Chemistry Questions
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Haha, my english is a bit lousy. Those kind of 'no matter how much newspaper you read also wouldn't improve' kind.
Well, not really sure about university though. But also partly because I looking for tuition to teach. Haha. I'm more well-versed in Chemistry and Biology when I was in school.
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Originally posted by d3sT1nY:
Haha, my english is a bit lousy. Those kind of 'no matter how much newspaper you read also wouldn't improve' kind.
Well, not really sure about university though. But also partly because I looking for tuition to teach. Haha. I'm more well-versed in Chemistry and Biology when I was in school.
Haven't apply uni ah? After A's can apply le mah, every yr just try your luck applying, 1 yr don't go in still got the next. Furthermore you pay the fees according to the year of admission so even if the uni fees rise, u don't pay the higher fees.
My english also bad wat. C5 in O's and went poly partly cos i worry GP will fail and still can get into uni so whats so why bother english lousy or not?
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Originally posted by dkcx:
Haven't apply uni ah? After A's can apply le mah, every yr just try your luck applying, 1 yr don't go in still got the next. Furthermore you pay the fees according to the year of admission so even if the uni fees rise, u don't pay the higher fees.
My english also bad wat. C5 in O's and went poly partly cos i worry GP will fail and still can get into uni so whats so why bother english lousy or not?
No no no. Haha, I got a place inside already since 2 years ago. Now waiting for August to come.
Alrighty. Will come out with more questions tonight then post tomorrow. Stay tune.
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Oh. So which uni and what course?
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I wouldn't want to expose myself here.
Well, you can always PM me if you keen to know.
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When we talk about acid, according to Arrhenius definition, acid is a substance that produces H+ ions when in aqueous state. So this definition limits acid to substances that can dissolve in water.
According to Bronsted-Lowry definition, acid is a proton donor. Acid is said to be dissociated after donating the proton (H+). So it encompasses acid that doesn't dissolve in water. But doesn't it also means that this definition limits acids to substances that contain the proton? Then what about those acidic oxides (non-metal oxides)?
Cl2O5(s) + 2NaOH(aq) ----> 2NaClO3(aq) + H2O(l)
I suppose the Cl2O5 is in solid state to start with. Correct me if I'm wrong.
When a substance is able to conduct electricity, it must contains ions in it that can carry the electric current, or charge carrier.
Deionized water is so-called pure water, that does not contains any ions, like calcium ions or magnesium ions, in it as compared to normal drinking water. And given that the dissociation of water is very low in normal room temperature, does it mean that deionized water cannot conduct electricity or has low electrical conductivity?
Methylamine is more basic than trimethylamine, less basic than dimethylamine. Electron-donating group on the N makes the electrons more available for protonation, so with an increase in the number of electron-donating group, it makes the amine more basic. Instead, trimethylamine is less basic than methylamine though it contains more methyl (electron-donating) group.
I remembered it has something to do with trimethylamine not being able to form hydrogen bonds with water thus the lower basicity. Or is it due to steric hindrance?
Thanks.
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Originally posted by d3sT1nY:
When we talk about acid, according to Arrhenius definition, acid is a substance that produces H+ ions when in aqueous state. So this definition limits acid to substances that can dissolve in water.
According to Bronsted-Lowry definition, acid is a proton donor. Acid is said to be dissociated after donating the proton (H+). So it encompasses acid that doesn't dissolve in water. But doesn't it also means that this definition limits acids to substances that contain the proton? Then what about those acidic oxides (non-metal oxides)?
Cl2O5(s) + 2NaOH(aq) ----> 2NaClO3(aq) + H2O(l)
I suppose the Cl2O5 is in solid state to start with. Correct me if I'm wrong.
Thanks.
An acidic oxide is not an acid by itself (depending on which definition of acid you use). To be precise, an acidic oxide undergoes hydrolysis to form an (Arrhenius and Bronsted-Lowry) acid.In your case, the hydrolysis of dichlorine pentoxide Cl2O5 yields chloric(V) acid HClO3, which then reacts with NaOH in a typical proton transfer acid-base reaction.
In terms of Arrhenius,
HClO3 (or Cl2O5) is the Arrhenius acid, while NaOH (or Na or Na2O) is the Arrhenius base.
In terms of Bronsted-Lowry,
HClO3 (from Cl2O5 + H2O) is the Bronsted-Lowry acid, while OH- (from NaOH) is the Bronsted-Lowry base.
In terms of Lewis,
H+ (from HClO3) is the Lewis acid, while OH- (from NaOH) is the Lewis base.
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Originally posted by d3sT1nY:
When a substance is able to conduct electricity, it must contains ions in it that can carry the electric current, or charge carrier.
Deionized water is so-called pure water, that does not contains any ions, like calcium ions or magnesium ions, in it as compared to normal drinking water. And given that the dissociation of water is very low in normal room temperature, does it mean that deionized water cannot conduct electricity or has low electrical conductivity?
Thanks.
Truly deionized water (ie. only ions present in low molarities are H+ and OH-) is a poor conductor of electricity, for that very reason. -
'A' Level Qn.
Originally posted by d3sT1nY:Methylamine is more basic than trimethylamine, less basic than dimethylamine. Electron-donating group on the N makes the electrons more available for protonation, so with an increase in the number of electron-donating group, it makes the amine more basic. Instead, trimethylamine is less basic than methylamine though it contains more methyl (electron-donating) group.
I remembered it has something to do with trimethylamine not being able to form hydrogen bonds with water thus the lower basicity. Or is it due to steric hindrance?
Thanks.
The stability of a conjugate acid (ie. when a base is protonated), depends on stabilization by induction, resonance, and solvation (hydration).
Recall that bond forming is exothermic (ie. products less energy hence more stable than reactants; energy lost to surroundings), and therefore favourable (enthalpic) intermolecular interactions such as ion-dipole interactions, hydrogen bonds, dipole-dipole interactions, all stabilize the species.
In the case of ammonium and alkyl ammonium cations (eg. protonated conjugate acid forms of methylamine, dimethylamine and trimethylamine), there is no resonance stabilization to speak of.
Purely in terms of induction effects (ie. the electron donating alkyl groups (in turn because C is more electronegative than H) stabilizing the positive formal charge on the N atom (a Grp V element with 0 lone pairs and 4 bond pairs) after protonation of the ammonia or alkylamine base), the greatest stabilization conferred by induction would be experienced in the tertiary alkyl ammonium cation, followed by secondary alkyl ammonium cation, followed by primary alkyl ammonium cation, and lastly the ammonium cation.
Purely in terms of solvation (hydration) effects, specifically hydrogen bonding with water molecules, the greatest stabilization conferred by solvation would be experienced in the ammonium cation (4 H-bonds), followed by primary alkyl ammonium cation (3 H-bonds), followed by secondary alkyl ammonium cation (2 H-bonds), and lastly the tertiary ammonium cation (1 H-bond).
(Note that hydrogen bonds rather than ion-dipole interactions, exist for the protonated cation in aqueous solution; the positive formal charged N atom is surrounded by hydrogens and/or alkyl groups tetrahedrally, preventing effective ion-dipole interactions with the polar water solvent molecules.)
Acknowledgements & Recommendation : Graham Patrick's "Organic Chemistry (Bios Instant Notes)" available from NUS co-op, Clementi bookstore, Amazon.com, etc. - Google's Book Search snapshot of page 92 ("Solvation effects").
Just as in real-life, it is often the (fascinating) case in Chemistry, that we have to consider opposing patterns/trends (for instance, solubility of Grp II compounds, boiling points of hydrogen halides, etc), and apply our theoretical conceptual understanding to explain observed experimental data.
In other words, based on experimental evidence, we know that such-and-such principle outweighs such-and-such principle at such-and-such a point. (A good case in point would be enthalpy vs entropy in solubility of Grp II carbonates - theoretically, enthalpy dictates carbonates become less soluble down Grp II; theoretically, entropy dictates that carbonates become more soluble down Grp II; based on experimental evidence, we know that enthalpy effect outweighs entropy effect from Be to Sr, and entropy effect outweighs enthalpy effect from Sr to Ba. Visit Jim Clark's ChemGuide.co.uk's "Solubility of Grp II compounds").
Chemistry (and all Sciences) teaches us that is an overall complex balance of (under varying circumstances, often) opposing principles/patterns/trends, and for the wise with the eyes to see, the mind to comprehend and the heart to feel; this may well serve as a ethical, moral, philosophical and spiritual lesson for humanity.
That in truth (or as Einstein would say, "relative leading edge truth"), there is no "right" and "wrong" (ie. dogma), but there is Ethics ("do unto others as you would like others to do unto you") and there is CosmoEthics ("that which results in the greatest and highest good for all beings involved and ultimately for the entire universe").
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Originally posted by UltimaOnline:
'A' Level Qn.
The stability of a conjugate acid (ie. when a base is protonated), depends on stabilization by induction, resonance, and solvation (hydration).
Recall that bond forming is exothermic (ie. products less energy hence more stable than reactants; energy lost to surroundings), and therefore favourable (enthalpic) intermolecular interactions such as ion-dipole interactions, hydrogen bonds, dipole-dipole interactions, all stabilize the species.
In the case of ammonium and alkyl ammonium cations (eg. protonated conjugate acid forms of methylamine, dimethylamine and trimethylamine), there is no resonance stabilization to speak of.
Purely in terms of induction effects (ie. the electron donating alkyl groups (in turn because C is more electronegative than H) stabilizing the positive formal charge on the N atom (a Grp V element with 0 lone pairs and 4 bond pairs) after protonation of the ammonia or alkylamine base), the greatest stabilization conferred by induction would be experienced in the tertiary alkyl ammonium cation, followed by secondary alkyl ammonium cation, followed by primary alkyl ammonium cation, and lastly the ammonium cation.
Purely in terms of solvation (hydration) effects, specifically hydrogen bonding with water molecules, the greatest stabilization conferred by solvation would be experienced in the ammonium cation (3 H-bonds), followed by primary alkyl ammonium cation (2 H-bonds), followed by secondary alkyl ammonium cation (1 H-bond), and lastly the tertiary ammonium cation (No H-bonds).
Acknowledgements & Recommendation : Graham Patrick's "Organic Chemistry (Bios Instant Notes)" available from NUS co-op, Clementi bookstore, Amazon.com, etc. - Google's Book Search snapshot of page 92 ("Solvation effects").
Just as in real-life, it is often the (fascinating) case in Chemistry, that we have to consider opposing patterns/trends (for instance, solubility of Grp II compounds, boiling points of hydrogen halides, etc), and apply our theoretical conceptual understanding to explain observed experimental data.
In other words, based on experimental evidence, we know that such-and-such principle outweighs such-and-such principle at such-and-such a point. (A good case in point would be enthalpy vs entropy in solubility of Grp II carbonates - theoretically, enthalpy dictates carbonates become less soluble down Grp II; theoretically, entropy dictates that carbonates become more soluble down Grp II; based on experimental evidence, we know that enthalpy effect outweighs entropy effect from Be to Sr, and entropy effect outweighs enthalpy effect from Sr to Ba. Visit Jim Clark's ChemGuide.co.uk's "Solubility of Grp II compounds").
Chemistry (and all Sciences) teaches us that is an overall complex balance of (under varying circumstances, often) opposing principles/patterns/trends, and for the wise with the eyes to see, the mind to comprehend and the heart to feel; this may well serve as a ethical, moral, philosophical and spiritual lesson for humanity.
That in truth (or as Einstein would say, "relative leading edge truth"), there is no "right" and "wrong" (ie. dogma), but there is Ethics ("do unto others as you would like others to do unto you") and there is CosmoEthics ("that which results in the greatest and highest good for all beings involved and ultimately for the entire universe").
I'm really speechless. Totally enlightened by your last 4 paragraphs. I have never seen anyone explain science in this manner.
Thanks for your help regarding those questions.
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Originally posted by d3sT1nY:
I'm really speechless. Totally enlightened by your last 4 paragraphs. I have never seen anyone explain science in this manner.
Thanks for your help regarding those questions.
Your appreciation is appreciated, d3sT1nY
. And you're totally welcome for my comments on your questions. In regard to the more spiritual aspects, anyone who is a (non-religious) free thinker with an open mind is invited to visit the other sections of my website.
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Alright, here I come again.
3 identical coins, made up of 2 metals, alloy.
1st one dissolved in concentrated nitric acid to form a blue solution.
2nd one added to excess diluted sulphuric acid, reddish brown precipitate and a colourless solution is formed.
Then it was filtered and ammonia solution added to the filtrate. White precipitate formed which dissolved in excess ammonia solution.
3rd one added to silver nitrate solution, after several hours, the solution turns pale blue and a grey solid is formed on the coin.
I have no idea what sulphate salt is reddish brown (provided that is the the iron salt that is formed).
The 1st coin formed Copper (II) nitrate salt which is blue in aqueous.
I'm completely baffled by this question.
Thanks in advance.
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I didn't know work in the prof office is so free that you still have time to be paid to think of chem qns...
Anyway, for white ppt to be formed with ammonia, 1 of the metals can't be a transition metal i think.
Cu is not the only compound that gives blue salts, Ni and some other ions give blue solutions as well but i don't remember too much.
Fe is 1 of the most common reddish brown ion i can think of but if theres metal iron in the coin, shouldn't it form Fe2+ before being oxidised to Fe3+ since the metal in an alloy should not be in its charged form.
Cu and Fe seems like the most ideal combination but the white ppt would be unaccountable.
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Originally posted by d3sT1nY:
Alright, here I come again.
3 identical coins, made up of 2 metals, alloy.
1st one dissolved in concentrated nitric acid to form a blue solution.
2nd one added to excess diluted sulphuric acid, reddish brown precipitate and a colourless solution is formed.
Then it was filtered and ammonia solution added to the filtrate. White precipitate formed which dissolved in excess ammonia solution.
3rd one added to silver nitrate solution, after several hours, the solution turns pale blue and a grey solid is formed on the coin.
I have no idea what sulphate salt is reddish brown (provided that is the the iron salt that is formed).
The 1st coin formed Copper (II) nitrate salt which is blue in aqueous.
I'm completely baffled by this question.
Thanks in advance.
'A' Level Qn.
'O' Level Qn (Challenging).
3 identical coins, made up of 2 metals, alloy.
1st one dissolved in concentrated nitric acid to form a blue solution.
2nd one added to excess diluted sulphuric acid, reddish brown precipitate and a colourless solution is formed.
Then it was filtered and ammonia solution added to the filtrate. White precipitate formed which dissolved in excess ammonia solution.
3rd one added to silver nitrate solution, after several hours, the solution turns pale blue and a grey solid is formed on the coin.
Identify all substances described above, including all relevant equations.
Answers :
1st experiment - copper(II) nitrate (aq) + zinc nitrate (aq)
2nd experiment - zinc sulfate (aq) + copper metal (s); zinc hydroxide (s); tetraaminezinc(II) complex ions (aq)
3rd experiment - copper(II) nitrate (aq) + zinc nitrate (aq) + silver metal (s)
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Ok can thanks, I'll go and work out all the chemical equations myself.
Indeed, it's very challenging for 'O' level student.
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Originally posted by UltimaOnline:
'A' Level Qn.
'O' Level Qn (Challenging).
3 identical coins, made up of 2 metals, alloy.
1st one dissolved in concentrated nitric acid to form a blue solution.
2nd one added to excess diluted sulphuric acid, reddish brown precipitate and a colourless solution is formed.
Then it was filtered and ammonia solution added to the filtrate. White precipitate formed which dissolved in excess ammonia solution.
3rd one added to silver nitrate solution, after several hours, the solution turns pale blue and a grey solid is formed on the coin.
Identify all substances described above, including all relevant equations.
Answers :
1st experiment - copper(II) nitrate (aq) + zinc nitrate (aq)
2nd experiment - zinc sulfate (aq) + copper metal (s); zinc hydroxide (s); tetraaminezinc(II) complex ions (aq)
3rd experiment - copper(II) nitrate (aq) + zinc nitrate (aq) + silver metal (s)
Hmm, 4got about displacement of copper metal but its called ppt ah. Been years since i did such experiments to remember what it looks like since all displacement reactions done these days involves plating.
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Sorry, I have got a question here regarding the 2nd experiment.
Why copper metal doesn't dissolve in sulphuric acid? Because it's an unreactive metal that does not react with acid?
Pardon my qualitative knowledge.
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Originally posted by d3sT1nY:
Sorry, I have got a question here regarding the 2nd experiment.
Why copper metal doesn't dissolve in sulphuric acid? Because it's an unreactive metal that does not react with acid?
Pardon my qualitative knowledge.
Cu's reactivity is below that of H in the reactivity series and thus it does not react with acids.
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Alright, then how do I explain experiment 3? And the slow reaction? Simple displacement reaction?
Wait, that doesn't explain why Cu is able to react with nitric acid. =S
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Originally posted by d3sT1nY:
Haha, my english is a bit lousy. Those kind of 'no matter how much newspaper you read also wouldn't improve' kind.
Well, not really sure about university though. But also partly because I looking for tuition to teach. Haha. I'm more well-versed in Chemistry and Biology when I was in school.
you havent seen really lousy english.like mine!
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Originally posted by d3sT1nY:
Alright, then how do I explain experiment 3? Simple displacement reaction?
Wait, that doesn't explain why Cu is able to react with nitric acid. =S
Just displacement. Cu is slightly more reactive than Ag.
Nitric acid is a very strong oxidising agent and thus will oxidise the Cu to Cu2+
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Originally posted by dkcx:
Just displacement. Cu is slightly more reactive than Ag.
Nitric acid is a very strong oxidising agent and thus will oxidise the Cu to Cu2+
Haha. Some interests just have to be cultivated. With reference to your edited away sociology.
And thanks, I forgot that nitric acid is oxidizing. That explains the use of sulphuric acid to acidify oxidizing agents. If I didn't remember wrongly.
Erm, looking back again, I see some contradiction. I meant why Zn is able to form ZnSO4 but Cu cannot form CuSO4. If you say HNO3 is strongly oxidizing, then experiment one would fail. Am I right?
CuSO4 is blue solution if I'm not wrong. But in experiment 2, the solution is colourless due to the ZnSO4.
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Originally posted by Angelababy:
you havent seen really lousy english.like mine!
That's kind of.. Erm.. Comforting?
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Originally posted by d3sT1nY:
Haha. Some interests just have to be cultivated. With reference to your edited away sociology.
And thanks, I forgot that nitric acid is oxidizing. That explains the use of sulphuric acid to acidify oxidizing agents. If I didn't remember wrongly.
When you clear your AHSS PEs then u can try to enjoy, some courses are interesting, some are nice to know bad for exams, some are downright there to just create vacancies...
H2S04 is mostly use for acidifying things since it doesn't have the strong oxiding characteristics that HNO3 has which might affect reactions.
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Question: What is means by hydroxy group on the phenol is strongly activating due to the delocalisation of lone pair of electrons on oxygen into the phenyl ring.
As in activate is an English term used here? Means to start something?
Question: I remember iron (III) chloride can also be used to distinguish between phenol and phenylamine. The phenol will form a violet complex with Fe3+, but what colour is phenylamine's complex.
Or I remembered wrongly?
Thanks.
