Chemistry 9202 | Paper 2 Mock 01 | Written Paper 2
Question 1 Report
This investigation is about using aluminium to remove copper ions from waste solution. Fig. 1 shows an insulated beaker fitted with a temperature probe. The student adds aluminium granules to copper sulfate solution and records the temperature every minute. Table 1 gives the results. The reaction produces copper metal and aluminium sulfate solution.
| time / min | temperature / degrees C |
|---|---|
| 0 | 20.2 |
| 1 | 24.7 |
| 2 | 27.9 |
| 3 | 29.1 |
| 4 | 28.8 |
(a) Record the temperature change at the maximum temperature. [1]
(b) Describe the evidence that the reaction is exothermic. [1]
(c) Give one observation, other than temperature, expected when aluminium reacts with copper sulfate solution. [1]
(d) Use the formula Q = mcΔT to calculate Q for 100 g of solution. [2]
Fig. 1 shows a student measuring the temperature change when magnesium reacts with dilute hydrochloric acid in a polystyrene cup. The cup contains 50.0 cm3 of acid. The student records the highest temperature after adding the metal. Assume that 1.0 cm3 of solution has a mass of 1.0 g and that the specific heat capacity of the solution is 4.2 J g-1 degrees C-1.
| measurement | value |
|---|---|
| initial temperature | 21.5 degrees C |
| highest temperature | 35.0 degrees C |
(a) Record the temperature change. [1]
(b) Use the table to calculate the energy transferred to the solution. [2]
(c) Give the sign of the energy change for the reaction. [1]
Aluminium and copper sulfate
(a) Temperature change at the maximum = 29.1 °C − 20.2 °C = 8.9 °C. [1]
(b) The temperature increases, showing that energy is transferred to the solution. This is evidence that the reaction is exothermic. [1]
(c) Brown-pink copper metal forms. Alternatively, the blue solution becomes paler or aluminium dissolves. [1]
(d) Q = mcΔT = 100 g × 4.2 J g-1 °C-1 × 8.9 °C = 3738 J, or 3.74 × 103 J. [2]
Magnesium and hydrochloric acid
(a) Temperature change = 35.0 °C − 21.5 °C = 13.5 °C. [1]
(b) 50.0 cm3 of solution has a mass of 50.0 g.
Q = 50.0 g × 4.2 J g-1 °C-1 × 13.5 °C = 2835 J, or 2.84 × 103 J. [2]
(c) The energy change is negative, because the reaction is exothermic. [1]
Answer Details
Aluminium and copper sulfate
(a) Temperature change at the maximum = 29.1 °C − 20.2 °C = 8.9 °C. [1]
(b) The temperature increases, showing that energy is transferred to the solution. This is evidence that the reaction is exothermic. [1]
(c) Brown-pink copper metal forms. Alternatively, the blue solution becomes paler or aluminium dissolves. [1]
(d) Q = mcΔT = 100 g × 4.2 J g-1 °C-1 × 8.9 °C = 3738 J, or 3.74 × 103 J. [2]
Magnesium and hydrochloric acid
(a) Temperature change = 35.0 °C − 21.5 °C = 13.5 °C. [1]
(b) 50.0 cm3 of solution has a mass of 50.0 g.
Q = 50.0 g × 4.2 J g-1 °C-1 × 13.5 °C = 2835 J, or 2.84 × 103 J. [2]
(c) The energy change is negative, because the reaction is exothermic. [1]
Question 2 Report
A bridge engineer selects metal for an expansion joint carrying heavy traffic. Fig. 1 shows the metallic structure of copper. Positive copper ions are arranged in layers, surrounded by delocalised electrons. The joint must conduct electricity for a monitoring circuit and must be shaped without breaking.
(a) Give the name of the bonding in copper. [1]
(b) Describe why copper conducts electricity. [2]
(c) Describe why copper can be bent into shape. [2]
(d) Give one other metal property useful for bridge components. [1]
(a) Copper has metallic bonding [1].
(b) Copper contains delocalised electrons [1]. These electrons move through the metal and carry electrical charge [1].
(c) Layers of metal ions can slide past one another [1]. Metallic attraction between the positive ions and delocalised electrons remains, so the metal does not break when bent [1].
(d) A useful additional property is high tensile strength [1]. A high melting temperature or corrosion resistance when alloyed would also be acceptable.
Answer Details
(a) Copper has metallic bonding [1].
(b) Copper contains delocalised electrons [1]. These electrons move through the metal and carry electrical charge [1].
(c) Layers of metal ions can slide past one another [1]. Metallic attraction between the positive ions and delocalised electrons remains, so the metal does not break when bent [1].
(d) A useful additional property is high tensile strength [1]. A high melting temperature or corrosion resistance when alloyed would also be acceptable.
Question 3 Report
A copper sulfate solution is warmed by a reaction in the apparatus in Fig. 1. A technician compares the reaction of zinc powder with copper sulfate solution at a recycling plant. The energy released heats the solution, but some energy also warms the cup and escapes to the air. Table 1 gives the recorded results. The solution has a mass of 75 g and a specific heat capacity of 4.2 J g-1 degrees C-1.
| time after mixing / s | temperature / degrees C |
|---|---|
| 0 | 19.8 |
| 30 | 28.4 |
| 60 | 31.2 |
| 90 | 30.6 |
(a) Record the maximum temperature shown in Table 1. [1]
(b) Use the results to calculate the energy gained by the solution. [2]
(c) Describe one reason why this calculated value is less than the total energy released by the reaction. [1]
(a) The maximum temperature is 31.2 °C. [1]
(b) Temperature rise = 31.2 °C − 19.8 °C = 11.4 °C.
Q = mcΔT = 75 g × 4.2 J g-1 °C-1 × 11.4 °C
= 3591 J, or 3.59 × 103 J. [2]
(c) The calculated value is smaller than the total energy released because some energy warms the cup or thermometer, or is transferred to the surroundings rather than heating the solution. [1]
Answer Details
(a) The maximum temperature is 31.2 °C. [1]
(b) Temperature rise = 31.2 °C − 19.8 °C = 11.4 °C.
Q = mcΔT = 75 g × 4.2 J g-1 °C-1 × 11.4 °C
= 3591 J, or 3.59 × 103 J. [2]
(c) The calculated value is smaller than the total energy released because some energy warms the cup or thermometer, or is transferred to the surroundings rather than heating the solution. [1]
Question 4 Report
This practical is being planned for a company that recycles aluminium drinks cans. The aim is to prepare aluminium sulfate solution. Fig. 1 shows two possible starting materials: cleaned aluminium strips and aluminium oxide powder. In a preliminary test, both are placed in separate beakers containing equal volumes of warm dilute sulfuric acid. The metal produces only a few bubbles at first, whereas the oxide powder reacts steadily and leaves a colourless solution.
| Starting material | Time until no solid remains / min | Observation |
|---|---|---|
| Aluminium strips | more than 20 | few bubbles |
| Aluminium oxide powder | 6 | no gas seen |
(a) Describe the difference in reaction rate shown in Table 1. [2]
(b) Explain why aluminium strips may react slowly when first placed in acid. [3]
(c) Use formulae to write a balanced equation for aluminium oxide reacting with sulfuric acid. [3]
(d) Give two reasons why aluminium oxide is a more suitable material than aluminium metal for this preparation. [3]
(e) Describe the method used to make dry aluminium sulfate crystals from the colourless solution. [4]
(f) Give one use of aluminium sulfate outside the laboratory. [1]
(a) Aluminium oxide reacts faster: all of its solid has disappeared after 6 minutes, whereas aluminium strips still remain after more than 20 minutes. [2]
(b) Aluminium metal has a protective layer of aluminium oxide. The acid must first react with or remove this layer, so initially little acid can contact the aluminium metal itself. This makes the initial reaction slow. [3]
(c) Al2O3 + 3H2SO4 → Al2(SO4)3 + 3H2O [3]
(d) Aluminium oxide is more suitable because it reacts more quickly, its powder has a larger surface area, and it produces no hydrogen gas. Avoiding hydrogen makes the preparation safer because hydrogen is flammable. The oxide also gives the salt solution directly. Any three of these points gain credit. [3]
(e) Gently heat the colourless solution to evaporate some water and concentrate it. Stop heating before it becomes dry. Leave the concentrated solution to cool so crystals form, then filter the crystals and dry them using filter paper. [4]
(f) One use is treating drinking water to remove suspended particles. It is also used in paper manufacture or dyeing fabrics. [1]
Answer Details
(a) Aluminium oxide reacts faster: all of its solid has disappeared after 6 minutes, whereas aluminium strips still remain after more than 20 minutes. [2]
(b) Aluminium metal has a protective layer of aluminium oxide. The acid must first react with or remove this layer, so initially little acid can contact the aluminium metal itself. This makes the initial reaction slow. [3]
(c) Al2O3 + 3H2SO4 → Al2(SO4)3 + 3H2O [3]
(d) Aluminium oxide is more suitable because it reacts more quickly, its powder has a larger surface area, and it produces no hydrogen gas. Avoiding hydrogen makes the preparation safer because hydrogen is flammable. The oxide also gives the salt solution directly. Any three of these points gain credit. [3]
(e) Gently heat the colourless solution to evaporate some water and concentrate it. Stop heating before it becomes dry. Leave the concentrated solution to cool so crystals form, then filter the crystals and dry them using filter paper. [4]
(f) One use is treating drinking water to remove suspended particles. It is also used in paper manufacture or dyeing fabrics. [1]
Question 5 Report
This reaction is used at a plastics factory to make ethene from a heavier hydrocarbon fraction. Fig. 1 shows a laboratory model of the cracking apparatus. Paraffin oil is soaked into mineral wool and heated. The vapour passes over hot aluminium oxide catalyst, then the products are collected over water. A student adds bromine water to a sample of the collected gas. The orange colour disappears. The student must not heat the delivery tube after removing the flame because water could be drawn back into hot glass.
(a) Give the name of the reaction occurring over aluminium oxide. [1]
(b) Describe the bromine water result that shows an alkene is present. [1]
(c) How does ethene differ in bonding from the alkane used at the start? [2]
Fig. 1 shows two structural formulae drawn by a student during a lesson on isomers. Both compounds have the molecular formula C4H10. The student has placed a box around the part of compound Y where the carbon chain branches. The two liquids have different boiling points, even though each molecule contains four carbon atoms and ten hydrogen atoms. This is because the atoms are connected in a different arrangement. The student is asked to use correct names rather than calling both samples butane.
(a) Give the name used for compounds with the same molecular formula but different structures. [1]
(b) Use Fig. 1 to state the name of compound X. [1]
(c) Describe one structural difference between X and Y. [2]
(a) The reaction over aluminium oxide is cracking. [1]
(b) Orange or brown bromine water becomes colourless. This shows that an alkene is present. [1]
(c) Ethene contains a carbon-carbon double bond. The starting alkane has only carbon-carbon single bonds, so it is saturated. [2]
(a) Compounds with the same molecular formula but different structures are called isomers. [1]
(b) Compound X is butane. [1]
(c) X has a straight carbon chain. Y has a branched carbon chain, with one carbon attached as a side branch. This different arrangement makes them structural isomers. [2]
Answer Details
(a) The reaction over aluminium oxide is cracking. [1]
(b) Orange or brown bromine water becomes colourless. This shows that an alkene is present. [1]
(c) Ethene contains a carbon-carbon double bond. The starting alkane has only carbon-carbon single bonds, so it is saturated. [2]
(a) Compounds with the same molecular formula but different structures are called isomers. [1]
(b) Compound X is butane. [1]
(c) X has a straight carbon chain. Y has a branched carbon chain, with one carbon attached as a side branch. This different arrangement makes them structural isomers. [2]
Question 6 Report
The manager of a water treatment plant stores dilute hydrochloric acid in a tank. A new student suggests making the tank from sodium because sodium is a metal. The manager rejects the suggestion after considering the reaction of sodium with water.
(a) Describe what would happen if sodium were put into water. [1]
(b) Give one more suitable material for the tank. [1]
This bridge is protected by sacrificial blocks of zinc attached to its underwater steel piles. Fig. 1 shows a zinc block bolted to a steel pile in seawater. The zinc block is replaced once much of it has reacted. The method is also used on the steel hull of some ships.
(a) Give the name of this method of protecting steel. [1]
(b) Describe why zinc reacts instead of the iron in the steel pile. [2]
(c) Give one metal, other than zinc, that could act as a sacrificial metal for iron. [1]
(d) Give one reason why copper would not be suitable as the sacrificial metal. [1]
Labelled answer diagram:
(a) Sodium reacts vigorously with water. It may move on the surface and produces hydrogen; the hydrogen or sodium may burn. [1]
(b) A suitable tank material is plastic, glass, or a suitable corrosion-resistant lined steel tank. [1]
(a) The protection method is sacrificial protection, also called a sacrificial anode. [1]
(b) Zinc is more reactive than iron, so zinc oxidises and loses electrons in preference to the iron in the steel pile. The zinc is used up instead of the iron. [2]
(c) Magnesium or aluminium could act as a sacrificial metal for iron. [1]
(d) Copper is less reactive than iron, so it would not oxidise in preference to iron and cannot provide sacrificial protection. [1]
Answer Details
Labelled answer diagram:
(a) Sodium reacts vigorously with water. It may move on the surface and produces hydrogen; the hydrogen or sodium may burn. [1]
(b) A suitable tank material is plastic, glass, or a suitable corrosion-resistant lined steel tank. [1]
(a) The protection method is sacrificial protection, also called a sacrificial anode. [1]
(b) Zinc is more reactive than iron, so zinc oxidises and loses electrons in preference to the iron in the steel pile. The zinc is used up instead of the iron. [2]
(c) Magnesium or aluminium could act as a sacrificial metal for iron. [1]
(d) Copper is less reactive than iron, so it would not oxidise in preference to iron and cannot provide sacrificial protection. [1]
Question 7 Report
Fig. 1 shows an automated dispenser filling small bottles with a glucose solution for a hospital training exercise. The stock solution has concentration 0.400 mol dm-3. Each bottle must receive 50.0 cm3 containing 0.0100 mol of glucose. The display gives the volume delivered by the pump.
(a) Use the amount of glucose and the concentration of stock solution to calculate the volume of stock solution needed, in dm3. [2]
(b) Give this volume in cm3. [1]
(c) Describe how water is used after the stock solution has been delivered to make the final volume correct. [2]
A chemist prepares aluminium nitrate solution for an etching test on a metal surface. Fig. 1 shows the labelled storage bottle and the volumetric flask used. The bottle must be labelled clearly because aluminium nitrate is a compound, not the metal aluminium. The required solution contains 0.0750 mol of Al(NO3)3 in 300 cm3 of solution.
(a) Use the information to calculate the concentration of aluminium nitrate in mol dm-3. [2]
(b) Give the unit used for molar concentration. [1]
(c) Describe one safety step when transferring this solution to the labelled bottle. [2]
Glucose dispenser
(a) Use \(V=\frac{n}{c}\):
\[V=\frac{0.0100}{0.400}=0.0250\text{ dm}^3\]
The required stock-solution volume is 0.0250 dm3. [2 marks]
(b)
\[0.0250\text{ dm}^3=25.0\text{ cm}^3\]
The volume is 25.0 cm3. [1 mark]
(c) After delivering the stock solution, add water until the total volume is exactly 50.0 cm3. Mix thoroughly so the glucose concentration is even throughout the bottle. [2 marks]
Aluminium nitrate solution
(a)
\[300\text{ cm}^3=0.300\text{ dm}^3\]
\[c=\frac{0.0750}{0.300}=0.250\text{ mol dm}^{-3}\]
The concentration is 0.250 mol dm-3. [2 marks]
(b) The unit for molar concentration is mol dm-3. [1 mark]
(c) Wear eye protection and use a funnel to avoid spills. Clearly label the bottle with the chemical identity and hazard information, and clean up any spill promptly. Any two valid safety steps gain credit. [2 marks]
Answer Details
Glucose dispenser
(a) Use \(V=\frac{n}{c}\):
\[V=\frac{0.0100}{0.400}=0.0250\text{ dm}^3\]
The required stock-solution volume is 0.0250 dm3. [2 marks]
(b)
\[0.0250\text{ dm}^3=25.0\text{ cm}^3\]
The volume is 25.0 cm3. [1 mark]
(c) After delivering the stock solution, add water until the total volume is exactly 50.0 cm3. Mix thoroughly so the glucose concentration is even throughout the bottle. [2 marks]
Aluminium nitrate solution
(a)
\[300\text{ cm}^3=0.300\text{ dm}^3\]
\[c=\frac{0.0750}{0.300}=0.250\text{ mol dm}^{-3}\]
The concentration is 0.250 mol dm-3. [2 marks]
(b) The unit for molar concentration is mol dm-3. [1 mark]
(c) Wear eye protection and use a funnel to avoid spills. Clearly label the bottle with the chemical identity and hazard information, and clean up any spill promptly. Any two valid safety steps gain credit. [2 marks]
Question 8 Report
A manufacturer of brass musical-instrument valves uses electroplating to give parts a hard nickel surface. Fig. 1 shows one valve connected in a plating tank. The electrolyte is nickel sulfate solution. The operator records the mass of a valve before and after plating at different currents for the same time. The coating must be even, so each valve is cleaned with detergent and rinsed with water before it enters the tank.
| Current / A | Plating time / min | Mass before plating / g | Mass after plating / g |
|---|---|---|---|
| 0.40 | 15 | 18.62 | 18.74 |
| 0.80 | 15 | 18.59 | 18.83 |
| 1.20 | 15 | 18.65 | 18.98 |
(a) Give the name of the electrode that the brass valve is connected to. [1]
(b) Give the name of the electrode made from nickel metal. [1]
(c) Describe the movement of nickel ions and electrons that produces a nickel coating on the valve. [3]
(d) Use Table 1 to calculate the mass of nickel deposited on the valve at a current of 0.80 A. [2]
(e) Use Table 1 to describe the relationship between current and mass deposited. [2]
(f) Describe why the valve is cleaned before electroplating. [2]
(g) Use a half-equation to show the reaction at the nickel electrode. [2]
(h) Give two changes that would increase the mass of nickel deposited without changing the metal compound in the solution. [3]
(a) The brass valve is the cathode, or negative electrode [1]. Nickel ions are reduced onto it.
(b) The nickel-metal electrode is the anode, or positive electrode [1].
(c) Nickel ions move towards the negative valve [1]. They gain electrons [1], forming nickel atoms that coat the valve [1].
(d) \[18.83\text{ g}-18.59\text{ g}=0.24\text{ g}\] The deposited nickel mass is 0.24 g [2].
(e) Mass deposited increases as current increases [1]. In 15 minutes, the gains are 0.12 g, 0.24 g and 0.33 g, showing approximate direct proportionality [1].
(f) Cleaning removes grease, dirt or oxide [1]. This gives good electrical contact and allows nickel to adhere evenly [1].
(g) At the nickel anode:
\[\mathrm{Ni(s)\rightarrow Ni^{2+}(aq)+2e^-}\] [2]
(h) Two valid changes are to increase the current and increase the plating time [maximum 3]. Increasing nickel sulfate concentration or using a suitable higher controlled temperature are also acceptable.
Answer Details
(a) The brass valve is the cathode, or negative electrode [1]. Nickel ions are reduced onto it.
(b) The nickel-metal electrode is the anode, or positive electrode [1].
(c) Nickel ions move towards the negative valve [1]. They gain electrons [1], forming nickel atoms that coat the valve [1].
(d) \[18.83\text{ g}-18.59\text{ g}=0.24\text{ g}\] The deposited nickel mass is 0.24 g [2].
(e) Mass deposited increases as current increases [1]. In 15 minutes, the gains are 0.12 g, 0.24 g and 0.33 g, showing approximate direct proportionality [1].
(f) Cleaning removes grease, dirt or oxide [1]. This gives good electrical contact and allows nickel to adhere evenly [1].
(g) At the nickel anode:
\[\mathrm{Ni(s)\rightarrow Ni^{2+}(aq)+2e^-}\] [2]
(h) Two valid changes are to increase the current and increase the plating time [maximum 3]. Increasing nickel sulfate concentration or using a suitable higher controlled temperature are also acceptable.
Question 9 Report
This experiment is a school demonstration of a carbonate reacting with acid. Fig. 1 shows sodium carbonate solution in a flask connected to a test tube of limewater. Dilute hydrochloric acid is injected through the bung. The limewater turns cloudy as gas reaches it. The student must keep the syringe tip below the bung to prevent acid leaking out.
(a) Give the name of the gas that turns limewater cloudy. [1]
(b) Use the substances to give the word equation for the reaction in the flask. [2]
(c) Describe the visible change in the flask while the reaction is taking place. [1]
(a) The gas that turns limewater cloudy is carbon dioxide. [1]
(b) The word equation is:
sodium carbonate + hydrochloric acid → sodium chloride + water + carbon dioxide [2]
(c) The reaction in the flask causes fizzing, or bubbles to be produced, as carbon dioxide gas forms. [1]
Answer Details
(a) The gas that turns limewater cloudy is carbon dioxide. [1]
(b) The word equation is:
sodium carbonate + hydrochloric acid → sodium chloride + water + carbon dioxide [2]
(c) The reaction in the flask causes fizzing, or bubbles to be produced, as carbon dioxide gas forms. [1]
