School holiday is here. It means that the chance of doing a proper revision has finally arrived!

So, how should your child start revising for Chemistry?

Step 1: "Curate" a strong set of notes

I read an article on the latest trend about #studygram and was amazed. Is this the trendy way to study nowadays?

Article link -> www.straitstimes.com/lifestyle/welcome-to-my-studygram

In my opinion, writing and decorating such beautiful notes as a study method is not sustainable at all. The focus is just so wrong. So much effort is used to decorate the notes and not "curating" the information that makes a difference to your results.

For my students, I always encourage them to use notes provided by their schools (if they pass my Quality Check) so that they will use the exact keywords expected from their teachers. You'll be surprised that different school teachers have different sets of keywords.

For some schools, the teachers provide notes which are either too brief or too elaborated. In worst cases, the teacher just asked the students to refer to their textbooks! (Yes, and that teacher is currently still a HOD of Science in the East.)

My job is to help my students "curate" a strong set of notes. I will provide my notes which will complement the notes provided by the school. All my notes are customised for my students depending on their needs. Together, we will analyse notes provided by the school and add in information (from my notes, ten-year series, exam questions, school worksheets) which are crucial for getting distinction. At the same time, I will also highlight the parts which are not important at all to minimise effort for studying.

Why do you need a good set of notes? Strong notes are the core of a good study regime. A good set of notes does not mean just a set of stapled notes per topic. It includes notes written on A4 exercise books too. All these should be "curated" from the start of the year, starting from the first topic.

What type of materials does your child use for revision? Start "curating" now before it's too late!

Step 2: Do practice questions frequently (Make it a routine)

I'm a firm believer of the Spaced Review Concept. It's impossible to retain information if we do not review them. Many students may not believe this at first, thinking that it's just common sense.

This is actually proven scientifically.

From the Forgetting Curve Theory, forgetting happens most rapidly right after learning occurs and slows as time passes. The more we review it, the longer we can remember it.

Where can I find practice questions for Chemistry revision?

• Topical Ten-Year Series (For Sec 3 and 4)
• Yearly Ten-Year Series (For Sec 4 only)
• Tuition worksheets
• Tuition test papers

Please, please, please DO NOT trust the answers from Ten-Year Series Publishers. There are lots and lots of mistakes especially for the structured questions. Not minor ones, but those that will cause misconceptions. The way the answers are structured is very different from what we expect in school. There's no way a student can learn how to answer properly by looking at the answers provided. Many students and parents think that the answers provided are from the examination board. NO! That's not true. The examination board only provides the questions and NOT the answers.

I discourage students from wasting their money buying assessment books. Many assessment books are published by random authors who are not NIE-trained. The questions are very different from what teachers set during exams. Do not study using notes from assessment books. You will never be sure where the source is from.

For my students, my first priority is for them to do my worksheets and test papers, followed by the ten-year series. I will mark the ten-year series using the guidelines from the marker's report and provide immediate feedback for your child. The more feedback you get the more you’ll improve! Is your child's ten-year series still in pristine condition?

If your child dedicates at least 2 hours a week to do the above 2 steps during my lesson, he will retain much more due to constant exposure to my quality notes, practice questions and answers.

Contact me if you're looking for extra help with your child's revision.

• If you are unsure of the answer to a multiple choice question, don’t spend too long on it. Put a star by it and return to it later.
  

• Within a single multiple choice question, use a pencil to cross out the WORD/PHRASE of the statements which are clearly incorrect, then choose between those left.

 

• In a multiple choice question don’t be swayed by one of the choices just because it has got a longer (or shorter) statement than the others.
  

 

• Don’t make any assumptions about the order of responses – just because there have been two answers ‘D’ in sequence, it does not mean that the next answer cannot be ‘D’.
  

 

• Take care to read the whole question word by word. For example, in the question ‘what is the ratio of the volumes of 2g of H2 and 16g of methane, CH4, at r.t.p?’ Many students will focus on the numbers and ignore the word ‘volume’. Just a quick look at the figures gives the incorrect answer 1:8 (using the molar gas volumes gives 1:1 as the correct choice)

• When given a choice of picking out a noble gas from a group of electronic structures, don’t jump to the conclusion that noble gases always have 8 electrons in their outer shell. Remember that helium has 2!
  

• When given a choice about electrical conductivity of ionic structures remember that the conduction is due to IONS moving (not electrons). The ions can only move when the ionic compound is molten or when dissolved in water.
  

 

• When given choices of why alloys are hard, it’s not the mass of the atoms which is important but their size. Remember that metals have layers which slip over each other. A different sized atom will distort the layers and stop them slipping over each other. This makes the alloy harder than the pure metals.
  

 

• When given choices about the rate of diffusion of gases, remember that the rate of diffusion depends on the mass of the molecules. Heavier molecules (lower relative molecular mass) move and diffuse slower than lighter molecules. If you are unsure which molecule is heavier, use your Periodic Table to calculate the relative molecular masses.
  

 

• If you are given a choice of tap water and several other substances as examples from which to select a pure compound, it’s not going to be tap water. It is a common error to think that tap water is pure. It contains compounds dissolved from the rocks or carried in the rain as well as the chemicals put in to purify it. It’s a mixture. (Don’t be fooled by the adverts of the mineral water companies which say ‘pure mineral water’!)
  

 

• If you are given choices of electronic structures of atoms to select to make a compound of type XY2, first check the type of compound that the examiner wants e.g. ionic or covalent. If it is ionic, then you can choose an atom with one or two electrons in its outer shell and combine it with a non-metal atom. If it is covalent look for the structures of two non-metal atoms i.e. those with 4 to 7 electrons in their outer shell. Remember that the number of electrons in the outer shell is equal to the group number.
  

 

• Remember that the valencies of the elements in Groups V to VII are found by taking the group number away from 8. For example, the valency of oxygen in an oxide is 8-6 = 2. (Oxygen is in Group VI)
  

Hope you find these useful! Will share more tips for structured questions in the future.

Recently, I got a call from a desperate mother who found my number through this website. Her daughter has not been doing well for Pure Chemistry and the school has advised her to drop to combined Science (chemistry/biology).

"What should I advise my child?" she asked me.

In order to give a good advice, there are multiple factors to consider.

The syllabus content of combined Chemistry is approximately 75% of the whole Pure Chemistry syllabus. Obviously, your child will need to study less content. What exactly is the difference?

The whole topic on the most hated ELECTROLYSIS will be removed! Yay!

Other significant portions removed are:

• Metallic bonding
• Giant molecular structures
• Ammonia
• Mole calculation - about 25% taken out
• Energy changes - about 70% taken out
• Air - about 50% taken out
• .............................. and so on ................................ (there are more)

Differences based on the scheme of assessment:

• MCQ Paper: Pure Chemistry (40 Questions) has a weighting of 30% compared to 10% for Combine Chemistry portion (20 Questions).
• Structured Questions Paper: 1 h 45 min for  for Pure Chemistry (80 marks) VS 1 hr 15 min for Combine Chemistry (65 marks)
• Structured Questions Paper: Pure Chemistry has a high weighting of 50% VS 32.5% for Combine Chemistry.
• Practical Paper: 1h 50min (40 marks) for Pure Chemistry while combine Chemistry takes approximately 45min (15 marks)

Scheme of Assessment taken from SEAB Website

Yes, it will.

By dropping to combine Science, the subject combination for JC entry will be more limited. (Do check the entry and subject combination requirements from the respective official school websites.)

However, some students are very sure of the path that they are going to take once they complete their secondary school education. Thus, they may choose to pursue their interest in theater studies, humanities etc.

So, it's important to discuss your child’s strengths as a family and decide base on your child's ambitions and interests and not choose base on what others will do!

Combined Science is so much easier to score. It's quite common for students who dropped to combine Science to score better as these students have more in depth knowledge compared to their peers who have only studied the combine Chemistry syllabus before.

Many tutors may think that by dropping from two subjects to one subject, your child will be taking a huge risk as there's only one science subject for the L1R5 calculation. But in my opinion, it's much easier to score an A1 or A2 for combine Chemistry compared to scoring an A1 or A2 or even B3 for pure Chemistry.

I'm confident to say that as all my combine Chemistry students score 100% distinctions despite coming from different backgrounds. Some met me after dropping from Pure Chemistry and others have taken combine Chemistry from the start.

There are some students who are doing poorly for both Sciences. In this case, it is wisest to drop to combine Science for sure.

However, if your child is doing very well and scoring distinctions for one of the Pure Sciences, I will suggest not to waste that effort already put in and continue to take up 2 Pure Sciences. Encourage your child to put in more time and effort for the weaker Science using whatever that worked for the stronger Science. It is essential to find a good tutor in order for your child to clarify doubts once and for all. If your child can be good at one Science, he will most likely have the skills and aptitude to score well in the other.

Sometimes, it also depends on the difficulty of the papers set. In certain schools, the papers are set to 'kill' while in others, the papers are so much easier compared to the O level standard. In this case, you will need an experience tutor to analyse the paper to know the 'actual' standard of your child. Do not base just on the percentage written on the paper itself. It may or may not be an accurate representation.

During my first session with the student, I looked through her Secondary 3 to 4 tests and exam papers. I also analysed her Secondary 4 Pure Chemistry mid-year papers which she just received back.

I advised her to drop to combine Science.

Why?

1. She has been consistently doing poorly in Pure Chemistry with a very weak foundation.
   
2. She has no interest in both Biology and Chemistry and would choose to drop both Sciences if that was possible.
3. She is intending to pursue Business Admin in Singapore Polytechnic the entry requirements do not include the need for Pure Science.
   
4. Time is not on our side. With only 5 months to go, it is better to strategise.
   

She is currently having intensive lessons with me and we are making fast progress. Our aim? A1 for combine Science. Nothing less than that.

I hope I have given you a balanced viewpoint based on my own experiences and opinions. In short, there's no right or wrong way to decide whether to drop to combine Science. It all depends...

Contact me if your child needs someone for advice.

The practical assessment incorporates assessment of Planning which has a weighting of 15% out of the entire paper. One, or more, of the questions may be set and require students to apply and integrate knowledge and understanding from different sections of the syllabus. Many students find it IMPOSSIBLE to do well in this section. And this is not true.

Students are expected to be able to:
• identify key variables for a given question/problem
• outline an experimental procedure to investigate the question/problem
• describe how the data should be used in order to reach a conclusion
• identify the risks of the experiment and state precautions that should be taken to keep risks to a
minimum

A typical question could be:

"Plan and produce a procedure to investigate the percentage yield of copper(II) oxide using appropriate reagents and chemicals in the laboratory. You are given a sample of copper(II) carbonate, P."

It is important to plan BEFORE writing your answers down. Just like planning for a composition. A systematic thinking process would be:

Step 1: Ask yourself this question -> What is the objective of the experiment?
- To investigate the percentage yield of copper(II) oxide

Step 2: THINK of the general approach that you would want to use for your experiment by applying scientific concepts that you have learnt.

• Copper(II) carbonate can be decomposed upon heating to form copper(II) oxide and carbon dioxide gas.
• A fixed mass of copper(II) carbonate is heated strongly until all has completely decomposed to form copper(II) oxide.
• Copper(II) oxide is then left to cool and weighed.
• The mass of the cooled copper(II) oxide is then measured to determine the percentage yield of copper(II) oxide.

Step 3: Identify variable(s) and conditions that will affect the experiment.

• Variable to be kept constant: Mass of copper(II) carbonate, P

Conditions:

• Heating of copper(II) carbonate till constant mass
• Size of copper(II) carbonate particles
• Clean and dry apparatus

Step 4: Write your suggested procedure as a series of step-by-step instructions.

• State the appropriate apparatus to be used.
• Describe how you would collect the data.
• Describe how the data collected should be processed to fulfill the purpose of the investigation.

In my next post, I will be sharing more on HOW the procedure should be written.

A picture tells a thousand words.
Tip: My students will save these 2 tables in their phones for reference.

Although a simplified QA table is given during practical exam, I will always make my students understand this table thoroughly before sitting for the practical exam. If a student requires the QA table during the exam, it only means that he is not ready or confident enough.

Calcium hydroxide is slightly soluble in water and would require a high concentration of hydroxide ions to react with it to form a precipitate.  Hence, since sodium hydroxide is a strong alkali, the calcium ions react with the high concentration of hydroxide ions to form a precipitate. Aqueous ammonia being a weak alkali do not have sufficient hydroxide ions and thus, no precipitate is seen.

The white precipitate is the hydroxide of zinc, aluminium and lead(II) which can react with aqueous sodium hydroxide to form soluble complex ions as they are amphoteric hydroxides.

Do put in extra effort for Qualitative Analysis. There is a chance that it may appear both in theory and practical exam!

Many students are uncertain of what sources of error are and what to write during practical exam. This article will give your child more confidence when he has some examples of sources of error in his mind when he sits for the practical exam.

Sources of error are errors that are inherent in an experiment due to the DESIGN of the experiment. We need to suggest IMPROVEMENT to reduce the sources of error in the experiment.

Sources of error are not due to the mistakes made by the student conducting the experiment.

There are times when an apparatus is chosen due to the ease of use. Hence, the degree of accuracy may be compromised and this can be a source of error for the experiment.

Example:
When a measuring cylinder is used to measure 25 cm^3 of a solution instead of a pipette, we can state the source of error this way -> The measuring cylinder used to measure the volume of solution is not as precise as a pipette. It can only measure accurately to 1 cm^3.

The improvement will be -> Use a pipette instead of a measuring cylinder to measure the 25.0 cm^3 volume.

The stability of the reagent used can be a possible source of error if

• it decomposes at room temperature.
• it reacts with oxygen in the air.

Example:
Hydrogen peroxide decomposes slowly into water and oxygen at room temperature even when no catalyst is added. The rate of decomposition increases with light and heat. Hence, the source of error will be -> Since hydrogen peroxide decomposes into water and oxygen at room temperature, there will be a loss of reagent before and during the experiment.

The improvement will be -> Store hydrogen peroxide in a dark glass bottle, away from light and heat.

When the dependent variable is temperature change, the source of error can be caused by the inherent inaccuracy when temperature is measured.

Example:
Heat is always being lost to the surrounding when the surrounding is cooler compared to the reacting mixture. The source of error can be written as -> Heat lost to the surrounding is caused by the poor insulation of the reactants, hence the temperature measured will be lower than expected.

The suggested improvement will be -> Use a polystyrene cup with a cover to minimise heat lost to the surrounding.

These are some general tips which I will go through with my students during lessons using concrete examples.  Share these tips with your child so that he is AWARE of the REQUIREMENTS of the examination.

• The correct spelling of chemical names is not always essential as long as they cannot be mistaken for other chemicals. However, in simple questions where you are asked to select the names of chemicals from a list, you are expected to get the spelling correct. Writing ammonium for ammonia or chlorine for chloride will not be given credit because this is a chemical mistake.
  

• Look for exactly what the question is asking. Many mistakes are made by not reading the question correctly. If the question says give two observations apart from temperature change’, then obviously you shouldn’t write ‘temperature change’. But many Candidates do!
  

• Read over your answers and ask yourself ‘have I contradicted myself?’ This generally refers to things written in the same sentence. A common error is to write something like – ‘On adding ammonia a soluble blue precipitate is formed‘. There is confusion here because if precipitate is not soluble. The correct answer to a question about adding excess ammonia to copper ions would be: ‘On adding ammonia a light blue precipitate is formed. The precipitate dissolves in excess ammonia solution.’ Notice that splitting it up into 2 sentences has altered the meaning.
  

• Significant figures are not the same as decimal places. For example 123.08 is to 2 decimal places but to 5 significant figures. Zeros before any definite numbers do not count as significant figures. So 0.000045 is to 2 significant figures.
  

• When doing calculations, your final answers to each section should be to the correct number of significant figures. Generally, it should be to the same number of significant figures as the data. You may get penalised if you write your answer with too many significant figures e.g. 1.257487 instead of 1.26.
  

• Make sure that you round up your answers correctly. For example, if an answer to 4 significant figures is to be rounded to 3 significant figures, the answer 22.56 should be rounded up to 22.6 not down to 22.5.
  

• Always show your working – even if your answer is wrong, you may get some marks for your method. It is not sensible to work everything out on your calculator then just put down the answer. If you make one slip you risk getting no marks for that question.
  

• Make sure that you know your syllabus statements and definitions exactly. For example, the use of naphtha as a feedstock for the chemical industry. This is because the Principal Examiner has to use the syllabus as a basis for the exam questions.
  

• Look out for the phrase ‘what you would observe’. This means that you must write down what you see/ hear or feel. For example, ‘the test tube gets hot’. It is a very common error to write something like ‘a gas is given off’ or ‘copper is deposited’. These are not observations.
  

• Don’t get caught out by the phrase ‘describe what you would see’. Some students put down observations about pops (sound) or heat given off.
  

• When drawings diagrams: (i) make sure they are large enough to fill the space given on the paper (ii) make sure that you draw apparatus for gas measurement without any places for the gas to escape. Don’t draw gas syringes with the plunger much smaller than the syringe barrel. This is a common error. (iii) always label your diagrams as fully as possible.
  

• Stick to the number of examples requested by the examiners. For example, if a question asks for two examples of a transition element, do not write three down. If one of the three is incorrect, you will lose a mark. If a question asks for a single use for a substance, stick to one – if you write long lists, the examiner will think that you are ‘playing safe’ and you won’t get the mark. Take for example in the question ‘State two properties of transition elements that are not shown by other metals’ (2 marks). The answer – ‘they are good catalysts, they form ions with different charges, they do not conduct electricity’ – will only gain one mark. This is because, although the first two answers are correct, the last one is incorrect.