ST JOSEPH’S INTERNATIONAL SCHOOL KUCHING Cambridge International AS & A Levels AS CHEMISTRY UNIT 5: CHEMICAL TREND Unit 5.1: Periodicity 5.2: Group 2 5.3: Group 17 5.4: Nitrogen and Sulfur 1) Define the term a) atomic radii c) effective nuclear charge e) Amphoteric b) ionic radii d) shielding effect f) periodicity 2) State the general trend for the following when going across the Period in the Periodic Table. a) atomic radii b) ionic radii c) melting point d) electrical conductivity e) metallic character f) structure of Period 3 oxide compounds 3) Apart from argon, the Period 3 elements all form oxides. a) Write an equation to represent the reaction of aluminium with oxygen. b) The reaction in (a) occurs very readily. Suggest why aluminium saucepans can be safely heated on a gas cooker. c) Complete the following table to show information about Period 3 oxides phosphorus (V) sodium oxide silicon(IV) dioxide sulfur dioxide oxide chemical formula physical state at room temperature type of bonding present d) Write equations for the reactions of oxides Period 3 elements with water (if any). In each case predict the approximate pH of an aqueous solution produced. In case of sodium oxide, explain with reference to the bonding, why this compound reacts with water to form a solution with the pH mentioned here. 4) The following two-stage method was used to analyse a mixture containing the solids magnesium, magnesium oxide and sodium chloride. Stage 1 A weighed sample of the mixture was treated with an excess of dilute hydrochloric acid. The sodium chloride dissolved in the acid. The magnesium oxide reacted to form a solution of magnesium chloride. The magnesium also reacted to form hydrogen gas and a solution of magnesium chloride. The hydrogen produced was collected. a) Write equations for the two reactions involving hydrochloric acid. Stage 2 Sodium hydroxide solution was added to the solution formed in Stage 1 until no further precipitation of magnesium hydroxide occurred. This precipitate was filtered off, collected, dried and heated strongly until it had decomposed completely into magnesium oxide. The oxide was weighed. b) Write equations for the formation of magnesium hydroxide and for its decomposition into magnesium oxide. 5) Describe the trend in pH of the solutions formed when the chlorides of the Period 3 elements, sodium to phosphorous, are added separately to water. Explain this trend by reference to the structure and bonding in the oxides and by writing equations for the reactions with water. ST JOSEPH’S INTERNATIONAL SCHOOL KUCHING Cambridge International AS & A Levels AS CHEMISTRY UNIT 5: CHEMICAL TREND 6) Samples of solid sodium fluoride, sodium chloride, sodium bromide and sodium iodide are each warmed separately with concentrated sulphuric acid. All four compounds react with concentrated sulphuric acid but only two can reduce it. a) Identify the two halides which do not reduce concentrated sulphuric acid. Write an equation for the reaction which does occur with one of these two halides. b) Identify the two halides which reduce concentrated sulphuric acid to sulphur dioxide. Using half-equations for the oxidation and reduction processes, deduce an overall equation for the formation of sulphur dioxide when concentrated sulphuric acid reacts with one of these halides. c) In addition to sulphur dioxide, two further reduction products are formed when one of these two halides reacts with concentrated sulphuric acid. Identify the two reduction products and write a half-equation to show the formation of one of them from concentrated sulphuric acid. 7) This question concerns the chemistry of the Group II metals Mg to Ba. An aqueous solution of a Group II metal chloride, XCl2, forms a white precipitate when dilute aqueous sodium hydroxide is added. A separate sample of the solution of XCl2 does not form a precipitate when dilute aqueous sodium sulphate is added. An aqueous solution of a different Group II metal chloride, YCl2, does not form a precipitate when dilute aqueous sodium hydroxide is added. A separate sample of the solution of YCl2 forms a white precipitate when dilute aqueous sodium sulphate is added. Suggest identities for the Group II metals X and Y. Write equations, including state symbols, for the reactions which occur. 8) Silicon and phosphorus are both covalent substance, but silicon has a much higher melting temperature than phosphorus. Fully explain the statement. 9) a) Suggest the formula of gallium chloride. b) Gallium chloride dissolves in water to form a solution containing ions. Suggest an experiment to show that the solution contains ions. State the result you would expect. 10) a) Hydrogen iodide, HI, has a boiling point of −35oC, and hydrogen chloride, HCl, a boiling point of −85oC. Explain why hydrogen iodide has a higher boiling temperature than hydrogen chloride. b) Hydrogen iodide and hydrogen chloride react with water to form acidic solutions. (i) Write the equation for the reaction of hydrogen iodide with water. (ii) State why the solution formed is acidic. c) (i) Excess dilute hydrochloric acid reacts with a lump of calcium oxide, CaO, to form an aqueous solution of calcium chloride. Write the equation for this reaction, including state symbols. (ii) In a similar reaction with dilute sulfuric acid and a lump of calcium oxide, the reaction stops after a short time even though some calcium oxide remains. State why the reaction stops so quickly. 11) a) Seawater contains aqueous bromide ions. During the manufacture of bromine, seawater is treated with chloride gas and the following reaction occurs: (i) Explain the term oxidation in terms of electron transfer. (ii) Explain the term oxidising agent in terms of electron transfer. (iii) State which of the elements chloride or bromide is the stronger oxidising agent and explain the importance of this in the extraction of bromine from seawater, as represented in the equation above. ST JOSEPH’S INTERNATIONAL SCHOOL KUCHING Cambridge International AS & A Levels AS CHEMISTRY UNIT 5: CHEMICAL TREND b) When sodium chlorate(I), NaClO, is heated, sodium chlorate(V) and sodium chloride are formed. (i) Write the ionic equation for this reaction. (ii) What type of reaction is this? c) During one process for the manufacture of iodine the following reaction occurs: 2IO3 + 5SO2 + 4H2O I2 + 8H+ + 5SO42− (i) Deduce the oxidation number of sulfur in SO2 and SO42−. (ii) Use your answers to part (c)(i) to explain whether SO2 has been oxidised or reduced in the above . reaction. (iii) Name a reagent that could be used to confirm that a solution contains iodine, and state what would be seen. 12) Barium and magnesium are both in Group 2 of the Periodic Table. Several bottles on the Group 2 shelf of the chemicals store had damaged labels. a) Two bottles are clearly labelled ‘sulfate’. The solid in bottle A dissolves easily in water but none of the solid in bottle B appears to dissolve when added to water. Which of these two bottles contains barium sulfate? b) Bottle C, labelled ‘magnesium carbonate’, contains a white powder. When heated, this powder produces a colourless gas that turns limewater cloudy. State whether this label is correct and explain your answer. c) Describe a test to show that the solid in bottle D is barium hydroxide and not magnesium hydroxide. d) Bottle E is clearly labelled ‘magnesium nitrate’. When a sample of the chemical is heated, it gives off a brown gas and a gas that relights a glowing splint. Give the name of each of the gases formed and write an equation for this chemical reaction. 13) a) Complete and balance the following equation: (i) Ca + O2 (ii) Na2O + H2O (iii) Na2O + HCl (iv) Ba + H2O (v) NaCl + H2SO4 b) Magnesium oxide is a basic oxide which produces an alkaline solution with water. Write an equation to show how the oxide ion, O2−, acts as a base in the reaction with water. c) State and explain the trend in thermal stability of the carbonates of the Group 2 elements as the group is descended. d) The solubilities of the sulfates and hydroxides of calcium and barium are shown below. Use the information in the table to answer the questions that follow. Substance Solubility Substance Solubility CaSO4 slightly soluble Ca(OH)2 slightly soluble BaSO4 insoluble Ba(OH)2 soluble (i) Both calcium and barium metals react with water to give the metal hydroxide and hydrogen gas. What difference would you expect to see after calcium metal and barium metal have reacted with water. (ii) The reaction between barium metal and excess dilute sulfuric acid stops after a very short time. Suggest an explanation for this. 14) When hydrocarbons such as petrol or paraffin wax are burned in an excess of air in a laboratory, carbon dioxide and water are the only products. When petrol is burned in a car engine, nitrogen monoxide, NO, is also formed. ST JOSEPH’S INTERNATIONAL SCHOOL KUCHING Cambridge International AS & A Levels AS CHEMISTRY UNIT 5: CHEMICAL TREND a) Explain how NO is formed in an internal combustion engine but not formed when a small sample of petrol is burnt in an evaporating basin. The engines of modern motor cars have exhaust systems which are fitted with catalytic converters in order to reduce atmospheric pollution from substances such as NO. b) (i) State three more pollutants, other than CO2 and H2O, that are present in the exhaust gases of a car engine. (ii) What is the active material present in the catalytic converter? (iii) Write one balanced equation to show how NO is removed from the exhaust gases of a car engine by a catalytic converter. 15) Magnesium burns in nitrogen to give magnesium nitride, a yellow solid which has the formula Mg3N2. Magnesium nitride reacts with water to give ammonia and magnesium hydroxide. a) Construct an equation for the reaction of magnesium nitride with water. b) Does a redox reaction occur when magnesium nitride reacts with water? Use the oxidation numbers of nitrogen to explain your answer. 16) Ammonium salts are widely used as fertilisers. A sample of a fertiliser was know to contain ammonium sulfate, (NH4)2SO4 and sand only. a) Write a balanced equations for the reaction (NH4)2SO4 and sodium hydroxide. b) The uncontrolled use of nitrogenous fertilisers can cause environmental damage to lakes and streams. This is known as eutrophication. What are the processes that occur when excessive amounts of nitrogenous fertilisers get into lakes and streams? c) Large quantities of ammonia are manufactured by the Haber process. Not all of this ammonia is used to make fertilisers. State one large-scale use for ammonia, other than in the production of nitrogenous fertilisers. 17) Sulfuric acid is an important chemical with a variety of uses. It is manufactured by the Contact process, the first stage of which involves the conversion of sulfur or a sulfide ore, such as galena, PbS, into sulfur dioxide, SO2. a) (i) Write an equation for the reaction between galena and oxygen to form sulfur dioxide and lead(II) oxide. (ii) Identify the oxidation number changes that take place during this reaction. b) Explain why sulfur dioxide is used as an additive in some foods and wine.