A level chemistry

Test 3 As Level

2011-11-14T10:49:00.002+08:00

SJ11 A Level Result Analysis

2011-08-11T11:55:00.003+08:00

Congratulations to those who did well in your recent A Level (May 2011)

The following is the unofficial analysis (analysis done by me)of the Chemistry results:
No of students taking Chemistry :97students

A* 12 students 12.4%
A 23 students 23.7%
B 20 students 20.6%
C 14 students 14.4%
D 9 students 9.3%
E 9 students 9.3%
e^ 4 students 4.1%
U 6 students 6.2%

Asbestos linked to ovarian and lung cancers

2011-06-10T13:13:00.000+08:00

It's well known that exposure to asbestos causes lung cancer, but there have been suspicions that it could also be linked with ovarian cancer. Now, researchers have shown that there is indeed a causal association between asbestos exposure and ovarian cancer.

Over the years, there have been several suggestions that asbestos might be a risk factor in ovarian cancer on top of links to lung cancer, mesothelioma and asbestosis. A working group at the International Agency for Research on Cancer (IARC) recently concluded there is sufficient evidence for a causal association, and now a study led by Leslie Stayner, from the School of Public Health at the University of Illinois at Chicago, US, confirms it.
A meta-analysis of 18 studies of women who had been exposed to asbestos through their work was carried out. Earlier studies failed to prove the link because of concerns that tumours had been mis-classified - until recently it was difficult to discriminate between peritoneal mesothelioma and ovarian cancer. Across all the studies, women exposed to asbestos were about one-and-three-quarter times more likely to develop ovarian cancer as those who were not. Particularly high rates were seen in UK women who manufactured gas masks, and thus had been exposed to high levels of the fibres.
Several mechanisms have been proposed as to how asbestos increases susceptibility to ovarian cancer, mostly involving chronic inflammation caused by fibres persisting in ovarian tissue. It is unknown how the fibres get into the ovaries - they might be transported through the reproductive tract, or fibres may be carried in the bloodstream or lymph system, penetrating the ovary through the mesothelium.
According to Hilde Langseth, a researcher at the Cancer Registry of Norway, the association between asbestos exposure and ovarian cancer has been an ongoing research question for a long time. 'The meta-analysis performed by Stayner and coworkers is an important quantitative evaluation of this association in occupationally exposed workers,' she says. 'They demonstrate an increase in the pooled estimate for ovarian cancer in relation to exposure to asbestos.'
However, she adds, even if asbestos use has been forbidden in some countries in the western world since the 1980s, a significant proportion of the world's population still works in environments in which they are exposed to asbestos. 'The authors report that at least 90,000 people die from asbestos-related cancers every year,' she says. 'The need for increased knowledge about the association and the carcinogenesis of ovarian cancer is therefore warranted.'
Sarah Houlton

Source : www.rsc.org

AS revision, atomic structure, bonding and periodicity

2011-06-10T12:48:00.002+08:00

A level as notes: atomic structure, bonding and periodicity

downloaded from www.lanther.co.uk

A level syllabus (CIE) for SN12

2011-05-09T11:24:00.001+08:00

A Level Syllabus for SN12

Trial Exam SJ11

2011-04-10T14:06:00.005+08:00

Paper 4 trial exam SJ11 Marking scheme Paper 4 Paper 5 trial exam SJ11 Marking scheme Paper 5

Recycling plastic

2010-06-29T11:03:00.003+08:00

Extracted from Infochem, May 2010

Most clear plastic bottles are made from the polyester, poly(etheneterephthalate), or PET(1). Triangular arrows surrounding the number 1 stamped on the bottle identify the plastic as PET. High-density poly(ethene), HDPE, is used to make milk bottles (number 2 in the recycling symbol). The caps and rings that keep the bottles’ content fresh or fizzy are made from poly(propene), PP. Like all plastics, PET, HDPE and PP are polymers – their molecules are long chains made from repeating units of smaller molecules. In the case of PET the repeating unit is ethane terephthalate; in HDPE it is ethene (2), and in PP is propene (3).
A large amount of plastic waste is shipped abroad, often to Asia, where it is processed to be re-used in low-grade products like fibres for clothing, carpets or plastic strapping. Some of it, PET in particular, is made back into bottles at plants like Closed Loop Recycling (CLR), in Dagenham, Essex. Used plastic bottles arrive at CLR in bales weighing about 500 kg and containing around 12 500 plastic bottles, along with items like carrier bags, yoghurt pots, and cans.
The contents of the bales have to be sorted because failure to separate the plastics will cause problems with the end product. Nick Cliffe, marketing manager at CLR, singles out polyvinyl chloride, PVC, poly(chloroethene) (4) as the main ‘headache substance’ for CLR. PVC is commonly used in blister packaging for batteries as well as in plastic pipes, and as Cliffe says ‘has similar properties and looks like PET to the naked eye, but it blackens at 200 °C’. A tiny black speck in a recycled PET bottle, he explains, will weaken it so much it could explode when filled with fizzy drink, and just one PVC bottle in a batch of 10 000 PET bottles could ruin the entire batch. Separating all the different types plastic is a challenge, but CLR has found that the solution lies in exploiting the chemical differences between the different polymers.
‘Different polymers reflect and absorb different amounts of light, and at different wavelengths, especially in the near infrared’ explains Cliffe. ‘As the bottles pass by a series of “optical sorters”, ie bright bulbs emitting in the near infrared, different polymers trigger a jet of air, which blows the bottle down a chute. This is also useful for removing coloured PET, which can’t be included in the final product but can be recycled for uses where colour is not so important’. Some bottles can make it past the optical sorters so another difference is exploited once the polymers have been shredded ready for processing: PET is more dense than water, while polyalkenes, like HDPE and PP, are less dense. So when the flake mixture is dumped into a tank of water, the PET flakes sink to the bottom, while the floating HDPE and PP can be skimmed off the surface. Recovered PP is recycled for low-grade uses. A final check of the PET flakes is done using Raman spectroscopy. In this process each flake is hit with a laser, causing the electrons in the flake material to absorb the laser energy and jump into a high-energy state. As the electrons drop back down to their original energy state, they release the absorbed energy as light. The range of wavelengths of light emitted (the spectrum) depends on the chemical structure of the compounds containing the electrons. Thus individual atoms and bonds can be identified. CLR uses Raman because the emitted light is a ‘unique molecular fingerprint’ of whatever is in the flake. When the Raman spectrum of a rogue flake or contaminant is detected it is ejected from the mix with a jet of air.
CHEMICAL PEELS
If the PET bottle is going to be re-used for food or drinks packaging it must have all contaminants removed. At CLR, this is done by stripping off a layer of plastic, a few micrometres thick, from the surface of the PET flakes in a reaction that Cliff e describes as a ‘chemical peel’. In fact, the reaction is a depolymerisation: the reverse of the polymerisation reaction that originally formed
the plastic. Each PET flake is coated with a vaporized solution of sodium hydroxide. The coated flakes are heated to 200°C in a rotating oven. At that temperature, the hydroxide ions attack the ester groups in the polymer chains nearest the flake surface. This hydrolysis reaction breaks up the PET chains into terephthalic acid and ethane-1,2-diol (ethylene glycol), the same two compounds which were originally used to make the polymer.
The terephthalic acid forms sodium terephthalate,with the sodium from sodium hydroxide. This salt is water soluble and can be washed away, along with the ethane-1,2-diol.
Volatile organic contaminants, such as the flavouring limonene, evaporate in the heat.
Other contaminants, mostly dried remnants of the original drink, are also removed by washing. The PET flakes that are left behind are clean enough to be melted down and made into new bottles. A similar process to hydrolysis, ie methanolysis, is used to depolymerise PET into its core ingredients by the Eastman Chemical Company in the US. Methanol at temperatures above 250 °C attacks the ester linkages in the PET chain, breaking it down into dimethyl terephthalate and ethane-1,2- diol. A catalyst such as sodium methoxide can be used to speed the reaction up. The product, dimethyl terephthalate, can be repolymerised or hydrolysed to form terephthalic acid.
Mitsubishi Heavy Industries in Japan has developed a variation of this reaction that uses supercritical methanol (ie methanol which is heated at high pressure to beyond its boiling point). At these conditions the reaction is faster and does not require a catalyst.
Ethane-1,2-diol can be used instead of methanol to attack the PET ester linkages. This reaction (glycolysis), which also requires high temperatures and pressure and can be catalysed by a compound such as zinc acetate, forms bishydroxyethyl terephthalate and shorter PET segments called oligomers.

These products can all be re-polymerised to make fresh PET. George Roberts, professor of chemical and biomolecular engineering at North Carolina State University, US, has recently developed a method for reacting PET with ethane-1,2-diol in a large corkscrew-type chamber, allowing the process to run continuously. As the extruder screw turns, it melts the PET, allowing it to react more rapidly with ethane-1,2-diol to form shorter PET oligomers. ‘Once we have these shorter segments, the viscosity of the material is significantly reduced. We can take out any solid, liquid or vapour impurities and wind up with a material that can be put through a normal polymerisation process’, said
Roberts. ‘We think it is more economical to make the oligomer because most polyester processes involve two stages, and the second stage starts with an oligomer.’
MILK BOTTLES?
Natural, white, HDPE can also be turned back into a food-grade plastic containers. The bottles are heated to 120 °C at low pressure. When the plastic melts, the contaminating remnants of the drink to simply evaporate. The molten plastic is then filtered through a fine mesh, cut into pellets and cooled, ready to be turned into new milk bottles.
So next time you drop your plastic water bottle in the recycling bin, think about the chemical journey it will take before it ends up as just another bottle.
Tom Westgate

Periodicity -Acid Base Character

2010-05-18T09:44:00.002+08:00

Acid-base character of oxides
Base behaviour : Na2O, MgO
Na2O(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l)
MgO(s) + 2HCl(aq)→MgCl2(aq) + H2O(l)

Amphoteric behaviour Al2O3
Al2O3(s) + 6HCl(aq) → 2AlCl3 + 3H2O(l)
Al2O3(s) + 2NaOH(aq) +3H2O(l) → 2NaAl(OH)4(aq) sodium aluminate

Acid behaviour : SiO2, P4O10, P4O6
SiO2 + 2NaOH(aq) → Na2SiO3(aq) + H2O
P4O10 + 12NaOH → 4Na3PO4 + 6H2O
P4O6 + 12NaOH → 4Na3PO3 + 6H2O

2010-05-18T09:00:00.008+08:00

Formulae of chlorides and reactions with water

NaCl + aq →Na+(aq) + Cl-(aq) dissolves to form neutral solution , pH = 7

MgCl2 + aq → Mg2+(aq) + 2Cl-(aq) dissolves with slight hydrolysis to form slightly acidic solution , pH = 6.5

AlCl3 + 6H2O(l) → [Al(H2O)6]3+(aq) + 3Cl-(aq) dissolves with hydrolysis to form acidic solution
[Al(H2O)6]3+(aq) →[Al(OH)(H2O)5]2+(aq) + H+(aq) , pH = 3

SiCl4 + 2H2O→SiO2 + 4HCl , pH = 2

PCl3 + 3H2O → H3PO3 + 3HCl, pH = 2

PCl5 + H2O → POCl3 + 2HCl, pH =2

2010-03-25T11:51:00.000+08:00

Useful websites
Chemguide
http://www.chemguide.co.uk/
If you are looking for quality revision notes

Doc Brown's Chemistry Clinic
http://www.wpbschoolhouse.btinternet.co.uk/page04/page04.htm
Notes and tests

Dr Rod Beavon's Chemistry Pages
http://www.rod.beavon.clara.net/chemistry_contents.htm

Notes and examination tips for the AS/A Level Chemistry.

Chemmy Bear
http://www.chemmybear.com/

Chemsoc Interactive Periodic Table
http://www.chemsoc.org/viselements/pages/pertable_fla.htm
Interactive Periodic Table of Elements

The Orbitron
http://www.shef.ac.uk/chemistry/orbitron/
3-D images of atomic orbitals and molecular orbitals.

The Organic Chemistry Review
http://www.organicchemistryreview.com/
Printable Notecards

S-cool! Revision Guide
http://www.s-cool.co.uk/topic_index.asp?subject_id=7&d=0
Extensive notes and sample questions.

RevisionNotes.co.uk
http://www.revision-notes.co.uk/A_Level/Chemistry/index.html
Revision notes

Beta-Theta.com Chemistry Section
http://www.beta-theta.com/Chemistry.html
Notes on topics relevant to AS/A Level Chemistry.

General Chemistry Online
http://antoine.frostburg.edu/chem/senese/101/index.shtml
Notes, articles, experiment simulations and tutorial for US students but relevant to A level students.

New students...SJ11

2010-02-03T08:48:00.002+08:00

Click this link for to download more past exam papers

Past exam papers

SJ 11 Chemistry Syllabus

2010-01-15T08:46:00.001+08:00

Chemistry Syllabus for 2010/2011

Chemical bonding

2010-01-11T09:38:00.003+08:00

Types of bonding

Ionic bond (between ions)
Ionic bond is the electrostatic force of attraction between the positive and negative ions as a result of transfer of electrons from an atom to another. (eg NaCl, MgCO3 )

Covalent bond (between atoms)
Covalent bond is the electrostatic force of attraction resulted by sharing of two electrons by two atoms.
Covalent bond can be found in simple molecular structure ( discrete molecules eg O2, CO2 ) and giant covalent structure (with a network of covalent bonds eg C(graphite), C(diamond), SiO2,,Si ]

Metallic bond ( between positive ions surrounded by sea of delocalised electrons)
Metallic bond is the electrostatic attractions between the cations and the delocalised electrons surrounding the cations. (eg Mg, Al , Na, Ag, Pb, Sn)

3 types of intermolecular forces ( weak forces between molecules)

London or dispersion forces occurs are weak forces occur between non- polar molecules , eg: CH4, Cl2, CO2

Dipole-dipole forces are forces occur between polar molecules, eg HCl , H2S, SO2

Hydrogen bonding is the electrostatic attraction forces between H atom bonded to a very electronegative atom and the lone pair of electrons from a very electronegative atom such as. F,O or N atom (eg HF, NH3, H2O ,amines and alcohols) Hydrogen bonding causes higher boiling points of hydrides, solubility of carboxylic acids, alcohols and amines, dimerisation of carboxylic acids and low density of ice.

2010

2009-12-31T11:51:00.001+08:00

Happy New Year 2010.

Enjoying my holiday at the moment.

Tar college Open day

2009-12-04T11:43:00.002+08:00

If you want an affordable and quality education, come and find out more at Tar College Open Day.

Yew Shy Gin

2009-11-04T23:42:00.004+08:00

On 2nd November 2009, three Utar students drowned after they were swept away by strong current during an outing to Batu Berangkai Waterfall, Kampar. (my hometown). One of them is Yew Shy Gin.
I used to go to this waterfall when I was a student. Well, this place is quite dangerous especially after it rains as there will be a water gush from the top.

By the way, Shy Gin did her A-level in Tar College.
She was my former student from the class of SN7c.

Rest In Peace

My condolences to her family.

Trial Exam Sept 2009 Paper 1 and 2

2009-10-23T10:15:00.002+08:00

Sorry, for the long silence. Take me some time to look for the soft copy.
Paper 1
Ans for Paper 1
Paper 2
Ans for Paper 2

Trial Exam Sept 2009 Paper 4 and Paper 5

2009-09-12T09:47:00.003+08:00

Trial Paper 4 2009

Marking Scheme Paper 4

Trial Paper 5 2009

Marking Scheme Paper 5

A2 Quick Revision Notes

2009-08-08T22:46:00.001+08:00

Quick revision downloaded from lanther.co.uk

http://www.4shared.com/file/123745687/3d38ace0/A2_notes.html

Video on Nanotechnology

2009-07-16T21:51:00.002+08:00

For those who want to watch again the video on nanotechnology which I had shown in my previous class , please click the link below:

http://www.youtube.com/watch?v=JqMh5NYsRck
http://www.youtube.com/watch?v=8Kg_Lyg_qcM&feature=related

Symbols in marking scheme and guide to writing a good answer

2009-07-04T13:55:00.002+08:00

Symbols used in marking scheme:

/ - means that the responses are alternatives and either answer should receive full credit.
( ) - means that a phrase/word is not essential for the award of the mark, but helps the
examiner to get the sense of the expected answer.
Phrases/words in bold - means that the phrase or the actual word is essential to the answer.
Ecf (error carried forward)- means that a wrong answer given in an earlier part of a question is
used correctly in answer to a later part of the same question.

Guide to writing a good answer

1) Make the meaning of your answer clear to the examiner.
2) Make sure that the answer makes sense.
3) Answers must be in the correct context. In other words, your answers must answer the
questions.
4) Write legibly – the examiner must be able to read your handwriting and the font of your
handwriting should be big enough for them to read easily. Don’t forget, most examiners are
40s or 50s something and many of them are short-sighted.
5) Your words or sentences should have the accurate use of spelling, grammar and punctuation
in order to make the meaning clear.
6) Organise information clearly and coherently.
7) Use specialist vocabulary when appropriate.

Change of ph to f

2009-06-30T22:38:00.003+08:00

CIE has changed the following terms:
New term for sulphate is sulfate
thiosulphate is thiosulfate
sulphite is sulfite
sulphur is sulfur
disulphide to disulfide

Xtreme link

2009-06-27T21:58:00.002+08:00

Change of Xtremepaper link

http://www.planet-master.com/

Many thanks to you, Leong Seek for your information

Important Notice

2009-06-03T15:41:00.002+08:00

To all students taking AS and A2 Examinations:

You are reminded again that you are not allowed to discuss anything about the question papers in the forum or blog within 24 hours after your paper. Don't forget some of the candidates in other parts of the world have not sat for the papers due to the different time zones. Failure to observe this rule means you are in trouble. Good luck

Paper 1 Question and Answer April 2008

2009-05-31T12:35:00.003+08:00

Paper 1 April 2008

Answer Paper 1 April 2008

Think before you use

2009-05-16T21:27:00.002+08:00

Waste decomposition Rate

Styrofoam is not composed
Plastic bottle takes at least 1 million years
Disposable diaper 500 to 600 years
Aluminium tin 200 to 500 years
Leather shoes 40 to 50 years
Newspaper 1 month

Source : Star

Never judge a book by the cover

2009-05-05T23:22:00.004+08:00

I was truly astounded by the talent of Susan Boyle when I watched her singing on the Britain's Got Talent (from Youtube). Her performance received a standing ovation from the live audience and later took the world by storm. The numbers who watched her videos on her audition have climbed to almost 200 millions and the figure is still growing.

What's so special about her? She is a 47 years old lady whose appearance is #@?/... but possess a golden voice. Watch her sing and you would understand what I meant.

http://www.youtube.com/watch?v=9lp0IWv8QZY

Organic A2 Reactions

2009-04-26T14:54:00.005+08:00

AS Practical Guide II

2009-04-15T10:29:00.004+08:00

Guide to Potassium manganate(VII) titration

· For KMnO4 titration, no indicator is added because KMnO4 acts as its own indicator and it would change to pale pink colour at the end point.
· KMnO4 titration is used to determine the concentration of Fe2+ (Iron(II) ions) , H2O2 (hydrogen peroxide) and C2O42- (ethanedioate).
· KMnO4 titrations must be carried out in acidified condition because in neutral or alkaline solution, brown solid MnO2 is formed and as a result it would be difficult to detect the end point.
· To acidify, sulphuric acid is used and not other acids such as hydrochloric acid and nitric acid because the chloride ions or nitrate ions would also be oxidised.
· Most KMnO4 titrations should be carried out at room temperature except titration involving C2O42- which is normally carried out at 70 oC. For ethanediote, any temperature lower than 70 oC could cause the precipitation of MnO2.
· Titration using KMnO4 solution should be carried out slowly. A brown precipitate of MnO2 is formed when KMnO4 is dropped from the burette too quickly.
.
Guide to Iodine-thiosulphate titration
· Starch is used as an indicator in this titration
· The starch solution should not be added at the beginning of the titration. The reason is at this stage, there is a high concentration of iodine and iodine would be adsorbed onto the starch molecule.
· The starch solution should be added towards the end of the titration when the reaction mixture turns pale yellow. (Warning: not too pale as you may overshot the endpoint)
· The starch solution will produce a dark blue colour with iodine.
· At the end point ,the solution turns colourless.
· Be careful, the solution may become blue again due to the atmospheric oxidation of iodide (from potassium iodide). You shouldn’t continue titrating again.

Good luck

2009-03-30T20:45:00.005+08:00

The AS Mock exam started today. Good luck to those who are taking the exam. I would be extremely busy these coming few weeks. First, I am involved in the time-table committee. I can foresee myself sitting for hours to come out with the new timetables for both the students and the teachers for the next Semester. The only good thing is I can prepare my own timetable to my likes.

Second, 'tons' of students' answer scripts waiting for me. I have five classes under my charge. Not only that, with different styles of handwriting: artistic type, doctor type, miniature type, hilly type (the one with the gradient at 45 degree), my eyesight power will double after that.

Third, need to plan for the coming AS practical exam. (Please don't ask me what will be coming out. Even I am 'tortured' or offered a bribe , I won't reveal a single thing.)

Fourth, need to complete my new book before the deadline.

Fifth...sixth...etc. Who said teaching is easy? Salary is low and plenty of work. The only reward is a good karma or maybe a place in the heaven. That would keep me motivated when I think of that.

Important AS equations for Inorganic Chemistry

2009-03-24T21:07:00.005+08:00

Practical P31/32 (Part 2)

2009-03-17T00:20:00.001+08:00

Maximum error

Maximum error is usually marked on the glassware.

Burette
• A pipette has a maximum error of 0.05 cm3 in each measurement.

Calculation of percentage error

Percentage error = (maximum error ÷ quantity measured ) x 100%

Reading burettes
A burette is graduated in divisions every 0.1 cm3.
Using the half-division rule, the estimation is 0.05 cm3.
Burette is recorded to two decimal places with the last figure either ‘0’ or ‘5’.
The maximum error in each measurement = 0.05 cm3.
The overall maximum error in any volume measured always comes from two measurements, so
the overall maximum error = 2 x 0.05 cm3 = 0.1 cm3.
In a titration, a burette will typically deliver about 25 cm3 so the percentage error is small.

Percentage error = (2 × 0.05 ÷25.00) x 100% = 0.4%

The percentage error becomes more significant when burette is used to deliver small volume
For delivery of 2.50 cm3,

Percentage error = (2 × 0.05 ÷ 2.50)× 100% = 4%

Practical 31/32 Learn More (Part 1)

2009-03-10T11:43:00.002+08:00

1. Titres should be within 0.20 cm3.
2. Candidates were expected to produce a single table.
3. The table should include correct headings and units.
4. Burette readings and the volumes added recorded to the nearest 0.05 cm3.
5. Select appropriate scales when plotting a graph
6. In plotting graph, a line should be best-fit straight line or a smooth curve.
7. A graph should contain at least five ponts.
8. Answer for calculation should be given to at least 3 significant figures
9. Thermometer readings and temperature differences expressed to the nearest 0.5 °C,
10. All weighings and the masses of the solid used should be recorded consistently to 1 decimal place or 2 decimal place depending on the sensitivity of the electronic balance. The balance in our lab can measure up to 2 decimal points.
11. To calculate mcT equation, the m is the mass of solution not the mass of solid.
12. +ve sign or –ve sign should be written on the H value.
13. Common error in thermochemistry experiments:
· heat loss/gain with the surroundings
· acid spray from the vigorous reaction
· the use of a thermometer calibrated by 1 °C
14. Suggested improvement for thermochemistry experiments :
· Suitable additional insulation or use of a lid
· Use of a thermometer with closer graduation or use of a digital thermometer

Answers for Trial Paper 2008 Aug

2009-03-01T15:10:00.002+08:00

Answer Paper 1 2008 Aug

Answer Paper 2 2008 Aug

FRIM Trip

2009-03-01T14:03:00.022+08:00

The Science and Maths Society (SMS) organized a trip to FRIM on Sat (28/2/09). I was invited to go along since I am the advisor for the society. This was my second trip to FRIM.

Here we come, leeches and mosquitoes

Assault on the forest

Canopy walk Can’t miss that shot

A view from the canopy

‘Trigonal shape’, that’s what I see. This was related to me by a student from SN9d when she saw this flower.

A view of 'delocalised electrons' in the nature

Safe and sound. Apart from some mosquitos’ bites, no one was victim of the leeches. Maybe our blood is a bit acidic after a strenuous climb or this is not the leech season.

Achieve enlightenment in the forest. I am in the 'nirvana' state. In chemistry, it is equivalent to triple point, a state in which solid , liquid and gas are in equilibrium.

I am the new spiderman

Mock Exam Paper 1 and Paper 2 2008 (Aug)

2009-02-20T21:05:00.003+08:00

Mid-course exam (Trial exam for AS) is coming soon. You can start practising some of the trial exam papers. Answers for the papers will only be published one week later.

Paper 1 2008

Paper 2 2008

Acidosis and alkalosis: good to know more

2009-02-11T22:52:00.001+08:00

Remember, I mentioned two pH related diseases acidosis and alkalosis in our lesson when I taught buffer solutions and explained why it’s important for our body to maintain a fairly constant pH. Here’s more information about these diseases. This information is just for your general knowledge.

A healthy person has a blood pH close to 7.4.
Acidosis is a state of excess acidity in the blood and occurs when blood pH falls below 7.35 Alkalosis is a state of excess alkalinity when blood pH is over 7.45.
When the blood pH falls below 7.0, it is diagnosed as severe acidosis and in severe alkalosis it may rise above 7.5. Acidosis is more common than alkalosis.

pH in our blood or fluids is controlled by three following mechanisms
1. Blood's protein that's acts as a buffer that limits changes in acidity.
2. Lung, which give off carbon dioxide to prevent accumulation of carbonic acid.
3. Kidneys which manufacture hydrogen carbonate ions and retain acids or bases.

Causes of Acidosis:
1. Kidney failure reduces the efficiency to regulate acidity.
2. Starvation produces excessive acid due to metabolism of large amounts of body fat which produce lactic acid
3. Increased protein intake – eat too much meat
4. Ingestion of large amounts of acidic substances eg pickled fruits
5. Diabetes

Causes of Alkalosis:
1. Severe diarrhea may cause excessive loss of basic fluids
2. Loss of carbonic acid because of fast or rapid breathing.
3. Excessive vomiting causing loss of hydrochloric acid (stomach content)
4. Excessive intake of antacids to relieve acid in the stomach.

Chemistry resources

2009-02-06T11:09:00.002+08:00

Recently, some students asked me to recommend them some good chemistry websites. For me, I usually look at these two websites.

LearnNet

Chemguide

Please take a look at these sites .
Do you find them useful? Please comment.

Dare to take this challenge

2009-02-02T13:54:00.003+08:00

Take this challenge and download the past year questions for the Chemistry Olympiad UK. Give yourself a Chemistry test. Reminder: Look at the answers only after you have tried the questions.
Chemistry Olympiad 2008 Examination

Answer

Important AS Definitions Part II

2009-02-02T00:08:00.006+08:00

Activation energy is the minimum energy required by colliding particles to start off a reaction.

A catalyst is a substance which changes the rate of a chemical reaction without itself undergoing any chemical change at the end of the reaction.

Homogenous catalyst is a catalyst in which the physical state is in the same phase as the reactants.

Heterogenous catalyst is a catalyst in which the physical state is in the different phase as the reactants.

Increase the concentration of reactants will increase the rate since there will be more molecules per unit volume resulting in an increase in the collision frequency between the reactants. This leads to higher number of effective collisions.

Increase in the temperature will increase the rate since at higher temperature the particles gain more kinetic energy resulting an increase in collision frequency at higher temperature. In addition, more molecules have kinetic energy greater than or equal to the activation energy. Consequently, the number of effective collisions increases.

A catalyst operates by providing an alternative route of lower activation energy for the reaction.

Geometric isomers are compounds with different spatial arrangement due to the restriction in the rotation about the double bond in an alkene. In geometric isomers, two different groups at each end of the double bond can either be on the same side (cis) or on opposite sides (trans)

Optical isomers are mirror images that have the same geometric and structural formula, but cannot be superimposed onto one another.

Cracking is a process to break long alkane into a shorter alkane and an alkene. Hydrogen may also be produced. Thermal cracking requires temperature between 400°C to 900°C and high pressure whereas catalytic cracking requires a zeolite catalyst and a temperature of about 450°C. The purpose of cracking is to form extra gasoline and to produce alkenes with higher commercial value

Homolytic fission is the breaking a covalent bond in which one electron goes to each atom to form free radicals.

Heterolytic fission is the breaking a covalent bond in which one atom takes both electrons forming negative and positive ions.

A free radical is a highly reactive atom or molecule with an unpaired electron.

An electrophile is an electron-deficient species that can form a new covalent bond by accepting an electron pair provided by the carbon compound. Example : positive ion such as hydrogen ion or nitronium ion and a polar molecule with a d+ charge

A nucleophile is an electron-rich species with a lone pair of electrons that can form a new covalent bond by donating a pair of electrons to the electron deficient carbon atom. Example : negative ions with at least a lone pair.

Red, red....almost everyone is red

2009-01-26T20:57:00.006+08:00

Class SN9p.. must act cute, you know

SN9deg..........wonder who's the 'old' student on the right hand corner in the first row?

Even the lecturers are not spared from red

SN9deg classes... even Indian students joined in the fun

SN 9pq .........very sporting ....is it the hand sign for the bull horn?

Year of the OX, ma.

Download past year papers for any exams

2009-01-23T10:26:00.006+08:00

I have discovered two websites that you can download past year papers for a number of international examinations such as Cambridge , AQA, TOEFL , SAT, ACCA etc...

Xtreme
Black

Gong Xi Fa Chai

Disclaimer:
I would not be responsible for the content of it.

Organic AS Reactions (Spider Diagram)

2009-01-20T11:21:00.009+08:00

Spider diagram is one of the methods used in mind mapping. Using spider diagram to study the organic reactions is an effective method to remember reactions. You can also see the links between the functional groups. You can magnify it by clicking the diagram.

My dear students, don't forget to wear red or pink this coming Friday 23/1/09 in conjunction with the Chinese New Year festival. Hopefully, it will bring us luck, success and happiness.

My new Chemistry workbooks

2009-01-14T23:27:00.004+08:00

Last year, I wrote some SPM workbooks. It was definitely not an easy job. I had to toil away countless night to finish the books. Finally, the books are ready and they are available in the bookstores now.

Important AS definitions (Part I)

2009-01-07T23:15:00.007+08:00

Atomic number or proton number is the total number of protons in the nucleus of an atom.

Mass Number or nucleon number is the total number of protons and neutrons in the nucleus of an atom.

Isotopes are atoms with the same number of protons but different numbers of neutrons.

The relative isotopic mass is the mass of one isotope of an element compared to 1/12 the mass of the 12C isotope.

The relative atomic mass is the average mass of one atom compared to 1/12 the mass of the 12C isotope.

First Ionisation Energy is the energy required to remove one mole of electrons from 1 mole of gaseous atoms to produce 1 mole of gaseous unipositive ions.

First Electron Affinity is the energy liberated when one electron is added to each atom in 1 mole of gaseous atoms to form 1 mole of gaseous ions with a uninegative charge.

Electronegativity is the power of an atom to attract bonding electrons.

Oxidation is loss of electrons. Remember OIL RIG
Reduction is gain of electrons.

Oxidising agent is a substance which removes electrons from another substance and itself is reduced.

Reducing agent is a substance which gives electrons to another substance and itself is oxidised.

Disproportionation is simultaneous oxidation and reduction of one species in a chemical reaction.

Metallic bond is the electrostatic attractions between the positive ions and a 'sea' of delocalised valence electrons surrouding the positive ions.

Ionic bond is the attraction between the oppositely charged ions formed by transfer of one or more electrons from one atom to another.

Covalent bond is the attraction of the nuclei for the shared pair of electrons between two atoms.

Sigma bond is the covalent bond formed by ‘head on’ overlap of atomic orbitals.

Pi Bond is the covalent bond formed by sideways overlap of atomic orbitals.

Valence Shell Electron Pair Repulsion (VSEPR) Theory states that the shape of a molecule is determined by the repulsion between the electron pairs in the valence shell. According to the VSEPR , the electron pairs will arrange themselves so as to be as far apart as possible.

Polarising power is the ability of a positive ion to attract electrons away from a negative ion.

Dipole-Dipole Forces are intermolecular attractions between molecules which are permanently polarised.

Hydrogen Bond is the electrostatic attraction between a hydrogen atom which is bonded to a very electronegative atom and an electronegative atom of a neighbouring molecule.

Van Der Waals Forces are intermolecular forces of attraction which arise from temporary
dipoles in molecules.

Standard Enthalpy Of Formation is the enthalpy change when 1 mole of the substances is formed from its elements at their natural states at 298K and 1 atm pressure.

Standard Enthalpy Of Combustion is the enthalpy change when 1 mole of an element or compound is completely burned in oxygen at 298K and 1 atm pressure.

Standard Enthalpy Of Neutralisation is the enthalpy change when 1 mole of water is formed from the reaction between an acid and a base at 298K and 1 atm pressure.

Hess’s Law states that the total energy change resulting from a chemical reaction is dependant only on the initial and final states of the reactants and is independent of the reaction route.

Bond energy is the energy required to break 1 mole of bonds from gaseous molecules into gaseous atoms.

Reference : Stephen Oakes

Economy rice in TAR college canteen

2009-01-04T16:08:00.005+08:00

How much does it cost for a plate of rice with 4 dishes? You won't believe it. RM2.20. I repeat RM2.20. Yummy...that's my lunch.

Grade Thresholds for Chemistry A level Cambridge

2008-11-24T18:51:00.004+08:00

The grade thresholds or minimum marks for Chemistry grades vary slightly from exam to exam. Attached herewith are two tables showing the minimum marks to achieve grades A, B, C, D and E for Jun 2007 and Nov 2007 A level Chemistry 9701 examinations respectively.

A level links

2008-11-16T21:14:00.006+08:00

The following links are useful especially when you are doing A level. You can find some past year questions and marking schemes from these sites.

CIE

OCR

EDEXCEL