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

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.

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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

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 C3H9N will 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

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

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?

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

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 NaHCO3solution 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 0.15 mol H2NC3H5(COOH)2(glutamic acid) to a 175 ml 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:

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

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

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

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

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,

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

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 H2that is equal to the number of moles of X reacted

How many substances simultaneously satisfy the given two conditions?

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

(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

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