HELP ME ! im on DEATH ROW T___T replied by teraexa @ Tue, 31 Jul 2007 23:37:52 +0800

teraexa — Tue, 31 Jul 2007 23:37:52 +0800

Originally posted by tanjun:

For the first qn,

For the 2nd qn, can u give me the chemical formula for toluene? I can't really rmb my chem stuff.

For the 3rd qn, I also can't rmb. Sorry that I am unable to help.

Oh and to add on for the benefit of those taking H3 Chemistry or even H2 Chemistry.

In the above mentioned reaction, since there's a ring and a different substituent on different carbons, some might invariably wonder if cis-trans isomerism may occur with this compound since the Br atoms can be on the same or different side of the ring plane and the rotation of the C-C bond is restricted by the rigid ring.

Ok, generally, if just given this compound (ie 1,2-dibromocyclohexane), yes such cis-trans (or E-Z if you are really fussy) isomerism can be present. However, if the compound is formed through the above reaction, no geometric isomers can be found. This is because all the products formed through the above reaction will always be of the trans (or E) isomer.

The exact mechanism is due to the formation of the bromonium ion. When the first Br atom, acting as an electrophile, is added across the double bond, it overlaps with the 2 carbon centers (due to its large electron cloud) to form a bromonium bridge. Hence it prevents the second Br atom from approaching from the same side of the double bond and the poor 2nd Br atom has to approach from the other side of the double bond and hence forming the trans isomer exclusively. This also happens when I2 is added to a double bond.

Do correct me if I am wrong. I didn't take uni level organic chemistry =p

And yes, this is just FYI. Ignore it if you do not understand.

HELP ME ! im on DEATH ROW T___T replied by teraexa @ Tue, 31 Jul 2007 23:30:17 +0800

teraexa — Tue, 31 Jul 2007 23:30:17 +0800

Originally posted by tanjun:

For the first qn,

For the 2nd qn, can u give me the chemical formula for toluene? I can't really rmb my chem stuff.

For the 3rd qn, I also can't rmb. Sorry that I am unable to help.

2) Toluene is the common name for methylbenzene.

So for the 2nd qn Toluene + Bromine:

C6H5CH3 + Br2 -------FeBr3 catalyst----------> C6H4BrCH3 + HBr

In this case, depends on the reagent and conditions. If there is uv light present, then free radical substitution will occur on the methyl side chain of toluene.

And just in case you were wondering since it's bromine water, why do we still need an iron(III) bromide catalyst and no tri-substitution occurs, remember that only on phenols and phenylamine rings will tri-substitution occur with bromine water (aka aqueous bromine). If you were to react phenols and phenylamine with bromine in CCl4, then mono-substitution occurs.

3) For cyclohexane, it is just basically free radical substitution. So the equation should ideally be:

C6H12 + Br2 -> C6H11Br + HBr
C6H11Br + Br2 -> C6H10Br2 + HBr

and so on and so forth...

HELP ME ! im on DEATH ROW T___T replied by WoAiMeiMei @ Tue, 31 Jul 2007 21:38:58 +0800

WoAiMeiMei — Tue, 31 Jul 2007 21:38:58 +0800

Originally posted by tanjun:

Ask u sumthing. Since this is an ion, it must be present in water. Am i rite to say that? If it is present in water, there should be water ligands attached to the ion itself. So, in the end, there are still six ligands attached to the ion, thus there are six bonds and hence shouldn't the bond angle be 90deg?

i dun think we consider water if it doesnt state

HELP ME ! im on DEATH ROW T___T replied by tanjun @ Tue, 31 Jul 2007 21:28:39 +0800

tanjun — Tue, 31 Jul 2007 21:28:39 +0800

Originally posted by teraexa:

With 2 ligands, you would expect it to be linear.

However you would need to cross reference with diamminesilver(i).

Turns out that both are linear in shape.

Hence bond angle is 180 deg.

Do not need to fret so much about inorganic chemistry. It is only 1/6 of your total weightage. Focus on your physical and organic chemistry.

And yes in fact the only reaction for Transition Metal is that of Cu2+ and what happens when you add ammonia and excess ammonia to it. Only need to memorise that.

Ask u sumthing. Since this is an ion, it must be present in water. Am i rite to say that? If it is present in water, there should be water ligands attached to the ion itself. So, in the end, there are still six ligands attached to the ion, thus there are six bonds and hence shouldn't the bond angle be 90deg?

HELP ME ! im on DEATH ROW T___T replied by WoAiMeiMei @ Tue, 31 Jul 2007 21:27:45 +0800

WoAiMeiMei — Tue, 31 Jul 2007 21:27:45 +0800

i dun noe myself >.<

HELP ME ! im on DEATH ROW T___T replied by tanjun @ Tue, 31 Jul 2007 21:24:10 +0800

tanjun — Tue, 31 Jul 2007 21:24:10 +0800

Originally posted by WoAiMeiMei:

need some assistance

write equations for bromine water and hydrocarbons

*observations*

cyclohexene + bromine --> clear

toluene + bromine --> orange/yellow

cyclohexane + bromine --> red + yellow

For the first qn,

For the 2nd qn, can u give me the chemical formula for toluene? I can't really rmb my chem stuff.

For the 3rd qn, I also can't rmb. Sorry that I am unable to help.

HELP ME ! im on DEATH ROW T___T replied by WoAiMeiMei @ Tue, 31 Jul 2007 19:26:43 +0800

WoAiMeiMei — Tue, 31 Jul 2007 19:26:43 +0800

need some assistance

write equations for bromine water and hydrocarbons

*observations*

cyclohexene + bromine --> clear

toluene + bromine --> orange/yellow

cyclohexane + bromine --> red + yellow

HELP ME ! im on DEATH ROW T___T replied by unclebutcher @ Tue, 31 Jul 2007 18:55:33 +0800

unclebutcher — Tue, 31 Jul 2007 18:55:33 +0800

Originally posted by caleb_chiang:

I tot observation thingy should be like done in lab or something....

no must memorise one.

HELP ME ! im on DEATH ROW T___T replied by caleb_chiang @ Tue, 31 Jul 2007 08:38:25 +0800

caleb_chiang — Tue, 31 Jul 2007 08:38:25 +0800

I tot observation thingy should be like done in lab or something....

HELP ME ! im on DEATH ROW T___T replied by <Precious> @ Tue, 31 Jul 2007 08:34:51 +0800

Tue, 31 Jul 2007 08:34:51 +0800

Death is as natural as birth.........
There's nothing to fear!

Where studies/tests/exams are concerned, fail to prepare, prepare to fail!

HELP ME ! im on DEATH ROW T___T replied by eagle @ Tue, 31 Jul 2007 08:12:57 +0800

eagle — Tue, 31 Jul 2007 08:12:57 +0800

jia you jia you

Me only stop at O level chem
And all return liao...

HELP ME ! im on DEATH ROW T___T replied by WoAiMeiMei @ Tue, 31 Jul 2007 07:06:20 +0800

WoAiMeiMei — Tue, 31 Jul 2007 07:06:20 +0800

thanks! you’re great help ^^

HELP ME ! im on DEATH ROW T___T replied by teraexa @ Mon, 30 Jul 2007 23:42:00 +0800

teraexa — Mon, 30 Jul 2007 23:42:00 +0800

Originally posted by WoAiMeiMei:

[Au(CN)2]-

wow awesome chem work!

With 2 ligands, you would expect it to be linear.

However you would need to cross reference with diamminesilver(i).

Turns out that both are linear in shape.

Hence bond angle is 180 deg.

Do not need to fret so much about inorganic chemistry. It is only 1/6 of your total weightage. Focus on your physical and organic chemistry.

And yes in fact the only reaction for Transition Metal is that of Cu2+ and what happens when you add ammonia and excess ammonia to it. Only need to memorise that.

HELP ME ! im on DEATH ROW T___T replied by lpx88 @ Mon, 30 Jul 2007 22:11:10 +0800

lpx88 — Mon, 30 Jul 2007 22:11:10 +0800

I tot O lvl...Gave me a big fright..I tot my chem was atrocious, but not that ridiculous

HELP ME ! im on DEATH ROW T___T replied by WoAiMeiMei @ Mon, 30 Jul 2007 22:08:42 +0800

WoAiMeiMei — Mon, 30 Jul 2007 22:08:42 +0800

Originally posted by unclebutcher:

jc2 chem issit? i havent learnt ligand and whatever crap

yup

HELP ME ! im on DEATH ROW T___T replied by unclebutcher @ Mon, 30 Jul 2007 22:07:28 +0800

unclebutcher — Mon, 30 Jul 2007 22:07:28 +0800

jc2 chem issit? i havent learnt ligand and whatever crap

HELP ME ! im on DEATH ROW T___T replied by dibilo @ Mon, 30 Jul 2007 21:55:08 +0800

dibilo — Mon, 30 Jul 2007 21:55:08 +0800

Originally posted by tanjun:

For a), this qn is a matter of memorising the facts of cation test. When NaOH is added to a suspension containing Lead(II) Hydroxide, a white ppt is formed which is soluble in excess NaOH, giving a colourless solution.
Chemical Eqn is as follows: Pb2+ + 2OH - reversible reaction sign Pb(OH)2
When added in excess,
Pb(OH)2 + 2OH- reversible reaction sign [Pb(OH)4]2-

For b), a green ppt soluble in excess aqueous NH3 to give a blue solution.
Chemical Eqn: Ni2+ + 2OH- reversible reaction sign Ni(OH)2

When added in excess,
Ni(OH)2 + 6NH3 [Ni(NH36)]2+ + 2OH-

For c), a blue ppt soluble in excess aqueous NH3 to give a deep blue solution.
Chemical Eqn: Cu2+ + 2OH- reversible reaction sign Cu(OH)2
When added in excess,
Cu(OH)2 + 4NH3 [Cu(NH34)]2+ + 2OH-

For d), I look at my QA book then I manage to find out the ans. lol
Blue solution turning to yellow solution as more concentratd HCl is added.

Chemical Eqn: Cu(OH)2 + 2H+ Cu2+ + 2H2O
Cu2+ + 6H2O reversible reaction sign [Cu(H2O)6]2+
Cu(H2O)6 + 4Cl- CuCl42- + 6H2O

These 4 qns are about ligand exchange. When solution such as NaOH is added into Ni2+ solution, the basic property of NaOH will react with nickel solution causing ppt to be formed. Then, when excess NaOH is added, ligand exchange occurs. As OH- ligand has more lone pairs of electrons than H2O ligand, the pd-pd attraction of OH- is stronger than H2O.

For the last qn, if you can give me the chemical formula of the compound, it will really help me in finding out the structure of the compound.

wah kaoz pro... and you are only 20? O_O

HELP ME ! im on DEATH ROW T___T replied by WoAiMeiMei @ Mon, 30 Jul 2007 21:50:06 +0800

WoAiMeiMei — Mon, 30 Jul 2007 21:50:06 +0800

[Au(CN)2]-

wow awesome chem work!

HELP ME ! im on DEATH ROW T___T replied by tanjun @ Mon, 30 Jul 2007 21:45:40 +0800

tanjun — Mon, 30 Jul 2007 21:45:40 +0800

Originally posted by WoAiMeiMei:

i just cant get it Argh!
/wrists =[

i cant go ionic to do these
[ionic equations]

a) excess sodium hydroxide is added to a suspension containing lead II hydroxide
Equation:
Observation:

b) Excess ammonium solution is added to dilute nickel II chloride solution
Equation:
Observation:

c) dilute ammonium solution is added drop wise to copper II chloride solution
Equation:
Observation:

d) excess (conc.) HCl is added to a suspension containing copper II hydroxide.

omg help ><

and

Write the formula for dicyanoargentate (I) ion. what would be its bond angle?

save me from the bitter depths of chem detention (jkjk)!

For a), this qn is a matter of memorising the facts of cation test. When NaOH is added to a suspension containing Lead(II) Hydroxide, a white ppt is formed which is soluble in excess NaOH, giving a colourless solution.
Chemical Eqn is as follows: Pb2+ + 2OH - reversible reaction sign Pb(OH)2
When added in excess,
Pb(OH)2 + 2OH- reversible reaction sign [Pb(OH)4]2-

For b), a green ppt soluble in excess aqueous NH3 to give a blue solution.
Chemical Eqn: Ni2+ + 2OH- reversible reaction sign Ni(OH)2

When added in excess,
Ni(OH)2 + 6NH3 [Ni(NH36)]2+ + 2OH-

For c), a blue ppt soluble in excess aqueous NH3 to give a deep blue solution.
Chemical Eqn: Cu2+ + 2OH- reversible reaction sign Cu(OH)2
When added in excess,
Cu(OH)2 + 4NH3 [Cu(NH34)]2+ + 2OH-

For d), I look at my QA book then I manage to find out the ans. lol
Blue solution turning to yellow solution as more concentratd HCl is added.

Chemical Eqn: Cu(OH)2 + 2H+ Cu2+ + 2H2O
Cu2+ + 6H2O reversible reaction sign [Cu(H2O)6]2+
Cu(H2O)6 + 4Cl- CuCl42- + 6H2O

These 4 qns are about ligand exchange. When solution such as NaOH is added into Ni2+ solution, the basic property of NaOH will react with nickel solution causing ppt to be formed. Then, when excess NaOH is added, ligand exchange occurs. As OH- ligand has more lone pairs of electrons than H2O ligand, the pd-pd attraction of OH- is stronger than H2O.

For the last qn, if you can give me the chemical formula of the compound, it will really help me in finding out the structure of the compound.

HELP ME ! im on DEATH ROW T___T replied by WoAiMeiMei @ Mon, 30 Jul 2007 21:36:47 +0800

WoAiMeiMei — Mon, 30 Jul 2007 21:36:47 +0800

thanks ><

HELP ME ! im on DEATH ROW T___T replied by unclebutcher @ Mon, 30 Jul 2007 21:24:33 +0800

unclebutcher — Mon, 30 Jul 2007 21:24:33 +0800

2HCl + Cu(OH)2 2H2O +CuCl2

observation: (color of cuoh2) changes to (Color of cucl2) cant rmb offhand what the colors are

HELP ME ! im on DEATH ROW T___T replied by WoAiMeiMei @ Mon, 30 Jul 2007 21:15:08 +0800

WoAiMeiMei — Mon, 30 Jul 2007 21:15:08 +0800

i just cant get it Argh!
/wrists =[

i cant go ionic to do these
[ionic equations]

a) excess sodium hydroxide is added to a suspension containing lead II hydroxide
Equation:
Observation:

b) Excess ammonium solution is added to dilute nickel II chloride solution
Equation:
Observation:

c) dilute ammonium solution is added drop wise to copper II chloride solution
Equation:
Observation:

d) excess (conc.) HCl is added to a suspension containing copper II hydroxide.

omg help ><

and

Write the formula for dicyanoargentate (I) ion. what would be its bond angle?

save me from the bitter depths of chem detention (jkjk)!

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