction: the drop in the refrigerator apparatus will move a __________ distance in 20 minutes. Explain your answer. [3]
(a) Potassium hydroxide solution [2] absorbs the carbon dioxide.
(b) [3] Bacteria use oxygen in respiration. The carbon dioxide they produce is absorbed by potassium hydroxide. This decreases the gas volume or pressure in the flask, pulling the coloured drop along the capillary tube.
(c) [3] The mass of leaves affects the amount of material available to bacteria. Different leaf masses could result in different respiration rates. Using the same mass makes the comparison fair, so temperature is the variable being changed.
(d) [3] The drop in the refrigerator apparatus will move a shorter distance in 20 minutes. Low temperature slows enzyme-controlled reactions in bacteria, so less oxygen is used in the same time. The pressure falls by less, so the drop moves less far.
Answer Details
(a) Potassium hydroxide solution [2] absorbs the carbon dioxide.
(b) [3] Bacteria use oxygen in respiration. The carbon dioxide they produce is absorbed by potassium hydroxide. This decreases the gas volume or pressure in the flask, pulling the coloured drop along the capillary tube.
(c) [3] The mass of leaves affects the amount of material available to bacteria. Different leaf masses could result in different respiration rates. Using the same mass makes the comparison fair, so temperature is the variable being changed.
(d) [3] The drop in the refrigerator apparatus will move a shorter distance in 20 minutes. Low temperature slows enzyme-controlled reactions in bacteria, so less oxygen is used in the same time. The pressure falls by less, so the drop moves less far.
