• Best of luck to the class of 2024 for their HSC exams. You got this!
    Let us know your thoughts on the HSC exams here
  • YOU can help the next generation of students in the community!
    Share your trial papers and notes on our Notes & Resources page
MedVision ad

Post your Q here (1 Viewer)

McLake

The Perfect Nerd
Joined
Aug 14, 2002
Messages
4,187
Location
The Shire
Gender
Male
HSC
2002
I'm ready and willing to answer ALL question from the chemisrty syllabus ...

[This was a bad idea ....]
 

BlackJack

Vertigo!
Joined
Sep 24, 2002
Messages
1,230
Location
15 m above the pavement
Gender
Male
HSC
2002
'I have not studied for Chemistry so far AT ALL..., HELP ME! I'M DOOMED!!! MY LIFE ENDS AT 9AM 8/11/2002!!!" :p

Plz describe/explain/critically analyse/discuss accuracy/justify the entire Chemistry syllabus to me.... :p (255 marks + one mark for spelling 'chemistry')

btw, if we were to just post our entire correspondence here, wouldn't it make 800 posts faster... :rolleyes: just j/k
 

McLake

The Perfect Nerd
Joined
Aug 14, 2002
Messages
4,187
Location
The Shire
Gender
Male
HSC
2002
Sorry can't help you BJ ...

(Your beyond the help of lesser mortals such as me)

Anyone else?
 

doctor

New Member
Joined
Oct 24, 2002
Messages
23
outline the role of a chemist employed in a named industry and describe thier role in this position
 

McLake

The Perfect Nerd
Joined
Aug 14, 2002
Messages
4,187
Location
The Shire
Gender
Male
HSC
2002
Originally posted by doctor
outline the role of a chemist employed in a named industry and describe thier role in this position
OK, for this question you can:

- Use Conquering Chem's answer (v. nice)
- Make it up on the spot (that's my plan)

OR

"Quality Assurance in Food Industry.
Uses AAS to check for trace elements in food, checks that product isn't poisonus. Also determines the amount of 'Na' and other substances found on the ingredients/nutritional information list."
 

McLake

The Perfect Nerd
Joined
Aug 14, 2002
Messages
4,187
Location
The Shire
Gender
Male
HSC
2002
Originally posted by Raser
which comes first
the chicken or the egg
Sadly outside the scope of the chemisrty syllabus (which I CAREFULLY MENTIONED ...)

My answer however is egg ...
 

molloby

New Member
Joined
Jul 29, 2002
Messages
5
From the Cranbrook trial:

21. (b)

Evidence shows that the overal global concentrations of NO2 in the atmosphere has not increased significantly over the last century.

Discuss the human activities that generate localised increases in NO2 concentratons and the chemical processes which prevent localised increases from being dispersed globally.

Explain how these chemical processes pose a further threat to the environment.

Support your answer with relevant chemical equations.

5 marks.

Eeeeep, I have no idea on this one.
 

spannar

New Member
Joined
Aug 13, 2002
Messages
22
Location
something called a "house"
From one of the dot points in Acidic Environment

Identify pH sd -log10[H+] and explain that a change in pH of 1 means a ten fold change in [H+]

thx in advance...i am so screwed for chem tmr
 

McLake

The Perfect Nerd
Joined
Aug 14, 2002
Messages
4,187
Location
The Shire
Gender
Male
HSC
2002
Originally posted by molloby
Discuss the human activities that generate localised increases in NO2 concentratons and the chemical processes which prevent localised increases from being dispersed globally.
NO2 comes from burning fossil fuels in factoies and cars:

N2 + 2O2 --> 2NO2

UNSURE OF PROCESSES PREVENTING SPREAD, SOMONE PLEASE EXPLAIN THAT.



Explain how these chemical processes pose a further threat to the environment.
NO2 can cause acid rain:

NO2 + H2O --> HNO3 (which I can't balance, hmm ...)

Acid rain destroys plants, kills fish and is genrally bad ...
 
Last edited:

spice girl

magic mirror
Joined
Aug 10, 2002
Messages
785
NO2 is produced from high-temp combustion:

N2 + O2 -> 2NO
nitric oxide reacts with atmospheric oxygen:
2NO + O2 -> 2NO2

This is localised pollution. NO2 causes photochemical smog:
NO2 -uv-> NO + O
O + O2 -> O3

O3 is a radical, irritating the respiratory system, and also can react with hydrocarbon pollutants to produce hydrocarbon radicals.

NO2 won't stay in atmosphere forever: NO2 reacts with water in atmosphere to produce acid rain.
2NO2 + H2O -> HNO2 + HNO3
2HNO2 + O2 -cat.-> 2HNO3

Acid rain is also bad. It damages plants and kills aquatic animals, as well as damages buildings, etc.
 

superhubert

Member
Joined
Oct 25, 2002
Messages
138
Location
half way between the gutter and the stars
help me, i think i'm screwed......
everytime i do a heat of something calculation i fuck it up. why does it change from neutralization to heat of combustion. in the second half of the equation you have to divide by molar mass of some shit and in the other you mulitiply by some number you pluck outa yer ass. could u plz explain??????????????????
to BJ, i'm a hoping chem is as easy as phys...then i might have a hope....
 

BlackJack

Vertigo!
Joined
Sep 24, 2002
Messages
1,230
Location
15 m above the pavement
Gender
Male
HSC
2002
/\H=mC/\T... (there is a negative, but it's to show that the chemicals have lost energy to heat)

For heat of combustion, this is the total energy that is used up to heat the water.

To get energy (molar heat of combustion) per mole of eg. CH3CH3OH
you'll need to take the change in mass of ethanol and divide it by the molar mass to get the moles of ethanol used.

Finally
molar heat of comb. = /\H / mol. of ethanol...

Heat of neutralisation is only slightly different. The same equation still gives the total amount of energy that is put into the water... this time calculate the total number of moles of the stuff that reacted, if you need to find molar heat of neutralisation.
Look at the equations... eg.
NaOH + HCl -> NaCL + H2O
One mole of each.... so if you put in .5 moles of NaCl and 0.5 moles of HCl, then the total moles that reacted awas 0.5 moles.
molar heat of neutralisation= /\H / 0.5 moles.
 

stuchie

New Member
Joined
Nov 6, 2002
Messages
11
Location
sydney
ok... i have a question

what is the equation for the leclanche cell

each of my textbooks say a different thing so i dunno which one i should learn....
 

Ozz^E

Member
Joined
Jul 6, 2002
Messages
256
Location
Sydney
Originally posted by molloby

Discuss the human activities that generate localised increases in NO2 concentratons and the chemical processes which prevent localised increases from being dispersed globally.
Human activites..combustion in stationary sources (power stations) and moving ones (vehicles). Basically:

N2 + O2 -> 2NO
2NO + O2 -> 2NO2

these occur at high temps both naturally in lightening and artficially in combustion chambers.

However, when oxides of nitrogen and suldur dioxide for that matter disperse through larger volume sof air, they dissolve in water droplets (rain) and so are washed out of the atmosphere:

for NOX: 2NO2 + H20 -> HNO2 + HNO3

nitrous acid in solution is catalyitically oxidised to nitric acid:

HNO2 + 02 -> 2HNO3

Hence we get ACID RAIN.

NOTE: this is important in assesing the evidence which indictaes increases in atmospheric concentration of Nox and SO2 gases.
 

Ozz^E

Member
Joined
Jul 6, 2002
Messages
256
Location
Sydney
Originally posted by spannar
From one of the dot points in Acidic Environment

Identify pH sd -log10[H+] and explain that a change in pH of 1 means a ten fold change in [H+]

thx in advance...i am so screwed for chem tmr
identify simply means that u recognise, so:

pH = -log[H3O+] (to base 10)

This scale is NOT linear, it is logarithmic to the base 10 and hence a decrease/increase by one corresponds to a 10 times more acidic/alkaline respectively substance.
 

doctor

New Member
Joined
Oct 24, 2002
Messages
23
in a titration which pieces of equipment have to be rinsed with the substance being placed in them and why is this important?
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top