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Originally posted by Nikkilyx:
Hi i need some help...
Which of the following will not reduce random errors in your experimental measurements?
a) double the weight of magnesium used to a calorimetry experiment
b) use a thermometer with a smaller scale
c) use activated and finer magnesium granules
d) use a larger calorimeter with the same volume of solution
i am thinking the answer is d since the rest will lead me to a more precise answer
Correcto. -
Originally posted by Flying grenade:
is the reactant CH3CH(OH)COOH?
what does the addn of water H2O do after generating PBr3 in situ ???
Obviously. If you don't add water, your final product will be different (hint : also look at the other parts of the molecule lah! wah biangz). -
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Originally posted by UltimaOnline:
Obviously. If you don't add water, your final product will be different (hint : also look at the other parts of the molecule lah! wah biangz).got it . thank u ultima.
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pg 57 and 58 made easy inorganic book
hydrolysis of both Mg2+ and Al3+ produces 1 mol of HCl.
However, pH of soln containing Al3+ is lower than Mg2+. means concentration of H+ is higher for the hydrolysis of Al3+ compared to Mg2+.
so what does 1 mol entails? it doesn't really mean equal amounts of a particular substance, even if two seperate solns have 1 mol of that particular substance? always must look at position of equilibrium, which one lies further to the right and, which equilibrium has its forward reaction of a greater extent to the right?
one way is to use ICE table?
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Originally posted by Flying grenade:
pg 57 and 58 made easy inorganic book
hydrolysis of both Mg2+ and Al3+ produces 1 mol of HCl.
However, pH of soln containing Al3+ is lower than Mg2+. means concentration of H+ is higher for the hydrolysis of Al3+ compared to Mg2+.
so what does 1 mol entails? it doesn't really mean equal amounts of a particular substance, even if two seperate solns have 1 mol of that particular substance? always must look at position of equilibrium, which one lies further to the right and, which equilibrium has its forward reaction of a greater extent to the right?
one way is to use ICE table?
You cockanaden! If hydrolysis of both Mg2+ and Al3+ produces 1 mol of HCl, wouldn't the pH be the same?!? Obviously the extent of hydrolysis is significantly greater for AlCl3, and lesser for MgCl2, hence the different pH values. Cambridge will require you to explain why, and the balanced equations will (of course) be required.
If a single source or book confuses you, cross-reference with other sources and books, to come to a better understanding of the subject matter. If you did so in this case, and you *still* came to the cockanaden conclusion that "hydrolysis of both Mg2+ and Al3+ produces 1 mol of HCl", then you might as well voluntarily withdraw from the 2016 A level exam, save yourself the pain of waiting for your U grade results in March 2017.
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Originally posted by UltimaOnline:
You cockanaden! If hydrolysis of both Mg2+ and Al3+ produces 1 mol of HCl, wouldn't the pH be the same?!? Obviously the extent of hydrolysis is significantly greater for AlCl3, and lesser for MgCl2, hence the different pH values. Cambridge will require you to explain why, and the balanced equations will (of course) be required.
If a single source or book confuses you, cross-reference with other sources and books, to come to a better understanding of the subject matter. If you did so in this case, and you *still* came to the cockanaden conclusion that "hydrolysis of both Mg2+ and Al3+ produces 1 mol of HCl", then you might as well voluntarily withdraw from the 2016 A level exam, save yourself the pain of waiting for your U grade results in March 2017.
ok i know liao
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complete reaction
is a complete reaction possible? : https://m.reddit.com/r/askscience/comments/2y3qfl/is_a_complete_reaction_possible/
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so for reversible , incomplete or reactions in equilibrium , one mol or the stoichiometric coefficient is just to balance equations. in reality, use ICE table to compute actual equilibrium concentrations of any substance.
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Originally posted by Flying grenade:
so for reversible , incomplete or reactions in equilibrium , one mol or the stoichiometric coefficient is just to balance equations. in reality, use ICE table to compute actual equilibrium concentrations of any substance.
Obviously!!! It's common sense, ain't it?!? Or your school teachers never taught you this?!? Singapore JC students don't know this?!? You suspect your peers in school don't understand or realize this?!? -
yes brudder. i like it when u ascertain. your "obviously" , gives me calmness, as u help ascertain. thank you ! :D ^^
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hmm there's approx 14000 people that sit for SG's A levels every year. some students dont know.
im glad i found BFJC. god bless me.
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Actions speak louder than words. See what grade you get for your Prelims.
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Hi, sorry to disturb again. For A level 09 P1 Q1, may I clarify if a cyclic structure is part of an "unbranched chain"? I drew a cyclohexane with -OH attached to all carbon atoms, which also fulfils the C6H12O6 formula.
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Originally posted by supercat:
Hi, sorry to disturb again. For A level 09 P1 Q1, may I clarify if a cyclic structure is part of an "unbranched chain"? I drew a cyclohexane with -OH attached to all carbon atoms, which also fulfils the C6H12O6 formula.
Cambridge was unfortunately somewhat ambiguous in this MCQ. Instead of "unbranched", Cambridge meant (and should have used the more correct term) "acyclic". As such, this TYS question required you to draw the acyclic isomeric form (below left). Being acyclic with 1 degree of unsaturation, you can deduce the double bond is C=O, since the question specified no C=C present. Hence, the answer to this MCQ is 5 mol of Na, 2.5 mol of H2.
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Ok, thank you very much, I got it =)
For A level 2010 Q17, Cambridge said "iron", so I looked at the redox potentials of -0.44V(Fe2+/Fe) and -0.04V(Fe3+/F3). Why is it the +0.77 redox potential instead? Do they mean "Fe (aq)"?
For A level 2010 Q22, regarding option B, may I ask if this is the correct mechanism?
http://imgur.com/a/2NdTG
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Originally posted by supercat:
Ok, thank you very much, I got it =)
For A level 2010 Q17, Cambridge said "iron", so I looked at the redox potentials of -0.44V(Fe2+/Fe) and -0.04V(Fe3+/F3). Why is it the +0.77 redox potential instead? Do they mean "Fe (aq)"?
For A level 2010 Q22, regarding option B, may I ask if this is the correct mechanism?
http://imgur.com/a/2NdTG
With each halogen in excess, after the Fe(s) is oxidized to Fe2+(aq), only Cl2 and Br2 can further oxdize Fe2+(aq) to Fe3+(aq), for which the standard oxidation potential is -0.77V.Your E2 mechanism is incorrect, try again.
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Is the mechanism like this??
http://imgur.com/qo9aGDQ
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Originally posted by supercat:
Is the mechanism like this??
http://imgur.com/qo9aGDQ
Yes, now that's correct. -
page 10 ks chan planning book
for a soln containing mixture of K2CO3 and KOH,
Ultima, can explain why
Volume of H+ required to convert HCO3- to CO2 and h2o is
equals to
vol used to convert CO32- to CO2+h2o , in addition to reacting with OH-
MINUS
vol used to convert CO32- to HCO3- in addition to OH-
ok i got it alr.
the few subsequent pages also helps
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page 23 planning book
dk why need divide by 4 for the mass of solid NaOH
figured out. because mass NaOH(s) required for 250cm3 = 1/4 the mass required for 1dm3
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Ilovechem
I love chem
I love bedokfunland jc
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Originally posted by Flying grenade:
page 23 planning book
dk why need divide by 4 for the mass of solid NaOH
figured out. because mass NaOH(s) required for 250cm3 = 1/4 the mass required for 1dm3
This sort of thing, full solutions given in the book, pls try to figure out yourself. This is not even an exam question. -
UPDATED
Sulfates(IV) = Sulfites.
page 221 ks chan planning book
all SULFITES(IV) are insoluble in water, except Na, K (Grp 1), NH4+ sulfites
All Sulfates(VI) are soluble except PbSO4, CaSO4, BaSO4
ks chan wrote sulfates on page 222