Can someone please help me out with these Multiple Choice questions? (1 Viewer)

[Equilibrium1]

I completed the 2010 Chemistry HSC paper and I found the multiple choice fairly challenging.

Can someone please explain to me how you solve Q 14? (And if you have time, can you also please explain Q 11 and Q 7?)

Thankyou very much, I really appreciate it.

Heres the paper:

http://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2010exams/pdf_doc/2010-hsc-exam-chemistry.pdf

 

[mathfreak94]

It's definately D mate...

 

[zeebobDD]

Q14 is A, the first two have hydrogen bonding it takes a lot of energy to break the bonds, the last one has a dipole dipole interaction, therefore it doesnt take as much enegery thus A

 

[mathfreak94]

^right right didnt see that.

 

[mathfreak94]

As for Q7 the answer must be citric acid, as the reaction does not go into completion with the NaOH. The weaker the acid, the more base is needed to change the colour of indicator. (compared to sulfuric acid where the reaction is complete).

 

[Cretepumpkin]

The weaker the acid, the more base is needed to change the colour of indicator. (compared to sulfuric acid where the reaction is complete).

The answer to Q7 is indeed A, but it's nothing to do with the strength of the acid. Citric acid is triprotic and so will require three equivalents of base for complete reaction, whereas sulfuric acid will require two equivalents; acetic and hydrochloric acids will require one equivalent.

Q11 must be producing an alkene from an alcohol, so C is correct. In Q14, Z is the least polar (no hydrogen-bonding possible) so will have the lowest boiling point of the three, given that they have identical molecular weights, so the answer is A.

 

[Equilibrium1]

Thanks for everyone, I really appreciate your help.

I think i might be getting confused with hydrogen bonding. I thought hydrogen bonds were formed between a hydrogen atom and a electronegative oxygen atom (i.e. 2 hydrogen bonds per oxygen atom)... doesnt that mean hydrogen bonding can be possible in the third molecule...? Im so confused =(

Can someone please correct me? thank you
=)

 

[zeebobDD]

Thanks for everyone, I really appreciate your help.

I think i might be getting confused with hydrogen bonding. I thought hydrogen bonds were formed between a hydrogen atom and a electronegative oxygen atom (i.e. 2 hydrogen bonds per oxygen atom)... doesnt that mean hydrogen bonding can be possible in the third molecule...? Im so confused =(

Can someone please correct me? thank you
=)

nope because the first two have a oh function group together like this :O-H where as the third one has a double bond carbon whos attached to a O and a H totally different

 

[Equilibrium1]

nope because the first two have a oh function group together like this :O-H where as the third one has a double bond carbon whos attached to a O and a H totally different

Does that mean hydrogen bonding can only form if you have an OH functional group present?

Thanks for your help

 

[nightweaver066]

Does that mean hydrogen bonding can only form if you have an OH functional group present?

Thanks for your help

HO
HN
HF
^^ what you want for hydrogen bonding.

 

[Equilibrium1]

Aaaaah that makes sense now... thanks so much everyone!