Chemistry: Post your doubts here!

[Studydayandnight]

Since this is obviously a decomposition reaction, we can conclude that one mole of N2F4 decomposes into 2 moles of NF2. Therefore, only the N-N bond in the middle is broken, and not the N-F bonds. Option 1 is incorrect.

Option 2 states that the enthalpy change of the reaction is +160kJ/mol. This is the approximate bond enthalpy of the N-N bond, so this is correct.

Since we have concluded that X is NF2, we can now begin to inspect it in detail. A nitrogen atom has 5 valence electrons, and 2 of these are involved in bonding. This leaves 3 other electrons in the valence shell, unbonded. Therefore, the molecule is non-linear. Option 3 is correct.

Since Options 2 and 3 are correct, the answer is C.

Thank you!!

 

[qwertypoiu]

Assalamu Alaikum
http://studentbounty.com/pastpapers/Cambridge International Examinations (CIE)/International AS and A Level/Chemistry (9701)/2007 Nov/9701_w07_qp_1.pdf
Can someone explain me statement 1 of Q33 :/

http://studentbounty.com/pastpapers/Cambridge International Examinations (CIE)/International AS and A Level/Chemistry (9701)/2012 Jun/9701_s12_qp_11.pdf
Q18 - iam confused...plz help :/

Thanks in advance

It says pressure inside will be greater than atmospheric pressure outside. This is not true. Rather, they must be equal because the gas has stopped expanding. If the pressure inside were greater, the gas would continue pushing against the plunger and expanding.

Q 18: X - the fumes produced are HCl. If it's dissolved in aqueous potassium iodide solution, nothing happens. It dissolves. So the solution is colourless.
Y - any silver chloride solid that precipitates would dissolve in the ammonia solution, by forming Ag(NH3)2Cl. So again colourless.

 

[fantastic girl]

It says pressure inside will be greater than atmospheric pressure outside. This is not true. Rather, they must be equal because the gas has stopped expanding. If the pressure inside were greater, the gas would continue pushing against the plunger and expanding.

Q 18: X - the fumes produced are HCl. If it's dissolved in aqueous potassium iodide solution, nothing happens. It dissolves. So the solution is colourless.
Y - any silver chloride solid that precipitates would dissolve in the ammonia solution, by forming Ag(NH3)2Cl. So again colourless.

Thankyew soo much

but see in Y- first it forms the complex Ag(NH3)2Cl then its being added to silver nitrate so wont their be a ppt now ?

 

[qwertypoiu]

Thankyew soo much

but see in Y- first it forms the complex Ag(NH3)2Cl then its being added to silver nitrate so wont their be a ppt now ?

You said first it forms the complex... How? Ag+ ions are introduced from the silver nitrate solution LATER as you said.

But I understand what you mean, that they are adding the reagents the other way around. First they made the chloride ions dissolve in ammonia solution. Then they added the silver ions. This does not make any difference. The solution now has silver ions that will attempt to precipitate with chloride ions, only to be joined by the ammonia molecules also present, thus forming the complex. Hope that made sense

 

[fantastic girl]

You said first it forms the complex... How? Ag+ ions are introduced from the silver nitrate solution LATER as you said.

But I understand what you mean, that they are adding the reagents the other way around. First they made the chloride ions dissolve in ammonia solution. Then they added the silver ions. This does not make any difference. The solution now has silver ions that will attempt to precipitate with chloride ions, only to be joined by the ammonium ions also present, thus forming the complex. Hope that made sense

Ohh yea...I completely forgot ammonia was still in the complex xP
Thanks alot...I got it now =)

 

[Xaptor16]

Use of the Data Booklet is relevant to this question.
Ethyl ethanoate can be obtained from ethanoic acid and ethanol by the following reaction.
CH3CH2OH + CH3CO2H = CH3CO2CH2CH3 + H2O (where the = is the double arrow arrow)
Ethanol (30 g) and ethanoic acid (30 g) are heated under reflux together, and 22 g of ethyl
ethanoate are obtained.
What is the yield of the ester?
A. 25%
B. 38%
C. 50%
D. 77%

Answer is C, I need the explanation or workout for the calculations please!

 

[Metanoia]

Use of the Data Booklet is relevant to this question.
Ethyl ethanoate can be obtained from ethanoic acid and ethanol by the following reaction.
CH3CH2OH + CH3CO2H = CH3CO2CH2CH3 + H2O (where the = is the double arrow arrow)
Ethanol (30 g) and ethanoic acid (30 g) are heated under reflux together, and 22 g of ethyl
ethanoate are obtained.
What is the yield of the ester?
A. 25%
B. 38%
C. 50%
D. 77%

Answer is C, I need the explanation or workout for the calculations please!

Convert the masses of ethanol and ethanoic acid to moles to figure out the limiting reagent.

Limiting reactant is acid, 0.5 moles. Expected moles of ester is thus 0.5 moles, 44g.

%yield = 22/44 = 50%

 

[The Sarcastic Retard]

Use of the Data Booklet is relevant to this question.
Ethyl ethanoate can be obtained from ethanoic acid and ethanol by the following reaction.
CH3CH2OH + CH3CO2H = CH3CO2CH2CH3 + H2O (where the = is the double arrow arrow)
Ethanol (30 g) and ethanoic acid (30 g) are heated under reflux together, and 22 g of ethyl
ethanoate are obtained.
What is the yield of the ester?
A. 25%
B. 38%
C. 50%
D. 77%

Answer is C, I need the explanation or workout for the calculations please!

n of alcohol = 30/46
n of acid = 30/60
limiting reagent is acid since its no of mole is smaller
so mass of theoretical yield of ester - 30/60 x 88 = 44
percentage = 22/44 x 100% = 50%

 

[nehaoscar]

One on the CH3 group on the far left, one on the CH2 beside it, the other on either one of the CH3 groups attached to the central carbon atom.

Oh! It can also join on the CH2 besides the CH3? Thanks!

 

[nehaoscar]

Thanks a lot everyone especially Mathemagical and qwertypoiu for your explanations! They really helped

 

[Mathemagical]

Thanks a lot everyone especially Mathemagical and qwertypoiu for your explanations! They really helped

No worries, always glad to help.

 

[princess Anu]

I can't find the answers for these questions so can somebody check my answers & see if they seem correct, please?
8B 9B 1D 6 D??

I

 

[nehaoscar]

Why A? Why not D?

 

[Mathemagical]

View attachment 54264
Why A? Why not D?

Ammonia has hydrogen bonding, which is the strongest intramolecular bond, so it is the least ideal.

 

[Mathemagical]

I can't find the answers for these questions so can somebody check my answers & see if they seem correct, please?
8B 9B 1D 6 D??

IView attachment 54261View attachment 54262 View attachment 54263

Yes, I got the same answers too. Where did you get these questions from?

 

[nehaoscar]

Why not D?

 

[Mathemagical]

View attachment 54265
Why not D?

A nucleophile is a chemical species which donates an electron pair to an electrophile. Therefore, it must have a lone pair of electrons to do this.

 

[nehaoscar]

.
How are 2 and 3 correct?

Cl stays -1 all through right?
And N goes from +5 to 0 right?
So N is reduced....

 

[nehaoscar]

Why are 2 and 3 wrong?

 

[nehaoscar]

Why is 3 wrong ... it reacts with Na so shouldn't it be an alcohol?