Chem p22

[Saad Sarfraz]

Guys the reaction of aluminium with chlorine i made AL2CL6 intead of AlCL3 how many marks do u think will be deducted? I personally think the examiner is gona allow this answer too

 

[aaditya menon]

Guys the reaction of aluminium with chlorine i made AL2CL6 intead of AlCL3 how many marks do u think will be deducted? I personally think the examiner is gona allow this answer too

I wrote Al2Cl6 too, darn! I'm not entirely sure if it's incorrect though.

[Although AlCl3 dimerises at low temperature to form Al2Cl6, there was heating involved so..]

 

[aaditya menon]

For Question 1, the element for liquid chloride was either phosphorus or silicon. For the coloured flame, it was sodium since it burns with a yellow flame in Cl2. For observations it could have been: Al glows, white solid formed/appears, Cl2 colour fades away/disappears (any 2) AlCl3 reacts with water to form Al2O3 and HCl, only Na dissolves, both Al and Si react. pH for Na was 7/neutral, for Al and Si the range of pH was 1-4 (any value in the given range) though i personally wrote 3 for Al and 2 for Si.

All correct, i'm not sure about one though.
Wasn't the question about the chloride of the period element which is burning? Na will burn with a yellow flame in Cl2 or any gas!
Im not saying that Na is incorrect, i'm confused myself. The burning of chlorides is something new to me.

 

[mhalvi]

rogue94
are u sure dat da ques was abt in chloride and not oxide??? coz i wrote it as sulfur burning with a blue flame in oxide...

No,it was just about the element,as far as I remember,wrote Sulphur as it burns wid blue flame.

 

[Saad Sarfraz]

I wrote Al2Cl6 too, darn! I'm not entirely sure if it's incorrect though.

[Although AlCl3 dimerises at low temperature to form Al2Cl6, there was heating involved so..]

I think they'll allow it caz as i read so it becomes solid at a very high temp. And i didnt expect it to go there just on heating in labortary

 

[Amy farvin]

ok so its wrong ryt... the ans is Na den..

 

[WhereAmazingHappens]

rogue94
are u sure dat da ques was abt in chloride and not oxide??? coz i wrote it as sulfur burning with a blue flame in oxide...

Sulfur DOES burn in blue flame hes wrong

 

[WhereAmazingHappens]

For Question 1, the element for liquid chloride was either phosphorus or silicon. For the coloured flame, it was sodium since it burns with a yellow flame in Cl2. For observations it could have been: Al glows, white solid formed/appears, Cl2 colour fades away/disappears (any 2) AlCl3 reacts with water to form Al2O3 and HCl, only Na dissolves, both Al and Si react. pH for Na was 7/neutral, for Al and Si the range of pH was 1-4 (any value in the given range) though i personally wrote 3 for Al and 2 for Si.

SULFUR burns in blue flame in chlorine and in oxygen. U got mixed up

 

[Amy farvin]

dats wat, i hav got mixed up...

 

[rogue94]

SULFUR burns in blue flame in chlorine and in oxygen. U got mixed up

Was it burning in oxygen or burning in chlorine?? :\

 

[Amy farvin]

i dont know dats wat i asked from u ppl..

 

[Amy farvin]

most probably den it must be in chlorine...

 

[Amy farvin]

den sulfur is correct if burning in chlorine or in oxygen ryt..

 

[rogue94]

If its chlorine then both sodium and sulfur are correct answers....no? :| bcuz i wrote sodium, i hope sodium isnt wrong :\ and i m sure sulfur is correct!

 

[Amy farvin]

yah.. hopefully..

 

[Saad (سعد)]

If its chlorine then both sodium and sulfur are correct answers....no? :| bcuz i wrote sodium, i hope sodium isnt wrong :\ and i m sure sulfur is correct!

It was burning in Chlorine. Its not confirmed that Sulfur burns in a blue flame in Chlorine, I'm 90% sure that Sulfur burns in a yellow flame in a chlorine atmosphere; producing a dark yellow liquid (S2Cl2).

Sodium was more correct, and safer.

I screwed up this question big time. I lost like at least 2 marks here just because of sheer stupidity, even though I knew the correct answers. I wrote 'Light yellow flame' for Aluminum's reaction in Chlorine, even though I could have written 'yellow color fades' (I had that in my mind then) as I wasn't sure of Aluminum's flame color - but I didn't. I made up something entirely new 'light yellow flame'.

Bleh.

Anyways, the correct observations were; white sparks, white solid produced, or yellow color of gas disappears.

Then I turned Aluminum chloride's reaction with water as Basic. >_< I wrote it as Acidic (ph 3), then I crossed it and wrote pH8. >_< How idiotic of me.

Question 1: The table in which the reactions of chlorides with water were asked;- was it worth 3 marks or 6?

Question 2: When writing the pH of SiCl4's reaction with water, I wrote 3-4. In the Book it says 2. Will mine be accepted or not?

Question 3: What was the enthalpy change of formation of Methanol? I got -129 kJ mol-1.

Question 4: How do we know that, one of those organic compounds we were told to draw the structure of; that contained 2 Alcohol groups?

Question 5: What was the empirical formula they asked us to calculate? I got C6H8O7 or something...

 

[aaditya menon]

Are you guyz sure it was burning in chlorine gas/oxygen gas, coz as far as I remember it was the flame test of the CHLORIDE they had asked, no?
Anyway.

SiCl4 forms HCl in water, I wrote pH 1.
Did they ask the enthalpy change of FORMATION of Methanol or the enthalpy change of the REACTION? I think it was the reaction and the answer was +129, most of my friends got that too :-/

1 mol of compound forms 2 mol of hydrogen atoms, one -OH group will give one H atom, so gotta be 2 -OH groups in 1 mol of compound to give 2 mol of H atoms.

Yea, C6H8O7.

 

[Amy farvin]

Assalamu Alaikum!!
brother now no need to worry about in past wat happened. anywayz answers for your questions are below..
ques-1: table was for 6 marks.
ques-2: i am not sure but most probably coz at school once i made that mistake and my teacher cut marks for that..
ques-3: it is +129 as combustion is an endothermic reaction.. am i correct i too have a doubt in that..
ques-4: i think its using the main formula of the compound G which was supposed to be C3H6O3. thats why the empirical formula was CH2O... that means it had 3 oxygen one was for ketone and the other two was for alcohols.
ques-5: it was CHO.

 

[aaditya menon]

Assalamu Alaikum!!
brother now no need to worry about in past wat happened. anywayz answers for your questions are below..
ques-1: table was for 6 marks.
ques-2: i am not sure but most probably coz at school once i made that mistake and my teacher cut marks for that..
ques-3: it is +129 as combustion is an endothermic reaction.. am i correct i too have a doubt in that..
ques-4: i think its using the main formula of the compound G which was supposed to be C3H6O3. thats why the empirical formula was CH2O... that means it had 3 oxygen one was for ketone and the other two was for alcohols.
ques-5: it was CHO.

I too think it was +129, but the reasoning is incorrect. Combustion is always exothermic, and they hadn't asked the enthalpy of combustion, it was of the reaction i guess. Empirical formula is C6H8O7

 

[Saad (سعد)]

Are you guyz sure it was burning in chlorine gas/oxygen gas, coz as far as I remember it was the flame test of the CHLORIDE they had asked, no?
Anyway.

SiCl4 forms HCl in water, I wrote pH 1.
Did they ask the enthalpy change of FORMATION of Methanol or the enthalpy change of the REACTION? I think it was the reaction and the answer was +129, most of my friends got that too :-/

I used the Hess Cycle and got -129...

someone please confirm this.

1 mol of compound forms 2 mol of hydrogen atoms, one -OH group will give one H atom, so gotta be 2 -OH groups in 1 mol of compound to give 2 mol of H atoms.

I wrote that since when Sodium is added to an alcohol, 1/2 mol of H2(g) are produced, but calculation shows that (and I did the calculation) that 1 mol of H2 gas is produced in this case; so there are 2 '-OH' groups present.

Would that work?