21 Feb, 04:05AM in sunny Singapore!

BedokFunland JC's A Level H2 Chemistry Qns (Part 2)

Subscribe to BedokFunland JC's A Level H2 Chemistry Qns (Part 2) 992 posts

Please Login or Signup to reply.
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    10,471 posts since May '05
    • In the 1st experiment, what's cool is that the slug fragmented into 2 equally lethal parts *in mid air* before reaching the target, *both* fragments subsequently penetrating the solid metal armor. In the 2nd experiment, what's cool is that upon hitting the solid metal armor, the slug fragmented into many dozens of molten metal shrapnel fragments, radiating spectacularly sideways (imagine if you were standing just beside where the slug hit), as illustrated by the explosions of the 2 filled soft drink bottles to the sides of the metal armor. Chemistry note : a "carbide" is a compound composed of carbon and a more electropositive element (eg. a metal), and isn't a metal per se, as erroneously stated by the YouTube video host. But let's not fault him, and appreciate his video making and sharing efforts instead. He can leave the Chemistry checks to us... makes you appreciate taking H2 Chemistry more and more everyday, don't it? ;Þ


      Edited by UltimaOnline 02 Jan `17, 3:45AM
    • [Medical Science] - An adenovirus causes obesity in humans and animals


      In the visitors comment below the article, Mindbreaker posted :

      There is too much money in treating chronic conditions. DARPA funded something that can cure all sorts of viruses, but it just disappeared into a black hole never to be seen again. It was called DRACO (Double-stranded RNA Activated Caspase Oligomerizer) and it killed every virus thrown at it.

      This adenovirus causing obesity is not a new revelation. This has been known for years. The first tip-off was that the obesity epidemic acted exactly like a spreading infection through the population. It followed the same geographic patterns. There is almost nothing else it could have been. There are at least 3 adeoviruses that likely cause or at least contribute to obesity, adenoviruses #5, #36, and #37. And possible several more that are more difficult to study. And Firmicutes have also been implicated.

      It is not just obesity, lots of conditions have been linked to infections. The Wikipedia page that listed them was removed. Fact is, the big pharmaceutical companies have lost billions when it is discovered that a bacteria causes something they were earning billions to treat. Perhaps you have heard that they discovered that ulcers are caused by a bacteria? That woke up the pharmaceutical industry. That hurt them. Then it was discovered that a bacteria causes lower back pain and damage. After that, amazingly it became very hard to get antibiotics. Doctors are getting in trouble for prescribing antibiotics for anything that is not proven to be caused by bacteria...they don't want another accidental cure. They say it is to stop the development of supper bugs. But most of the antibiotics used in the US are used on millions and millions of animals everyday...just to make them grow faster...nothing to do with illness. If there are super bugs being born that is likely where they are coming from. The reality is that they can develop new antibiotics very easily. They avoid it. And there were things that killed bacteria before antibiotics that still work on "super bugs", but you never hear about them.

      The evidence for staph bacteria causing diabetes has not been followed up even though the evidence was more than trivial. They gave staph infections to rabbits and they got diabetes. Coincidence? I doubt it. You can have a staph infection and not even know it. Infections can be invisible.

      Most of the chronic conditions we have are because of these infections be they viral, bacterial, fungus or other. Did you know human cytomegalovirus (HCMG) causes more cases of serious birth defects than Down Syndrome, Fetal Alcohol Syndrome, Spina Bifida, or HIV/AIDS? But I bet you have never heard of it. Why? Because the thing is everywhere. They can't isolate the infected from the uninfected. And they don't bother to create a cure because it is likely the condition slowly kills you...very slowly, that means lots of symptoms to treat for decades. 60%-70% of us are infected, and the older you are the more likely that someone will infect you. Hard to separate the affects of old age from the effects of infections the immune system is just loosing the long battle against. HCMG is a herpes virus. They never get eliminated, they just do damage for decades (without vigorous treatment). And it is spreading fast. Rates have gone up dramatically since the 1970s. I don't think it is an accident that Americans' life expectancy is starting to move downward despite really impressive progress against cancer. Doctors know many cancers are caused by viruses. They call them oncoviruses. They currently acknowledge that they cause 17.8% of human cancers, but it probably is a far larger proportion. Perhaps 50% or more. I find it interesting that the success they have had recently is due to revving up the immune system. Coincidence that that might be a way to fight tough viruses in your body? I don't think so.

      We are all carrying around dozens of infections. If they do not kill quickly, or produce clear identifiable symptoms, doctors say it is "normal". Well, it isn't. Before people could go all over the planet and things were not spread all over, the average person almost certainly had far fewer infections cruising around in their bodies. I bet you do not even know that sweets do not cause cavities; that it is a bacteria, just one of over 100 types of bacteria in your mouth. And there are tribes who don't have this highly contagious infection. No, it is not "normal" it is an infection that has gone everywhere and infected almost everyone on the planet, but was probably very rare and limited to one small area in the past. But with nothing done about it...its everywhere. Believe it or not, but they have a cure. But so many ridiculous barriers were erected that it never got enough funding to survive the tests. The FDA asked them to do ridiculous things like test only on adults with no teeth. I don't know about you, but if I was down to 2 or 3 teeth I would not give up those last few. Who then would have no teeth? And did you know that tooth problems are linked with heart disease. Those plaques in your arteries are just like that bacterial plaque on your teeth. The bacteria that causes dental carries is a different one than the one that causes gum disease, rots your jaw and infects your arteries and your pancreas.

      The biggest impediment to recognizing the cause of disease in our day is the "weakness" stigma. The, "well just control yourself", "use good hygiene"...sort of blame stuff. I think virtually all mental illnesses are caused by infections including anxiety and depression. And much of the rest caused by heavy metals, other toxins and nutritional deficiencies. I believe genetics has been greatly exaggerated...just one more "weakness" story to make others feel superior and invulnerable.

      In the Southern US people got the reputation for being lazy. But it was hookworm. Just sucks the energy out of you. Fortunately people finally saw the light and made the changes necessary to infrastructure and cured the infections, and that lousy thing is gone. Still in Africa and other places infecting half a billion people. People who no doubt are still looked down on as lazy, and worthless.

      It is entertaining to think it is a conspiracy, that pharmaceutical companies prefer treating chronic people to curing people and obstruct the development of cures. But it probably is not. It is probably just a defect with the way medicine is developed in the US, the economics of it. Turf protection, and barriers to market entry do exist, how much that has played into policy and harmed the pubic is an open question.

    • Originally posted by cienhan:

      hello ultimaonline,


      when heated with carbon, azurite produces copper, carbon dioxide and steam as the only products. write a balanced eqn for the reaction of azurite with hot carbon. azurite is Cu3(OH)2(CO3)2


      thank you in advance.

      Decomposition :

      OH-, OH- [proton transfer] O 2-, H2O.

      CO3 2-, CO3 2- [elimination] O 2-, CO2, O 2-, CO2.

      Cu2+, Cu2+, Cu2+, O 2-, O 2-, O 2- as ionic solid + CO2, CO2, H2O as molecular gases.

      Redox :

      Cu2+, Cu2+, Cu2+, O 2-, O 2-, O 2- + 1.5 C [electron transfer + covalent bond formation] Cu, Cu, Cu as metallic solid + 1.5 CO2 as molecular gas.

      Hence overall balanced equation is :

      1 Cu3(OH)2(CO3)2 (s) + 1.5 C (s) ----> 3 Cu (s) + 3.5 CO2 (g) + 1 H2O (g)

      This is the BedokFunland JC way, seeing clearly the mechanisms involved (proton transfer, elimination, electron transfer, covalent bond formation) in the type of reactions occurring (decomposition, redox) and recognizing the underlying thermodynamic motivation (positive entropy change) for it.

      Edited by UltimaOnline 06 Jan `17, 5:05PM
    • image

    • image

    • image

    • image

    • image

    • To all JC students, here's a BedokFunland JC teaser for your entertainment :

      The N atom in both amines and amides have the same no. of lone pairs and bond pairs. Yet the hybridization of the N atom in both types of molecules are different. See if you can figure out why before googling out the answer.

    • If you're burning anything or have your stove on, always make sure the windows are open. I could explain to you the underlying chemistry involved (ie. as carbon is a relatively non-electronegative element, a uninegative formal charge on the sp hybridized C atom in the major resonance contributor of carbon monoxide results in an unusually strong Lewis base, which thus behaves as a competitive inhibitor ligand to nucleophilically attack the electrophilic Lewis acidic Fe atom in the haemoglobin molecule in red blood cells generating the kinetically and thermodynamically stable carboxyhaemoglobin with a much larger Kstab value than oxyhaemoglobin... etc) but just be sure you remind your family and friends to be mindful.


    • Both medical doctors (Dr Daniel Neides and Dr Zubin Damania) may furiously disagree with each other, but I agree with both of them, ie. they both make valid points. As with almost everything in life, it's not a simple case of right or wrong, black or white. It's more a matter of pros and cons, risks versus benefits, and making informed choices (philosophical musing : or can there really be such a thing?).

      Dr Daniel Neides : http://www.cleveland.com/lyndhurst-south-euclid/index.ssf/2017/01/make_2017_the_year_to_avoid_to.html

      Dr Zubin Damani : https://www.facebook.com/ZDoggMD/videos/10154799367477095/

      Btw, Dr Zubin Damania hates Dr Mehmet Oz



      Edited by UltimaOnline 19 Feb `17, 6:53AM
    • Originally posted by hoay:

      Activation energy is not affected by increasing temperature.It is the catalyst which decreases the Ea but when we say increasing temperature increases the proportion of molecule having energy greater or equal to the activation energyit seems that Ea is linked to temprature. Please explain. 

      Say you have 10 employees, but as a stingy CEO, you underpay them with unethically low wages. One night after work, the 10 of them try to enter a high-class nightclub, but only 2 of them have enough money to afford the $100 entrance fees and enter, while the remaining poorer 8 of them can only wait pitifully outside the club.

      Some years later, after having a near-death experience, your perspectives as a CEO have changed, and now you decide to pay all your 10 employees generously. Now all of them have enough money to pay the $100 entrance fees to enter the nightclub. Happy ending.

      Originally posted by hoay:

      It means that if we increase the temperature the the demand or the parameter for Ea is increased also ....but i am unable to deduce catalyst here...the CEO or salary?


      Catalyst isn't a factor in this story. This story is about increasing their pay so they've enough money to enter, ie. more employees now have enough money (energy) to afford the entrance fee (activation energy).

      For a catalyst story, it would be a near-death experience for the nightclub boss, causing him to decide to lower the entrance fee (activation energy) required to enter (for reaction to occur).

      So EITHER increasing the emplyees' pay (molecules' energy), OR reducing the entrance fee (activation energy) required, would help to increase the % of employees who can enter, hence speed up the rate of the reaction.

      You can of course, do both. But for A levels, Cambridge will test your students on each factor separately, not simultaneously.

      Edited by UltimaOnline 10 Feb `17, 5:46AM
    • [Medicine] - If you go to medical school, you will be stressed. Bigly.


      [Medicine] - Female medical doctors told to get out of the way during emergencies as patients nearly die on planes


    • image

    • Originally posted by keefay:

      Ascorbic acid (vitamin C), an essential nutrient for humans, is an organic compound containing carbon, hydrogen & oxygen. when 1.000g of ascorbic acid was completely burnt in oxygen, 1.500g of carbon dioxide and 0.405g of water were formed. Calculate the empirical formula of ascorbic acid and determine its molecular formula if its relative molecular mass is 176.

      Hi UltimaOnline, how should i start the question? i tried to form the equation of the combustion of a carboxylic acid but i couldn't get the answer :(

      Thank you so much! :)   

      That's because Vitamin C isn't a carboxylic acid.


      From moles of CO2 generated, find moles of C in sample to be 3.4091x10-2 mol, ie. 4.0909x10-1 g.

      From moles of H2O generated, find moles of H in sample to be 4.5x10-2 mol, ie. 4.5 x 10-2 g.

      Hence mass of O in sample = 1.00 - (4.0909x10-1 + 4.5x10-2) = 5.4591x10-1 g, ie. 3.4119x10-2 mol.

      Moles of Vitamin C = 1.00 / 176 = 5.6818x10-3 mol.

      Hence mole ratio of VitaminC to C to H to O is 5.6818x10-3 : 3.4091x10-2 : 4.5x10-2 : 3.4119x10-2, which simplifies to 1 : 6 : 8 : 6.

      Hence molecular formula of Vitamin C = C6 H8 O6

      No prob, KeeFay! :)


      BedokFunland JC Challenge Qn

      Cambridge can ask as an A grade H2 A level exam question, "Identify the most acidic H atom, hence or otherwise, explain why Vitamin C is acidic."

      (Interested JC students go ask your school teacher or private tutor for the answer)

      Edited by UltimaOnline 19 Feb `17, 4:45AM
    • Originally posted by keefay:

      hi ultimaonline, 

      for S2O8^2-, the OS of S is +6. i figured it out through drawing the structure but i don't get the same answer using O level method. why is it so? 

      thank you so much! (: 

      Edited to add in italics

      Because the O level method is just an average value and makes simplified assumptions about common OS values for various elements which aren't always correct in context, while my BedokFunland JC formula for OS (which only the best few Singapore JC teachers are familiar with) is superior in that you can use it to calculate the OS of individual atoms in individual resonance contributors.

      In more complicated molecules and ions such as the S2O8 2- ion, you *must* use my BedokFunland JC formula to arrive at the correct OS. A recent Singapore H2 A level exam question in which Cambridge asked for the OS of a certain atom, also requires my BedokFunland JC formula to arrive at the correct OS.

      BedokFunland JC FTW! ;Þ

      Edited by UltimaOnline 20 Feb `17, 5:12AM
    • A disgrace to us Chemists! :(


Please Login or Signup to reply.