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

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    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    14,109 posts since May '05
    • _

      Edited by UltimaOnline 13 Oct `17, 2:30AM
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      Edited by UltimaOnline 13 Oct `17, 2:30AM
    • You do realize, that the Mad Hatter became mad as a result of toxic mercury heavy metal poisoning from his hat?

      image

      https://sg.style.yahoo.com/look-inside-secret-alice-wonderland-themed-pop-dinner-singapore-055048931.html

    • Atrocious karma for atrocious acts. If Cambridge asks, you do know how to explain why and how acid attacks cause tissue damage and disfigurement, don't you?

      Man throws acid on ex-lover before killing himself

      https://sg.news.yahoo.com/man-throws-acid-ex-lover-killing-himself-235300093.html

      Also see :

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

      http://www.acidviolence.org/

    • _

      Edited by UltimaOnline 13 Oct `17, 2:30AM
    • Originally posted by Carychidestar:

      Hi ultima,how do you solve this question?

      "A 0.01 mol sample of an oxochloride of vanadium,VOCly, required 20.00cm3 of 0.1mol dm3 acidified potassium manganate(VII) solution for oxidation of the vanadium to the +5 oxidation state"

      Find the value of y"


      Hi Carychidestar,

      Find OS of V (in VOCly) in terms of y.

      Find moles of MnO4- used.

      Find total moles of electrons transferred based on stoichiometry.

      Find moles of electrons transferred per mole of V.

      Initial OS (in terms of y) + moles of electrons transferred per mole of V = Final OS (ie. +5)

      Solve for y.

      Edited by UltimaOnline 16 Apr `17, 4:36PM
    • "If you train early in the day, Ms Bernardes recommends water with a pinch of sea salt when you wake up, to replenish the salts you lose breathing throughout the night."

      Source :
      http://www.straitstimes.com/world/the-trouble-with-setting-a-blistering-pace
      http://www.oanow.com/news/local/training-tips-for-new-runners-beware-raw-thighs-tummy-troubles/article_ea92c190-206d-11e7-b461-03037cf8dccd.html

      What nonsense! Now I don't doubt that Debi Bernardes is an expert triathlon coach, but she seems to have failed her H2 Chemistry, to make such a ridiculous error in her statement. If Cambridge asks, you do know how to explain what her conceptual error is, don't you?

    • A classic question that is now making the rounds in Singapore JCs' tutorials again. Have fun with it. As usual, BedokFunland JC students can ask me how to solve it during tuition, all other students can go ask their school teacher or private tutor.

      Xenon and fluorine were mixed in a 1:1 ratio by volume and sealed in a vessel attached to a barometer. After some time, crystals were found to have formed on the walls of the vessel and the barometer showed that the pressure had dropped to 70% of the original pressure. Analysis of the gases remaining indicated 4 parts xenon to 3 parts fluorine. Construct a balanced equation for the reaction. Assume constant temperature throughout.

    • _

      Edited by UltimaOnline 13 Oct `17, 2:31AM
    • 1st qn : qn is flawed becoz the counter-anion is not specified (so let's assume it's uninegative), and the molarity of sulphite solution not given (so let's assume it's also 0.1M). 2 mol of M3+ reacts with 1 mol of SO3 2-, which when oxidized to SO4 2-, releases 2 mol of e-. Hence 2 mol of M3+ accepts 2 mol of e-, ie. final OS of metal = +2.

      2nd qn : each mol of FeC2O4 releases 3 mol of e- upon oxidation (as each Fe2+ is oxidized to Fe3+, and each C2O4 2- is oxidized to 2 CO2). Each mol of MnO4- accepts 5 mol of e- upon reduction in acidic pH. Hence each mol of FeC2O4 will react with 3/5 mol of MnO4-.

      Originally posted by Carychidestar:

      Hi ultima,how do you solve these two questions?

      '50cm3 of a 0.1 mol dm3 of a solution of a metallic salt reacted exactly with 25cm3 of sulphite solution.The half equation for the oxidation of sulphite ion is 

      SO3^2- + H2O -> SO4^2- + 2H^+ +2e

      If the original exidation number of the metal in the salt was 3, calculate the new oxidation number of the metal'

      I only managed to find the no.moles of the salt and I'm stucked.

      'Half-equations

      2CO2 + 2e -> C2O4^2-

      FE^3+ + e -> FE^2+

      MNO4^- + 8H^+ + 5e -> MN^2+ + 4H2O

      Calculate the no.moles of MNO4^- ion that will react with 1 mol of iron(II) ethanedioate;FeC2O4 in acidic solution'

      This one,I dont even know where to start since there are no numbers provided.


      Edited by UltimaOnline 13 Oct `17, 2:31AM
    • _

      Edited by UltimaOnline 13 Oct `17, 2:33AM
    • Originally posted by flowerd:

      what is the difference between heat and heat under reflux for organic chemistry conditions? for example, is it acceptable to write "heat" instead of "heat under reflux" when converting halogenoalkane to nitrile?


      While in many instances, Cambridge will accept either term (unless of course, "warm" or "heat with distillation" is specifically required for some reactions), however as a general rule, it is advised that students write "heat" for distinguishing chemical tests, and "heat under reflux" for organic synthesis pathways.

      Cambridge can ask, and in the past, have indeed asked, questions on drawing the reflux apparatus, and on when or why reflux is preferred or required in certain practical setups. For this, the following Wikipedia page is useful for students.

      image

      https://en.wikipedia.org/wiki/Reflux#Reflux_to_regulate_energy_in_chemical_reactions

    • _

      Edited by UltimaOnline 13 Oct `17, 2:31AM
    • Acid-Base Equilibria remains one of the toughest topics for many H2 Chem students. Here is an excellent 2016 NYJC Qn for your practice.

      20.0cm3 of an unidentified weak monoprotic Bronsted-Lowry base of unknown molarity was titrated with 0.01M of a strong monoprotic Bronsted-Lowry acid at 25 degrees C. The initial pH at the start of the titration was 11.0, and equivalence point was reached when 25.0cm3 of acid was added. Calculate the Kb of the weak base, as well as the pH of the solution when 35.0cm3 of acid was added.

    • Originally posted by qixx:

      Can you give a crash course on what lattice energy is about and what are some possible questions that can be tested relation to lattice energy? Also, is lattice energy & ionisation energy the same ?

       


      Sounds like you could really use some help from tuition. Consider BedokFunland JC for your H2 Chem tuition needs.

      For A level Chem crash courses, the most widely used website on the internet is (retired A level examiner) Jim Clark's ChemGuide website :

      http://www.chemguide.co.uk/

      No, lattice energy and ionization energy have different definitions, both of which you're required to memorize. You can easily Google or Wikipedia these definitions for yourself.

      Reminder to all : for crash courses or definitions or factual info, please Google or Wikipedia out these for yourself. I'll only guide you, not spoonfeed you, nor do your homework for you.

    • Here's a BedokFunland JC example of a possible A level exam question which includes (but not limited to) lattice energy. I won't reveal the answer here, but if you (ie. JC students) wanna try posting your attempted answer here, I'll let you know if you got it correct. Students can go ask their school teacher or private tutor.

      Explain why (under standard conditions), when magnesium and chlorine reacts, the formation of MgCl2(s) is thermodynamically favored over the formation of either MgCl(s) or MgCl3(s).

    • A BedokFunland JC H2 Chemistry Question

      Explain how radiocarbon dating works for determining the age of an object containing organic material.

    • _

      Edited by UltimaOnline 13 Oct `17, 2:32AM
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      Edited by UltimaOnline 13 Oct `17, 2:33AM
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      Edited by UltimaOnline 13 Oct `17, 2:34AM
    • [Physics / Chemistry / Biology / Medicine] - Global warming is causing disease epidemics through complex mechanisms humans never suspected possible.

      Haley remembered, it had not been very cold that year. There was only one night of hard frost; everyone had talked about it, grateful they did not have to dash out to wrap plants and turn off hose taps while thermometers plunged. The investigators downloaded federal weather data for each year since West Nile first arrived in Texas and plotted the metrics against the case counts. The epidemic year was an outlier on every measure, with the warmest winter, the warmest spring and the heaviest early rainfall in 10 years. As it turns out, the climate changes such as heavier rainfall resulted in greater breeding numbers, allowed more mosquitoes to survive the warmer and shorter winters, causing them to wake sooner, spill out earlier from their winter hiding places, and bite more people than in any other previous year, transmitting so many deadly viruses that killed an unprecedented number of victims.

      https://www.nytimes.com/2017/04/20/magazine/why-the-menace-of-mosquitoes-will-only-get-worse.html?_r=0

      Global warming is also now melting permafrost and ice that have been frozen for thousands or even millions of years, slowly releasing long-dormant bacteria and viruses that could potentially wipe out humanity.

      https://www.google.com.sg/#q=global+warming+viruses+frozen

    • Originally posted by glitter58:

      do both the statements mean the same thing?

      -compound A has intermolecular permanent dipole–permanent dipole attractions 

      -pd-pd attractions exist between A molecules

      or should i write something like "Intermolecular pd-pd attractions exists between A molecules"  which of the statements is the most correct?

      also do i call pd-pd and id-id as interactions or attractions or forces of attraction?

      sorry if my question sounds confusing becuase i am a bit confused about the phrasing of answers. 

       


      You're not allowed to use acronyms such as pd-pd in the A level exams. Zero marks.

      Interactions include both attractions and repulsions, and depending on context, either or both can be used.

      Students are advised to use the following phrasing in the A level exams :

      Between polar molecules, the intermolecular interactions are permanent dipole - permanent dipole Keesom van der Waals forces.

    • [Chemistry / Biology / Medicine] - Indeed, extremely high dose caffeine can be fatal. Nonetheless, low dose caffeine is helpful, eg. significantly enhances the anti-headache and anti-migraine effects of panadol and/or aspirin.

      But caffeine aside, energy drinks are seriously unhealthy, containing dangerously high doses of many questionable ingredients other than caffeine. I recommend you go for isotonic drinks or coconut juice instead of energy drinks, if you're looking for a healthier alternative to soft drinks (which ironically, is still healthier than energy drinks).

      Coca Cola (always go for original flavor, 'less sugar' or 'no sugar' = artificial sweeteners, way unhealthier than sugar) is actually healthier than Mountain Dew, which is somewhere between a soft drink and an energy drink.

      https://sg.news.yahoo.com/us-teen-dies-caffeine-overdose-004737947.html

      Edited by UltimaOnline 17 May `17, 5:34PM
    • [Medicine] - Could Breast Milk Be the Next Cancer Treatment?

      image

      https://sg.yahoo.com/news/breast-milk-latest-cancer-treatment-161252298.html

      More on the Biology, Chemistry and Medicine of HAMLET (Human Alpha-lactalbumin Made LEthal to Tumour cells)

      Endogenous human alpha-lactalbumin is complexed with a calcium ion and serves as a cofactor in lactose synthesis, but has no tumoricidal properties. The alpha-lactalbumin must be partially unfolded to allow for release of the calcium ion and replacement with an oleic acid molecule. The partially folded conformation is essential to the cytotoxicity of HAMLET, as mutagenesis studies have shown that completely unfolded alpha-lacalbumin does not retain the functional properties of HAMLET. The oleic acid is necessary for stabilizing this molecule in this partially unfolded state.

      HAMLET carries out independent attacks on many distinct cell organelles, including mitochondria, proteasomes, and histones, and interferes with cell processes such as macroautophagy. It has been shown that HAMLET binds to the cell surface and rapidly invades cells, with tumor cells taking up far more protein than healthy, differentiated cells. The mechanism of its entry is poorly understood, but recent studies indicate that the oleic acid in the HAMLET complex interacts with phosphatidylserine and o-glycosylated mucin on the plasma membrane, both of which are expressed in greater amounts on the plasma membrane of tumor cells, possibly providing for HAMLET’s specificity.

      One of the most prominent targets of HAMLET once inside the cell is the mitochondrion. Electron microscopy has revealed physical damage to the mitochondrial membranes and assays have found cytochrome c release and activation of the caspase cascade, the most notable ones being caspases 2, 3, and 9. It is interesting to note that cell death is not prevented by caspase inhibitors, or by BCL-2 or p53 mutagenesis, indicating that the traditional apoptotic caspase cascade is not the ultimate cause of cell death.

      Another target of HAMLET is the proteasome. 26S proteasomes are activated in response to large quantities of unfolded HAMLET protein in the cytoplasm, but degradation of HAMLET by the proteasome is unusually slow. Furthermore, in vitro studies have shown that HAMLET is capable of binding the catalytic 20S subunit of the proteasome and disabling its enzymatic activity, an effect that has never before been demonstrated for any protein. However, proteasome inhibition alone does not seem to be responsible for HAMLET-induced cell death, as proteasome inhibitors have been shown to reduce the cytotoxicity of HAMLET.

      HAMLET also targets the nucleus, where it interacts with histones to interfere with transcriptional processes. Studies have shown that HAMLET is mostly localized to the nucleus within one hour of invading a tumor cell. Hamlet has been shown to bind with high affinity to individual histone proteins, to be specific H2a, H2b, H3, and H4, as well as entire nucleosomal units. This interaction irreversibly blocks transcription and leads to activation of p53. This process has been demonstrated to be similar to histone hyperacetylation and it was found that histone de-acetylase inhibitors potentiated the effects of HAMLET.

      HAMLET cells showed the physiological characteristics of macroautophagy, a process in which cellular components are sequestered in double membrane-bound vesicles that fuse with lysosomes for degradation. Cells also showed decreased levels of mTOR, a known inhibitor of macroautophagy. HAMLET cells and cells under conditions of amino acid starvation (a known initiator of macroautophagy) showed similar expression patterns of autophagocytotic proteins and responded equally well to addition of macroautophagy inhibitors.

      https://en.wikipedia.org/wiki/HAMLET_(protein_complex)

    • Reminder for JC2 students taking A level exams in 5 months time : Only a few days left before the May 2017 Special Conditional Offer for JC2 Students expires, and the more exacting June 2017 Special Conditional Offer for JC2 Students applies.

      A BedokFunland JC Original H2 Chemistry Question

      Calculate the value of
      i) pKa of water
      ii) pKa of hydroxonium ion
      iii) pKb of water
      iv) pKb of hydroxide ion
      Show all relevant working, and assume water solvent and room temperature, obviously.

      My BedokFunland JC students can check the answers with me during tuition. All other students can check the answers with your school teacher or private tutor.

      Edited by UltimaOnline 20 May `17, 7:19PM
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