chemistry as paper

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of Group 2 elements. Explain why the first ionisation energy of the Group 2 elements decreases down the group. [2 marks] Give an equation, including state symbols, to represent the process that occurs when the third ionisation energy of magnesium is measured. [1 mark] Explain why the third ionisation energy of magnesium is much higher than the second ionisation energy of magnesium. [2 marks] IB/M/Jun22/7404/1 Do not write outside the box 5 02 02.1 02 03 2 3 This question is about acid-base titrations. Citric acid reacts with sodium hydroxide. C6H8O7(aq) + 3NaOH(aq) Na3C6H5O7(aq) + 3 H₂O(l) A student makes a solution of citric acid by dissolving some solid citric acid in water. Describe a method to add an accurately known mass of solid to a beaker to make a solution. [2 marks] The student dissolves 0.834 g of citric acid in water and makes the solution up to 500 cm³ Calculate the concentration, in mol dm-3, of citric acid in this solution. Concentration [3 marks] mol dm-³ Turn over ► IB/M/Jun22/7404/1 Do not write outside the box 02 04 3 4 The student uses this method to complete a titration. • Rinse a burette with distilled water. • Fill the burette with sodium hydroxide solution. • Use a measuring cylinder to transfer 25 cm³ of the citric acid solution into a conical flask. • Add 5 cm³ of indicator. Slowly add the sodium hydroxide solution from the burette into the conical flask. • Add the sodium hydroxide solution dropwise near the end point until the indicator just changes colour. • Repeat the titration to get concordant results. The method used by the student includes three practical steps that will lead to an inaccurate final result. For each of these three steps • identify the mistake • explain why it is a mistake • suggest how the mistake can be overcome. [6 marks] IB/M/Jun22/7404/1 Do not write outside the box 05 5 Turn over ► IB/M/Jun22/7404/1 Do not write outside the box 02 02 06 4 Table 1 shows the student's burette readings after the mistakes in the practical procedure have been corrected. Final reading / cm³ Start reading / cm³ Titre / cm³ Rough 23.65 0.00 6 23.65 Table 1 Run 1 22.95 0.00 Complete Table 1. Use the data in Table 1 to calculate the mean titre. Run 2 46.05 22.95 Mean titre Run 3 Percentage uncertainty 26.30 3.40 5 The total uncertainty in the use of the burette is ±0.15 cm³ Calculate the percentage uncertainty in the use of the burette in Run 1. [2 marks] cm³ [1 mark] IB/M/Jun22/7404/1 Do not write outside the box 14 0 3 Diagram of shape This question is about shapes of molecules. Complete Table 2 by drawing the shapes of both the AsF5 and KrF2 molecules, showing all lone pairs of electrons that influence the shape. Deduce the bond angle(s) in AsF5 Bond angle(s) 07 7 AsF5 Table 2 Turn over for the next question KrF₂ [3 marks] Turn over ► IB/M/Jun22/7404/1 Do not write outside the box F 3 0 4 0 4 1 08 Atom This question is about intermolecular forces. Complete the diagram to show how one molecule of ammonia can form a hydrogen bond with one molecule of ethanol. Include all lone pairs of electrons and partial charges on atoms involved in the hydrogen bond. H H H-C C H H H H Electronegativity 2.1 8 Table 3 shows the electronegativity values of atoms of some elements. 04 2 Define the term electronegativity. Table 3 C 2.5 N 3.0 O 3.5 04 3 Deduce the two atoms from Table 3 that will form the most polar bond. [3 marks] Br 2.8 [1 mark] [1 mark] IB/M/Jun22/7404/1 Do not write outside the box 0 4 04 09 4 5 9 The C-Br bond is polar. Explain why CBr4 is not a polar molecule. [2 marks] Suggest, in terms of the intermolecular forces for each compound, why CBr4 has a higher boiling point than CHBr3 [3 marks] Turn over for the next question Turn over ► IB/M/Jun22/7404/1 Do not write outside the box 10 0 5 10 10 A sample of antimony is analysed in a time of flight (TOF) mass spectrometer and is found to contain two isotopes,121 Sb and 123Sb After electron impact ionisation, all of the ions are accelerated to the same kinetic energy (KE) and then travel through a flight tube that is 1.05 m long. A 121Sb* ion takes 5.93 x 10-s to travel through the flight tube. The kinetic energy of an ion is given by the equation KE = = 1/2mv² KE = kinetic energy / J m = mass / kg v = speed / m s-1 Calculate the mass, in kg, of one 12¹Sb+ ion. Calculate the time taken for a 123Sb+ ion to travel through the same flight tube. The Avogadro constant, L = 6.022 x 1023 mol-1 Mass of one 121Sb+ ion Time taken by a 123Sb+ ion [5 marks] kg S IB/M/Jun22/7404/1 Do not write outside the box 5 0 6 06 06 06 1 1 1 2 3 lodide ions can be oxidised to iodine using oxidising agents such as iodate(V) ions (103) and concentrated sulfuric acid. State, in terms of electrons, the meaning of the term oxidising agent. In acidic solution, 103 ions oxidise iodide ions to iodine. 103 +51 + 6H+ → 312 + 3H₂O Give a half-equation for the oxidation of iodide ions to iodine. Deduce the half-equation to show the reduction process in this reaction. Oxidation half-equation 11 Reduction half-equation Give an equation to show the reaction between iodide ions and concentrated sulfuric acid to form the yellow solid. Identify the foul-smelling gas. Equation When iodide ions are oxidised using concentrated sulfuric acid, sulfur dioxide, a yellow solid and a foul-smelling gas are all formed. Identity of foul-smelling gas [1 mark] [2 marks] [2 marks] Turn over ► IB/M/Jun22/7404/1 Do not write outside the box 5 07 07 12 12 This question is about gaseous equilibria. Figure 1 shows the effect of pressure on the percentage yield of a reaction at equilibrium at two different temperatures. Percentage yield Figure 1 Pressure T = 300 K T = 600 K 1 Explain how Figure 1 shows that the forward reaction in this equilibrium is exothermic. [2 marks] IB/M/Jun22/7404/1 Do not write outside the box 07 07 13 2 State whether the forward reaction in this equilibrium results in an increase, decrease or no change in the amount, in moles, of gas. Explain your answer. Tick (✓) one box. increase decrease no change 13 Explanation 3 Explain why using a catalyst has no effect on the percentage yield. Question 7 continues on the next page [3 marks] [1 mark] Turn over ► IB/M/Jun22/7404/1 Do not write outside the box 07 4 14 14 Hydrogen and nitrogen react to form ammonia. 3H₂(g) + N₂(g) = 2NH3(g) At 745 K, the equilibrium constant, Kc = 0.118 mol-² dm6 At 745 K, 0.150 dm³ of an equilibrium mixture contains 0.0285 mol of hydrogen and 0.0870 mol of nitrogen. Calculate the amount, in moles, of ammonia present in this equilibrium mixture. [5 marks] Amount of ammonia 07 5 Calculate the value, at 745 K, for the equilibrium constant K, for this dissociation of ammonia to give hydrogen and nitrogen. State the units. 2NH3(g) 3H₂(g) + N₂(g) Value mol Units [2 marks] IB/M/Jun22/7404/1 Do not write outside the box 13 15 15 Turn over for the next question DO NOT WRITE/ON THIS PAGE ANSWER IN THE SPACES PROVIDED Turn over ► IB/M/Jun22/7404/1 Do not write outside the box 0 8 08 08 16 1 A student does two test-tube reactions on four colourless solutions (A, B, C and D). Table 4 shows the student's observations. Solution A B C D Identity of gas 16 Test Effervescence Table 4 Test 1 Add Na₂CO3(s) Effervescence No visible change No visible change Identify the gas formed in Test 1. Describe a further test to confirm the identity of this gas. Test 2 Add acidified AgNO3(aq) No visible change White precipitate No visible change Very pale yellow precipitate [2 marks] 2 Explain how the observations from Test 1 and Test 2 can be used to show that solution B contains hydrochloric acid. [2 marks] IB/M/Jun22/7404/1 Do not write outside the box 08 3 Describe a series of tests that the student can use to show that solution C contains ammonium sulfate. [4 marks] 08 17 4 17 The student does an additional experiment to show that solution D contains a mixture of halide ions. One of the halide ions is chloride. Method: Step 1 Step 2 Step 3 Step 4 Add an excess of AgNO3(aq) to 10.0 cm³ of solution D. Filter, wash, dry and weigh the precipitate. Add an excess of dilute ammonia to the dry precipitate. Filter, wash, dry and weigh the solid that remains. Explain how the masses recorded during this experiment can be used to show that solution D contains a mixture of halide ions. [2 marks] Turn over ► IB/M/Jun22/7404/1 Do not write outside the box 10 CORRECT METHOD Only one answer per question is allowed. For each answer completely fill in the circle alongside the appropriate answer. 0 9 10 If you want to change your answer you must cross out your original answer as shown. If you wish to return to an answer previously crossed out, ring the answer you now wish to select as shown. 18 You may do your working in the blank space around each question but this will not be marked. Do not use additional sheets for this working. 18 A 54 Cr B 50 Cr C 56 Fe D 56 Fe Section B Answer all questions in this section. WRONG METHODS A Helium B Beryllium C Oxygen D Iron O € $ Which atom has two more protons and two more neutrons than 22 Cr? An atom has all its electrons in their lowest energy levels. Which atom contains only two unpaired electrons? [1 mark] [1 mark] IB/M/Jun22/7404/1 Do not write outside the box 1 1 12 13 19 The first six ionisation energies, in kJ mol-¹, of an element are: 1090, 2350, 4610, 6220, 37 800, 47 000 What is the element? A Boron B Carbon C Nitrogen D Oxygen A In which pair is the first ionisation energy of atom Y greater than that of atom X? [1 mark] B 19 Electron configuration of atom X 1s²2s² 1s²2s²2p³ 1s²2s²2p5 1s²2s22p Electron configuration of atom Y 1s²2s²2p¹ 1s²2s²2p4 1s²2s²2p6 1s²2s²2p63s¹ Which statement about isotopes of an element is not correct? A They have the same chemical properties. B They have the same number of electrons in ions of the same charge. C They have the same number of neutrons. D They have the same number of protons. [1 mark] |0|||0| [1 mark] Turn over ► IB/M/Jun22/7404/1 Do not write outside the box 1 4 15 1 6 20 5.0 g of an oxide contains 4.0 g of molybdenum. What is the empirical formula of this oxide? A MoO₂ B MOO5 C M0₂O3 D MO3O2 The equation for a reaction is 20 A Co-ordinate bond What type of interaction forms in this reaction? B Dipole-dipole force C Hydrogen bond D lonic bond AsH3 + H+ →→ AsH4* Which is a correct trend down Group 7 from fluorine to iodine? A The boiling point of the element decreases. B The oxidising ability of the element decreases. C The electronegativity of the atom increases. D The first ionisation energy of the atom increases. [1 mark] [1 mark] [1 mark] IB/M/Jun22/7404/1 Do not write outside the box 17 18 19 21 Which of these ions has the largest ionic radius? A S²- B CL- CK+ D Ca²+ Which statement is correct? A Chloride ions reduce concentrated sulfuric acid to form sulfur dioxide. B Bromide ions reduce concentrated sulfuric acid to form sulfur. O C Bromide ions reduce iodine to form iodide ions. 21 D lodide ions reduce chlorine to form chloride ions. A OF2 In which of these substances is oxygen in the highest oxidation state? B H₂O C 0₂2 D H2Oz O O |0|0| [1 mark] [1 mark] [1 mark] Turn over ► IB/M/Jun22/7404/1 Do not write outside the box 20 2 1 22 22 Which block in the Periodic Table contains the element samarium (Sm)? A d block B f block C p block D s block A CL- Which species is not a possible product of the reactions between chlorine and water? [1 mark] B CIO- с 02 22 D OH- Which statement is correct? [1 mark] A Magnesium reacts with steam to give magnesium oxide as one of the products. B Magnesium acts as an oxidising agent in the extraction of titanium. C Magnesium has a lower melting point than sodium. D Magnesium hydroxide is very soluble in water. [1 mark] IB/M/Jun22/7404/1 Do not write outside the box 2 3 23 23 Which is not responsible for conducting electricity? A The sodium ions in molten sodium chloride B The electrons between layers of carbon atoms in graphite C The bonding electrons in a metal D The lone pair electrons in liquid water molecules END OF QUESTIONS 000 |0|| [1 mark] IB/M/Jun22/7404/1 Do not write outside the box 15 24 24 There are no questions printed on this page DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED IB/M/Jun22/7404/1 Do not write outside the box Question number 25 25 Additional page, if required. Write the question numbers in the left-hand margin. IB/M/Jun22/7404/1 Do not write outside the box Question number 26 26 Additional page, if required. Write the question numbers in the left-hand margin. IB/M/Jun22/7404/1 Do not write outside the box Question number 27 27 Additional page, if required. Write the question numbers in the left-hand margin. 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