Login

Welcome, Guest. Please login or register.

March 28, 2024, 11:15:19 pm

Author Topic: HSC Chemistry Question Thread  (Read 1040539 times)  Share 

0 Members and 2 Guests are viewing this topic.

horse9996

  • Trendsetter
  • **
  • Posts: 123
  • Respect: +11
Re: Chemistry Question Thread
« Reply #3615 on: November 02, 2018, 09:20:59 am »
+9
A 2001 HSC INDUSTRIAL CHEM QUESTION:
"Evaluate how environmental issues are addressed in the Solvay Process"
How would u go about answering this quesiton?

I would recommend planning your answer first. Consider: what are the issues? How do they impact the environment? How are they addressed? Make sure to include a judgement.

Some examples:
Carbon dioxide (greenhouse gas) is recycled
Calcium chloride (waste cause there are limited uses) is pumped into oceans or the solid can be put in landfill (but this can pollute groundwater through leaching if the rock is porous so specific criteria must be met)
Waste water must be cooled (thermal pollution)
Ammonia is recycled but some is lost to the atmosphere (pollutant_
Solids were previously put in rivers and waterways but this is ugly and blocks rivers. How used for things like fertiliser, bricks or landfill

Overall, as most reactants/products are natural, good waste management means that there is minimal environmental issues.
HSC 2018
Advanced English (88) | Maths Ext 1(47) | Chemistry (88) | Earth & Environmental Science (94 - 5th in state) | Geography (89)

ATAR 98.2

Bells_123

  • Trailblazer
  • *
  • Posts: 32
  • Respect: +9
Re: Chemistry Question Thread
« Reply #3616 on: November 02, 2018, 11:50:58 am »
0
Yep this is a good place to ask  :) I think it could be asked again, as you said maybe as a shorter answer rather than a longer response or vice versa. I doubt you would get a question exactly the same as last year, but you could get one using similar principles. I would revise it to be safe, but I guess it's up to you, if you don't feel like you have enough time to study everything, that could be one of the things you leave until last because it would be less likiely to come up. I don't really know about previous years though.
I struggle with this as well, I think everyone does  :-\  I have 2 strategies, one is using flashcards (I find flashcards good for chemistry for things like polyatomic ions and solubility rules, as well as this). My other strategy is writing it out as a process/flowchart, because I find it is easyier to remember one longer process rather than the individual results. I think you need to remember this anyway so you know in which order the tests need to be conducted. So I have just written it out a few times, trying to do as much of it from memory as I can each time (I find just copying it doesn't help me remember as much). Hope this helps!
For your first question I thought they can be in the same electrolyte, for example if you are using intert electrodes to electrolyse a salt solution. Where did you hear that they can't be in the same electrolyte?

For sulfate reducing bacteria there are 2 different equations depending on if it is occurring in an acidic or non-acidic microclimate, so this might have caused your confusion? I think you only need to remember 1 though. This is the one I am using for an acidic microclimate:
oxidation: Fe (s) ---> Fe2+ (aq) + 2e-
reduction: SO42- (aq) +10H+ (aq) + 8e- ---> H2S (aq) + 4H2O
overall: 4Fe (s) + SO42- (aq) +10H+ (aq) ---> 4Fe2+ (aq) + H2S (aq) + 4H2O

Hope this helps  :)

Thanks for the reply! For the first question I was wondering why the electrodes can be in the same electrolyte for electrolytic cells unlike a lot of galvanic cells which are in different electrolytes - does it have something to do with the flow of ions in the solution when an electric current is applied?
Class of 2018

Subjects:
Chemistry | Biology | Economics | Advanced English | Advanced Maths | Extension Maths

"Always remember than you are absolutely unique, just like everyone else." ;)

jazcstuart

  • MOTM: SEP 18
  • Forum Obsessive
  • ***
  • Posts: 231
  • Respect: +180
Re: Chemistry Question Thread
« Reply #3617 on: November 02, 2018, 12:51:12 pm »
0
Thanks for the reply! For the first question I was wondering why the electrodes can be in the same electrolyte for electrolytic cells unlike a lot of galvanic cells which are in different electrolytes - does it have something to do with the flow of ions in the solution when an electric current is applied?
Oh sorry, I must have read your question wrong!

Tbh I don't really know why this is usually the case (maybe someone else can clarify?). I think it depends on what you are trying to achieve with the cell, for example with electrolytic cells often you are trying to separate a solution, which is why they have the same electrolyte.

Electrolytic cells can be in different electrolytes if you want to reverse a typical galvanic cell, and galvanic cells can be in the same electrolyte (for example the corrosion of iron in seawater acts as a galvanic cell). So it's not a case of electrolytic cells can't be in separate electrolytes or vice versa, I think it's just how they are usually written.

Sorry that wasn't super helpful, if anyone else has a better answer that would be great.
HSC 2017 - Mathematics, Music 1
HSC 2018 - English (Advanced), Maths Extension 1, Chemistry, Geography, Earth and Environmental Science

2019 - B Renewable Energy Engineering @ University of Newcastle

Bri MT

  • VIC MVP - 2018
  • Administrator
  • ATAR Notes Legend
  • *****
  • Posts: 4719
  • invest in wellbeing so it can invest in you
  • Respect: +3677
Re: Chemistry Question Thread
« Reply #3618 on: November 02, 2018, 01:24:19 pm »
0
Thanks for the reply! For the first question I was wondering why the electrodes can be in the same electrolyte for electrolytic cells unlike a lot of galvanic cells which are in different electrolytes - does it have something to do with the flow of ions in the solution when an electric current is applied?

The reductant wants to give its electrons to the oxidant right? 
So the reductant will donate its electrons and they go through the external circuit to reach the oxidant & you have current!  But if the reductant and oxidant are in contact with each other, you're not going to push electrons through the external circuit - you'll just directly transfer them. 
So if they aren't separated,  you'll have a spontaneous reaction with an associated enthalpy change but no electricity generation. 

With an electrolytic cell,  you're forcing movement of electrons that would not spontaneously occur - so you wouldn't have a spontaneous reaction occurring between the oxidant and reductant when they're in contact.


Little bit of an oversimplification, but I hope this helps & addresses your question :)

preliminary17hsc18

  • Trailblazer
  • *
  • Posts: 33
  • Respect: +2
Re: Chemistry Question Thread
« Reply #3619 on: November 02, 2018, 01:28:51 pm »
0

Need some help with this absolutely horrendous question for shipwrecks:
How does iron corrode in acidic conditions, because:
Oxidation: Fe --> Fe2+ 2e-
Reduction: O2 + 4H+ + 4e- --> 2H20
So in the end you are left with iron ions and water so how does the iron form the hydroxide that's the actual rust?

Mate2425

  • Trendsetter
  • **
  • Posts: 145
  • "A rolling stone, gathers no moss!"
  • Respect: 0
Re: Chemistry Question Thread
« Reply #3620 on: November 02, 2018, 02:29:08 pm »
+1
Hey guys, i always seem to not get full marks in heat of combustion questions mainly due to not knowing what equations to specifically use. If possible could someone please send the equations we need to answer these questions and also the general process i should apply in order to gain a better mark in these questions.

Thanks to you all!  :) :)

cocopops201

  • Forum Regular
  • **
  • Posts: 51
  • She believed she could, so she did.
  • Respect: +7
Re: Chemistry Question Thread
« Reply #3621 on: November 02, 2018, 02:57:43 pm »
0
Whats a sample response for the 2007 forensic science:

Evaluate the implications of the use of DNA as an identification molecule for society

horse9996

  • Trendsetter
  • **
  • Posts: 123
  • Respect: +11
Re: Chemistry Question Thread
« Reply #3622 on: November 02, 2018, 03:01:24 pm »
+3
Hey guys, i always seem to not get full marks in heat of combustion questions mainly due to not knowing what equations to specifically use. If possible could someone please send the equations we need to answer these questions and also the general process i should apply in order to gain a better mark in these questions.

Thanks to you all!  :) :)

1. Calculate the change in heat of the water (convert to kJ by dividing by 1000, delta H = mc delta T)
2. Calculate the mass and following that the moles of the alkanol which was combusted (number of moles  = mass/molar mass)
3. Heat of combustion = change in heat (part 1) divided by number of moles of the alkanol (part 2)
HSC 2018
Advanced English (88) | Maths Ext 1(47) | Chemistry (88) | Earth & Environmental Science (94 - 5th in state) | Geography (89)

ATAR 98.2

jazcstuart

  • MOTM: SEP 18
  • Forum Obsessive
  • ***
  • Posts: 231
  • Respect: +180
Re: Chemistry Question Thread
« Reply #3623 on: November 02, 2018, 03:21:13 pm »
+2
1. Calculate the change in heat of the water (convert to kJ by dividing by 1000, delta H = mc delta T)
2. Calculate the mass and following that the moles of the alkanol which was combusted (number of moles  = mass/molar mass)
3. Heat of combustion = change in heat (part 1) divided by number of moles of the alkanol (part 2)
Just to add to this, the m in the first formula is the mass of the liquid being heated, NOT the mass of the alkonol burned. I always used to get confused by this. The c is the specific heat capacity (generally of water, which is on the back of the periodic table). Make sure everything is in the same units, so if you use grams for the mass you must use grams for the specific heat capacity as well.
So essentially in the first step you are finding delta H, which is just the heat of combustion, and in the third step you are finding (delta H)/mol, which is the molar heat of combustion.

Need some help with this absolutely horrendous question for shipwrecks:
How does iron corrode in acidic conditions, because:
Oxidation: Fe --> Fe2+ 2e-
Reduction: O2 + 4H+ + 4e- --> 2H20
So in the end you are left with iron ions and water so how does the iron form the hydroxide that's the actual rust?
Not sure about this sorry, the only thing I can think of is that the Fe2+ reacts with OH- already in the water, but I have no idea if this is right.
« Last Edit: November 02, 2018, 03:23:28 pm by jazcstuart »
HSC 2017 - Mathematics, Music 1
HSC 2018 - English (Advanced), Maths Extension 1, Chemistry, Geography, Earth and Environmental Science

2019 - B Renewable Energy Engineering @ University of Newcastle

Mate2425

  • Trendsetter
  • **
  • Posts: 145
  • "A rolling stone, gathers no moss!"
  • Respect: 0
Re: Chemistry Question Thread
« Reply #3624 on: November 02, 2018, 11:16:15 pm »
+1
Just to add to this, the m in the first formula is the mass of the liquid being heated, NOT the mass of the alkonol burned. I always used to get confused by this. The c is the specific heat capacity (generally of water, which is on the back of the periodic table). Make sure everything is in the same units, so if you use grams for the mass you must use grams for the specific heat capacity as well.
So essentially in the first step you are finding delta H, which is just the heat of combustion, and in the third step you are finding (delta H)/mol, which is the molar heat of combustion.
Not sure about this sorry, the only thing I can think of is that the Fe2+ reacts with OH- already in the water, but I have no idea if this is right.

Thanks jazcstuart!
When you said the specific heat capacity must be in the same units e.g grams does that mean i have to times the value from formula sheet by 10^3.


horse9996

  • Trendsetter
  • **
  • Posts: 123
  • Respect: +11
Re: Chemistry Question Thread
« Reply #3625 on: November 03, 2018, 08:07:07 am »
0
Thanks jazcstuart!
When you said the specific heat capacity must be in the same units e.g grams does that mean i have to times the value from formula sheet by 10^3.

I'm not sure, I always use 4.18 and get the right answer. Its more grams vs kilograms and joules vs kilojoules I think
HSC 2018
Advanced English (88) | Maths Ext 1(47) | Chemistry (88) | Earth & Environmental Science (94 - 5th in state) | Geography (89)

ATAR 98.2

horse9996

  • Trendsetter
  • **
  • Posts: 123
  • Respect: +11
Re: Chemistry Question Thread
« Reply #3626 on: November 03, 2018, 08:54:11 am »
0
2012 q33

"Chemists can assist in reversing or minimising the environmental problems caused by technology and the human demand for products and services.

With reference to this statement, assess the need for chemists to collaborate when monitoring the environmental impact of a named electrochemical cell."

Thoughts?
HSC 2018
Advanced English (88) | Maths Ext 1(47) | Chemistry (88) | Earth & Environmental Science (94 - 5th in state) | Geography (89)

ATAR 98.2

Dragomistress

  • Trendsetter
  • **
  • Posts: 162
  • Respect: 0
  • School: James Ruse Agricultural High School
  • School Grad Year: 2018
Re: Chemistry Question Thread
« Reply #3627 on: November 03, 2018, 09:04:13 am »
0
Hey,
How do I know which the anode and which is the cathode in an electrochemical cell?

Bri MT

  • VIC MVP - 2018
  • Administrator
  • ATAR Notes Legend
  • *****
  • Posts: 4719
  • invest in wellbeing so it can invest in you
  • Respect: +3677
Re: Chemistry Question Thread
« Reply #3628 on: November 03, 2018, 09:09:15 am »
+1
Hey,
How do I know which the anode and which is the cathode in an electrochemical cell?

The anode is always the site of oxidation and the cathode is always the site of reduction

jazcstuart

  • MOTM: SEP 18
  • Forum Obsessive
  • ***
  • Posts: 231
  • Respect: +180
Re: Chemistry Question Thread
« Reply #3629 on: November 03, 2018, 09:11:29 am »
0
Thanks jazcstuart!
When you said the specific heat capacity must be in the same units e.g grams does that mean i have to times the value from formula sheet by 10^3.
Like horse9996 I usually just use 4.18J g-1 K-1 because usually the information given is in jules and grams. The one on the formula sheet is 4.18J kg-1 K-1, so to get it in grams you actually have to divide it by 103 (since it is ^-1). Don't worry about it too much, I think it's easiest to just use 4.18J g-1 K-1 and make sure all your other information is in jules and grams.
2012 q33

"Chemists can assist in reversing or minimising the environmental problems caused by technology and the human demand for products and services.

With reference to this statement, assess the need for chemists to collaborate when monitoring the environmental impact of a named electrochemical cell."

Thoughts?
Yeah this is a really hard question, I've had a go at it in class. Essentially you need to choose a cell and talk about it's environmental impact, an talk about the different skills chemists need at different stages in the use of the battery (eg. production, use and disposal) to minimise this impact. Have a look at the sample answer if you haven't already, I think it will give you a better idea  :)
« Last Edit: November 03, 2018, 09:14:59 am by jazcstuart »
HSC 2017 - Mathematics, Music 1
HSC 2018 - English (Advanced), Maths Extension 1, Chemistry, Geography, Earth and Environmental Science

2019 - B Renewable Energy Engineering @ University of Newcastle