Introductory Chemistry — Final Exam Equations and Data pV = nRT where p = pressure, V = volume, n= no. of moles, R = ideal gas constant T = temperature R = 8.3144 J K–1mol–1 or R = 0.082057 L atm K–1mol–1 ∆Hrxn = ∑ ∆Hf products – ∑∆Hf reactants Avagadro number = 6.022 x 1023 mol–1 Solubilities of various substances in H2O: calcium carbonate: 14 mg dm–3 calcium acetate: 29.7 g dm–3 sodium carbonate: 450 g dm–3 calcium chloride: 75 g dm–3 sodium acetate: 46.4 g dm–3 Enthalpies of formation: ∆Hf CH4(g) = –74.81 kJ mol–1 ∆Hf COCl2(g) = –223.0 kJ mol–1 ∆Hf H2O(g) = –241.8 kJ mol–1 ∆Hf CH3CH2OH(l) = –277.7 kJ mol–1 ∆Hf CO2(g) = –393.5 kJ mol–1 1 Introductory Chemistry — Final Exam 2 Introductory Chemistry — Final Exam 3 Question 1 A) [Part A omitted from this sample] B) ‘Hard’ water is saturated with calcium carbonate (CaCO3). i) Kettles in CaCO3
layer
areas with hard tap water often build up solid layers of CaCO3 on their surfaces over a period of several months. Why? water
[2] ii) Devices called ‘water softeners’ exchange the Ca2+ ions in hard water with Na+ ions, forming sodium carbonate, which does not form layers on the surfaces of kettles. Complete the equation below and make any necessary corrections to the formulae: Ca2+ CO32– + Na+ —> Na+CO32– + Ca2+ [1] iii) Use information from the data sheet to explain why sodium carbonate does not form layers on the surfaces of kettles. [2] Introductory Chemistry — Final Exam 4 Question 2 A) An engineer claims that refrigerators reduce the entropy of their contents by lowering their temperature. Does this statement contradict the second law of thermodynamics? Why? [2] B) Some cars now use methane gas (CH4(g)) instead of petrol (gasoline). They use gas cylinders that can carry about 10 kg of methane when full. An engineer plans to use hydrogen gas (H2(g)) instead of methane and wants to use the same volume gas tank at the same pressure. Use information from the data sheet to calculate the total energy released from burning i) a full tank of methane and ii) a full tank of hydrogen. Include balanced chemical equations for the oxidation of CH4 and H2, assume both fuels behave as ideal gasses. [6] iii) Which fuel releases the most energy per kilogram? Show your working. [2] Introductory Chemistry — Final Exam 5 Question 3 A) Use some or all of the following terms to answer parts i)—iv). exothermic entropy enthalpy energy activation energy endothermic The oxidation of diamond (a carbon crystal) in oxygen follows the equation: C(diamond) + O2(g) —> CO2(g) i) This reaction releases heat so it is __________________. ii) The total ________________ of the products is greater than that of the reactants. iii) The total _______________ of the products is lower than that of the reactants. iv) Diamonds can last for millions of years without noticeably oxidising so the _______________________ must be very high for this process. [4] B) Oxygen reacts with carbon monoxide gas according to the following equation: 2CO(g) + O2(g) —> 2CO2(g) ∆H = –283 kJ mol–1 Can we predict the rate of reaction from this data? Why? [2] ii) In terms of kinetic theory, how does raising the temperature and/or pressure affect the rate of this reaction. [2] iii) This reaction occurs slowly at low temperature. How could we make it occur quickly at low temperature and at the same pressure? Give one reason why we would do this. [2] Introductory Chemistry — Final Exam Question 4 [This question is omitted] 6 Introductory Chemistry — Final Exam 7 Question 5 [This question is omitted.] [2] Introductory Chemistry — Final Exam 8 Question 6 The ease of oxidation of the following metals are in the order: <— Easier to oxidise magnesium (Mg —> Mg2+), iron (Fe —> Fe2+), tin (Sn —> Sn2+), copper (Cu —> Cu2+), silver (Ag —> Ag+) harder to oxidise —> A) i) Steel (mostly iron, Fe) is often protected from rusting by applying paint. Explain two ways that paint prevents rusting. [2] ii) Underground steel pipes are often protected from rusting by using sacrificial anodes. Choose any metal from the above list that would make a suitable sacrificial anode for steel pipes. Explain your choice. [2] B) i) a) Will any change be observed if Sn wire is immersed in a beaker of copper sulfate (CuSO4)? b) Will any change be observed if Ag wire is immersed in a beaker of magnesium sulfate (MgSO4)? [2] ii) Choose a reaction from part i) and write the full equation, the ionic equation and the pair of half equations: [4] Introductory Chemistry — Final Exam 9 Question 7 A) Which of the following diagrams are correct? Mark correct diagrams with a tick (√) Correct any mistakes. O
i) NH2 –
ii) CH3
O
H3C
NH2
iii) NH2
iv) H
[4] B) What is the chemical formula of the following compounds? (Write CnHn followed by other elements, e.g. C2H4O2) OH
H 2N
i) ii) OH [2] C) Which of the following diagrams show a pair of isomers (constitutional or configurational)? Write ‘isomers’ or ‘not isomers’. i) and ii) and [2] O
NH2 D) a) b) c) d) Cl Which of the above functional groups i) is the strongest base ii) has the strongest inductive effects? i) ii) [2]