HSC Chemistry Question Thread

[g98]

"Nephelometric Turbidity Units", but you don't even need to know that.

Ok Thanks, and do we need to know the Winkler method?

[RuiAce]

Ok Thanks, and do we need to know the Winkler method?

Yeah nope

Unless Jake did..

[tennis1]

When the water molecules dissolve into the water you end up messing up the volume of the water as well. Plus you don't know the chemical formula for hydrous sodium carbonate to properly calculate the moles


With the burette it honestly depends on if you put acid or base in the burette, so you need to figure it out for your own scenario.

right that makes sense!
just one more thing sorry-
is there a 'general rule' that I can just memorise, because the burette thing confuses me, and I have a feeling it will be in the exam (as it's part of the new course.)
Like if there was acid in burette VS. if there was a base in burette (do we add more or less of the acid/base in burette if it's diluted, and what would be the overall effect on the concentration) thanks

[gabe.ralph]

Hey Guys, Not quit sure about the last question, can anyone give me an answer?

[FallonXay]

Hiyaa~

So now that HSC is over, I was thinking of self-teaching HSC Chemistry. So in regards to this, I wanted to ask how relevant the preliminary course is (Because textbooks and resources are quite pricey - so if the prelim course isn't too big, I won't overly bother with getting resources for it  )

Thanks 

[RuiAce]

Hiyaa~

So now that HSC is over, I was thinking of self-teaching HSC Chemistry. So in regards to this, I wanted to ask how relevant the preliminary course is (Because textbooks and resources are quite pricey - so if the prelim course isn't too big, I won't overly bother with getting resources for it  )

Thanks 

Actually, let me be honest with you.

Prelim chemistry is more useful for science than HSC chemistry. It's more worthwhile to learn that one instead.

P.S. Congrats on 100th post

[Yasminpotts1105]

Future applications of knowing how to ferment sucrose to ethanol?

[Yasminpotts1105]

Uses in society of knowing about the fermentation of sucrose to ethanol, apart from production of ethanol?

[RuiAce]

Future applications of knowing how to ferment sucrose to ethanol?

Uses in society of knowing about the fermentation of sucrose to ethanol, apart from production of ethanol?

Both of these are not in the scope of the HSC course.

The process of fermentation only serves as a means of going from cellulose to ethanol. Everything else is centered around ethanol itself, not the fermentation process.

[mbdtHSC]

When evaluating the impact on society for silver-oxide button cell, is it enough to mention its use in wristwatches and calculators due to small size and high constant voltage? I know it is used in pacemakers to force the ventricle? I think to contract with greater force, but is that kind of detail even needed and how long would a button cell last in a pacemaker anyway?

[Dolphax]

When evaluating the impact on society for silver-oxide button cell, is it enough to mention its use in wristwatches and calculators due to small size and high constant voltage? I know it is used in pacemakers to force the ventricle? I think to contract with greater force, but is that kind of detail even needed and how long would a button cell last in a pacemaker anyway?

No, it's definitely not needed to talk about "forcing ventricles." You really only need to list some properties of the button cell relating to its cost/practicality and relates it to impacts on society.

Some could include:

- very small and light
- relatively long life
- expensive metal
- constant output voltage
- non rechargeable
- non toxic metal

and then you can relate these to watches, cameras, hearing aids etc (e.g. small size allows for miniature electric appliances, non-toxic nature allows use inside body etc)

[mjorfian]

This is from the 2009 HSC paper:

20a) Calculate the mass of ethanol that must be burnt to increase the temperature of 3 210 g of water by 65°C, if exactly half of the heat released by this combustion is lost to the surroundings.
The heat of combustion of ethanol is 1367 kJ mol −1.

I got through the first step which was calculating heat of combustion, but i don't understand why they they divided the answer by 1367 in the second step to find the moles? It's probs super basic but I just can't wrap my head around WHY. (the solutions used the formula n = q/n) Would you mind explaining it to me please?

link to solutions: http://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2009exams/pdf_doc/chemistry-sample-answers-09.pdf

[RuiAce]

This is from the 2009 HSC paper:

20a) Calculate the mass of ethanol that must be burnt to increase the temperature of 3 210 g of water by 65°C, if exactly half of the heat released by this combustion is lost to the surroundings.
The heat of combustion of ethanol is 1367 kJ mol −1.

I got through the first step which was calculating heat of combustion, but i don't understand why they they divided the answer by 1367 in the second step to find the moles? It's probs super basic but I just can't wrap my head around WHY. (the solutions used the formula n = q/n) Would you mind explaining it to me please?

link to solutions: http://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2009exams/pdf_doc/chemistry-sample-answers-09.pdf

[Yasminpotts1105]

'The enthalpy of combustion of ethanol is 1364kJ mol. If you use ethanol to heat 250L of water, calculate the mass of ethanol you must use to heat the water from 20 degrees to 80 degrees. Show your working. (Data: density (H2O) = 1 g L , specific heat of water = 4.18 J g C.)

[RuiAce]

'The enthalpy of combustion of ethanol is 1364kJ mol. If you use ethanol to heat 250L of water, calculate the mass of ethanol you must use to heat the water from 20 degrees to 80 degrees. Show your working. (Data: density (H2O) = 1 g L , specific heat of water = 4.18 J g C.)

Did you mean the density of water is 1 kg/L