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

last SG · 2010-07-26T23:40:35+00:00

With Singapore having the highest incidence of diabetes in the world, every Singapore should take Berberine. Berberine helps to prevent diabetes if you don'...

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Though often placed at the top of the alkali metal column in the periodic table, hydrogen does not, under ordinary conditions, exhibit the properties of an alkali metal. Instead, it forms diatomic H2 molecules, analogous to halogens and non-metals in the second row of the periodic table, such as nitrogen and oxygen. Diatomic hydrogen is a gas that, at atmospheric pressure, liquefies and solidifies only at very low temperature (20 degrees and 14 degrees above absolute zero, respectively). However, Eugene Wigner and Hillard Bell Huntington predicted that under an immense pressure of around 4,950,000 bar or 4,890,000 atm or 71,800,000 psi, hydrogen would display metallic properties: instead of discrete H2 molecules (which consist of two bonding pair electrons bound between two nuclei protons), a bulk metallic phase would form with a solid metallic lattice of protons and the electrons delocalized throughout.

https://en.wikipedia.org/wiki/Metallic_hydrogen

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See if you can solve this riddle without googling the answer.

You have 2 blue pills and 2 red pills, the 4 pills all mixed together in one hand, and you need to swallow exactly 1 red pill + 1 blue pill at the same time within the next 1 minute, or you will die. If you swallow more than 1 pill of the same color, you will also die. Problem is, you're trapped in a pitch dark room with no light source, so you can't see the colors, you can only feel the pills. How sial?

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Time yourself. If you can complete this question within 5 mins, you're an A grader. 10 mins, you're a B grader. 15 mins, you're a C grader, and so on.

VJC 2012 P3 Hess Law Qn

ZnO(s) + 3C(s) --> ZnC2(s) + CO(g) ; enthalpy change = + 462 kJ mol-1

ZnO(s) + H2O(l) --> Zn(OH)2(s) ; enthalpy change = - 65 kJ mol-1

ZnC2(s) + 2H2O(l) --> Zn(OH)2(s) + C2H2(g) ; enthalpy change = - 126 kJ mol-1

2C(s) + O2(g) --> 2CO(g) ; enthalpy change = - 221kJ mol-1

2H2O(l) --> 2H2(g) + O2(g) ; enthalpy change = + 572 kJ mol-1

Calculate the formation enthalpy of C2H2(g).

Final Answer = +225.5 kJ mol-1

BedokFunland JC extension :

For each equation, state the type of reaction occurring, and draw the curved-arrow electron-flow reaction mechanism for each reaction.

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[Chemistry / Medicine] -

Just because you didn't know that the salt used at Macs contains aluminium, doesn't make the salt any less toxic for your body and in particular for your brain :

http://www.dailymail.co.uk/health/article-4047426/Aluminium-DOES-cause-Alzheimer-s-Expert-says-new-findings-confirm-metal-devastating-brain-disease.html

Being unaware of a problem doesn't make it go away.

McDonalds (including Singapore Macs) uses an aluminium salt, just read the ingredient list on the small Macs salt packs the next time you're at Macs.

https://www.quora.com/What-kind-of-salt-does-McDonalds-use-on-their-fries

At the very least, always ask for UNSALTED fries at Macs and all fast food restaurants. Of course, quite separate from the aluminium problem, are the French Fries itself (or for that matter, all deep fried foods).

http://time.com/4811136/fried-potatoes-mortality-study/

Also see :

http://www.top10grocerysecrets.com/2015-07-02-top-10-toxic-ingredients-used-mcdonalds.html

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[Chemistry / Medical ] - Concerns over Aluminium toxicity and Bisphenol A toxicity from soft drinks, including Coca Cola (btw : all artificial-sweeteners sugar-free 'diet' soft drinks are always more toxic than regular-sugar soft drinks).

"Without the invisible layer of BPA-based epoxy coating, an aluminium can of acidic Coca Cola would disintegrate in just three days!"

https://www.wired.com/2015/03/secret-life-aluminum-can-true-modern-marvel/

Also see :

http://www.coca-colacompany.com/contact-us/faqs

http://www.bisphenol-a.org/human/epoxycan.html

https://www.stevespanglerscience.com/lab/experiments/can-ripper/

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[ Biology / Medical ] - "The Upside of Bad Genes" by Moises Velasquez-Manoff

https://www.nytimes.com/2017/06/17/opinion/sunday/crispr-upside-of-bad-genes.html

Sickle cell was a case in point. The gene is usually found in people who live in, or whose ancestors came from, sub-Saharan Africa, the Arab world and India; in those places, having one copy of the gene can prevent the worst symptoms of malaria. Of every four children our imaginary couple might have, one will probably be afflicted with sickle cell disease, but two would most likely be protected from malarial disease.

Ditto with the gene variants that cause the lung disease cystic fibrosis. In parts of northwest Europe, about 1 in 25 people carries a single copy of the gene. And while two copies cause disease, it has long been hypothesized that having just one protects against tuberculosis — the White Plague that ravaged Europe for a few hundred years.

Carriers of the ApoE4 variant have an up-to-fourfold increased risk of Alzheimer’s disease. In 2010, scientists at Northwestern University found that the gene was more prevalent in tropical and polar populations than in those from mid-latitudes, presumably because it served some function in those regions. Then, strangely, the gene was linked to enhanced cognitive performance in children living in Brazilian slums. And last year, Ben Trumble, an anthropologist at Arizona State University, and colleagues published an intriguing study suggesting that the gene might improve brain function in elderly people living in the Bolivian Amazon. The tribe he studied, called the Tsimane, subsist mostly on what they grow and hunt in the jungle, and about two-thirds have intestinal parasites. Dr. Trumble discovered that if elderly ApoE4 carriers harbored parasites, their cognitive abilities improved relative to noncarriers with parasites. Only carriers without parasites suffered cognitively.

Scientists at Albert Einstein College of Medicine in New York City had recently discovered that ingesting cyanate salts could prevent the “sickling” of red blood cells that leads to the anemia and pain of sickle cell disease. Dr. Jackson knew that a related compound, cyanide, was common in foods across Africa, particularly in the staple crop cassava (which you may know as tapioca). She was also aware that, at the right dose, cyanide could directly protect against the malaria parasite. She realized that regular consumption of cassava — more common in the Southeast than the Northwest — could, by working as an antimalarial drug, affect the prevalence of the sickle cell trait, by making it less advantageous.

Something different was happening in the Northwest, though. Dr. Jackson, who is now at Howard University, thinks that while cassava consumption in the region was insufficient to protect against malaria directly, people who had two copies of the sickle cell gene still ate enough to partly avoid sickling. In that population, diet may have prevented a genetic disease from fully manifesting.

We evolved in environments that are radically different from today’s, and some of our genes may work better in those environments. This complicates the idea of trying to perfect the human genome with technology. Given how much the world has changed in just the past 150 years, and how much it’s likely to change again in the next 150, the question is, “What environment will we optimize our genes for?”

https://www.nytimes.com/2017/06/17/opinion/sunday/crispr-upside-of-bad-genes.html

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Here's a BedokFunland JC classic question that most JC students (and even many private tutors and JC school teachers) get wrong.

Is Ozone polar or non-polar? By drawing out the molecule, explain your answer.

My BedokFunland JC students can check their answer with me during tuition, all other students can go ask their private tutor or school teacher.

You can check out my compilation of BedokFunland JC H2 Chemistry questions on my website.

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Hello! May I ask a question on The Periodic Table?

Qn : When sodium chloride is added to water, a solution is formed which has a pH of 7. When phosphorous pentachloride is added to water, the resulting solution has a pH of 1. Explain these observations, and why these chlorides differ in their reaction with water.

Yo!

Due to relatively low ionic charge densities, neither the Na+ ion nor the Cl- ion undergoes significant hydrolysis, hence pH of NaCl(aq) remains neutral.

PCl5, being a covalent chloride, is electrophilic (since each Cl is significantly more electronegative than P), hence readily attacked by water nucleophiles to generate 1 mol of the weak acid H3PO4(aq), as well as 5 mol of the strong acid HCl(aq). Hence a strongly acidic solution results.

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1) A 4.50g sample of a carbonate of a Group 2 metal (known to be either calcium or strontium) lost 1.34g in mass when heated strongly. Identify the metal, showing clearly your working.

2) Group 2 hydroxides and nitrates decompose to give the same solid residues but different gaseous products.

A group 2 hydroxide exists as a hydrate, M(OH)2.nH2O. When a 1.575g sample of this hydrte was heated, the mass if the sample decreased by 0.720g. Subsequent hearing to constant mass produced a further mass loss of 0.090g. Calculate the value of n, and deduce the identity of the metal M.

Q1. From 1.34g of CO2(g), find mol of CO2(g). By stoichiometry, this is also the mol of metal carbonate. Giving sample mass of metal carbonate as 4.50g, and now you know the mol of metal carbonate, you can find the molar mass of the metal carbonate, hence can identify the metal.

Q2. The first 0.720g of water lost is from the water of hydration, ie. nH2O. The 2nd 0.090g of water lost is from the decomposition of the hydroxide. From 0.090g of water lost, you can find the mol of water lost, which by stoichiometry is also the mol of the entire hydrated metal hydroxide. Hence n = (mol of water lost 0.720g) / (mol of water lost 0.090g).

Now that you know the value of n, you can work out the molar mass of the hydrated metal hydroxide in terms of an algebraic variable, eg. let M be the molar mass of the metal M. Since you know the mol of the hydrated metal hydroxide, and you know its sample mass is 1.575g, and you have its molar mass (in terms of M), hence you can equate the 3 terms together and solve for M, and therefore identify the metal M.

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Hey UltimaOnline, heres a question from my sch paper

A sample of positively charged chromium ions, Cr^n+, was beamed through an electric field and was deflected by an angle of +8 degrees. A sample of No2^+ was beamed through the same elctric field and was deflected by an angle of +3.01 degrees. With reference to data booklet, calculate the amount of energy required to form 0.2 mol of gaseous Cr^n+ ions from 0.2 mol of gaseous Cr^(n-1)+ ions.

Ans: angle of deflection of Cr^n+=(1/46 divide n/52)x8=3.01

I dont understand why the angle of deflection of Cr is being derived as such. Thanks for the help!

(+1/46)x = +3.01, hence x = 1.3846x10^2
(+n/52)x = +8, hence n = +3

Hence energy required to form 0.2 mol of gaseous Cr^3+ ions from 0.2 mol of gaseous Cr^2+ ions = 0.2 mol x 3rd ionization energy (kJ/mol)

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[Medicine / H2 Biology] - https://en.wikipedia.org/wiki/Thalassemia

[China] - Father brings little daughter to play inside grave everyday, because he can no longer afford her expensive medical bills for her severe thalassemia, and hopes this will get her used to the grave so she won't be frightened when she dies soon.

http://stomp.straitstimes.com/singapore-seen/dad-in-china-takes-sick-2-year-old-daughter-to-grave-to-play-for-heartbreaking-reason

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[Chemistry / Medicine] - Be careful. There is some unidentified chemical species in A&W Root Beer that gives some people (not sure if you're one of them? just drink up to find out) a terrible instant-onset long-lasting migraine / headache that panadol & aspirin can't help with. In comparison, the only other brand available in Singapore, Mug Root Beer, doesn't cause headaches. So it's not Root Beer per se, but the A&W brand which is problematic.

http://mothership.sg/2017/07/aw-confirms-return-to-spore-in-2018/

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Apparently, very few, if any at all, Singapore JC students (even with the help of their private tutors and school teachers) are able to solve this excellent Vietnamese question, so I'll be gracious and give you the following hints : mathematically (based on the data provided in the question) there are infinite possible solutions, thereafter based on the periodic table you can narrow this down to only a few possible solutions, thereafter applying your knowledge and understanding of Chemistry, you can further narrow this down to only 1 possible solution, ie. the correct answer.

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Taiwan : http://wenr.wes.org/2016/06/education-in-taiwan

Indonesia : https://link.springer.com/article/10.1007/BF00598171

Malaysia : http://multilingualmania.com/english-or-national-language-thoughts-from-malaysia/

Hong Kong : http://www.scmp.com/lifestyle/family-education/article/1583037/argument-continues-over-using-cantonese-or-putonghuaM

Are you kidding? The best language of instruction (eg. when learning Chemistry, Physics, Biology, Medicine, etc) is obviously English, the lingua franca of the world, in order to effectively communicate with the rest of the world (ie. not just with America ; for instance in Europe, the many different Europeans all have their own distinct mother tongue language, but almost all are at proficient in English for the sake of communication with the rest of the world). Having English as the language of instruction has conferred the single most important educational advantage Singapore has had over other Asian countries (eg. Malaysia, Indonesia, Taiwan, Hong Kong, etc), and as Singapore's bilingual policies have proven, does not necessarily require sacrificing your mother tongue or ethnic culture altogether.

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A BedokFunland JC H2 Chemistry Challenge

99% of Singapore JC students will get this wrong, and about 50% of private tutors and school teachers will get this wrong.

Calculate the pH of 1.0 x 10^-8 mol/dm3 of HNO3.

Go ahead and calculate it, and if you like, post your final answer here to 3 decimal places (note : don't show your working, coz in case you get it right, don't ruin the fun for others). I'll only state if your final ans is correct or wrong, nothing more nothing less.

To elaborate, barring any silly mathematical errors, there are only 3 possible answers commonly given, depending on your level of Chemistry conceptual understanding : the U grade answer, the D grade answer, and the A grade answer. Based on your answer, I'll assign you your grade.

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This is a repost from 2013, but I just wanted the new JC students to know about this. Back in 2013, a RJC student named Kevin Wee, burnt his A level certificate in his bedroom, and video recorded the burning on YouTube, together with a 4 hour verbal exposition on why he did this, together with his personal take on the Singapore Education System, and on being a student in Raffles Junior College. It's a pity the video has since been taken down (he must have kena a lot of threats). At that time, Kevin posted about his experience and his A level cert burning video, on many different Singapore forums on the internet. I'll reproduce one of his posts here (the one he sent to TheRealSingapore), together with RJC Confeesions Facebook link, and Kevin's Facebook link.

My name is Kevin Wee, 19 this year. I hope you will take some time to hear my story. I was from Victoria School (VS) and Raffles Junior College (RJC). Growing up, I was taught to work and study hard, for it will give me a secure and good future. I excelled in sports and studies, working extremely hard at both. I never had time for a relationship and spent little time going out with friends. I played badminton for VS in sec 1 and 2, and switched to tennis in sec 3 and 4. I achieved a national ranking, which helped me get into RJC through DSA. In RJC, we won a double gold and I represented Singapore in the ASEAN schools games in 2012.

I had everything going for me, and just needed to work hard for A levels, get good grades, and get into medicine. Or so I naively thought. 1 month before the A levels, there was construction above my house. I got nervous and agitated, but managed to compromise and study 14 hrs a day for a month.

First day of As, I was placed at the side of the hall where I never sat before and the aircon was blowing in my face. I have asthma, and I couldn’t breathe properly. I got shifted to a ulu place whr I got distracted by some sounds (prob due to the anxiety) and ""scrwed up"" GP. I went into mild depression and couldn’t concentrate on the following papers (kept worrying where ill sit) I didnt sleep at all before math, and had a complete mental block in both papers, when to the toilet and sat there...handed up 2sheets of paper. Aft that, I wanted to withdraw, but my mum encouraged me and took me to the doc and got medication. I struggled through the rest of the papers...trapped by my thoughts of the future and all kinds of weird sensations that distract me. I barely made it through As and I thought it was going to be fine.

I was wrong. I had death thoughts (of myself getting hanged, getting cut up,etc) and I couldn’t sleep or control them. Aft 4 days of no sleep, I honestly thought without a doubt I was going to die. I was admitted and the doc gave me a sedative. It didn’t work. I lay awake for 4 hrs, and then woke up trembling from head to toe, I called my parents and said ""goodbye"". The doc gave me a stronger sedative and I fell asleep.

Anyway, I was stuck in depression for 4 months...I was suicidal in January. Some of you may be thinking, exams are a very stupid reason to go into depression like that, but it wasn’t my fault per say. I had dreams, I studied exceedingly hard for so many years. To me, my future was gone to trash, all my hard work over 18 yrs rendered useless. Furthermore, my mind was too spent from all that studying and it shut down because it had reached its limit. Depression is as much a physical as it is mental illness.

Somehow, I recovered slowly. In late march, with medication, love, support, and letting go of everything. I told myself, I really don’t need a degree to survive, there are other ways to make ends meet.

One day, as I was watching youtube, I decided hey, I could do that, share my story u know, try and inspire people from there. So I did it. In my first video I shared my story and eventually burned my A level cert. You may think its stupid, but its not. That piece of paper almost murdered me, and its worthless to me now, I never want to see it again. The video is long but the first 1hr20mins is the crux. If its too long to tahan, do try and watch it in parts if you can It has 18k views so far and good reviews. After my video, some people with mental illnesses have also come to me for help. It’s tiring helping them, but nonetheless I will never give up, for I was once that person, desperate and yearning for help.

I also made two subsequent videos where I interviews elderly cleaners and gave out masks during the haze periods. I do not understand why in our country when our GDP is one of the highest in the world, elderly cleaners, whose faces are riddled with wrinkles, have to bend over and clean tables.

Also, after I woke up from the nightmare, I begin to see clearly the shortcomings of the education system. It is cruely competitive and places too much emphasis on grades. From a young age, some parents bombard their children with two preschools, piano classes, tuition, sports classes, you name it. Children should be able to enjoy their childhood and slowly find their dreams, not having them forced on them. Because parents want “the best” for their child’s future, they may unknowingly put too much stress on kids from a young age. I remember clearly during my PSLE results, a boy was crying over the phone in the toilet, saying “Mummy, sorry, I got below 200, how?” No child at the age of 12 should feel that their life is over because of a stupid piece of paper.

In secondary schools, many “neighbourhood” school kids are struggling to keep up with the content of the O levels with 6-8 subjects, and face tremendous stress. Some simply give up, and worse still develop mental illness. These claims are not made into jest. For my upcoming videos, I’ve interviewed “neighbourhood school” kids and this is what they tell me. So too do taxi driver uncles (about their sons) whom I talk to.

Of course, when grades are held in high regard, there are other perils and implications on society like elitism and social stratification, which are also serious problems.

Also, though my interactions with my new friends, I realised I was very sheltered, and I finally see the neglected side of society-namely people with disabilities, mental illnesses, learning disabilities and the elderly.

Coming out of depression, I have a clearer dream and conviction; That is to inspire a more inclusive, loving Singapore, where we look out for those falling through the cracks, for those crushed under the weight of a fast paced society, for those who are underprivileged and in need of help. I hope we can achieve that dream together as Singaporeans :)

https://www.facebook.com/kevin.wee.16

Another (unidentified) ex-RJC student subsequently posted this on RJC Confessions Facebook page :

To the Kevin Wee dude who did the video on the education system:

The surest way for one to realise his dreams is to go through the given system that works and aim to be the best. In any society, regardless of what systems there are, there will always be the better and lousier people - that's a fact of life and there's nothing you can do to change that.

You flunked your A levels because you hate the system- you have an extremely defeatist attitude and you're unwilling to work hard. Your mistake was not that you were bad, but you were senseless to not take the guaranteed path RJ or any JC offers you and instead tried challenging and finding fault with the system. You claim that "other alternative less competitive" paths can get you to success to. Well sure, if these methods worked you wouldn't be here making vlogs for a living, see?

Competition and comparison between the better and the poorer people in any country is inevitable. You hate the system because it's competitive, and people who lag or are left behind suffer a horrible fate. But it is only with this system that the top few people even work hard in the first place. If we didn't have to compete or work hard for our success, then nobody would study hard at all.

It is people like you who kill the determination and driving force in Singapore. It doesn't help that the "lousier" people as we call it are lagging behind, but people like you have to exacerbate things by telling them that JC is hard, PW stress is crazy and whatnot. Yes it is stressful, but are you telling me this stress is necessarily bad? Will you not face stress and failure in your career in future? Clearly, no pain no gain. If you're unwilling to put in 1000%, you'll never make it big. Maybe that's why you're into making vlogs now eh?

And WHAT THE FUCK stop hitting on your juniors by asking them if they're cute, that's just creepy. I have already notified relevant authorities too, have fun.

https://www.facebook.com/RJConfessions/posts/228031204011708

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If you (as a JC student) found RJC Kevin Wee's personal story inspiring or at least helpful to you in some way, you might also be interested in hearing HCJC Xin Lin's story as well. She too, was stressed out by the life as a student in an elite JC, but in case you're wondering, she didn't burn her A level certificate.

Truth behind my JC life :

https://stopthe-pretence.blogspot.sg/2012/03/truth-behind-my-jc-life.html

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