Originally posted by Ng.keebin:Why is 4-aminobenzenesulfonic acid a much weaker acid than benzenesulfonic acid?
The amino group is electron-donating by resonance, hence destabilizing the negatively charged sulfonate group in the conjugate base. In addition, 4-aminobenzenesulfonic acid exists as a zwitterion in aqueous and solid states, and because ammonium groups (ie. conjugate acid of amines) are very weak acids with small Ka values, hence zwitterionic 4-aminobenzenesulfonic acid is a much weaker acid than non-zwitterionic benzenesulfonic acid.
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Ultima, Im quite lost as to where to begin with preperation for planning, should I just straight up do the question in the booklet and try to finish by november?
Originally posted by theophilus:Mr Heng, Im quite lost as to where to begin with preperation for planning, should I just straight up do the question in the booklet and try to finish by november?
http://www.worldscientific.com/worldscibooks/10.1142/9565
http://www.amazon.com/Understanding-Experimental-Planning-Advanced-Chemistry/dp/9814667900
Why when inert gas is added to a mixture of gases, the total pressure increases but partial pressures of each gas stay the same?
For heterogenous equilibrium, why is pure solids and liquids not included when calculating Kc and Kp?
Originally posted by Ng.keebin:For heterogenous equilibrium, why is pure solids and liquids not included when calculating Kc and Kp?
Originally posted by Ng.keebin:Why when inert gas is added to a mixture of gases, the total pressure increases but partial pressures of each gas stay the same?
If you're asking why the position of equilibrium doesn't shift, it's because the molarities of the active reactants and products (of the reaction) doesn't change upon addition of inert gases, so neither Qc nor Kc changes, hence the position of equilibrium doesn't shift.
Ultima, for A levels purposes can I simple assume that polar will always be able to be soluble in polar reagents and non polar solvents wil mix with non polar reagents ? Ionic salts will always dissolve because they can form ionic like bonds with polar water molecules. Anything that can form hydrogen bonds iwith water can dissolve in water. as long as the bonds holdingh the solid together is weaker than the bonds that will form with the solvent, solid will surely dissolve. please correct any misconceptions ! im struggling with the whole solubility thing ( not the energetics kind but the bonding of solvent solution )
Also e.g say when an amine is added into HCl, the solution surely dissolves and forms a salt rite? but isnt it reacting with the acid which permanently changes its chemical formula and not dissolving ? compared to maybe amine being dissolved in water which only forms hydrogen bonds with water and does not react.
Also Hormones must be made up of 2-amino carboxylic acids like proteins or any kind of amino acid?
Originally posted by theophilus:Ultima, for A levels purposes can I simple assume that polar will always be able to be soluble in polar reagents and non polar solvents wil mix with non polar reagents ? Ionic salts will always dissolve because they can form ionic like bonds with polar water molecules. Anything that can form hydrogen bonds iwith water can dissolve in water. as long as the bonds holdingh the solid together is weaker than the bonds that will form with the solvent, solid will surely dissolve. please correct any misconceptions ! im struggling with the whole solubility thing ( not the energetics kind but the bonding of solvent solution )
'Like dissolves like' is usually applicable for most cases, but the question can add in more variables to get you to discuss relative solubilities of a polar solute in 2 or 3 different solvents, all of which are polar (for example).
Not all ionic salts are soluble, hence you have Qsp and Ksp. But species like phenylammonium ions and phenoxide ions, are indeed more soluble than their molecular conjugate acid/base forms, due to ion - permanent dipole interactions which are stronger than hydrogen bonds (provided the formal charge is on a small period 2 atom).
Even if a molecule can form hydrogen bonds with water, it may not be very soluble, because of the non-polar parts of the molecule (eg. benzene ring) thermodynamically preferring to form van der Waals forces with the non-polar parts (eg. benzene ring) of the other solute molecules, while the snobbish water solvent molecules thermodynamically prefer to form hydrogen bonds with other water solvent molecules. Hence, aqueous solubility of alcohols decrease with increasing length of its non-polar hydrocarbon chain.
So once you see it as a beautiful complex spectrum of solubilities, rather than an oversimplistic black-and-white binary system of just 'soluble' or 'insoluble', you can let go of your frustrations and it will finally make logical sense for you.
Originally posted by theophilus:Also e.g say when an amine is added into HCl, the solution surely dissolves and forms a salt rite? but isnt it reacting with the acid which permanently changes its chemical formula and not dissolving ? compared to maybe amine being dissolved in water which only forms hydrogen bonds with water and does not react.
Also Hormones must be made up of 2-amino carboxylic acids like proteins or any kind of amino acid?
Hormones may or may not be protein in nature (H2 Bio students have an advantage over H2 Physics students for this topic). Only proteins are polymers of alpha-amino acids.
Hello UltimaOnline,
I have returned with some questions to clarify and would appreciate your help :)
Q1 VJC/Prelim 09/P1/38
Why is 3 not an answer, given that ethanol could be formed from the hydrolysis of ester, and the potassium dichromate (VI) would oxidise the ethanol to ethanoic acid, thereby changing its colour from orange to green?
Q2 A sample of apple juice has a pH of 3.50. A sample of HCl also has a pH of 3.50. If 1dm³ of each of apple juice and this hydrochloric acid were treated separately with the same excess amount of zinc powder, which would yield a larger volume of hydrogen gas at room temperature? Explain. (From previous parts it was found out that the concentration of the apple juice is 0.110M; Ka of apple juice ~9.08x10^-7M)
- I think both would yield the same volume of hydrogen gas - even though the concentration of the apple juice greater than that of hydrochloric acid, it is the number of moles of H+ that will react with the excess zinc power that will affect the volume of hydrogen gas produced. Even though apply juice has a higher concentration than HCl, the number of moles of H+ produced from the apple juice and that of HCl are the same given they have the same pH (same H+ concentration, same volume = same no of moles).
- However the suggested answer states “the apple juice would yield a larger volume of H2 as [HA] (0.110) > [HCl] 3.16x10^-4)
Q3
DHS/Prelim 09/P1/25
Remarks: The answer is B. However why would the O-H2C be formed on the left hand side instead of HOH2C (as suggested by A)?
Originally posted by gohby:Hello UltimaOnline,
I have returned with some questions to clarify and would appreciate your help :)
Q1 VJC/Prelim 09/P1/38
Why is 3 not an answer, given that ethanol could be formed from the hydrolysis of ester, and the potassium dichromate (VI) would oxidise the ethanol to ethanoic acid, thereby changing its colour from orange to green?
Q2 A sample of apple juice has a pH of 3.50. A sample of HCl also has a pH of 3.50. If 1dm³ of each of apple juice and this hydrochloric acid were treated separately with the same excess amount of zinc powder, which would yield a larger volume of hydrogen gas at room temperature? Explain. (From previous parts it was found out that the concentration of the apple juice is 0.110M; Ka of apple juice ~9.08x10^-7M)
- I think both would yield the same volume of hydrogen gas - even though the concentration of the apple juice greater than that of hydrochloric acid, it is the number of moles of H+ that will react with the excess zinc power that will affect the volume of hydrogen gas produced. Even though apply juice has a higher concentration than HCl, the number of moles of H+ produced from the apple juice and that of HCl are the same given they have the same pH (same H+ concentration, same volume = same no of moles).
- However the suggested answer states “the apple juice would yield a larger volume of H2 as [HA] (0.110) > [HCl] 3.16x10^-4)
Q3
DHS/Prelim 09/P1/25
Remarks: The answer is B. However why would the O-H2C be formed on the left hand side instead of HOH2C (as suggested by A)?
VJC/Prelim 09/P1/38, all 3 options are correct, including the ester, which as you pointed out will be hydrolysed to a carboxylic acid and a primary alcohol, which will be oxidized by the K2Cr2O7.
Apple juice qn : the given answer is correct, because as predicted by Le Chatelier's principle, additional H+ from the weak acid will dissociate to oxidize the Zn to Zn2+, and be reduced to additional H2(g).
DHS qn : you're right, the answer should be A, not B.
Is it possible to remove 2 carbon atoms at one go from the oxidation of an alkene? How
Does elimination reaction still occur for alcohol to form alkene when alcohol is REFLUXED with conc H2SO4 instead of carrying out the reaction at 170 degree celsius?
Originally posted by LavXuan:Is it possible to remove 2 carbon atoms at one go from the oxidation of an alkene? How
The =CH2CH2= group will be oxidized to ethandial, then ethandioic acid, then 2 mol of carbonic(IV) acid, which decomposes into 2 mol of CO2(g) + H2O(l), with thermodynamically favorable positive entropy change (since CO2(g) is gaseous), and as predicted by Le Chatelier's principle, since CO2(g) leaves the reaction solution, pulling the position of equilibrium over to the RHS.
Originally posted by LavXuan:Does elimination reaction still occur for alcohol to form alkene when alcohol is REFLUXED with conc H2SO4 instead of carrying out the reaction at 170 degree celsius?
" Comparing HF and NH3 F is more electronegative than N, thus H-F bond is mote polar than N-H bond" What does it mean when a bond is more polar than the other?
Originally posted by Christabellw:" Comparing HF and NH3 F is more electronegative than N, thus H-F bond is mote polar than N-H bond" What does it mean when a bond is more polar than the other?
Eg. the dipole moment in H-F is 1.91 D, which is larger than the dipole moment in H-Cl which is 1.08 D, which is larger than the dipole moment in H-Br which is 0.80 D.