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Question 1 Report
This reaction is used in a school demonstration of sodium metal. A very small piece of sodium is placed on water in a trough. It moves across the water, producing hydrogen gas and sodium hydroxide solution. Fig. 1 shows a model for sodium before it reacts. The outer electron from each sodium atom has become part of a shared group of electrons. A student uses the model to compare sodium with magnesium, which has two outer electrons per atom.
(a) Complete the word equation for the reaction.
sodium + water → sodium hydroxide + __________ [1]
(b) Give the charge on each sodium ion in Fig. 1. [1]
(c) Explain how sodium atoms form the ions and electrons shown in Fig. 1. [3]
(d) Which metal, sodium or magnesium, is expected to have stronger metallic bonding? Give a reason. [2]
(e) State two safety precautions the student should take in this reaction. [3]
(a) The missing product is hydrogen. [1] Sodium reacts with water to make sodium hydroxide and hydrogen gas.
(b) Each sodium ion has charge 1+. [1]
(c) Each sodium atom loses one outer electron [1]. Loss of this electron produces a Na+ ion [1], and the lost electrons become delocalised, able to move through the metal lattice. [1]
(d) Magnesium has stronger metallic bonding. [1] Each magnesium atom supplies two delocalised electrons, giving stronger electrostatic attraction between its positive ions and the electron sea than in sodium. [1]
(e) Any three suitable precautions gain the marks: use a very small piece of sodium [1], wear eye protection [1], and handle sodium with tongs/forceps [1]. Other acceptable precautions include standing behind a safety screen or well back, and storing sodium under oil before use. Sodium reacts vigorously with water and produces flammable hydrogen.
Answer Details
(a) The missing product is hydrogen. [1] Sodium reacts with water to make sodium hydroxide and hydrogen gas.
(b) Each sodium ion has charge 1+. [1]
(c) Each sodium atom loses one outer electron [1]. Loss of this electron produces a Na+ ion [1], and the lost electrons become delocalised, able to move through the metal lattice. [1]
(d) Magnesium has stronger metallic bonding. [1] Each magnesium atom supplies two delocalised electrons, giving stronger electrostatic attraction between its positive ions and the electron sea than in sodium. [1]
(e) Any three suitable precautions gain the marks: use a very small piece of sodium [1], wear eye protection [1], and handle sodium with tongs/forceps [1]. Other acceptable precautions include standing behind a safety screen or well back, and storing sodium under oil before use. Sodium reacts vigorously with water and produces flammable hydrogen.
Question 2 Report
The table below shows the substances chosen for a laboratory display about elements and compounds. Small sealed samples of carbon, chlorine, sodium chloride and ethene are kept in a box. The teacher uses the melting temperatures to decide which substances need special storage at room temperature. Formulae are included so that students can identify the elements present in each substance.
| substance | formula | melting temperature / °C | classification |
|---|---|---|---|
| carbon | C | 3550 | ................. |
| chlorine | Cl2 | -101 | ................. |
| sodium chloride | NaCl | 801 | ................. |
| ethene | C2H4 | -169 | ................. |
(a) Complete the classification column using element or compound. [4]
(b) Which two substances are gases at a laboratory temperature of 20 °C? [2]
(c) State what the formula NaCl shows about the types of element in sodium chloride. [2]
(d) Use Table 1 to give the substance with the highest melting temperature and the substance with the lowest melting temperature. [2]
(e) Write the balanced chemical equation for the complete combustion of ethene in oxygen. [3]
(a) Carbon is an element because its formula contains one type of atom. Chlorine is an element because \(\mathrm{Cl_2}\) contains only chlorine atoms. Sodium chloride and ethene are compounds because each contains more than one element. [4]
| substance | classification |
|---|---|
| carbon | element |
| chlorine | element |
| sodium chloride | compound |
| ethene | compound |
(b) Chlorine and ethene are gases at \(20\ ^\circ\mathrm{C}\), because their melting temperatures are below this laboratory temperature. [2]
(c) \(\mathrm{NaCl}\) shows that sodium chloride contains two different elements: sodium and chlorine. [2]
(d) Carbon has the highest melting temperature, and ethene has the lowest melting temperature. [2]
(e)
\[\mathrm{C_2H_4+3O_2\rightarrow2CO_2+2H_2O}\]
This is complete combustion, so the products are carbon dioxide and water. [3]
Answer Details
(a) Carbon is an element because its formula contains one type of atom. Chlorine is an element because \(\mathrm{Cl_2}\) contains only chlorine atoms. Sodium chloride and ethene are compounds because each contains more than one element. [4]
| substance | classification |
|---|---|
| carbon | element |
| chlorine | element |
| sodium chloride | compound |
| ethene | compound |
(b) Chlorine and ethene are gases at \(20\ ^\circ\mathrm{C}\), because their melting temperatures are below this laboratory temperature. [2]
(c) \(\mathrm{NaCl}\) shows that sodium chloride contains two different elements: sodium and chlorine. [2]
(d) Carbon has the highest melting temperature, and ethene has the lowest melting temperature. [2]
(e)
\[\mathrm{C_2H_4+3O_2\rightarrow2CO_2+2H_2O}\]
This is complete combustion, so the products are carbon dioxide and water. [3]
Question 3 Report
This experiment is used by a metal-finishing company to decide the temperature of an acid cleaning bath. Equal strips of magnesium are placed in hydrochloric acid solution at different temperatures. The students record the time until each strip has disappeared. Fig. 1 represents the collision model for a reaction between magnesium and acid particles. In box A, the collision does not have enough energy. In box B, the collision has enough energy to lead to reaction.
(a) State the gas formed when magnesium reacts with hydrochloric acid. [1]
(b) Give the balanced chemical equation for this reaction. [2]
(c) Use the collision model to explain why increasing temperature decreases the time taken for the magnesium to disappear. [3]
(d) Name one variable, other than temperature, that must be controlled in this experiment. [1]
(e) Calculate the mean rate of reaction if a magnesium strip of mass 0.36 g disappears in 90 s. Give the answer in g/s. [2]
(f) Suggest why the company should not use a very high temperature, even if it gives a fast rate reaction. [1]
(a) Magnesium reacting with hydrochloric acid produces hydrogen gas. [1]
(b) The balanced equation is:
\[\mathrm{Mg+2HCl\rightarrow MgCl_2+H_2}\]
[2]
(c) At higher temperature, particles have more kinetic energy. They move faster and collide more often. Also, a greater proportion of collisions have enough energy to react, so magnesium disappears in less time. [3]
(d) One variable that must be controlled is the concentration of hydrochloric acid. The volume of acid, mass or surface area of magnesium, and type of magnesium strip are also acceptable controls. [1]
(e) Mean rate is mass used divided by time:
\[\frac{0.36\text{ g}}{90\text{ s}}=0.004\text{ g s}^{-1}\]
[2]
(f) A very high temperature increases energy costs. It may also make hot acid more hazardous, and hydrogen, which is flammable, would be produced more rapidly. [1]
Answer Details
(a) Magnesium reacting with hydrochloric acid produces hydrogen gas. [1]
(b) The balanced equation is:
\[\mathrm{Mg+2HCl\rightarrow MgCl_2+H_2}\]
[2]
(c) At higher temperature, particles have more kinetic energy. They move faster and collide more often. Also, a greater proportion of collisions have enough energy to react, so magnesium disappears in less time. [3]
(d) One variable that must be controlled is the concentration of hydrochloric acid. The volume of acid, mass or surface area of magnesium, and type of magnesium strip are also acceptable controls. [1]
(e) Mean rate is mass used divided by time:
\[\frac{0.36\text{ g}}{90\text{ s}}=0.004\text{ g s}^{-1}\]
[2]
(f) A very high temperature increases energy costs. It may also make hot acid more hazardous, and hydrogen, which is flammable, would be produced more rapidly. [1]
Question 4 Report
A manufacturer is checking a batch of brass fittings used in water taps. Fig. 1 shows a simplified particle model of the solid. Copper atoms are shown as unshaded circles and zinc atoms as black circles. The fittings are hard and do not have a fixed chemical formula. Brass is melted and poured into moulds to make the final product.
(a) Which type of substance is brass: an element, a compound or a mixture? [1]
(b) Give the names of the two elements in brass. [2]
(c) State why brass is not a compound. [1]
(a) Brass is a mixture, specifically an alloy. [1]
(b) The two elements are copper and zinc. [2]
(c) Brass is not a compound because copper and zinc are not chemically combined in a fixed ratio. Its composition can vary, so it has no fixed chemical formula. [1]
Answer Details
(a) Brass is a mixture, specifically an alloy. [1]
(b) The two elements are copper and zinc. [2]
(c) Brass is not a compound because copper and zinc are not chemically combined in a fixed ratio. Its composition can vary, so it has no fixed chemical formula. [1]
Question 5 Report
The diagram shows a portable gas generator used by a field team to produce carbon dioxide for calibrating an air-quality sensor. Marble chips, which are mainly calcium carbonate, are placed in the flask. Dilute nitric acid is added through the funnel. The gas is dried before entering a calibrated collection tube.
(a) Give the formula of nitric acid. [1]
(b) Complete the balanced equation for the reaction.
CaCO3 + 2HNO3 → Ca(NO3)2 + ........ + CO2 [1]
(c) State why the gas is passed through a drying tube before its volume is measured. [1]
(d) Calculate the amount, in moles, of calcium carbonate in 5.00 g of marble chips. Assume the chips are pure CaCO3. Mr(CaCO3) = 100. [2]
(e) Use the equation to calculate the mass of carbon dioxide made from 5.00 g of calcium carbonate. Mr(CO2) = 44. [3]
(f) Suggest why large marble chips are safer than powdered calcium carbonate for this gas generator. [3]
(a) Nitric acid is HNO3 [1].
(b) \[\mathrm{CaCO_3+2HNO_3\rightarrow Ca(NO_3)_2+H_2O+CO_2}\] The missing product is H2O [1].
(c) The drying tube removes water vapour, so the measured volume is carbon dioxide only [1].
(d) \[n(\mathrm{CaCO_3})=\frac{5.00\text{ g}}{100\text{ g mol}^{-1}}=0.0500\text{ mol}\] [2].
(e) The equation gives a 1:1 mole ratio, so \(0.0500\) mol CaCO3 produces \(0.0500\) mol CO2 [1]. \[m=0.0500\times44=2.20\text{ g}\] [2].
(f) Large chips have less surface area than powder [1], so the reaction is slower and easier to control [1]. This reduces rapid gas production, splashing and pressure build-up [1].
Answer Details
(a) Nitric acid is HNO3 [1].
(b) \[\mathrm{CaCO_3+2HNO_3\rightarrow Ca(NO_3)_2+H_2O+CO_2}\] The missing product is H2O [1].
(c) The drying tube removes water vapour, so the measured volume is carbon dioxide only [1].
(d) \[n(\mathrm{CaCO_3})=\frac{5.00\text{ g}}{100\text{ g mol}^{-1}}=0.0500\text{ mol}\] [2].
(e) The equation gives a 1:1 mole ratio, so \(0.0500\) mol CaCO3 produces \(0.0500\) mol CO2 [1]. \[m=0.0500\times44=2.20\text{ g}\] [2].
(f) Large chips have less surface area than powder [1], so the reaction is slower and easier to control [1]. This reduces rapid gas production, splashing and pressure build-up [1].
Question 6 Report
A refinery compares two zeolite catalysts for converting a heavy gas oil fraction into smaller hydrocarbons. Fig. 1 shows the pilot plant used for the test. In one run, 2.50 kg of feed is passed over catalyst A. Analysis shows that 18.0% by mass of the products is ethene. The process is carried out continuously so that the catalyst can be regenerated.
(a) State two conditions shown in Fig. 1 that are needed for this cracking reaction. [2]
(b) Complete the equation: C10H22 → C8H18 + ________. [2]
(c) Give two ways in which a catalyst changes a reaction. [2]
(d) Calculate the mass of ethene produced in the run using catalyst A. [2]
(e) Explain why ethene is removed from the products and collected separately. [2]
(f) Name the type of reaction when many ethene molecules join to form poly(ethene). [1]
(g) State why catalyst regeneration is needed in a continuous process. [1]
(a) The required conditions shown are a zeolite catalyst [1] and high temperature, 500 °C [1].
(b) \[\mathrm{C_{10}H_{22}\rightarrow C_8H_{18}+C_2H_4}\] The missing product is C2H4 [1]; this gives 10 carbon and 22 hydrogen atoms in total [1].
(c) A catalyst speeds up a reaction [1] and is not used up, remaining chemically unchanged at the end [1].
(d) \[\frac{18.0}{100}\times2.50\text{ kg}=0.450\text{ kg}\] ethene [2].
(e) Ethene is a useful chemical feedstock, particularly for making polymers [1]. Separating it gives a purer product and prevents it being mixed with fuel fractions [1].
(f) Joining many ethene molecules is addition polymerisation [1].
(g) Regeneration is needed because carbon, or coke, coats the catalyst and makes it less effective; the coating must be removed [1].
Answer Details
(a) The required conditions shown are a zeolite catalyst [1] and high temperature, 500 °C [1].
(b) \[\mathrm{C_{10}H_{22}\rightarrow C_8H_{18}+C_2H_4}\] The missing product is C2H4 [1]; this gives 10 carbon and 22 hydrogen atoms in total [1].
(c) A catalyst speeds up a reaction [1] and is not used up, remaining chemically unchanged at the end [1].
(d) \[\frac{18.0}{100}\times2.50\text{ kg}=0.450\text{ kg}\] ethene [2].
(e) Ethene is a useful chemical feedstock, particularly for making polymers [1]. Separating it gives a purer product and prevents it being mixed with fuel fractions [1].
(f) Joining many ethene molecules is addition polymerisation [1].
(g) Regeneration is needed because carbon, or coke, coats the catalyst and makes it less effective; the coating must be removed [1].
Question 7 Report
The table and Fig. 1 show trials at a recycling facility that changes long-chain hydrocarbons from used lubricating oil into smaller molecules. Oil is heated until it forms a gas, then passed through a reactor containing hot aluminium oxide catalyst. The products enter a cold trap. The liquid collected is tested separately from the gas leaving the trap. Ethene is wanted because it can be used to make polymers. The reaction does not involve acid, sodium chloride solution or water.
Table 1 gives the masses obtained from equal masses of oil.
| Catalyst temperature / degrees C | Mass of ethene collected / g | Mass of liquid product / g |
|---|---|---|
| 450 | 8.0 | 71.5 |
| 550 | 14.0 | 65.0 |
(a) State what happens to the long-chain hydrocarbon molecules in the reactor. [2]
(b) Complete the equation for one possible cracking reaction.
C16H34 → C2H4 + ................. [2]
(c) Explain why the oil is vaporised before it reaches the catalyst pellets. [2]
(d) Calculate the increase in mass of ethene when the temperature is changed from 450 degrees C to 550 degrees C. [2]
(e) Give a chemical test for ethene in the gas leaving the cold trap, including the positive result. [2]
(a) In cracking, large hydrocarbon molecules are broken into smaller molecules. The products include smaller alkanes and alkenes such as ethene. [2]
(b) Balance the atoms:
\[\mathrm{C_{16}H_{34}\rightarrow C_2H_4+C_{14}H_{30}}\]
The missing product is C14H30. [2]
(c) The oil is vaporised so it can flow or pass over the catalyst. Gas particles contact the catalyst surface more effectively, increasing the rate at which cracking can occur. [2]
(d) \[14.0-8.0=6.0\text{ g}\]
The ethene mass increases by 6.0 g. [2]
(e) Bubble the gas through bromine water. A positive result for ethene is that bromine water changes from orange or brown to colourless. [2]
Answer Details
(a) In cracking, large hydrocarbon molecules are broken into smaller molecules. The products include smaller alkanes and alkenes such as ethene. [2]
(b) Balance the atoms:
\[\mathrm{C_{16}H_{34}\rightarrow C_2H_4+C_{14}H_{30}}\]
The missing product is C14H30. [2]
(c) The oil is vaporised so it can flow or pass over the catalyst. Gas particles contact the catalyst surface more effectively, increasing the rate at which cracking can occur. [2]
(d) \[14.0-8.0=6.0\text{ g}\]
The ethene mass increases by 6.0 g. [2]
(e) Bubble the gas through bromine water. A positive result for ethene is that bromine water changes from orange or brown to colourless. [2]
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