2010 HSC Chemistry Revising Marathon (2 Viewers)

[Pwnage101]

To all '10 HSC Chemistry students,

With your trial examinations fast approaching, i thought it would be a good idea to start a thread where you can help each other learn.

Rules:
The OP posts a question, first person to get it correct asks the next question, and so on.

Note: try to give a full solution (As you would in the exam). If you think someone else's solution is incomplete, add to it!

You can use the Equation Editor for any calculation questions, or when presenting chemical equations. For a guide on how to use it, refer to this thread created by Jetblack2007 on the Mathematics forum.

Remember to keep it relevant to the HSC Syllabus!

[Since there are several different options, please stick to the 3 core modules.]

First Question:

The oxides of the elements in the third period of the Periodic Table demonstrate a trend in acid-base properties.

Identify ONE element from this period which forms an oxide which is described as amphoteric. Write the formula for the oxide of this element and explain why it is classified this way. Include relevant chemical equations. (4 marks)

EDIT: This thread is intended fro 2010 HSC Chemistry students. As such, only these students should attempt to answer the questions posed first, then previous HSC Chemistry students can criticise/add to their answers.

 

[hello-there]

Sulfur - sulfur trioxide
SO3 + 2H ---> H2SO3
lol im stuck now someone finish this off

 

[ibbi00]

I was thinking more like:
AL2O3(s) + 6HCL(aq) -> 2ALCL3(aq) + 3H2O(aq) (Exhibiting acidic properties)
and
Al2O3(s) + 6NaOH(aq) -> 2Al(OH)3(aq) + 3Na2O(aq) (Exhibiting basic properties)

What more could I say to tie this up nicely?

 

[Pwnage101]

Sulfur - sulfur trioxide
SO3 + 2H ---> H2SO3
lol im stuck now someone finish this off

Sulfur forms acidic oxides.

I was thinking more like:
(1) AL2O3(s) + 6HCL(aq) -> 2ALCL3(aq) + 3H2O(aq) (Exhibiting acidic properties)
and
(2) Al2O3(s) + 6NaOH(aq) -> 2Al(OH)3(aq) + 3Na2O(aq) (Exhibiting basic properties)

What more could I say to tie this up nicely?

Good work on the equations, but you've mixed them around!

(1) is demonstrating AL2O3 exhibiting basic properties because it is neutralising an acid.

(2) is demonstrating AL2O3 exhibiting acidic properties because it is neutralising a base.

Make sure you explicitly state 'Aluminium (Al) is an element whose oxide is amphoteric. Al<SUB>2</SUB>O<SUB>3</SUB>(s) , because it can neutralise both acids and bases...'.

Also i'm not too sure about your second equation, because a base (OH)- is formed in the products, so it's not that great.

Can anybody come up with an alternate equation (2) to demonstrate AL2O3 exhibiting acidic properties by neutralising a base?

EDIT: Also remember, if you've solved the question (to a reasonable standdard, more detail can always be added to it later) to post a new question.

 

[ibbi00]

Aluminium (Al) is an element whose oxide is amphoteric (Al2O3)
(2) AL2O3(s) + 6HCL(aq) -> 2ALCL3(aq) + 3H2O(l)
(1) Al2O3(s) + 2NaOH(aq) -> 2Na2AlO(aq) + H2O(l)

(1) is demonstrating AL2O3 exhibiting basic properties because it is neutralising an acid.

(2) is demonstrating AL2O3 exhibiting acidic properties because it is neutralising a base.

It's therefore evident that the oxide of Aluminium (Al2O3) is amphoteric as it has the ability to neutralise both acids and bases by exhibiting both acidic and basic properties.

EDIT:
Question: Account for the difference in boiling point and melting point of alkanoic acids, alkanols and alkenes of a similar chain length. (4 mks)

 

[mtsmahia]

Question: Account for the difference in boiling point and melting point of alkanoic acids, alkanols and alkenes of a similar chain length. (4 mks)[/quote]

The strength of the intermolecular bonding in a hydrocarbon chain accounts for its boiling point & melting point.
As compared to alkanoic acids & alkanols, alkenes (of the same molecular weight) Alkenes have the lowest boiling point/melting point. This is due to their non-polar nature, subsequently resulting in weak intermolecular forces (in the form of dispersion forces) forming between molecules.
Alkanols have relatively higher boiling/melting points, as they contain the hydroxyl functional group (-OH). Due to this Alkanols can form strong hydrogen bonds between molecules.
Alkanoic acids have the highest boiling/melting points as they have the strongest levels of intermolecular bonding. They have 3 polar bonds in each molecule: C-O, C--O, & OH bonds. Hence stronger intermolecular bonding occurs between molecules (as well as hydrogen bonding), accounting for their high boiling.melting points, [ENTER DIAGRAM ]

Please criticise my answer ... is it alrite to talk about dipole-dipole forces in Alkanoic acids?

Question: Outline the historical development of ideas about acids including those of Lavoisier, Davy & Arrhenius (6 mrks)

 

[random-1005]

Question: Outline the historical development of ideas about acids including those of Lavoisier, Davy & Arrhenius (6 mrks)[/quote]


Lavoisier --> thought oxygen was responsible for acidic properties ( i remember there was something about tree bark or something to do with this).

Davy --> Observed that HCL is acidic and didnt not contain oxygen, hence he though hyrogen gave acidic property

Arrenius --> acid forms H+ in solution and a base forms OH- in solution (however this could still not explain somethings, there were 3 points lol, but i dnt remember, look up in excel chem book)

Bronsted Lowry --> acid is proton donor, base is proton acceptor ( i know it didnt ask for last one)

QUESTION: Assess the potential of ethanol as an alternative fuel source

 

[hello-there]

ethanol has great potential being a sustainable, renewable resource being derived from biomass.
FERMENTATION TO FORM C2H5OH
C6H12O6 ------> 2CO2 + 2C2H5OH

NEGs:
-lower energy generated than respective hydrocarbons
-area of land must be dedicated for sugar cane growth
-leads to increase fert use
-contamination into waterways due to increase run off--> drinking water--->death\
-extremely expensive process

POSitives:
-burn cleanly due to O in its formula
-thus better for environment
-less CO2 emissions and unburnt products

Question: Why are flame tests considered confirmatory tests.

Also can someone explain why you need to keep the anions the same e.g. all chlorides or nitrates in flame tests. (statement from dotpoint)

 

[kazoku93]

Question: Why are flame tests considered confirmatory tests.

Flame tests qualititavely identify the presence of a metal ion. They are considered confirmatory because all metal ions have different emission spectrums. This means that when metal ion is heated by the flame, the electrons in the atom are pushed to a new position by the energy. When the electrons fall back down and leave the excited state, energy is re-emitted in the form of a photon, hence the colour of the flame allows us to identify the metal ion present

 

[random-1005]

No one seems to be posting questions.

QUESTION: Explain the formation of acid rain, and its impacts on the environment.

 

[hello-there]

SO2 from the smelting of sulfurous ores enter the atmosphere:
It then reacts with oxygen (or directly with H2O

2SO2+O2---->2SO3
OR SO2+H2O--->H2SO3
Then H2SO3+0.5O2---> H2SO4

CO2 from the burning of FF.
CO2+H2O ---> H2CO3
etcetc....
-Thse equations shwo the formation of acid rain causing the pH in waterways to drop and hence aquatic life die as they cannot survive in acidic waters.
-Buildings especially lime stone statues react causing degradation and erosion and consequently can result in death due to ifnrastructure weakening (breaks)
-Many plants wil die due as they cannot grow in acidic soil

OK back to my question "Also can someone explain why you need to keep the anions the same e.g. all chlorides or nitrates in flame tests."

 

[nat_doc]

is it becuase you can get ppts with clorides?

 

[hello-there]

The solutions can be all nitrates so i dont know what your saying
I was thinking that it may have something to do with the validity accuracy or something along those lines

 

[random-1005]

The solutions can be all nitrates so i dont know what your saying
I was thinking that it may have something to do with the validity accuracy or something along those lines

that is probably it, but i am pretty sure when i did it they didnt need to be the same

 

[random-1005]

Question: Assess the effectiveness of methods used to purify mass water supplies

 

[random-1005]

Bump

 

[iMAN2]

Question: Assess the effectiveness of methods used to purify mass water supplies

Might take a long time to type up.

In the meantime:
Explain why the rate of a reaction is increased by higher temperatures and other ways the rate of a reaction can be increased.

 

[susanpowell]

higher temperatures favour an increase in reaction rate as the molecules have higher kinetic energy and can overcome the activation energy barrier

other factors include adding a catalyst


write an ionic equation to represent the ionisation of the acid formed when SO2 gas dissolves in water

 

[random-1006]

higher temperatures favour an increase in reaction rate as the molecules have higher kinetic energy and can overcome the activation energy barrier

other factors include adding a catalyst


write an ionic equation to represent the ionisation of the acid formed when SO2 gas dissolves in water

increasing concentration of reactants is one i think, i also think decreasing volume of reaction vessel ( since reactions are based on molecules colliding) i think there is one more, its been so long since ive done chem lol

 

[hello-there]

Might take a long time to type up.

In the meantime:
Explain why the rate of a reaction is increased by higher temperatures and other ways the rate of a reaction can be increased.

to add:
Increasing pressure