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  1. K

    Help with Chi-Squared Test: Probability Link to \chi^2 Value using the above table, first thing you select the row for your degrees of freedom. in your case, it is 3. now this row tells us, if your chi square value is less than 0.35, then the probability of this particular event occurring is greater...
  2. K

    Guidance on finding the pressure and density of nitrogen

    i would suggest that since air is made up of about 78% nitrogen, you could substitute the nitrogen with air. anyway, there is already a 15% error in the equation. the error due to the substitution of nitrogen by air should not be very significant. i might as well be wrong!
  3. K

    Does the APF depend on the temperature

    how about expansion and contraction due to temperature changes?!
  4. K

    Phospholipids characteristics

    Using the Le Chatelier's Principle, then there will be no charge on the phosphate because it would remain undissociated! Is that it? ooo but then, the charge will depend on the pH, while, the polarity will always be here! so, in a sense, it is better to say C! right?
  5. K

    Phospholipids characteristics

    since phosphoric acid is a weak acid, it's pKa should be between 2 - 6. Therefore at physiological pH 7.4, the acid will be dissociated, giving the negatively charged anion. Am I correct? If, the pH is very low, in strongly acidic conditions, then the phospholipid will be uncharged.
  6. K

    Phospholipids characteristics

    Homework Statement Phospholipids have headgroups and hydrocarbon chains as follows: A. amphipathic, non polar B. non polar, polar C. polar, non polar D. charged, non polar Homework Equations phospholipids have a phosphate head group and fatty acid residue hydrocarbon tails...
  7. K

    Number of chromosomes in each step of mitosis in human

    for interphase g1 you meant 23 chromosomes? it should be 23 pairs of chromosomes! making you 46 chromosomes in all. 23 chromosomes from mum and 23 chromosomes from dad. then you should correct all the numbers accordingly. and why would the number of chromosomes be halved from interphase s...
  8. K

    Organic Chemistry Mechanism Question

    i never came across benzoyl peroxide. I would suggest that it would break Br2 into Br+ and Br-. The Br+ is accepted by the benzene ring (electrophilic substitution rxn) and the Br- would attack the hydrocarbon as a radical. but i really don't know.
  9. K

    Help w/ Gravimetric Anaylsis of Mercury Oxide

    I don't think fractional distillation would be called gravimetric analysis. You should go for a heat to constant mass analysis. What do you know about mercury oxide when heated?
  10. K

    Alcohol Property Trends

    what can be observed is that when the molecular mass increases, ie you are adding more -CH2 groups, the boiling point is increasing. you can use a knowledge of temporary dipole forces of attractions. probably for the solids, the shape the alcohols take matters more. methanol, ethanol and...
  11. K

    Empiric formula question

    hint: can you calculate the number of moles of CO2 you obtain?! If the products are CO2 and H2O only, then all the Carbon from the initial material have gone into CO2. so, if you have x mol of CO2 formed, then you should have had x mol of Carbon in the initial substance. Using this same logic...
  12. K

    Do larger seeds need less water to germinate?

    maybe the question wants you to look at the surface area to volume ratio. just like children will require more energy than adults for their daily metabolic activities!
  13. K

    Phases You Can't See with Spindle Inhibition

    i may be wrong but i think that you would see up to metaphase. because, if i remember my biology well, the chromatids will line up at the equator of the cell. It is only in anaphase that the spindle come into action to pull apart the sister chromatids to opposite poles. the absence of spindles...
  14. K

    Air conditioning unit work more effectively when it is placed high up

    hint: think about density of hot and cold air.
  15. K

    Starch, commercial bleach and halides

    if I'm not wrong, you should consider the typical test for starch, with iodine forming a blue black complex with the starch. the halides are reducing agents. and the bleach is an oxidising agent.
  16. K

    Amide for esterfication

    awww... i put only a few drops of concentrated H2SO4... but it's only 2 marks...nvm we had to distinguish between an amide and a primary amine. i had completely forgotten about the NaOH reaction which could have been used... thnks
  17. K

    Amide for esterfication

    Homework Statement does ethanamide react with ethanol forming an ester?! Homework Equations CH3CONH2 + CH3CH2OH -------> CH3COOCH2CH3 + NH3 The Attempt at a Solution
  18. K

    Comparing acidity among 3 compounds - pic included

    i would use the inductive effect to explain the acidity of acetic acid and 2 hydroxy acetic acid. the oxygen on the hydroxyl group of 2 hydroxy acetic acid is of course electronegative. it tends to pull electrons towards itself. the carbon of -COOH will have a lesser electron density, and the...
  19. K

    Reverse of optical isomerism in a reaction

    niice analogies lol... thank you borek and epenguin... i can get the picture now:)
  20. K

    Reverse of optical isomerism in a reaction

    so you mean that when the carbanion forms a trigonal bipyramidal structure, the R1, R2 and R3 lie on one plane with the Br and OH perpendicular to that plane. but how does the switching occur?! does it occur after the Br- leaves? thnks
  21. K

    Reverse of optical isomerism in a reaction

    i had a look at the mechanism but i can't find how there could be a reversal in chirality. a hint would be well appreciated. thnks
  22. K

    Reverse of optical isomerism in a reaction

    ermmm well i tried to imagine but i still can't see how a dextro or leavo enantiomer could become the opposite?! because the Br- will go and the OH- will just attach to the electron deficient carbon. does that have something to do with the SN2 mechanism?
  23. K

    Reverse of optical isomerism in a reaction

    Homework Statement when chiral 2-bromobutane reacts with aqueous hydroxide ions, the optical activity of the product is reversed. Suggest why the optical isomerism is reversed. The Attempt at a Solution i have no idea... but i don't know if the fact that the hydroxide ion will attack...
  24. K

    Organic, nitrogen compounds

    ooo ok... the question is from a past past past exam i guess we won't be getting such questions in the finals... because i didn't find any deamination or dealkylation reaction in the syllabus... thnks again...:)
  25. K

    Organic, nitrogen compounds

    it seems that hydrogen has been added. but i can't find any type of reaction involving hydrogen like this. i would rather think of a species which is a stronger nucleophile than the 'ammonium stuff' since the carbon attached to the - NH - has a partial positive charge. but could it be a...
  26. K

    Why densities of pure and salt water are different

    density of pure water and impure water are different... as you said, density = mass/volume. what do you think will happen to the mass and volume when salt is added to the water?!
  27. K

    Applying Oxidation Numbers to Al + KClO4

    i'm afraid i may not be an exact source for the equation of perchlorate as an oxidising agent. but, i know that Cl can have oxidation states: -1, +1, +3, +5 and + 7. if the perchlorate (+7) is reduced to chlorate (+5), then the equation is: 2H+ + ClO4- + 2e- ------> ClO3- + H2O i placed H+...
  28. K

    Applying Oxidation Numbers to Al + KClO4

    metals are reducing agents and the perchlorate is an oxidising agent.
  29. K

    Organic, nitrogen compounds

    Homework Statement Part of a long question: suggest the type of reaction occurring: (C6H5)3C-NH-CH(CH3)-CO-NHCH2COOH -----> (C6H5)3C-H + NH2-CH(CH3)-CO-NHCH2COOH The Attempt at a Solution what i got in mind is that it could a free radical substitution reaction?! using H2...
  30. K

    Quick question on iodination of acetone.

    i guess this makes more sense!
  31. K

    Quick question on iodination of acetone.

    the rate of reaction is already slow because of the acetone and H+ reacting. if you use low concentrations of them, the reaction would be even slower. and since iodine is zero order, using a very low concentration does not affect the rate. probably you have been given low concentration because...
  32. K

    Two-Step Mechanism: A + B -> D

    if A and B are solids, then, adding either of them to the reacting solution would increase their concentration, and shift the equilibrium more to the right. you are increasing the number of moles of A or B, but keeping the volume fixed. if A and B are solutions, then the concentration does not...
  33. K

    Iron Ore Extraction Methods: Open-Cut Mining & Smelting Processes

    hello so the main ore of iron is hematite Fe2O3. hint: concentration will serve to put the ores together reduction will serve to liberate the metal from its oxidised form as an ion (because most metals exist in compounds, and not as elements)...
  34. K

    Does salts react with acids?

    there are many acids, and each one has its own 'strength'. sulphuric acid is a stronger acid than ethanoic acid. if you have ethanoic acid reaction with NaOH, you will get the salt sodium ethanoate. but if you then add sulphuric acid to this salt, the weaker ethanoic acid will be displaced by...
  35. K

    Balanced Net Ionic Equation

    In ionic equations, you need only consider those ions that 'change' in the solution. 'change' in your questions refers to a change of state from aqueous to solid. spectator ions(those which remain 'unchanged') should be ignored and you have to ensure that the charges are balanced, that is the...
  36. K

    Help Society: Conduct Tests for Health Benefits

    have a test of tap water to see the ions it contains... O.o
  37. K

    Electrochemistry - Standard Cell Potentials

    the standard cell potential is more the tendency of an element to form its hydrated ion in a standard half cell. the standard half cell would consist of the element in contact with a solution of its own hydrated ion. in a standard cell, the aqueous solutions are 1 molar, the gases are at 1 atm...
  38. K

    Electrode Potential: Manganate(VII) vs Dichromate(VI) for Fe(II) Titration

    yeah that makes sense for the colour when chromate is added in excess!
  39. K

    Electrode Potential: Manganate(VII) vs Dichromate(VI) for Fe(II) Titration

    i think dichromates/chromates are quite soluble. i remember a practical we did at school to find its Ksp and the solubility in water was high if I'm not wrong. the solution will become green!
  40. K

    Electrode Potential: Manganate(VII) vs Dichromate(VI) for Fe(II) Titration

    Homework Statement Suggest why manganate(VII), rather than dichromate(VI) is used to titrate with Fe(II) in volumetric analysis. The Attempt at a Solution i have figured out 2 possible answers but both may not be correct... 1. the colour change is sharper with manganate (purple to...
  41. K

    Alkaline phenol + chloroethanoic acid

    nopes, i never heard of that?! (yet) i tried googling a lil bit - no results. what i learned is that phenols are too unreactive for esterification using carboxylic acids.
  42. K

    Calculate the oxidation number of carbon

    i think that if the process producing the fuel liberates more energy, then on oxidation of the fuel, less energy will be liberated. and, i think it is easier to separate the methane from CO2 (maybe cooling the mixture to make the CO2 solidify?!) than taking the ethanol out of the broth. i had...
  43. K

    Kinetics/reaction rate

    Homework Statement cyclopropane isomerises to propene at a temperature of 500\circC. The kinetics of the reaction was studied by measuring the volume of propene formed at every minute. The results obtained were tabulated below: Plot these experiemntal results graphically. *please...
  44. K

    Alkaline phenol + chloroethanoic acid

    Homework Statement chloroethanoic acid is added to an alkaline solution of phenol. Give the structural formula of the organic product formed and state what type of reaction takes place. it is from a past exam paper and i got no one to check my answer, which I'm a bit unsure of...
  45. K

    Calculating Average C-H Bond Energy in Methane

    yeah that makes sense! thnks
  46. K

    Calculating Average C-H Bond Energy in Methane

    Homework Statement by means of a balanced equation, including state symbols, illustrate the term the average C-H bond energy in methane. The Attempt at a Solution i know what that all the C-H bonds in methane are not the same, and the mean of these bond energies give the average...
  47. K

    Calculate the oxidation number of carbon

    Homework Statement C6H12O6\rightarrow 3CO2 + 3CH4 \DeltaH = -132 kJmol-1 C6H12O6\rightarrow 2CO2 + 2C2H5OH \DeltaH = -68 kJmol-1 1. Calculate the oxidation number of carbon in each of the products of the first reaction. 2. Comment on the relative advantages and disadvantages...
  48. K

    Identifying the strongest acid

    the stronger the acid, the easier it will be to remove a proton(H+) from it.
  49. K

    Chemistry Acid strenth of aromatic organic molecules

    is released. *edit* a mistake in posting...
  50. K

    Chemistry Acid strenth of aromatic organic molecules

    hint: a strong acid is one having a stable conjugate base(that is the anion formed after it loses a proton). or the extent to which the O - H bond is polarised. the more polarised it is, the easier the H+