HSC 2012-2015 Chemistry Marathon (archive) (1 Viewer)

[HeroicPandas]

re: HSC Chemistry Marathon Archive

2

good try, every human doing chemistry will say this in one point of their life, but its wrong

@eqz

Natural systems (of an organism) requires buffers to maintain a narrow pH range for cells and enzymes to function optimally (i.e. it resists changes in pH when a small quantity of an acid/base is added to the system).

Example, hydrogen carbonate ion (biocarbonate ion) - HCO3(-)

HCO3- + H3O+ --> H2CO3 + H2O (counteracting acid)
HCO3- + OH- --> CO3(2-) + H2O (counteracting base)

This substance can behave as a buffer by neutralising any added acid/base, thus stabilising the natural system and preventing chaos such as acidosis or alkalosis

 

[hayabusaboston]

re: HSC Chemistry Marathon Archive

good try, every human doing chemistry will say this in one point of their life, but its wrong

@eqz

Natural systems (of an organism) requires buffers to maintain a narrow pH range for cells and enzymes to function optimally (i.e. it resists changes in pH when a small quantity of an acid/base is added to the system).

Example, hydrogen carbonate ion (biocarbonate ion) - HCO3(-)

HCO3- + H3O+ --> H2CO3 + H2O (counteracting acid)
HCO3- + OH- --> CO3(2-) + H2O (counteracting base)

This substance can behave as a buffer by neutralising any added acid/base, thus stabilising the natural system and preventing chaos such as acidosis or alkalosis

You must include more detail than that. You must specify how that buffer system works, in a natural system, there's never plain balance, things build up here and there, and then other things counteract that, it is an ACTIVE system, you have to describe what happens with buildup of certain things.

 

[someth1ng]

C3H7F does have 2 isomers?

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

C3H7F does have 2 isomers?

Sorry, wrote the question wrong

HOw many isomers does C4H9F have?

 

[someth1ng]

I think 4 then - I'm on the train and doing it in my head.

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

I think 4 then - I'm on the train and doing it in my head.

Close, but u got the idea haha

 

[Menomaths]

re: HSC Chemistry Marathon Archive

Sorry, wrote the question wrong

HOw many isomers does C4H9F have?

5? Not wild guess

 

[someth1ng]

1-fluorobutane
2-fluorobutane
2-methyl-1-fluoropropane
2-methyl-2-fluoropropane

I don't think I'm missing anything.

 

[Menomaths]

re: HSC Chemistry Marathon Archive

1-fluorobutane
2-fluorobutane
2-methyl-1-fluoropropane
2-methyl-2-fluoropropane

I don't think I'm missing anything.

Can you make 1/2 3/4? as in counting it from the other side. If that's the case then 6 isomers

 

[hayabusaboston]

re: HSC Chemistry Marathon Archive

Hi guys



Sent from my iPhone 6 using Tapatalk

 

[someth1ng]

Can you make 1/2 3/4? as in counting it from the other side. If that's the case then 6 isomers

No, they would be the same then. You ALWAYS use the smallest possible numbers.

 

[Menomaths]

re: HSC Chemistry Marathon Archive

Oh alright, I'm getting 4 isomers too then

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

1-fluorobutane
2-fluorobutane
2-methyl-1-fluoropropane
2-methyl-2-fluoropropane

I don't think I'm missing anything.

I am very sorry, u are correct!

This shows that chronic-multitasking is very detrimental to an individual

 

[AnimeX]

re: HSC Chemistry Marathon Archive

Compare the boiling points of alkanes, alkanols, alkanoic acids and esters. Justify your answer.

 

[albertcamus]

re: HSC Chemistry Marathon Archive

Compare the boiling points of alkanes, alkanols, alkanoic acids. Justify your answer.

dont have much time atm

but i'd draw structure of ethane, ethanol and ethanoic acid depending on mark value of question

ethane only dispersion forces so less b.p

ethanol 1 hydrogen bond due to polar, hydroxyl end which is hydrophilic so more b.p than ethane

ethanoic acid 2 hydrogen bonds (from diagram) so stronger intermolecular forces than both ethane and ethanol so highest b.p

 

[bedpotato]

re: HSC Chemistry Marathon Archive

Compare the boiling points of alkanes, alkanols, alkanoic acids and esters. Justify your answer.

alkanes < alkanols < alkanoic acids

The boiling point depends on intermolecular forces. Alkanes are non-polar molecules and weak dispersion forces are the only intermolecular forces. In alkanols, a polar OH group is present, allowing strong hydrogen bonds to be formed between molecules. Hydrogen bonds are stronger than dispersion forces and more energy is required to break the stronger hydrogen bonds than the weak dispersion forces, resulting in alkanols having higher boiling points than alkanes. Alkanoic acids can form two hydrogen bonds between each molecule, resulting in a higher boiling point than alkanols.


I don't think we need to know about boiling points of esters. Do we?


Question:

Describe the standard conditions in a galvanic cell and explain why they are necessary.

 

[Menomaths]

re: HSC Chemistry Marathon Archive

The electrolytes concentrations are 1 M, the temperature is 25°C and the pressure is 1 atmosphere. I don't know why it is like that though

 

[someth1ng]

If it's not 1M, you can create a different emf due to the phenomenon of entropy. This results in a tendency to increase in disorder - lower concentrations tend to increase in concentration more while higher concentrations will tend to decrease in concentration. This effectively changes emf to allow for more entropy to increase.

(That's how a concentration cell works)

 

[AB940]

re: HSC Chemistry Marathon Archive

Compare the boiling points of alkanes, alkanols, alkanoic acids and esters. Justify your answer.

You need to look at what kind of intermolecular forces occur between these compounds. Alkanes interact with Van Der Waal's forces due to them not being polar, which are quite weak, hence they have the lowest boiling point of the three. Alkanols and alkanoic acids both interact with hydrogen bonding. This happens when there's a disparity between the electronegativity of certain elements in a covalent bond. But, because alkanols have the functional group -OH and alkanoic acids have the functional group -OOH, the extra oxygen atom creates more polar 'sites' on the molecule, which means the intermolecular forces are stronger. The order from lowest to highest is alkanes, alkanols, then alkanoic acids.

(Someone please correct me if I just made a huge mistake)

 

[Menomaths]

re: HSC Chemistry Marathon Archive

I see
Question; Explain why in spring there is more ozone depletion in Antarctic regions. Include relevant equations