Errors in university entrance exams (Organic chemistry) and suggestions on how to elimate them

JOURNAL OF SCIENCE OF HNUE Interdisciplinary Science, 2013, Vol. 58, No. 5, pp. 53-59 This paper is available online at ERRORS IN UNIVERSITY ENTRANCE EXAMS (ORGANIC CHEMISTRY) AND SUGGESTIONS ON HOW TO ELIMATE THEM Pham Van Hoan1 and Hoang Dinh Xuan2 1Ministry of Education and Training, 2Hanoi Department of Education and Training Abstract. In recent years, the university entrance exam has been considered both fair and practical. However, there has been some dissatisfaction with the organic chemistry exam questions. This paper discusses errors in university entrance exams (Organic Chemistry) and suggestions on how to elimate them for improving quality of teaching Organic Chemistry in high schools. Keywords: Organic Chemistry, teaching, high school, university entrance exam, errors. 1. Introduction Recently, there has been a lot of talk about university entrance exam preparation in general and particularly preparation for the chemistry questions. An increased amount of preparation materials enables high school students to spend more time reviewing and consolidating their knowledge. However, much of the information presented in study texts is inaccurate. The books are poorly referenced by outstanding publishers and there seems to be no strong desire to correct this situation. In this paper we give some examples of faulty university exam questions that have already been widely acknowledged as such. Since it began using the three general subject plan, the Ministry of Education and Training requires that exam questions be based on publications of questionable quality. In general, books used in teaching from which exam questions are procured have been carefully edited and are being used quite effectively. We looked at the accuracy of the science texts and exam questions and found that a number of the exam questions and text exercises are not accurate in scientific content, have no association with real life and do not allow hands-on practice. Thus they do not meet the requirements associated with the practical teaching of Chemistry. This paper discusses errors in university entrance exams (Organic Chemistry) and suggestions on how to elimate them for improving quality of teaching Organic Chemistry in high schools. Received June 2, 2013. Accepted June 30, 2013. Contact Pham Van Hoan, e-mail address: pvhoan@moet.edu.vn 53 Pham Van Hoan and Hoang Dinh Xuan 2. Content 2.1. Errors of the concept of isomers Compared to inorganic materials, organic materials have a number of additional characteristic concepts that need to be understood. Due to the isomer phenomenon of organic compounds, the use of only the molecular formula is insufficient except for simple homologous series such as CH4, C2H4, CH2O and CH4O. However, when stating "the substances C3H7Cl, C3H9N, and C2H4O2", this description is totally insufficient to describe the compound. To speak of a substance, it has to be written "the substance with the molecular formula of C3H7Cl, C3H9N and C2H4O2", and the characteristics of the molecular structure and properties must be full and accurate [3]. However, it was seen that in some current exam questions the error regarding the expression of isomers and isomeric phenomenon has not been corrected. In the 2010 University Entrance Exam, Chemistry subject, code 253, Question 14, it was written: Question 14: Of the substances C3H8, C3H7Cl, C3H8O and C3H9N, the compound that has the most structural isomers is A. C3H9N. B. C3H7Cl. C. C3H8O. D. C3H8. Comment: Here, students might misunderstanding the question even though it is shown that there is one more isomer of C3H7Cl. Similarly, because there are 4 amino isomers of C3H9N, the amino molecular formula C3H9Nwill have 3 composition isomers. However, in general, using only the molecular formula for a substance is not accurate. Here, it should be said to what is written is not grammatically correct in that the colon and the semicolon were both misplaced. The concept "The structural isomers with the same molecular formula, etc." and "The structural isomers of the substance X of molecular formula, etc." should be distinguished from each other. As already mentioned [3], structural isomers of X do not include X. For example, there are two carboxylic acids with the molecular formula C4H8O2 that have the structural formulas of CH3CH2CH2COOH and (CH3)2CHCOOH. In fact, there is one acidic structural isomers of X with the molecular formula C4H8O2, not two. Unfortunately this has not been corrected in a few recent exams. It is worth mentioning that sometimes a wrong expression will lead to a correct answer - to the detriment of students. For example, in the 2009 University Entrance Exam, Chemistry subject, code 175, Question 18, it was written: Question 18: 10 grams of the monoamine X completely reacts with HCl (excess) to obtain 15 grams of salt. Number of structural isomers of X is A. 4. B. 8. C. 5. D. 7. Comment: The answer B, said to be correct, but it is incorrect. Monoamine with M = 73 g.mol-1 has a molecular formula of C4H11N. With that molecular formula it has 54 Errors in university entrance exams (Organic Chemistry) and suggestions on how to elimate them 8 amino acyclic isomers (4-amine isomer I; 3-amine isomer II and 1-amine isomer III). Excluding X there are 7 structural isomers to it, so the correct answer is D, not B as the author says. Similarly, in the 2011 University Entrance Exam, Chemistry subject, code number 273, Question 13 is written as: Question 13: 13.8 grams of organic substance X of molecular formula C7H8 reacts with an excess of AgNO3 solution in NH3 and the obtained precipitate is 45.9 g. How many X isomers satisfy the above properties? A. 2. B. 5. C. 4. D. 6. Comment: Answer C is said to be correct but it is not correct. With a C7H8 molecular composition, characterized as HC≡C3H6-C≡CH, there are 4 hydrocarbon composition isomers with the following structures: One of them is substance X, so the number of structural isomers of X is 3, and not 2, 4, 5 or 6. Therefore, students are not given a correct choice in this problem. Comments: Obviously the answer is wrong. The error is the editor’s because he did not understand what was written. The problem here is this: If students are taught correctly and answer correctly, they will lose points. The loss of 0.20 p/question could alter the future of a student due to ‘errors’ they did not make. 2.2. A wrong expression leads to learning something that’s not true Question 6 of the 2009 University Entrance Exam, Chemistry subject, code 175, was written as: Question 6: A Hydrocarbon X does not discolor bromine solution at room temperature. The name of X is A. xyclohexane. B. xyclopropane. C. styrene. D. ethylene. Comment: If it was expressed like this, students would think that ‘the hydrocarbon (X) that does not discolor a bromide solution at room temperature is xyclohexane’. However, in this case, a discoloration of the bromine solution could be due to a chemical reaction or simply a dissolving phenomena. For the chemical reaction of X and bromine, only xyclohexane does not react with bromine and therefore xyclohexane is the correct answer. When considering both a chemical reaction and a dissolving phenomena, all of them discolor a bromine solution: xyclopropane, styrene and ethylene can react with a bromine solution. Xyclohexane does not react with a bromine solution. However, bromine 55 Pham Van Hoan and Hoang Dinh Xuan could dissolve in xyclohexane and the color of the bromine solution could disappear. In this case, no answer is correct. In the same exam, Question 23: Question 23: Organic compound X reacts with a NaOH solution and bromine but does not react with a NaHCO3 solution. The name of X is A. aniline. B. phenol. C. acrylic acid. D. methyl acetate. Comment: Students will think that “an organic material that reacts with a NaOH solution and bromine but does not react with a NaHCO3 solution” would have to be phenol. Students will think that the question is asking:What will react with a NaOH solution that contains bromine but not with a NaHCO3 solution which does not contain bromine? In the 2010 University Entrance Exam, Chemistry subject, code 253, an error is found: Question 29:Add 0.15mol H2NC3H5(COOH)2 (glutamic acid) to a 175ml solution of 2M HCl to obtain solution X. Add an excess of NaOH solution to solution X. After a completed reaction, the number of moles of NaOH that reacted is: A. 0.70. B. 0.50. C. 0.65. D. 0.55. Comment: This is not clear because there are several compounds with the structural formula H2NC3H5(COOH), one being glutamic acid. If it was written, "Add 0.15 mol glutamic acid (structural formula H2NC3H5(COOH)2) to...,” it would be more accurate. Comments: It’s not that hard to devise good questions if the editor has sufficient knowledge of Chemistry and the Vietnamese Language. Question 35 of the 2009 Block A University Entrance Exam, Chemistry subject, code 175, is written as: Question 35: The full hydrogenation of X acyclic hydrocarbon obtains isopentane. The number of possible structural formulas of X is A. 6. B. 7. C. 4. D. 5. Comment: What is said to be correct is totally wrong because one organic compound has a unique 1 structural formula that determines its molecular structure; therefore it’s impossible for a substance to have up to 7 structural formulas. However, 7 different acyclic hydrocarbons can, after complete hydrogenation, form isopentane. One could misunderstand the difference between a reaction of organic compounds with a solution of bromine and a bromine solution discoloration. We know that weak or non-polar substances will dissolve in organic solvents better than they will in water. Therefore, when an organic substance that is not soluble in water (such as the hydrocarbons) comes in contact with a solution of bromine in water, an extraction of bromine from the water will take place to form organic solvents. This is when bromine water is discolored but no chemical reaction occurs. However, in a few recent exams it 56 Errors in university entrance exams (Organic Chemistry) and suggestions on how to elimate them was to be understood otherwise. For example, in the 2012 University Entrance Exam, Chemistry subject, code 296, it was written: Question 16: For the range of chemicals: styrene, benzylic alcohol, aniline, toluene, phenol (C6H5OH). The number of substances in the range that can discolor bromine solution in water is A. 5. B. 4. C. 3. D. 2. Comment:Because all 5 substances are not water soluble, bromine is less soluble in water than it is in organic solvents, thus bromine will be extracted from the water phase to the organic phase and bromine water will be discolored. Thus, while 3 of the 5 substances can discolor bromine solution in water, in this problem, the correct answer is 5. There is a similar error in question 52. Question 52: For the range of chemicals: cumen, styrene, isoprene, xyclohexane, acetylene and benzene. The number of substances in this range that can discolor a bromine solution in water is A. 5. B. 4. C. 2. D. 3. Comment: With regards to discoloring a bromine solution in water (probably due to a chemical reaction with styrene, isoprene or acetylene; or an extraction of bromine from the aqueous solution and accompanying transference to an organic solvent), all 6 substances can do that. Therefore no correct answer was provided for this problem. To get the answer the author wants, it should be written as "The number of substances in the range that can react with bromine solution is ..." Comments: These errors probably won’t affect the exam results because students will probably guess that the question is badly worded and give the most probable answer. However, that is not the correct answer to the problem given. 2.3. Grammatical errors A few sentences of text in the exam questions are not clear because they are not grammatically correct. For example, Question 57 of the 2010 University Entrance Exam, Chemistry subject, code 253, is written as: Question 57: Among the sources of energy: (1) hydro power, (2) wind, (3) sun and (4) fossil; cleaner energy sources are: A. (1), (2), (3). B. (1), (3), (4). C. (1), (2), (4). D. (2), (3), (4). Comment: This sentence is not correct in terms of punctuation because instead of the semicolon, a comma should have been used. In addition, it should read “...the cleanest three energy sources are:” Similar errors are in Question 14 of the 2010 University Entrance Exam, Chemistry subject, code 253, given above. One other error was made in question 40 in the 2012 University entrance exam, 57 Pham Van Hoan and Hoang Dinh Xuan Chemistry subject, code 296: Question 40: For the range of aromatic compounds: p-HO-CH2-C6H4-OH, p-HO-C6H4-COOC2H5, p-HO-C6H4-COOH, p-HCOO-C6H4-OH, p-CH3O-C6H4-OH. How many substances simultaneously satisfy the following two conditions? (A) React with NaOH at a ratio of 1 : 1. (B) React with Na (excess) to generate the number of moles of H2 that is equal to the number of moles of X reacted. A. 3. B. 4. C. 1. D. 2. Comment: This sentence itself is an error because ".... following two conditions?" cannot have a clause. Comments: These kinds of errors do not change the test results of students. However, it does mean a loss of clarity which we should be trying to preserve. It should read: "Question 40: For the range of aromatic compounds: p-HO-CH2-C6H4-OH, p-HO-C6H4-COOC2H5, p-HO-C6H4-COOH, p-HCOO-C6H4-OH, p-CH3O-C6H4-OH. Some of these compounds also have the following properties: (A) React with NaOH at a ratio of 1:1. (B) React with Na (excess) to generate a number of moles of H2 that is equal to the number of moles of X reacted. How many substances simultaneously satisfy the given two conditions? A. 3. B. 4. C. 1. D. 2. 2.4. Practical conformity in tests Teachers and those in education should be associating theory with practice. This is most important when teaching Chemistry. Thus, when giving a mixture, a solution of certain levels or a manufacturing process, it should be realistic and respectable. However, in current textbooks and exams, little attention is given to this and exam editors are more concerned with testing computing skills. For example: Question 44: From 180 grams of glucose, using fermentation, obtain one gram of ethyl alcohol (80% efficiency). Oxidizing 0.1 grams of ethyl alcohol by fermenting vinegar, obtain mixture X. In order to neutralize mixture X you need 720 mL of 0.2 M NaOH solution. The vinegar fermentation process is A. 90%. B. 10%. C. 80%. D. 20%. (2010 University Entrance Exam, Chemistry subject, code 253) Question 48: Ethyl alcohol obtained from starch by fermentation, efficiency of the whole process being 90%. Absorb all the CO2 produced during the fermentation of m (grams) starch into lime solution to obtain 330 grams of precipitate and solution X. Knowing that the mass of X reduces 132 grams in comparison with the mass of the lime solution before reaction. The value of m is 58 Errors in university entrance exams (Organic Chemistry) and suggestions on how to elimate them A. 486. B. 297. C. 405. D. 324. (2011 University Entrance Exam, Chemistry subject, code 273) Comment: This statement is unrealistic because the production process occurs in this manner: (C6H10O5)n→ C6H12O6 → C2H5OH. In fact, no ethanol production process can yield even 80%. Comment: Students and teachers can make the calculation but if in the future they work with chemical technology they might remember that the test question was nonsense. 3. Conclusion To make exam questions which are grammatically correct, realistic and accurate is apparently not easy. In particular, organic compounds have the characteristics of complicated molecular structures (isomer phenomenon), nomenclature and properties (low reactive capabilities, generation ability of many different products in the same reaction conditions). Therefore, in the expression or selection of experimental data, questions and problems should contain correct information and correspond to the practice of Chemistry. REFERENCES [1] Nguyen Cuong and Nguyen Manh Dung, 2002. Teaching Chemistry. University of Education Publishing House, Hanoi. [2] 2009 University Entrance Exam (subject code 175), and also the university exams of 2010 (subject code 253), 2011 (subject code 273) and 2012 (subject code 296). [3] Nguyen Huu Dinh, 2006. Organic Chemistry. Part 1. University of Education Publishing House, Hanoi. 59