header image

Archive for Chemistry NSS

(A)  Nowadays, most people would electronic devices for measurements –  due to its sensitivity, speed (faster), and “accuracy”.

This is no exception for measuring temperature.      Digital thermometers are easy to use without calibration, etc.    Quick to read is the most convenient advantage.

(B)   Is it good for CHEMISTRY EXPTS??   –   Yes & No !!

Yes, it is good for quick check.

No –  due to the material nature of the D-thermometer;  it can’t be used in ALL expts –  especially those involve “heating”,  “boiling”,  “organic”,  “acids / alkalis with high concentration”,   “OA/RA”, etc…

(C)    WHY ?   –  check what’s the D-thermometer made up of.

–  The temperature probe is metal and the attached electronic device (the reading pad) are also electrical in nature.      Most metals will have reaction with acids/alkalis/…many diff chemicals …  and are harmful to the electronic devices.

–    For boiling / heating,  though some D-thermometers can read up to 150 deg C;  the electronic devices can’t withstand reactions that may occur with the vapour bubbling into the device.       A very short measurement is ok (in matter of seconds), but not for a prolonged experiment.

(D)   So, traditional thermometers using “alcohol / mercury” are still standard apparatus for your experiments!     

under: apparatus_setups, Chemistry NSS, HKDSE, Metals, Practical Chem, Study Methods_Skills
Tags: , , ,

F.4 students should know that many crystals (esp ionic compounds) could have “water of crystallization” inside their “dry solid crystals”.    The most famous and commonly  used is copper(II) sulphate-5-water.    It is used because it could easily form BIG beautiful BLUE crystal and it is quite soluble in water.

   {** Note that the “anhydrous CuSO4″ (no water) is WHITE powder!}

However, some ionic cpds have quite special behaviour in relation to the formation of such crystals.   Calcium sulphate is one!     This is famous for making the mould on broken arms / legs to protect them while bones are joining or growing back to normal.      The work is easily done by mixing it with water and paste them in a mould!

YET, the anhydrous CaSO4(s) can’t form crystals (or used to make the mould as above).    Though it could have 2 hydrated crystals:   one is “half-water” and the other “2-water”!

In order  to make the “mould” (plaster) for broken leg, you must use the hydrated forms (and NOT from just Ca2+(aq) & SO4^2-(aq)!!!        WHY?       Luckily, you WILL NOT be examined in this aspect because that involves difficult Physical Principles which is out of your syllabus.       A simple reason is that when we make salt from “ppt” rx,  that may NOT include the water.      Other methods must be used to make the hydrated salt!

That is why we still need to learn some more things in Chp 16 (bk 2A) after the Exam……   about “different methods to prepare ionic compounds”  … and …  of course, why!?     :) :) :)

under: Chemistry NSS, F4 Chem, HKDSE, Reactions, Salt preparation
Tags: ,

Bubbling27/3 Test will be 1 period.

Topic majoring – Chp. 12 {mole & all sorts of calculation — formula, equation [reacting masses, limiting reagent, yield, % yield,..],  % composition and etc.. }   and   Chp. 13  {rust, rusting, methods of prevention, methods of investigaion, … other metals’ corrosion and  factors affecting them,  advantage(?) of rust? … }

Qn Types — similar to all DSE papers –  will include MC, Qns,  Essays.

***  Tips ***:

1. Don’t forget that most calculations involve (a) the mole [just a number of particles, check the types (ion / molecule / atom)];    (b) UNITS for mass (g),  volume of gases (dm3 / cm3),  volume and concentration of solutions (MxVx = no. of moles of X).    {Unit for molarity = mole per dm3}.

2.  In answering some Qns,  “DIAGRAMS” help — e.g.  the EXPT 13.2 about “investigation” of rusting using “rust indicator”,  you can’t describe or explain accurately what happens without refering to the diagrams of the experimental set-up, … with different colour patches around the various location of rusting or formation of OH- ions.

3.   In answering essay Qns –  remember to use “paragraphs” instead of numbering your points.    One paragraph for one major point.   e.g./   2 necessary factors control rusting — so you need to describe the effect of oxygen and water separately or with the help of a set-up of 3 test-tubes, … about HOW the issue is investigated.

Good Luck….   Don’t forget to bring your calculator!!!

under: F4 Chem, HKDSE, Metals, Mole calculation, Reactions, Redox Chemistry, Study Methods_Skills
Tags: , , , , ,

Rusting is a common phenomenon in our daily life as iron objects are around Seawater_Corrus everywhere — your keys, gates, doors, chairs, tables, food can. etc…

For chemistry, it is a rather complicated process as ”rusting” refers to reaction of Fe with different substances in the air / surrounding (e.g. sea, river, or anything in contact with them,..).   The more common substances considered are 1. oxygen,   2. water,   3. ions present,   4. acids,   5. alkalis,   5.  metals of different reactivity, etc…

4 days after the missing MH370 airplane (9th March,2014 travelling from Malaysia to Beijing) – though with International efforts, nothing was found or concrete proof of any possible of the missing.    ONE deduction is a report from the ” 2013 Federal Aviation Authority (FAA) Airworthiness Directive for the 777 which spotted a weakness in the plane”.      “There had been a report of “cracking in the fuselage skin underneath the satellite communication (satcom) antenna adapter”.

According to such data, rusting could be a cause of the missing plane which had occurred in the past when metal fatigue caused disintegration of the plane in the air in matter of seconds.

So, rusting and the prevention of it is a very important science-tech research.    There are many “rust doctors” in the www (try search that online).

And, most important of all, you have to learn this topic in details in Bk 1C, Chapter 13.   :):):)

>> Basic Note –  the intial rusting includes TWO aspects:

(1) the iron oxidized –  from Fe to Fe2+ (losing 2 e’s)… to Fe3+ (lose one more e’).     Colour detected:  pale green surrouding … then yellow or brown colour (Fe3+ ions).      However, due to the presence of different anions around and their concentration, the colour of the rust observed will be very different with varying degree of brown stains (SEE diagram above).

(2) the anion & crystal formation — with the essential conditions (presence of O2 and H2O), the reaction must be learnt is:

4e’ + O2 + 2 H2O  —>  4 OH-(aq)   ….   This is why the Fe(OH)3 is the initial product from the rusting.   As time passes, the hydroxide could change to “iron(III) oxide” and then “hydrated iron(III) oxide”.   That is, the common “brown rust” is actually  “Fe2O3.nH2O”.    The colour of the rust depends on the no. of moles of water attached, which in turns depends on the surrouding factors (e.g. air humidity).

So, have fun!   –>  try to calculate how much iron is lost if 20 kg of iron object has 5% rusted.     And, of course, how to prevent its corrosion is another important aspect of learning.



under: Careers, Electrochemistry, F3 Chem, F4 Chem, HKDSE, Mole calculation, QA Qualitative Analysis, Reaction, Redox Chemistry
Tags: , , , , ,

BalancingEqn How-to-read_mindFuture?  

Yes — what we are studying (no matter what subjects / topics you like or not) ARE FOR OUR FUTURE.

University Study? — also YES, FREE for all …  !!!

For F.3 and above::  if you want to get a taste / prepare for “University Studies”, one very good site is www.futurelearn.com

All you have to do is to register at the site with your email.    Then, you can choose a lot of courses — depending on your interests and time.   Some courses have no pre-requisite (prior knowledge requirement) WHILE some may need an advanced study background.     ALL courses are supported by various famous universities in the West!

If you want courses in Chinese, you can go to our Open U –  www.ouhk.edu.hk   They also have FREE courses now!     WHY not give yourself a try — to see what would you need to prepare for your future FURTHER STUDIES!

Some examples for you :

“Preparing for Uni”  (good for ALL F.3 to F.6) — different things that you SHOULD KNOW about IF you really want to study for Universities.

“English for university studies”

“Kitchen Chemistry”


…  many more!   Have fun and gain your academic calibre. :):):)

under: Careers, F3 Chem, HKDSE, How Science Work, STSE, Study Methods_Skills
Tags: , , , , ,

F.4 DSE-Chm 2nd Term …

Posted by: | February 2, 2014 | No Comment |

ChemDef-ClassifySUbst1.  Reminder about 1st Term Exam ==  Topics include:  Bk 1A (Earth Resources: air, rocks, sea).   Bk 1B: Atomic Structure,  Bonding-Structure–> Properties (both physical & chemical).     Bk 1C:  Metals – extraction, reactions & compounds’ properties  (reduction of metal oxides [diff ways], reactivity series & displacement rx,   carbonate decomposition to oxides,    metal oxides + acid = neutralization [gives "salt + water" ONLY]), …  other general properties of metals:  esp.  group I (v. reactive, alkali), II  (reactive, earth-alkaline metals),  ..  transition metals (coloured ions: eg/  iron(II, III),  copper(II), … ),  etc…

**>>   ALL the above topics esp. Bk 1B (B,S–>P) is the most important for explaining all kinds of reactions and properties — WILL be used again and again in 2nd Term & later topics!!!   :)

2.   Term 2 topics  {to FINAL Exam} == format of Qns will be similar to 1st Term Exam… [MC, Qns & Essay]

2a.) cont’d on bk 1C:  Chemical calculations {about mole, % of elements in cpds, various formulas,  reacting masses & yield of products, etc… };   metal corrosion & protection.

2b.)  Bk 2A:   Acids, Bases (alkalis are soluble bases *),  Salts (ionic cpds) & Neutralisation, etc..

* Common side-bench reagents are solutions of A/B/S used for QA {see (2c)}, common alkalis are NaOH, aqueous ammonia and lime water.   3 common acids = dil. HCl, H2SO4, HNO3. ….

2c.)   SBA trials == some important example experiments,  skills, theory, apparatus & special set-ups, QA of inorganic cpds, quantitative analysis of cpds {linked to Bk 1B calculations},  design, safety / pre-cautions,  …   :)

Real SBAs are all practical related.     Will be assessed in lesson time or during supplementary lessons.   Practices will be given, but in group-form.      SBA for QA & VA (titrations in acid-base) will be assessed individually, other EXPTs in group form (but still have to complete worksheets on your OWN).

ALL SBA assessments will contribute to 20% of your Public Exam (DSE) marks.

2d.)   Exam skills –  for those who had not obtained satisfactory results in 1st Exam are due to the following reasons:    (i)  lack of practices on Q & A;    (ii)  careless in read & write [e.g.  names, formulas, equations, spelling, … ;     (iii)   misconcepts / not able to work logically with all basic stuff (classification of substances, reactions & properties — most linked to BS–>P in Bk 1B. )

In order to keep you alert of the above,  you need to hand in 2 things after holiday:  (1) at least ONE essay Qn.        (2)  a supplmentary exercise bought for your daily routine practices — in order to get used to Qn types and read & write carefully.     :):):)





under: Chemistry NSS, F4 Chem, HKDSE, Practical Chem, QA Qualitative Analysis, Reactions, Safety, SBA, Study Methods_Skills, VA
Tags: , , , ,

Chemistry & Chinese New Year …

Posted by: | February 2, 2014 | No Comment |

China_ZodiacyearspageHappy Chinese New Year (CNY, Lunar Calendar) …or .. Year of the Horse.

1.   What’re related to Chemistry?   –  as said,  you don’t need a book to revise Chemistry.     Because chemistry is all around us — even inside us as most of our body are made up of C, H, O, N, … and bits of P, S, and metals (e.g. Ca in our bones,  Fe in our blood [makes it red due to Haemoglobin], Na+ & K+ ions in our blood [blood pressure control], etc… ).

2.   So, what do you do in Chinese New Year?    Lots of food, drinks, fun, …. and their chemistry!  

2a.)   Explosives only ?  –   First must be the expected “explosive plays” –  the fireworks, firecrackers, pop-ups, … and all sorts of party things.       Most fireworks are explosives and should be handled with great care.      Sad news already appeared in news when people played without safety precautions.       Apart from that,  air pollution is another undesirable results of playing such.    WHY?     This leads to the need for understanding “what explosion is”.

Actually, explosions could be brought about by TWO methods:   (1) chemical reactions that gives out a lot of gases from solid mixtures when burnt.    (2)  by sudden change of pressure –  pressure change, … could be simply done by piercing through a balloon.

(2) is easily explained.    For (1), you need to know the details of the reactions inside.   Two of such reactions are from the potassium compounds (nitrate and chlorate):    (i) 2 KNO3 (s)  —>   K2O (s)  +  N2 (g)  +  2.5 O2  (g)      and    (ii)    2 KClO3 (s)  —>   2 KCl(s)  +  3  O2(g) …..  BOTH give larger amount of gases from solid which create sudden change of volume (also due to heat evolved) and hence sudden “BANG”!!!        Also, that involves some reaction types: “decomposition” (breakdown); ”redox reactions” (oxidation & reduction, by HEAT!)

Another results of fireworks is “visual” colours —   which you could easily checked by burning group I compounds (LiCl,  NaCl, KCl, ….  ) –  giving red, yellow, purple, …   colours.     This is also a famous tests for such compounds, by “Flame Test” (not a reaction).       And, the study of such originates from a famous scientist  “Bunsen” –  YES,  the scientist that modified the “Bunsen Burner”.

2b.)    How about other party stuff?   –   some “explosions” do not contain explosives.    That works by “air pressure”.      Another one is by the unstable nature of “phosphorus”, which is also an element in our matches — when strike or rub on the ground, it “explodes”!       Furthermore, there are colorful “plastic sprays” — actually a polymer that turns the molecules into chains of it when it meets air.      Also, there are fluorescent lights — containing chemicals that react to give such “coloured lights” when the inside tube breaks and the chemicals mix to react.

2c.)   FOOD ?  –  of course, all food are some kind of chemicals.     What we specially eat in CNY are “fried snacks”,  “cakes of diff styles”, etc …

2d.)   Red-packs ?  –   related to Chem?    Yes!     While most red-packs are in paper form, some are plastic.     Even the money could be plastic !       So, plastic is surely a chemical (called polymer) that is made from simple small molecules.      BUT, remember that most green activists consider plastic as NOT environmental.      What do you think?     Will you reject plastic money?   :):)

2e.) ??? ….   Surely, you can name MANY more in your holiday visits and fun meetings with your friends and relatives.

Have fun and learn something (by way of thinking & association) in your CNY  :) :) :)


under: Elements, F3 Chem, QA Qualitative Analysis, Reactions, Redox Chemistry, Safety, Seasonal Chemistry, Study Methods_Skills
Tags: , , ,

The aims of the “F.3 to F.4 Summer Chemical Calculation Ex” are :

1.  to assess some examination skills — e.g. follow instructions, some basic classification, calculations (formula mass), some basic search (atomic masses, states of compounds) and high-order thinking skills (Q5).

2.  to revise basic classification of elements (metal vs. non-metals) and compounds (ionic vs. covalent)

3.  to learn about relation between different characteristics or properties


General performance:– generally fair with some very good cases and a few with missing items.

– The range is large showing the need of more practices and “deeper-understanding” of the given data and examples.     Carelessness is another common problem (e.g. weak in checking accuracy in simple “add-up” calculation).


Answer to further practice:

8. MgSO4 :  ionic (Mg2+ ion,  sulphate ion);   f.m. =24 +32.1 + 4(16) = 120.1  ,   (s)

9.  Na3PO4: ionic (Na+ ion, phosphate ion);  f.m. = 3(23) + 31 + 4(16) = 141  ,   (s)

10. NO2 : covalent (molecule),   f.m. = 14 + 2(16) = 46 ,  (g) – an air pollutant

11.  H2O2: covalent (molecule), f.m. = 2(1) + 2(16) = 34,  (l) — an oxidizing agent that can be bought from drug-stores.

:) :) :)  Check the rule again :  ALL ionic compounds are solid at r.t.p.  WHILE   covalent molecular compounds could be s / l / g depending on the molecular mass as the intermolecular force is proportional to the relative masses.

under: F4 Chem, F5 Chem, Periodic Table, Study Methods_Skills
Tags: , , ,

1.   Practical Chemistry is difficult to study and revise.   And, this is particular for DSE as there is NOT enough time for more Lab Lessons / experiments.     So, WHAT SHOULD YOU DO in order to get familiar with the “Practical Qns” in the DSE Exam??

    Don’t panic!   There are lots of references and tools to help … and … easily accessed online!    Of course, you may use the “Activity Books” (of your textbook) as reference.   BUT they are not easy to study and revise.     So, you must keep NOTES of your OWN while working along with others in the Experimental  Lessons.      

2.  Know about the basic elements in “Practical Chemistry” — (1)  SAFETY: General Lab Rules,  Specific rules for different branches of chem,  Risk and Risk-Assessment.     (2)  Lab Apparatus — there are lots of diff types (from conventional to micro-scale).     (3)  Practical steps / Procedures –  some are typical (e.g.  QA, VA, …Org Prep, … ..)  (4)   Results / Observatrions & Explanations – sp. terms, deduction, verification…  (5)   Expt Design for particular purposes / aims –  e.g.  deduce the reactivity of a M.

3.   Tools and References online –  there are lots of them.      Below are some general ones:

http://www.chem-ilp.net/labTechniques/TitrationAnimation.htm    ==  has several parts.    Mostly match those in parts (1) to (5) above!       ** Best of all is that there are some “Animations” to show the actual process of some typical exp’ts, e.g.   VA / titration. 

http://www.rsc.org/learn-chemistry/resource/listing?searchtext=Classic+Chemistry+Experiments     ==   has Classical Expts (common for ALL exams) categorized by — age / level (F.1 to F.6),   type,  with videos, handouts, ….

**  ….  There are many out there –  just search with Google!     Bookmark those useful for your OWN revision!!!     Of course, there are SOME special reference titled “Experimental Chem”,  “Practical Chem”, etc… in the Libraries     :) :) :)

under: Animations, Chemistry NSS, F3 Chem, HKDSE, Practical Chem, Safety, Scientic Method, VA, Videos
Tags: , , , ,

Prepare for new Sch-Year :)

Posted by: | August 20, 2013 | No Comment |

Just 2 weeks before summer ends, AND,… new School Year (2013-14) begin.    This is another SPECIAL YEAR (2013) — as there are some new things for EACH FORM. 

F.2 to F.3 — the first batch with ONLY 4 classes.

F.3 to F.4 – DSE-2016 has changes.   And, there are just 2 years of DSE and JUPAS results for reference.    They are not strong rules as things continue to change in the NEW 334-system (only end by 2016).

F.4 to F.5 & F.5 to F.6 — of course, you should pay MUCH attention to your DSE Exam and SBA.    And, for some subjects, there are immediate changes in the DSE (2014, 2015).     Hope you REALLY have used your SUMMER TIME wisely!  :) :)  

For Chemistry — there is NOT much change.   Though there are some minor changes (7 topics only), so the overall time saved actually is NOT much.   Good news is that the SBA remain the same without compulsory investigations.   

There is no more “Comb-Science”.   Everyone will take Science as the FULL subject.   BUT, you can use the CS-books as they are the SAME as the MAJOR Basic Chemistry Parts (bk 1A to bk 3B).    Such referneces are still in the Library — use them wisely!    

***  Tips for Good Exam results *** – just (1) revise with the total no. of topics in mind — as Chem Topics are ALL related (vs. TIME).     (2) try at least 5 years’ past papers  (best be 10)!     (3)  ASK if any problem.   (4)  If time is really tight, check if the MOST important principle topics are revised!    (5) Check for some TOOLS to help your revision – not just rote memory.   e.g./  animations for PRACTICAL parts…   (see NEXT Blog).    (6)  Youtube also have many good revision topics!   

Best Wishes to your New Year Targets!    :) :) :)

under: Chemistry NSS, F3 Chem, F4 Chem, F5 Chem, HKDSE, Practical Chem, Study Methods_Skills, Videos
Tags: , , , , ,

Older Posts »