Physics AS P3

Okay you people, Sir Puran has been kind to say most of there is to know about Paper 3, so this part of the exam shouldn't bee too much to worry about. I'll list some points to remember when doing this paper.

I ran out of time, so I wouldn't say that this would be a complete work, but I hope it'll still be helpful.

I've covered all aspects of graph-making (I hope), and some of measurements. However, I'm unable to post a say on the others, so I really encourage you to read this particular handout:

PHYSICS A/AS
9702

DEFINITIONS AND FORMULAE

That's the title of the handout, but that part is none of our concern; what's important in that paper is the next part; it has all the information minus graph drawing. (Nearly a bible, but hey, I did graphs already; scroll down)

If you're not reading it, then it's your own problem if you lose marks because some idiot asks you to plot the graph logarithm style, or if you mess up your significant figures.

Measurements

• Read and follow the instructions carefully to the letter.
• Wherever your common sense tells you to, take repeated readings. (Usually around 4 to 6 times) Also, make sure these repeated readings are not uselessly repeated. (e.g. Measuring the diameter of the wire at the same location and without rotating it. Go figure why)
• Be aware of the Power of Tens.
• And check your formulae.
• Do make sure that you have utilised most of the given range in taking your measurements. (i.e. If given a range between 0 to 1 metre, at least use 0.1 to 0.9 metres)
• The difference between each measurement should be roughly equal. (i.e. Take, for example, 0.2, 0.4, 0.6, 0.8, and so on)

Graphs

Since I lack the software needed to draw graphs + I'm too lazy to make one on mspaint.exe, there will be no illustrations here.

Also, since it has been ages since CIE released a paper where candidates are required to plot a curve, I suggest you bring your flexible ruler.

Anyway,

For graphs, here are the 5 points to remember:

• Choice of scale
• Plotting of points
• Line of best fit
• Calculation of gradient
• Determination/calculation of the y-intercept

Choice of scale

• You must make sure that the scale you choose will make your graph occupy more than half of the graph paper.
• Label the axes. (Include the quantity in question and its unit)
• Make sure that your scale is conventional! (As in: Don't make it so that people will have to read it right to left, like Arabian script; etc.) Remember this when plotting negative numbers, ja?
• No fancy scales. That means on the big squares, don't try using 3, 6, 9, 12, etc. or anything that 1) Makes it hard for you to read, and 2) Makes it hard for you to plot.
• It is recommended to not leave space for labeling each big square. (i.e. Do: 0, 5, 10, 15; not 0, nothing, nothing, 15)
• Scaling must also be regular. (e.g. 5, 10, 15; not 5, 11, 20)

Plotting of points

• Don't plot outside the given area/margin. (Outside the big, boxy thingies)
• All data must be plotted. (e.g. If you have made 7 observations, the examiner must see 7 plots in the graph)
• If you must plot let's say, 0.43 m, and your smallest box represents 0.2 m, you will have to approximate this plot. The room for error given by the examiner is half of this value. (In this case, ± 0.1)
• The plot must be clear enough for the examiner to see.
• Don't make your plots very thick, as they examiner may not be able to see accurately whether you have plotted the corresponding observation correctly in the graph, resulting in the loss of marks. It is also due to this that you use crosses to mark plots and not dots.

Line of best fit

• There must be at least 5 plots for the 'best fit' mark to be awarded. (No problem, really, given that the question usually requests for 6)
• The line of best fit must be 'balanced', at least roughly. Simply put, if you have 3 plots above the line of best fit, then have 3 plots below the line of best fit too.
• Lines must thin and clear. This is not an art examination, so avoid unnecessary ornaments like making thick lines and having jembut branch from it et cetera et cetera. Curves are usually prone to this. (Let's hope you didn't throw away your flexible ruler)
• Lines must extend reasonably further than the last greatest plot, reach x = 0, but not extend to less than x = 0. (At least so far, don't ask me if this still applies if we have to plot both negative and positive values)

Calculation of gradient

• Make a right triangle to indicate from where are you taking the coordinates to include in your calculation.
• Take the coordinates which lie on the line of best fit, not from the plot which is used to make the line of best fit.
• Indicate those coordinates in the graph. (e.g. If you take one value to be (1.24, 3.22), then write (1.24, 3.22) on (1.24, 3.22) on the graph)
• The triangle must cover more than ⅔ of the whole curve.
• ∆y and ∆x must be accurate to the smallest square in your graph.
• I cannot say if we would need units for the gradient, since my own experience and various sources conflict. Therefore, use your own judgment, or go ask somebody credible.
  
• Workings workings workings! Show them!

Determination/calculation of the y-intercept

• y-intercept is always read from x = 0, x = 0, x = 0.
• If you cannot read the y-intercept of the graph, then you have to calculate it using the equation y = mx + c. To do this, take any value from the line of best fit and substitute those values into the equation. (I'm not sure, but to be on the safe side, do indicate these values on the graph, like you would with a gradient-calculation coordinate)
• The y-intercept has units. (Usually)
  

Biology P3 Tips 03

note: I'm using Vika's account since i'm too lazy to make one =_=, for those who failed to guess who am I, I wont tell ^.^

The third one, last but not least.
This post is about the last part of the microscope question, just after the labelled-drawing question, and the things to expect from the practical (just so that we will not be surprised).

Q2: The Drawing Features and Comparisons

So, the last part of the question will give you a picture, and it will ask you to compare and contrast the picture given with the image of a section of the slide. Definitely, absolutely, inevitably, you MUST draw a table. Drawing an appropriate table with correct headings gives you one mark out of a total of five. The second mark is given if you use comparative statements, which means your statements in the table are indicating that you are comparing or contrasting the features on both images (you may want to see the 2008 marking scheme for clarification). That's two marks already. The other three marks are given to correct contents in the table.

That is basically all I can say on this question...

Last Tips and Final Overview Briefing:

These are things I forgot to say, or things that I've just discovered along the way.
In all drawings, you should use more than half the space provided, no matter how large it is, this is just in case that the marking scheme requires you to do so. Oh and by the way, in the new 2008 practical, I think that you will be asked to draw twice, first is the unlabelled drawing, in which you will be asked to draw a section of the image in the slide (you need to draw more than half of the page), and the second one is the labelled drawing (eventhough the question does not ask you to label it, you should, and for this one, the marking scheme does not say anything about drawing for more than half the space, but just in case, if you want to...).

Next, there is also the calibration part. You should all be familliar with the calculations (if not, immediately ask assistance from your teacher or Ms.Yanti, in our current case). In the calibration part, they will tell you to look for a certain part (not necessarily a cell) from the image of the slide, record the value of the divisions blablabla, and simply measure it. Dont forget to write the units, and show a clear working. In the end of the calibration question, they may ask you to identify a source of error in the measurement.

Turn back to question one..

In the experiment question or the test-tube practicals, after the table question, you will be asked do describe and explain on your experiment, which means that you must explain on the theory behind the experiment given. This question worth three marks. After this should be the error and improvements, see my Biology P3 Tips 02 for this. (And I suggest you remember all the 'Common Errors' that I listed)

In the beginning of Graph questions,you will be given a printed table containing the values that you will plot in the graph. Now, some of the values may be obviously missing, this means extra mark for everyone, so don''t fail to notice it. And yet, thankfully, another extra mark follows; there will be a question like: "Explain why that guy discarded the funny value, and repeated the experiment balblalblalbla". Simply answer that the value does not fit the pattern, or the result was an error and it is incorrect, so it is proper to discard and repeat balblabl.

Next is the graph. Plot all the points and use, if possible, all of the space provided. Label the axis properly with correct units. After the graph, there is this funny question that give you a hypothesis/statement. You will be asked to judge whether the hypothesis is supported by the experiment or not, and give a correct hypothesis if the answer is NO. Yes, ladies and gentlemen, this leads to another one of extra mark. Because the question is worth two marks, the answer will obviously be NO. Just say why the experiment does not support that guy's hypothesis and give a new one.

Oh and one or two (usually one) extra pesky question(s) may pop out anywhere in this practical. What I mean by extra pesky question(s) is like those "Suggest why this is like that." These question(s) may give you another extra mark, but that also depends on your knowledge and creativity, of course.

Yay, that's it for my tips and suggestion, I hope it helps. Sorry because I did not put the questions in order. One last thing to say is a quote from Vika's chemistry P3 tips:

"Last but not least doa. Biarpun udah disiapin seperfect mungkin, tapi selalu ada uncertainty. By conducting our experiment accurately and precisely, we should reduce those uncertainty by a great amount. But still, it is always good to have faith."

Woohoo, good luck on your biology practicals. I may be back for P2 and P1 tips (or even A2 biology if Vika forces me to do so (again)).
(Please note that my tips are based on past year papers of 2007 and May/June 2008, so if anything goes mismatch, don't be blame this blog.)

Biology P3 Tips 02

note: I'm using Vika's account (again) since i'm too lazy to make one =_=, for those who failed to guess who am I, I wont tell ^.^

Hey ho, next for the tips.
Did this the day before chemistry practical.
This time I'm going to list a compilation of things to remember about errors and improving-the experiment-questions in biology practicals and just a bit of comments on those labelled drawings and how to draw them.

Q1 part 02:
Error identification and countermeasures
This is it, the valuable list of improvements which I have listed and categorized for the sake of convenience. You can deduce what error they represent by yourself, its pretty obvious.

1. Common Improvements (applicable for almost all kinds of experiment)

• Repeated readings
  
• Keep the temperature constant
• Keep the pH constant
• Same amount of time
• Constant concentration
• Constant volumes of reactants and reagents
  

2. Improvements on tests with serial dilution (like Benedict Dilution and Enzyme Inhibitor test)

• Use colorimeter to identify colour difference more accurately
• Increase range of dilution
• More accurate use of equipments

3. Improvements on potato strip tests

• Thickness and/or width of the strips should be same
  
• Use strips from the same potato
• Weigh the strips
• Increase length of strips

4. Improvements on bubble count experiment

• Measure the volume of the bubbles produced

5. Errors that you cannot improve (haha..), i think you can write these on the sources of error questions.

• Difficult to put enzyme at the same time (in Enzyme Inhibitor serial dilution)
• Inaccurate serial dilution
• Volume of Benedict added is not exactly the same

6. Errors involving measurement of lengths on cells/diagrams etc, that ocassionally pop out on question 2 (these are..real)

• Not viewing the ruler from the right angles / Parallax error
• Thickness of ruler lines affects the reading
• Difficult to focus both ruler and specimen at same time

Well that's basically almost everything I know on errors. Yes, I know and have noticed some unclear or funny things on the list above, like 'Difficult to focus both ruler and specimen at same time' and 'Thickness of ruler lines affects the reading', but these are taken from marking schemes, so its all real. Cambridge sure has its own ways of doing (or marking) things...

Next I'd like to comment on drawing with labels on question 2. On the subject of drawing things that you see on the light microscope, what I've noticed from the marking scheme is that it generally speaks about the drawings should have the right orientation, shape and proportional sizes (like a red blood cell should be smaller than a white blood cell). No shadings or colouring is allowed. Make sure your label lines do not intersect each other. And the lines on your drawing should be clean and continuous (like drawing a smooth plasma membrane). Just a simple and clear drawing is good.

This is all for the second part of the p3 tips. I hope you can benefit from it. Dont panic and try to remember all the things on errors I wrote.. Instead focus on two to three things that you dont know yet or that you find easy to remember, since the questions on errors usually only ask for 2 or 3 points.

Ok then guys, good luck on chemistry and Vika's tips are awesome, hands down.

Some extra tips for P3

Here are some extra tips:

• In case (just in case), the first part of the question is not about titration, don't panic. Usually, if not titration, it will be about rate of reaction. Unlike biology, here we need to use the data that we get in practical and make a graph out of it. Marks will mostly be counted in the quality of the graph, just like Physics. The good (OR bad) things about this kind of practical, instead of calculation and stoichiometry, you will be asked to comment on the experiment or suggest/improve a hypothesis. This is like the fusion of both Biology and Physics. And yes I do realize some of the questions asked has an extremely nerdy instructions (believe me, I took 15 minutes to fully grasp the concept on some questions) but don't worry. Usually for this kind of experiment, you will be asked to vary certain values (concentration/mass) while keeping the other values constant. O/N 2007 P3.2 is a good example (freeexampapers.com) (thx to Kenny Buntara). Here you are asked to determine the rate of reaction H2O2 and we need to vary the concentrations of H2O2. So those long and confusing instructions is just basically tell us on how to vary the concentrations. See, if we limit the volume of H2O2 to be only 40 cm3 and you add 20 cm3 of water and 20 cm3 of H2O2, it's just dilution, nothing special. How to make it more concentrated? Simple. Add less water but more H2O2, but make sure the total volume is still 40 cm3 (10 cm3 of water+30 cm3 of peroxide).
  

• Now about qualitative analysis. On some occasion, we are also required to determine unknown organic compound (holy s***!). But don't worry, on scope of our knowledge, we only need to know how to identify :
  
• Alkane
• Alkene
• Alcohol
• Halogenoalkane
• Aldehyde
• Ketone
• Organic acid (carboxylic acid)
• And we don't need to know what exactly it is (you don't need to know that it is pentane or pentanol, you just need to know whether it is alkane or alcohol)
  
• Now here's the catch. At our current level, it is impossible for us to handle combustible material such as alkane and alkene. Anyway, to identify alkane and alkene is to use liquid bromine and source of UV light. So if the question doesn't show such reagents in the question, you can easily forget about alkane and alkene. Halogenoalkane, to identify this is actually the same as identifying Cl-, Br- or I-. So that will leave us out with Alcohol, Carboxylic acid, Aldehyde and Ketone.
• Start with an easier one first, identifying carbonyl compound. The only way to identify them is to use DNPH (2,4-Dinitrophenylhydrazine) and it will produce this precipitate:

left picture is negative test, right pic. is positve test

• To identify between aldehyde or ketone, we will use Tollen's reagent (silver dissolved in ammonia) or Fehling's reagent (basically it looks like Benedict's reagent). Picture on the book at page 354 shows a good picture of positive Tollen's test.
  

The picture labelled 2 shows the positive result of Fehling's test.

• Take note though. Sometimes if our preparation is a little bit messed up, carboxylic acid will sometimes give positive result for DNPH. I suggest that you clean everything after usage. If the result is still the same, I suggest do the Tollen/Fehling test first to identify the aldehyde.
  
• Now identifying alcohol and carboxylic acid. The simplest way to identify them is to put carbonate/bicarbonate (magnesium/calcium is fine) inside the two unidentified liquid. The one that gives off bubble is the carboxylic acid. It's like adding baking powder with antiseptic alcohol and vinegar (ethanoic acid). The one that will react is the acid. Note that both of them will react with reactive metal (not salt) such as magnesium.
  
• If you are still not assured, usually in the test, they will ask us to make an ester (add carboxylic acid with alcohol, boil then add water). Remember it will gives sweet smelling odour (if you ever play those balloon with straw, then you can imagine that smell).
• And remember to put all of your evidence that indicates that those tests shows this compound is "this" or "that". Don't take the risk!
• Last form of the test is usually measuring of enthalpy change. Usually they will ask us to react something and record the temperature. The only tips that I can get here is that you need to be extremely, extremely, d*** accurate! Although the marks are not really high, but their marks for accuracy is really and impossibly strict. Let's say that the examiner get a value of 2.7 and their limit of accuracy is 0.05 while some of our equipments can't measure until that degree of accuracy. Even slightest difference will give us wrong answer, such as finding the average of 2.7 and 2.8. This accuracy limit is also applied during our calculation. So our only hope is to get the measurement right. Fortunately, their marks are not really high and they are quite fair, such that they can miraculously design the test that it is possible for us to get the marks in one part but not the other.

So this is the end of extra tips. Comments are much appreciated.

Biology P3 Basics and Tips 01

(note: I'm using Vika's account since i'm too lazy to make one =_=, for those who failed to guess who am I, I wont tell ^.^)

Finally, a biology section.
Anyways,
Since Vika told me to do biology, and bio p3 is first, so I'd like to share some bio p3 tips.
You can request any clarifications on A Level Biology later, and I or Vika will try our best to answer it.

First, the basics, just for your information.
The practical usually consists of 2 questions. The first one should be some test-tube-practical, and the second one should be microscope-related-practical
Total mark is 40, according to 2009 syllabus it consists of:

• Manipulation, Measurement, and Observation (16 marks or 40% of total mark)
  
• Presentation of Data and Observation (12 marks or 30% of total mark)
• Analysis, Conclusions and Evaluation (12 marks or 30% of total mark)

Well, basically all three is important since their respective marks have the ratio of 40 : 30 : 30 which is well spread. I find the syllabus for the biology practical quite helpful because it simply explains what will happen in the practical. I suggest you take your time to read the practical syllabus. My writings are actually a summary of the syllabus and what I know.

Q1 part 01: The Tedious Test Tube Practicals.

In this practical, the first question will ask you to do certain things with clear set of instructions like put 2cm³ of starch into solution A and then put some inhibitor blablabla, and it will ask you to record your observation in sentences. That is all there is to it, only worth 2 marks.

Ah, the main part. The second question, based on the info given on the first, will tell you to do an experiment and record your observation in a table, you know how it goes. You are given a set of apparatus, but you may or may not use them all. The experiment is repeated with varying sets of values of the factors like time or concentration, and oftenly 3 readings for each value set is enough. Make a neat table to record your observations, label each coloumn, AND DON'T MESS UP THE UNITS ON THE LABEL (and it goes like length/mm or length (mm)). Use pen for your writings.

This is basically manipulation of apparatus, use the apparatus given efficiently and smartly, don't mix up the syringe or beaker, and note that you should read on the meniscus. This question worth 6 marks and should take anywhere from 20-40 minutes depending on the question. DON'T SPEND TOO MUCH TIME IN LEISURE AND COMFORT OR HESITATION, YOU'RE KILLING YOURSELF; RESIST THE TEMPTATION! If the experiment takes a long time you can do the next questions first. Immediately afterwards, they will ask you to draw a conclusion from your results, pretty simple.

Oh before I forget.. I'd like to give some tips on the ultimately-luck-based-ambiguous-colour type test tube practicals, like benedict dilution (i hate this the most, inhibitor comes next on my hate list), use the word 'pale' or 'dark' AND DONT INVENT YOUR OWN COLOUR LIKE PURPLISH GREEN OR PINKISH BLUE, believe me, its written on the syllabus. I'm unsure whether you can use comparison like paler red than at 0.1 mol, but darker than at 0.5 mol. Use precise and simple language for it.

That's it for part one, I wont discuss all aspect of the practical though, i'll just discuss what seems important or tricky to me. Its roughly a week to the actual practical when this is written, expect it to be finished maybe 3 days before the practical. And again, the practical syllabus really helps, just read it.

Special Posting: Practical Chemistry a.k.a. P3

Oke tinggal sehari atau dua hari lagi buat practical. Menurut gw, nih paper yg paling sulit, soalnya kesalahan dikit aja bisa bikin resultnya ngaco dan amburadul. Such small stupid mistakes can be irrelevant and sometimes unnoticeable. Example, using the same dropper for different unknown substances. Klo misalnya precipitatenya warnany bisa kuning atau merah atau ungu atau putih, I say it is still safe to combine them. Tp klo ada 3 unknown substance, trus ada 2 yg precipitare warnanya putih, good luck.

Usually they will provide two droppers, I suggest you use one for to add the acids and bases (you know, you will need to use droppers to add ammonium hydroxide or HCl) and use the other one to add the unknown substance to empty test tube. Terus siapin satu beaker kosong isinya distilled water buat bersihin droppernya. Jadi abis pake buat satu reagent lu pake droppernya buat ambil air trus buang lah airnya kemana. Minimal bisa buat reduce contamination.

Trus buat calculation. Inget biarpun titrasi lu ngaco, calculation nggk ada accuracy marknya. Jadi, sebisa mungkin, try to get full mark in calculation part. 5 marks mungkin kecil, tapi bisa nyelamatin kita. Klo perlu hapalin semua calculationnya biar lebih confident. Confidence is the key to succeed in this exam. Also in qualitative analysis, sometimes you can actually guess which substance is which even if you haven't finished the whole set of questions. You can actually save time here by writing the possible outcome before we actually test it. Jadi biarpun salah waktu kita coba, tp nulis observasinya bener, kita masih dapet mark.

Klo lu orang lebih confident, boleh juga coba kerjain qualitative nya dahulu. Jawaban di qualitaive lebih exact. Pengecualian kalau titrasinya menggunakan oxidising agent (KMnO4 dan yg lainnya). Klo kelamaan ditinggalin, nanti reagentnya bisa keoxidize duluan, resulting in inaccurate measurement.

Trus klo ada yang ambidextrous atau at least bisa kerja pake 2 tangan, gunakanlah dua tangan anda. Tp klo misalnya lu orang begitu pake 2 tangan langsung tangan kanannya stop bekerja, jangan dicoba.

Klo ada dilution (yg musti dimasukin ke dalam tube aneh terus dikocok), lu orang buka distilled water tubenya, terus tumpahin, terus klo udah level tertentu, baru pake tube kecilnya. Dan klo udah approaching the line, ganti pake dropper biar meniscus readingnya pas di line. Beda sedikit aja bisa deviate the result by a lot. Trus pas di shake, ati2 jgn sampe ada yg tumpah airnya (sedikit gpp), reason same as above.

Jangan lupa tabulate all of the results, even though if you are not asked to. Gw pernah ilang 2 mark gara2 nggk nulis table di bagian awal2. Jangan panik waktu ngerjain, kejadian dulu ada anak ngambil A-level, saking groginya sampe mecahin apparatusnya (nggk tau apparatusnya apa). Trus semua data harus 2 decimal places, klo nggk bisa ilang tuh 1 mark.

Klo bisa, hapalin semua perubahan warna saat titrasi. Klo misalnya diminta titrasi sampe warna pink pake methyl orange, harus bener2 exact warna itu. Always use white tile to let us differentiate the colour better. Klo bener2 kepepet (definisi kepepet: udah coba 3 kali tapi bedanya sampe 5 cm3 atau warnanya lu bener2 nggk tau) (*warning* very risky), cb ngintip temen2 yg lain atau invigilator punya practical. Glancenya of course jgn ketauan, main mata dikit aja. Sebaiknya klo bingung tanya dulu, klo nggk dihiraukan baru.... (anak baek jangan menyontek. Inget ini bener2 risky. Klo ketahuan bisa automatic failure, so jangan main api klo nggk mau kebakar). Trus klo misalnya Ms. Ine liatin lu orang punya practical, try to just ignore her face and body language and expression.

Klo kerjain, tolong-tolong dengan sangat jangan pernah buru-buru kaya dikejar setan atau mau show off. With proper time planning and by realizing your ability, you should be able to allocate your time wisely and judgmentally. No need to rush with reason such as "later I don't have time to do the written work". Plan, plan, plan!

Jangan cheat your result, bcos most probably the examiner will notice. (I don't now actually how to cheat here though)

Trus klo ada pertanyaan yg regarding improve the quality of experiment atau why such experiment is blablabla, jgn panik. The best answer is always the simplest answer but we should not simplify our point. Pikir pake kepala dingin, klo mereka mintany simple modification, jgn pikir yg aneh aneh. Conduct experiment in vacuum is one of the most desperate answer. Liat sekitar lu dan liat apparatus2nya, trus pikir lagi. Klo nggk bisa lompatin aja daripada ngabisin waktu.

Last but not least doa. Biarpun udah disiapin seperfect mungkin, tapi selalu ada uncertainty. By conducting our experiment accurately and precisely, we should reduce those uncertainty by a great amount. But still, it is always good to have faith.