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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Physicist Stephen Hawking got this right.

The internet and the platforms that it makes possible allow very small groups of individuals to make enormous profits while employing very few people (eg. Facebook, Google, etc). This is inevitable, it is technological progress, but it is also socially destructive.

We need to put this alongside the financial crash, which brought home to people that a very few individuals working in the financial sector (eg. Wall Street bankers) can accrue huge rewards and that the rest of us underwrite that success and pick up the bill when their greed leads us astray.

So taken together we are living in a world of widening, not diminishing, financial inequality (ie. worsening Gini coefficient), in which many people can see not just their standard of living, but their ability to earn a living at all, disappearing. It is no wonder then that they are searching for a new deal, which Trump and Brexit might have appeared to represent.

https://www.unlimited.world/unlimited/this-is-the-most-dangerous-time-for-our-planet

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H2 Chemistry

Qn : What happens when you mix together solid carbon dioxide (−78.5 °C) and liquid nitrogen (−195.79 °C)? State the expected observations, expected temperature changes and/or changes in state for both species, giving the underlying chemical explanations.

Ans : https://www.youtube.com/watch?v=mwpLg6-ZZcM

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Did they all fail their A level Chemistry? --____--

This happened in Anhui’s Lu’An city in China. Birthday party-goers who were adjourning for the night got into a lift together with 20 balloons filled with hydrogen on Dec. 4.

According to one of the victims, several people kept asking for the balloons to be lit, some even shouting for it. Despite protest from other lift-riders, light it they did.

What should have been the popping of one balloon turned into a chain reaction of 20. The blast, described as deafening, was strong enough to cause the lift to apply its emergency brakes and the lift was stuck between the first and second floor. Wails were heard.

Firefighters arrived to extract the trapped victims of idiocy. What they found were eight individuals with varying degrees of burns on their faces mixed with tears of regret.

http://mothership.sg/2016/12/chinese-party-goers-felt-it-was-great-idea-to-light-up-20-hydrogen-filled-balloons-in-lift-bam-its-not/

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Hello, I have a question, how exactly does a non-polar solvent dissolve a non-polar solute?

Whether the solute and solvent are polar or non-polar, the same consideration below applies. It's just that "like dissolves like" is a shortcut guideline that usually works.

In terms of enthalpy change (delta H), heat released is comparable with heat absorbed (overall enthalpy change preferably exothermic, but can be slightly endothermic), in terms of physical interactions (van der Waals, and if applicable, hydrogen bonds or ionic bonds) formed and broken.

In terms of entropy change (delta S), there will be a favourable positive entropy change upon mixing.

Overall quantitatively, Gibbs free energy change must be negative for the dissolving to be thermodynamically favourable, according to the formula delta G = delta H - T x delta S.

When you (ie. all students using this forum) ask me qns, and if you don't fully understand my replies, I won't spoonfeed you on the forum, so you'll have to research it further online (Google by thy sword, Wikipedia be thy shield), and/or ask your school teacher or private tutor, and/or join my BedokFunland JC tuition for more detailed, personalized guidance.

So the 'energy' explaination for why something dissolves is more relevant than describing the physical process?( like how the polar water molecules pulls away the NaCl crystals)

Of course, because the physical process is able to occur only because the overall thermodynamics is favourable enough to allow it.

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In order to calculate the most accurate mass of an ideal gas using the relationPV= nRT

what conditions of presuusre and temperatur would be used?

Ans. We need mass to put into the final equation.....gases dont have masses they have volumes....so we have to liquefy them by applying high pressure and low temperature. Is this correct?

Gases do indeed have masses.

The weights of gases are dependent on the gravitational force acting upon them, and difficult to measure directly, but the masses of gases are independent on the gravitational force acting upon them, and can be calculated using PV=nRT if simplified to ideal gas behavior, where P, V and T can be directly measured with appropriate apparatus, and sample mass = number of moles x molar mass. The mass of the gases obtained will be the weighted average of all gases present.

Here is the full MCQ from CIE....

Measured values of the pressure, volume and temperatureof a known mass of a gaseous compound are to be susbstituted into the equation

Pv= nRT

In order to calculate the relative molecular mass of the compound

Which conditions of pressure and temperature would give the most accurate valuesof Mr?

pressure temperature

A high high

B high low

C low high

D low low

For this particular MCQ, the answer is C, because the behavior of gases approach ideal gas behavior most closely at high temperatures and low pressures. PV=nRT only holds true for ideal gases, not real gases.

Okay. thank you.

Can you through some light on the triplet point?

Has this anything to do with the triplet point?

No, the "high temperature low pressure" for ideal gas behavior is a separate concept from the triple point of a species.

A gas behaves more like an ideal gas at higher temperature and lower pressure, as the potential energy due to intermolecular forces becomes less significant compared with the particles' kinetic energy, and the size of the molecules becomes less significant compared to the empty space between them.

Wikipedia (Uni level) : https://en.wikipedia.org/wiki/Ideal_gas
A level syllabus relevance : http://www.chemguide.co.uk/physical/kt/realgases.html

The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.

Wikipedia (Uni level) : https://en.wikipedia.org/wiki/Triple_point
A level syllabus relevance : http://www.chemguide.co.uk/physical/phaseeqia/phasediags.html

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Given the strutucre of chloropyll what is correct

1 dative covalency

2 sigma bond

3 sp3 hybridization

1 and 2 are correct...but not sure about 3??

Ohh....Is'nt due to dative and covalent bonding the shape around Mg is tetrahedral so sp3 hybridization ould be correct also....? Is this correct?

Not sp3, because the aromatic ring (either porphyrin or chlorin, depending on the exact chlorophyll type) is planar.

okay.

but what is he hybridization of Mg in this question? sp ?

dsp2

Now it is clear.

What about Carbon atoms in hexagonal rings in graphite in each layer...they are co-planar.

More accurately periplanar rather than exactly coplanar, but Cambridge will accept coplanar.

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Hello, does water form 2 or 4 hydrogen bonds? Im not too sure about this, thanks

Depends on state. As gaseous (assuming ideal gas behavior), 0. As liquid, fluctuates (many times per second) between 2 to 4. As solid, 4 (for the specific crystalline structure of ice relevant to A level syllabus).

Thank you, I have another question, for ammonia, i dont understand why it forms just 2 hydrogen bonds, why can't the two hydrogens(left over after nitrogen and hydrogen) take part in hydrogen bonding?

They can, but when you're talking about intermolecular H bonding between NH3 molecules, notice the ratio of H bond acceptors (ie. the N atoms) to H bond donors (ie. the H atoms) is 1:3, while the required ratio per H bond is 1:1.

Analogously, in a class of 1 guy and 3 girls, how many (monogamic heterosexual) couples can you have at most? Concordantly, on average only 2 atoms (1 N and 1 H) can participate in H bonding between NH3 molecules.

Sorry, i dont quite understand your explanation , going by your analogy, if 1 'guy' gets 1 'girl', whats going to stop the other 'girls' from getting other 'guys'? (unless you are talking about just 3 ammonia molecules)

Then you'll run out of guys much sooner than girls, in a school of 10 classes, each class with 1 guy and 3 girls.

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Bone cancer survivor scores four distinctions
http://www.straitstimes.com/singapore/education/bone-cancer-survivor-scores-four-distinctions

To be realistic, the odds are stacked against her, because of her 'N' level academic background, and (this applies to all Singaporean students) because of the overly small number of places available in local medical schools. And if her medical condition does not resolve itself immediately or fully (only her oncologist will know her medical prognosis), it may continue to post further financial and time burdens that may distract her from performing her best along the way.

However, should she indeed perform spectacularly well (ie. perfect scores for all subjects and all modules all the way here on out), her 'N' level academic background and her bone cancer medical condition, could actually help her stand out amongst the pool of candidates vying for a coveted place in medical school, as positive indications of her tenacity, perseverance and determination.

Of course, the rich (especially ultra-rich) will always have multiple advantages over everyone else. If her family can afford it, then applying for overseas medical schools (of which there are thousands, though only a few dozen or so are recognized for practicing medicine in Singapore), in addition to local medical schools, will naturally increase her chances of fulfilling her career ambitions. And if you're rich enough to locate yourself overseas permanently, you could even go for medical schools not recognized for practicing medicine in Singapore, as a last resort.

I wish her all the best in her health and in her medical doctor career ambitions.

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CO2 has same melting and boiling point. Is is due to the structure and non-polar nature?

Yes, the fact that CO2 is overall non-polar, yet possesses 2 significant individual dipoles in a linear molecular geometry, results in its sublimative property (ie. only existing at solid and gaseous states) at 1 bar or 1 atm. The liquid state is only possible at significantly higher pressures, as illustrated in its phase diagram.

Image credits : Wikipedia

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Drinkable ethanolic drinks (eg. beer, wine, liquor, etc) are taxed heavily by governments (a considerable source of money for governments because who doesn't like an ethanolic drink?), so unethical and unscrupulous importers, distributors or retailers sometimes adulterate their ethanolic drinks with cheap, untaxed methanol to sell to unsuspecting customers. In many cases, most of the victims go permanently blind as a result of methanol poisoning, if they manage to survive at all.

Toxic liquor kills 24 in Pakistan
https://sg.news.yahoo.com/toxic-liquor-kills-21-pakistan-police-051343831.html

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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

https://www.youtube.com/watch?v=voM13PNFYZI

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[Medical Science] - An adenovirus causes obesity in humans and animals

https://www.wired.com/2016/12/mysterious-virus-cause-obesity/

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.

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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.

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