hsc questions + answers
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General notes Averaged over the four years, about 30% of the marks have been for problem-solving (qualitative and quantitative) and 70% for recall of information with some interpretation of it, not a situation that those of us who think that chemistry is a problem-solving discipline are happy with. Extended response questions Extended response questions are the ones that require the most careful attention from students to make sure that they give the information asked for. With no guidance about how much emphasis to place on each aspect of the question, it is easy to give too much information about one aspect and completely neglect another equally important one. In tackling extended response-questions (questions that are just one or two sentences but worth 5 to 7 marks) you should start from the rule of thumb that the question requires one significant piece of information per mark, so a six mark question will require six pieces of relevant information; that probably means at least six sentences, often more. And it is going to require about 1.8 minutes per mark to answer as fully as the examiners want (11 minutes for a 6 mark question). Analyse the question carefully before you start writing to make sure you understand exactly what the question is asking for. If it contains two verbs such as saying 'describe' something and 'discuss' its importance or role in ..., then you need to split the marks between the two parts, say 3 for 'describe' and 3 for 'discuss'. If you feel that it is difficult to give 3 significant facts for the 'discuss' part, perhaps you could do a 4/2 split but a 5/1or 6/0 split would not be answering the question as asked. Even if you could easily give 6 significant facts for the 'describe' part, you must give some for the 'discuss' part even though that might be a struggle. Note that verbs such as evaluate and assess require you to make some judgment, so even if you cannot give a deep and insightful one, at least give some judgment even if it seems trivial – it's a good thing, it's really important or it's of no great significance – because the examiners are looking for some sort of judgment and they do not have to agree with you to give you the mark (but they cannot give you the mark if the judgment is not there). Only then are you ready to write your answer in the answer booklet. With extended-response questions be very careful that you answer the question asked and not answer a related question that you know a good answer for. Try to answer the question exactly as asked. If you cannot give enough detail about that question to fill the time allocation, then perhaps you could provide related but not strictly asked-for information, but do that only as a last resort. One reason for suggesting this is that sometimes it is not possible to spend the allocated time on the question asked; it was not a good question. Production of Materials. Nuclear Chemistry. HSC 2001 Question 16 (3 marks) Radioisotopes are used in industry, medicine and chemical analysis. For ONE of these fields, relate the use of a named radioisotope to its properties. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... Answer : http://www.cci.net.au/conqchem/ExamCommentsFrameset.htm Question 19 (5 marks) (a) Describe the conditions under which a nucleus is unstable. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... (b) The following is a flow diagram showing the sequence of products released during the decay of uranium. See a diagram on http://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2002exams/pdf_doc/chemistry_02.pdf, q.19 Use examples from the flow diagram to describe processes by which an unstable isotope undergoes radioactive decay. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... See the answer on http://www.cci.net.au/conqchem/ExamComments02Frameset.htm HSC 2003 Q18* (4 marks) Describe how commercial radioisotopes are produced, and how transuranic elements are produced. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... HSC 2004 Q26* (4 marks) Discuss the benefits and problems associated with the use of ONE radioactive isotope 4 in industry. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ....................................................................................................................................................................................................................... HSC 2006 Q1 Which is the main industrial source of ethylene? (A) Ethanol (B) Glucose (C) Petroleum (D) Polyethylene Q.3 Which set contains only stable nuclei? (A) 2H 12C 238U 1 6 92 (B) 16O 39K 12C 8 19 6 (C) 65Zn 18O 24Mg 30 8 12 (D) 14C 16O 1H 681 Question 16 (3 marks) Describe how technology has enabled the transuranic elements to be produced. 3 ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... See the answers to questions 1 and 16 on http://www.cci.net.au/conqchem/ExamComments06Frameset.htm (q 1 and 2)and http://www.cci.net.au/conqchem/ExamComments06Frameset.htm (q 16). HSC 2007 1 Which of the following is a renewable resource? (A) Ethanol (B) Uranium (C) Petroleum (D) Aluminium 2 What type of reaction describes the polymerisation of glucose into cellulose? (A) Addition (B) Hydrolysis (C) Substitution (D) Condensation 5 Two metals have been placed in a solution containing their respective metallic ions. The metals are connected to a voltmeter. Which of the following combinations of metals would produce the highest reading on the voltmeter? (A) Tin and zinc (B) Copper and zinc (C) Copper and silver (D) Magnesium and lead See the answers on http://www.cci.net.au/conqchem/ExamComments07Frameset.htm 19 (7 Marks) There are many benefits and problems associated with the use of radioisotopes in industry and medicine. Evaluate the impact on society of the use of radioisotopes in both industry and medicine. In your answer, give examples of specific radioisotopes, making reference to their chemical properties. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... See the answer on http://www.cci.net.au/conqchem/ExamComments07Frameset.htm HSC 2008 1 Which of the following radiations is measured with a Geiger counter? (A) Beta (B) Infrared (C) Microwave (D) Ultraviolet Answer : http://www.cci.net.au/conqchem/ExamComments08Frameset.htm HSC 2009* 1 Which of the following is an important factor in predicting the nuclear stability of an isotope? (A) Atomic radius (B) Nuclear radius (C) The ratio of neutrons to protons (D) The ratio of electrons to protons HSC 2010 1 Water is released during a polymerisation reaction. Which monomer is likely to have been involved in the reaction? (A) Ethene (B) Glucose (C) Styrene (D) Vinyl chloride 2 Which of the following is an example of a transuranic element? (A) C–14 (B) Co–60 (C) U–238 (D) Cm–249 HSC 2011 7 Which of the following lists contains ONLY unstable isotopes? ( A) 207Pb, 99Tc, 12N B) 214 Pb, 46 Ca, 99 Tc (C) 238 U, 40 Ca, 12 N (D) 238 U, 40 Ca, 99 Tc 23 (3 marks) Element 112 was first synthesized in 1996 and officially named in 2009 as copernicium, Cn. Explain why the transuranic isotope 278Cn is unstable. 1mark ............................................................................................................................... ............................................................................................................................... Describe a method by which transuranic elements can be synthesized. 2 marks............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... 23 (a) Sample answer: Isotopes such as copernicium-278 are unstable because they are heavy nuclei with high neutron: proton ratios, e.g. Cn-278 = 166:112. Question 23 (b) Sample answer: Transuranic elements can be synthesized in a particle accelerator (positive ion accelerator). There are three types of accelerators: linear accelerators, cyclotrons and synchrotrons. Each uses alternating electric and magnetic fields to accelerate particles at high speed to penetrate a target nucleus. Answers could include: Bombardment with neutrons, which occurs in a nuclear reactor, as no acceleration is necessary for neutrons to be absorbed by a target nucleus. Answers to the question that do not have a link to the answers: HSC 2003 Q18* (4 marks) Describe how commercial radioisotopes are produced, and how transuranic elements are produced. Commercial radioisotopes are made in nuclear reactors or in cyclotrons. -In a nuclear reactor, target nuclei are bombarded with neutrons that they absorb into their nuclei, e.g. technetium-99 (used in medical diagnostics) is made by bombarding molibdenium98 with neutrons. -In a cyclotron, charged particles such as electrons, protons and small nuclei (He, C) are fired at great speed at larger nuclei so that they fuse together when they collide. This results in neutron-deficient radioisotopes, e.g. iodine 123 (used to diagnose thyroid disorders) results from proton being fired at xenon 124. Transuranic elements, with atomic number greater then uranium, are made in nuclear reactors, linear accelerators and cyclotrons. The target nuclei (e.g. uranium, plutonium, lead) are usually already large. One transuranic element, americium-241 (used in domestic smoke detectors), is made in a nuclear reactor by bombarding plutonium with neutrons. Another transuranic element, californium, is made by bombarding uranium 238 with a carbon nucleus in a linear accelerator. HSC 2004 Q26* (4 marks) Discuss the benefits and problems associated with the use of ONE radioactive isotope 4 in industry. Sodium24 is a radioactive isotope used as a leak detector in underground water, gas and oil pipes. Minimal radiation is detected from it inside a pipe, but if the tracer leaks into the soil surrounding the pipe it can be detected and the leak located without have to dig up entire pipeline. It also enables pipes in inaccessible spots to be examined. Another benefit is that it only has a half-life of 15 hours, so it lasts long enough to find leaks, but quickly decays afterwards. This means that the water, gas or oil become safe to use again and the environment is quickly decontaminated. Since sodium24 emits beta radiation it does not pose a major health hazard to living things because the radiation will be absorbed by the pipe itself or by its surroundings. Sodium 24 presents problems if it is mishandled as the radiation from it can cause undesirable reactions in living tissue and so can cause tissue damage, cancers and/or genetic damage leading to deformities in offsprings. Sodium24 is made in a nuclear reactor, so anyone involved in its production must observe stringent safety precautions to protect themselves and others from the effects of the radiation. Please note that Americium 241 that is used in domestic smoke detectors is not strictly industrial radioisotope. However , Am241 has an industrial use – to monitor thickness of gauges in glass industry. HSC 2009* 1. C Isotopes are atoms of the same element with different numbers of neutrons. A change in p:n ration effects nuclear stability, so C is the answer. The atomic radius and the nuclear radius show little variation between isotopes of one element and show much more variation from one element to the next so both a) abs B) are incorrect. All isotopes of the one element have the same p:n ration, so D is incorrect. HSC 2010* 1. B Explanation: Water is released in a polymerization reaction if an _OH group in the monomer is eliminated along with a H atom. Ethylene (ethane) is C2H2, glucose is C6H12O6, styrene is C6H5.Ch.Ch2 and vinyl chloride is CH2.CHCl. Only glucose has one or more _OH groups.
