Download pdf - exam /study tip # 18 - TSFX€¦ · VCE Exam Advice – Units 3 and 4 Chemistry Examination preparation is a two-step process. Step 1: Ongoing examination preparation. A thorough

VCE Exam Advice – Units 3 and 4 Chemistry Examination preparation is a two-step process. Step 1: Ongoing examination preparation. A thorough knowledge of the course work is required before you attempt practice examinations. This involves understanding core concepts and the memorisation of some areas of the course. This part of your examination preparation should be an ongoing process throughout the year. Making the mistake of doing this in the weeks prior to your examination severely limits the time you have to practice examination style questions. Chapter summaries are a good way to start revising. Also going back over text questions helps keep the various topics

current in your mind. The more questions you complete in this subject the faster you will be in an examination and the better your result.

You must be able to correctly define terms/concepts as specified in the Study Design. Learn these and practice them when writing practical reports or undertaking revision.

Rote learn the necessary sections of the course e.g. solubility rules; nomenclature rules, catalysts and conditions needed for

organic chemistry reactions.

Familiarise yourself with the information provided in the Data Booklet which is incorporated into each VCAA Chemistry examination paper. If you do come across something in the examination that seems incomplete or requires additional information – you will most likely find what is missing in this Data Booklet.

Always use the calculator that you are going to use in the examination during class time.

You can practice on the appropriate sections of practice examinations throughout the year but make sure you leave 2 VCAA

papers until closer to the examination.

Step 2: Practice examinations. While completing questions from textbooks can help you consolidate core concepts, they are rarely complex enough to prepare you thoroughly for the types of questions you will receive in the examination. Therefore, it is essential that you devote a substantial amount of time to practicing multiple choice and short answer questions from examination papers. This will highlight

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exam /study tip # 18

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your strengths and weaknesses and allow you to gain an understanding of how quickly you need to work in order to finish the examination in the allotted time. It will also be a good indicator of the depth to which you need to understand the course. As you complete each practice paper, annotate your notes with any extra content or additional detail that can be obtained from the solutions. In some short answer questions there are key words or phrases that the examiners look for so be sure to take careful note of this. An example schedule for completing practice examinations:

1 month prior to the exam

By this stage you should have a good grasp of most of the course content. Make sure that you have completed re-writing notes or chapter summaries by this point. Start practicing examination papers but do not be too concerned about how long they are taking you to complete. At this stage you may only complete some sections of the paper depending on whether or not you have finished learning the course work at school. Use the extra information found in the solutions to improve the depth and accuracy of your notes. If there are particular sections that you have difficulty with, spend some time relearning this section of the course. Try to complete 2-3 papers in this week.

Three weeks out

Continue using practice examination papers but start trying to complete whole examination papers and take note of the time they are taking you. Continue to annotate your notes with any extra information you find. Try to complete 2-3 papers in this week.

Two weeks out

By this stage you should have a very thorough grasp of the course content and be getting used to examination style questions. In this week, concentrate on completing the papers in the allotted time. Start doing past VCAA examination papers which are available on line. Keep in mind the course changed slightly in 2008 and 2013. Complete 2-3 papers in this week.

One week out

The most recent VCAA examinations will give you the best indication of what to expect in your examination. At a minimum, complete the 2012 and 2011 examinations using the allotted time.

Generally, the more practice papers you can do the better. However, completing copious amounts of papers without absorbing new information or examination tricks will lead to ‘burn out’. You need to take a balanced approach to your study which can best be done by being organised and not leaving it until the last minute. Many students struggle to complete the examination within the allocated time so excellent exam technique is critical in this subject. Strategies to maximise examination scores are being addressed in our free “Mastering the Exams” lectures, as well as during the course of the “Essentials – Final Exam Revision Lectures” that are being held during the Term 3 school holidays. You should also read through the previous Assessment Reports that have been written by the Chief Assessors so that you can secure the best possible examination scores. These reports include valuable information regarding how to set out answers, key phrases and words that are expected in short answer responses as well as common errors made by students. Students should work through at least 15 examination papers if they are aiming for the higher scores. Remember that new Study Designs were implemented in 2008 and 2013, so not all the questions from past papers are relevant to the new Study Design. PTO


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Major changes made to the Study Design in 2013 include: Unit 3

In Unit 3, students are no longer required to learn the features of instrumentation and operation of chromatography and

spectroscopy techniques so disregard these questions in practice papers

Reaction mechanisms and rate laws are now a part of collision theory and rates of reaction. Unit 4

In Unit 4, students will investigate the production of one industrial chemical selected from ammonia, sulfuric acid or nitric

acid. This will be assessed through School-assessed Coursework only. Therefore, disregard these questions in practice papers as well as any on ethene (which used to be one of the chemicals studied).

Petroleum has been included as one of the energy sources to be studied.

Although many other changes were made, they were mainly clarifications of the course and expanded explanations of the dot points from the previous Study Design. More details on the changes made in 2013 can be found at the following website. http://www.vcaa.vic.edu.au/Documents/bulletin/2012/2012julsup.pdf Also remember that this is the first year in which students will be assessed via one paper at the end of the year. This means that concepts from Unit 3 and 4 may be linked together in ways that were not possible in previous years (e.g. an equilibrium reaction could be monitored using some type of spectroscopy). Every opportunity should be taken to do these types of questions so look out for them in practice papers. You can find details of the new format and a practice examination on the VCAA website: http://www.vcaa.vic.edu.au/Documents/vce/chemistry/Chemistryexamsample.pdf Those students who plan to attend “The Essentials” final examination revision lectures will further benefit from exposure to hundreds of additional potential examination questions, most of which are unique questions designed to expose students to the finer details of the Chemistry course, as well as the possible tricks, traps and extended applications that students could be presented in the examinations.

General Comments Regarding the Unit 3 & 4 Chemistry Examinations 2012:

Table 1: Distribution of Unit 3 Examination Scores

A+ A B+ B C+ C

Ideal Paper 90% 80% 70% 60% 50% 40%

2012 90% 83.3% 76% 67.3% 56.7% 47.3%

2011 85.4% 79.2% 72.9% 65.3% 54.9% 45.1%

2010 89.3% 82% 74.7% 66% 56% 46%

2009 78% 69% 60% 51% 41.8% 32.2%

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These results suggest that the 2012 Unit 3 examination incorporated sufficient numbers of difficult questions to “seed out” the A and A+ students, but was otherwise too easy, which is why so many C to B+ students felt they had performed so well in the actual examination. Therefore, it would be expected that the hardest questions in this section of the course will not be any harder than the questions found in 2012 but overall, the difficulty of the paper may be increased this year.

Table 1: Distribution of Unit 4 Examination Scores

A+ A B+ B C+ C

Ideal Paper 90% 80% 70% 60% 50% 40%

2012 84% 78% 71% 63% 52% 42%

2011 87% 79% 71% 61% 50% 40%

2010 88% 82% 74% 65% 54% 43%

2009 88% 80% 71% 61% 51% 40%

These results suggest that the 2012 Unit 4 examination incorporated a number of difficult questions that lowered the percentage needed to obtain an A+, but was otherwise pitched at about the right standard. Therefore, it would be expected that the questions used to “seed out” the A+ and A student may be a little easier than last year but the overall difficulty of this section of the paper may be about the same. Statistics can be found at: http://www.vcaa.vic.edu.au/Documents/statistics/2012/section3/vce_chemistry_ga12.pdf Problem Areas in the 2012 Examinations: The Unit 3 examination was generally well done. Some students struggled with identifying monomers and linkages in a polymer, drawing the structure of a polymer, doing stoichiometric manipulations, writing accurate equations and identifying a back titration. Therefore, these are areas that the examiners may focus on again in order to encourage a better understanding of these sections. The main problem encountered in the Unit 4 examination was applying knowledge to new contexts. Basic application and identification of facts was addressed well, but many students missed out on marks as they were not familiar with the finer points in Chemistry Students should keep in mind that well-learned responses are sometimes inaccurate in the context given. Dealing with such applications does require exposure to specific questions and materials (rather than standard questions from text books), and our teachers involved in the “Unit 3 Exam Revision Lectures” have spent considerable time compiling unique and targeted questions so as to give students the greatest possible edge in the forthcoming examination.

Things to Watch Out For

Unit 3: Chemical Pathways Volumetric and Gravimetric Analysis Examiners are good at finding new errors for you to analyse. Make sure you are competent at determining the effect of

errors on volumetric and gravimetric procedures. Remember that the effect of the error may change depending on whether the unknown solution is in the burette or in the flask under the burette.

Learning the solubility rules is a MUST. PTO


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Chromatography:

Ensure that you are familiar with both normal and reverse phase chromatography.

The role of the mobile phase in GLC is to act as a carrier gas. All gases are miscible with the carrier gas, so separation is not based on the relative affinities of sample components and the 2 phases. Separation is solely based on the strength of the interparticle bonding formed between sample components and the stationary phase.

The solvent used in GLC is not the mobile phase. The solvent is the liquid that is used to dissolve the sample, which is then injected to the GLC and vapourised. The solvent may therefore produce a peak in the spectrum.

Area of study 2: Organic Chemical Pathways: The hydroxyl group is OH not OH (this is called the hydroxide ion eg. as in NaOH ).

The carbonyl group is a family of functional groups containing C O . As an example, ketones, aldehydes etc. The C O

by itself is not a functional group. Therefore, the functional group in carboxylic acids is the carboxyl group (COOH ) and not the hydroxyl and carbonyl groups. The only time you can treat the carboxyl group as being made up of two functional groups (C O and OH is in infra-red spectroscopy.

When stating systematic names of organic compounds, students must apply the IUPAC system and ignore what has been

accepted in previous Assessment Reports. Students must also be aware of the order of priority of the principle functional groups, something that is not addressed in most VCE textbooks.

Learn combustion, fermentation and respiration reactions involving glucose.

Unit 4: Chemistry at Work Area of Study 1: Industrial Chemistry Practice writing concise and accurate answers on rates and equilibrium. There are often key phrases and words that the

examiners are looking for in this section.

pH is an area of the course that is often poorly handled. Make sure that you can find the pH of mixtures of acids, mixtures of acids and bases and solutions that have been diluted. The pH of weak acids is also often poorly handled. You should review this section thoroughly.

Area of Study 2: Supplying and Using Energy The Electrochemical Series is almost always written as reduction half equations. If necessary, to answer a redox question, put

equations in order of strongest oxidant on the top left and strongest reductant on the bottom right. The predominant redox reaction occurs between the strongest oxidant and the strongest reductant, which in this case would be the highest species on the left and the lowest species on the right.

Include all redox half equations that involve water when dealing with an aqueous solution.

When using the electrochemical series don’t assume 2O is present unless actually stated.

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When writing overall redox equations, remember to balance the number of electrons in the oxidation and reduction equations before adding the half equations together.

Practice writing overall equations from two half equation and also be able to deduce the missing half equation from the

overall equation and one of the half equations.

During the Examination

If a theory question is worth two marks then be sure that you have clearly made two distinct points, particularly if it is asking for an explanation.

Never ever move onto a new question in any subject without reading the question that you have just completed. Many students miss out on valuable marks as they did not provide the required answer.

If you do come across a question that looks similar to what has appeared in previous examinations, proceed with caution.

Read the question very carefully as it is quite likely that the requirements or answers being sought are different from what was asked in previous years.

Use reading time to analyse the questions in Section B and begin the complex thought processes required to answer these

questions adequately.

Use the marks and the space provided for the answers as a guide to the amount of information required in a response. Generally, a 2 mark question requires 2 points of information be given. Don’t spend too long on a question particularly if it is only worth 1 mark.

Formulate an answer that clearly covers all parts of the question and uses the key terminology. Read the Assessment Reports

to gain a good understanding of which key terms must be mentioned in order to obtain full marks.

You are more likely to be awarded full marks for a question when answers are clearly expressed and the information included is organised logically and addresses the question directly.

Read each question thoroughly before putting pen to paper. It may help to underline key words in the question such as best

option, glossary words, required data etc.

Non-standard abbreviations should be avoided as they may be open to misinterpretation.

Use legible handwriting and correct spelling. If an assessor cannot read an answer, the response cannot be awarded marks.

Read the multi-choice questions carefully and answer appropriately before looking at the options available. Remember that 2 of the options are generally distracters, and are based on common mistakes and/or misconceptions – so tread carefully.

Remember to be consistent. In a calculation involving more than one stage you will be awarded consequential marks if you

correctly use a wrong answer from part a) in part b).

Show working in your calculations. Again you may still be awarded marks even if your final answer is wrong.

Include units for all numerical answers. Look carefully at units in calculations. In the majority of responses, you will need to convert to SI units before using data in a formula.

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When working through calculation based problems, ensure that final answers for each section are given to the correct number of significant figures. Use standard form if required.

All equations must be balanced and all states of reactants/products shown.

Ionic equations do not include spectator ions. Solid ionic substances must not be split into their component ions.

Know what the question is asking for before attempting to answer it. For example, the amount of substance does not mean

mass.

One Mark Questions. Even though they are worth one mark, one-word answers are often unlikely to be awarded marks.

Name Questions. If asked to name something, it is important that you do so. It is not necessary to elaborate and if incorrect information is given in your elaboration, the mark cannot be awarded.

Using data. These questions expect you to explain how the data is used to arrive at a conclusion. More successful answers

specifically mention numbers from the data.

What is the difference? These questions require you to state a specific feature of the first term mentioned and then a statement on how it is different from the second term. For example, how is titre different to aliquot.

Supply the right formulae: A question may ask you to supply your answer using a specific type of formulae. Make sure you

know the difference between all types of formulae including empirical, molecular, structural and semi-structural.

Additional Advice: Significant Figures: Do not count/consider the number of significant figures in data that has been given but hasn’t been used.

The number of significant figures in molar masses must be considered.

Do not include counting numbers in significant figures e.g. 20 atoms.

The number 1000 is counted as 4 significant figures in Chemistry – even though rightly, you could express 1000 as 31 10 (which would only count as 1 significant figure)!!!!

When adding numbers, do not count significant figures. You must state your answers to sums and differences to the same

number of decimal places as that present in the information with the smallest number of decimal places. We only round answers to the smallest number of significant figures in data being multiplied or divided.

Students must use their unrounded answers in subsequent questions, but remember to take the number of significant

figures into account when stating subsequent answers. For example: If the answer to Part (a) is 4.1575 and the answer must be rounded to 3 sf to give 4.16, you must use the value 4.1575 when using this value in Part (b). If the remaining data in Part (b) is written to 5 sf, you will be required to state the answer to Part (b) to 3 sf, as this was the lowest level of significance in the data used to calculate the value 4.1575.

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Structural Equations/Formulae:

You do not need to provide states or show lone pairs or valence electrons in structural formulae and equations.

Although the current Chief Assessor accepts structural formulae drawn with right angles, we do encourage students to draw molecules showing the appropriate 3-D shape i.e. tetrahedral or triangular etc.

If asked to show “all bonds”, do not forget to expand CH3 and OH groups etc.

Always consider the pH of the environment and include the charges that would be found under the given conditions.

Only use continuous lines for covalent bonds. Use dashed lines for interparticle bonds (dispersion, H, dipole-dipole, ion-

dipole etc).

More subject specific advice will be issued to students at our “Essentials – Final Exam Revision Lectures”.

Good luck with your exam preparations! TSFX