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Originally posted by Flying grenade:
OMG ULTIMA THANK UUU!!!!!!!!! superb !!! BJC Ftw
It's actually BFJC ftw!
(Coz BJ sounds like the BJ in BBBJ).
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superb
clap clap
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The decomposition of Methanoyl chloride (under standard conditions) into 2 covalent gases, one acidic and one neutral , is driven by both thermodynamic driving forces, entropy and enthalpy.
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if break 3 sigma bonds to form 2 sigma bonds, the overall enthalpy change may, or may not be exothermic. it may be endothermic.
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2013/p1/qn36
how do we know if group III(now group 13)salts form (highly) colored salts or not?
we know NaCl, Ag salts, (insoluble) sulfate salts, carbonate salts, transition metal salts, all have color
dont think we have learn color of group 3 salts in whole jc life before?
a wikipedia search shows that AlCl3 : "appearance white or yellow solid " . will these count as highly colored (ionic) salts, as posited by an option from the qn?
Thanks Ultima
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Originally posted by Flying grenade:
2013/p1/qn36
how do we know if group III(now group 13)salts form (highly) colored salts or not?
we know NaCl, Ag salts, (insoluble) sulfate salts, carbonate salts, transition metal salts, all have color
dont think we have learn color of group 3 salts in whole jc life before?
a wikipedia search shows that AlCl3 : "appearance white or yellow solid " . will these count as highly colored (ionic) salts, as posited by an option from the qn?
Thanks Ultima
As far as the A level Chemistry syllabus is concerned, you'll ONLY be asked to explain the origin in color of transition metal coordination complexes, for the flame tests, or why non-transition metal complexes or salts (eg. zinc salts), or certain transition metal complexes or salts with certain OSes (eg. copper(I) salts) do not have color.You will be required to memorize colors of all other species relevant to the H2 syllabus, but questions will NOT be asked on how any color present in any other species (whether covalent or ionic, inorganic or organic) arises. Eg. you need to know the color of halogens (on it's own in gaseous/liquid/solid states, or as a solute in aqueous solvent or organic solvent), but you won't be asked on why each halogen has that color.
Bottomline, as far as color is concerned, don't worry about Group 13 compounds (not examinable in syllabus), just focus on memorizing and explaining the colors of transition metal coordination complexes.
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page 223 cs toh advanced guide
how do we know element Y exists in two oxidation states, and how do we know it could belong to group IV(group 14) or V(grp 15) ?
group 16 chlorides also decomposes on heating to liberate Cl2
from pg 218 , the oxidation number of an element corresponds to the number of e- used for bonding
but still can't deduce why element Y exists in two oxidation states
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Page 158 cstoh advanced guide polybasic acids
for example 1
where only NaHSO4 and H2O is left in the soln, the soln is still pH≈2 , strongly acidic
is the acidity due to
HSO4- 《》SO42- + H+
or
NaHSO4 + H2O 《》H2SO4 + H+ ?? idk
why for only NaHSO4 and H2O in soln, soln is acidic?
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Originally posted by Flying grenade:
page 223 cs toh advanced guide
how do we know element Y exists in two oxidation states, and how do we know it could belong to group IV(group 14) or V(grp 15) ?
group 16 chlorides also decomposes on heating to liberate Cl2
from pg 218 , the oxidation number of an element corresponds to the number of e- used for bonding
but still can't deduce why element Y exists in two oxidation states
Because as part of the H2 syllabus, you're supposed to be familiar with (ie. have already memorized) the various chlorides that exist for the different Groups. Eg. PbCl2 & PbCl4 for Group 14, and PCl3 & PCl5 for Group 15.And the data given in the question tells you that 2 different formula of the chloride of Y are able to exist (coz 1 sample was heated to liberate some Cl2, giving a different chloride of Y), that's why you're expected to deduce element Y exists in two oxidation states in its chloride.
It's true that Group 16 is also possible (SCl4 is unstable under standard conditions, but indeed 2SCl2 can decompose into S2Cl2 and Cl2), but it's not within the H2 syllabus, so you're not required to include Group 16 in your answer, but go ahead and write it in if you like, as a 3rd possibility.
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Originally posted by Flying grenade:
Page 158 cstoh advanced guide polybasic acids
for example 1
where only NaHSO4 and H2O is left in the soln, the soln is still pH≈2 , strongly acidic
is the acidity due to
HSO4- 《》SO42- + H+
or
NaHSO4 + H2O 《》H2SO4 + H+ ?? idk
why for only NaHSO4 and H2O in soln, soln is acidic?
HSO4- is technically amphiprotic, and if you're given both Ka1 and Ka2 values (unlike for A levels, since Cambridge usually simplifies it to be a strong diprotic acid), go ahead and use the amphiprotic formula to calculate the pH.Otherwise, because even the Ka2 value (for HSO4-) is still much larger than the Kb1 value (for SO4 2-), you're allowed to just regard it as acidic rather than amphiprotic : either method of calculation should give the same pH value to 3 sig fig.
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ultima i confused , that the acidity of soln, is due to the donation of H+ by HSO4- ,
or the previous example SA-WB titration in cs toh book,
the acidity due to the (acidic) salt formed somehow react with H2O undergo pseudo acid base reaction to somehow form H3O+ (NH4+ donate proton, H2O accept proton)
Which Equation , that has H+, or H3O+ as the product, so the soln is acidic?
help !
hmm yes, HSO4- is amphiprotic and amphoteric
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TL;DR : given acid color of methyl orange is red, phenolphtalein is colorless , alkaline color is, yellow and red , respectively
Wouldn't methyl orange stay Red in color when the end pt of a SA-WB titration, is at a acidic pH?? Why will methyl orange turn Yellow at the end pt , that occured at a acidic pH(for pg 157 SA-WB titration example, end pt pH≈5.5)? (given pH range methyl orange 3.1-4.4)
why/what the reason/mechanism a soln containing an indicator can suddenly change color when moles of acid = base ??
wouldn't methyl orange be red, phenolphtalein be colorless, at pH <7 ? also, yellow and red respectively for pH>7?
Wouldn't the indicators already change color at acidic/alkaline pH before reaching the end point of the reaction?
will phenolphthalein alr change color on the way to pH ≈ 8.5 for the WA-SB example?
why will phenolphtalein suddenly turn to pink from colorless at end pt when moles of acid=base?
and then for WA-WB titration , color change is gradual
This is very confusing. I'm trying very hard to understand the many numbers and terms here, it's difficult
for example, regarding pg 155, indicator table, and page 157, the WA-SB titration example
im trying to rationalise this, nt sure if it's correct or not. here goes;
Basic salt yield pH at end pt greater than 7 (pH≈8.5) . Titration curve shows a marked change in pH between 7.5 and 10.5( this means with only few drops of OH- , pH has drastic change)
the end point is within the pH range of phenolphtalein(8.3-10.0)
if the end pt of the reaction occurs within this pH range, soln color will turn from colorless to pink
Then there's thia Acid color and Alkaline color column
will phenolphtalein turn red immediately after pH>7 ?
Why will phenolphtalein suddenly turn pale pink at the end pt when whats left is the salt(CH3CO2-Na+) and H2O?
is it because theres excess acid until eqv. pt (when moles of WA and SB is the same). but then at eqv pt there's OH- due to hydrolysis of the basic salt
then shouldn't soln be red in color due to alkaline color of phenolphtalein is red?
also considering HIn is a WA,
it can also undergo WA-SB reaction
then the color is mixture of the acid color and alkaline color?
But, only a few drops of indicator added, must this be taken into consideration?
HIn + H2O 《》H3O+ + In-
HIn + NaOH 《》In-Na+ + H2O
In-Na+ +H2O 《》HIn + Na+ + OH-
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Originally posted by Flying grenade:
ultima i confused...
Yeah, I knew u would be. U got too many weaknesses in ur understanding of this topic. U need face-to-face help. Go ask ur school teacher or private tutor. With ur great wall of text, u didn't seriously think I would reply ur 1001 qns on the forum, did u?
Originally posted by Flying grenade:it can also undergo WA-SB reaction
And quit ur nonsensical acronym usage. All I see is WASABI. Be prepared to be heavily penalized by Cambridge if u use acronyms in the A levels.
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Originally posted by UltimaOnline:
HSO4- is technically amphiprotic, and if you're given both Ka1 and Ka2 values (unlike for A levels, since Cambridge usually simplifies it to be a strong diprotic acid), go ahead and use the amphiprotic formula to calculate the pH.Otherwise, because even the Ka2 value (for HSO4-) is still much larger than the Kb1 value (for SO4 2-), you're allowed to just regard it as acidic rather than amphiprotic : either method of calculation should give the same pH value to 3 sig fig.
ooh okay i understand the reasons alr !
regard HSO4- as acidic
so HSO4- 《》SO42- + H+
Thankss Ultima !!!
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nice wasabi pic !
won't use acronyms for the exams !
use here so can make some posts shorter, or can lessen the effort of repeatedly typing out the same words
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Explain why the boiling points of water(H2O), ethanol(CH3CH2OH), ethoxyethane(C2H5OC2H5) are in reverse order of their molecular masses, unlike those of their analogous sulfur compounds : H2S, C2H5SH , C2H5SC2H5
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Originally posted by Flying grenade:
Explain why the boiling points of water(H2O), ethanol(CH3CH2OH), ethoxyethane(C2H5OC2H5) are in reverse order of their molecular masses, unlike those of their analogous sulfur compounds : H2S, C2H5SH , C2H5SC2H5
Also, I told u liao, don't just post qns only (I'm not here to do ur homework for u), post ur own answer, together with ur school's given answer, and ask exactly what u dun understand or agree with, then I'll guide & advise.
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oh i got it liao. H bonds.
water higher bp than ethanol cos can form 2 H bonds per molecule
sulfur compounds only have weaker(compared to H bonds) intermolecular PdPd
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Originally posted by Flying grenade:
oh i got it liao. H bonds.
water higher bp than ethanol cos can form 2 H bonds per molecule
sulfur compounds only have weaker(compared to H bonds) intermolecular PdPd
Correct. But don't anyhow *pom* out a number for H bonds. Each water molecule can form up to 4 H bonds, while each ethanol molecule can form up to 2 H bonds.So what you need to say, is that water molecules form a larger number of H bonds between them, compared to the number of H bonds between ethanol molecules.
But you also need to add that ethanol molecules also have intermolecular van der Waals forces (all 3 types of van der Waals forces, which you also need to state are also the intermolecular interactions between ethoxyethane molecules), which you have to specify are weaker than H bonds.
So just becoz u got the idea of what's happening liao, but u will still lose marks in the A levels if ur answer doesn't specifically have all the specific points.
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Thanks Ultima !!!
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mesomeric effect and resonance same?
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why is the first I.E. of Al and Ga the same value, +577kj/mol?
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Originally posted by Flying grenade:
mesomeric effect and resonance same?
Yes.