Login

Welcome, Guest. Please login or register.

March 29, 2024, 05:11:36 am

Author Topic: VCE Chemistry Question Thread  (Read 2313322 times)  Share 

0 Members and 3 Guests are viewing this topic.

Chocolatepistachio

  • Science Games: Silver
  • Forum Obsessive
  • ***
  • Posts: 470
  • Respect: +51
Re: VCE Chemistry Question Thread
« Reply #8790 on: September 23, 2020, 05:42:28 pm »
0
i need help with this question

and is this reaction exothermic or endothermic because i thought it was exothermic

Thanks!

Unknown-111

  • Forum Regular
  • **
  • Posts: 54
  • Respect: +2
Re: VCE Chemistry Question Thread
« Reply #8791 on: September 23, 2020, 06:32:41 pm »
0
Hey guys I need help with redox reaction questions, I still find it quite hard.

Chocolatepistachio

  • Science Games: Silver
  • Forum Obsessive
  • ***
  • Posts: 470
  • Respect: +51
Re: VCE Chemistry Question Thread
« Reply #8792 on: September 23, 2020, 07:11:35 pm »
0
i need help urgently. pls

how do you work out solution 5 has the highest pH

tigerclouds

  • Trendsetter
  • **
  • Posts: 147
  • Respect: +27
Re: VCE Chemistry Question Thread
« Reply #8793 on: September 23, 2020, 07:31:45 pm »
0
You do not need to know how to answer pH calculation questions. This question is getting asked so often tho, I should put it in my sig
LOL I love how you actually did it - soz I don't exactly check every question that's ever been asked. So we don't need to know anything about Ka? Also would we need to know about the concentration fraction? (I'm just seeing all these terms in past VCAA exams and want to know if they're still assessable)

Can you give context for when you've been asked to calculate percentage ionisation? Because that could mean a few different things
I've attached a picture of a question from the 2013 VCAA exam

Thank you.
« Last Edit: September 23, 2020, 09:57:23 pm by tigerclouds »

Chocolatemilkshake

  • MOTM: JAN 21
  • Forum Obsessive
  • ***
  • Posts: 344
  • Respect: +371
Re: VCE Chemistry Question Thread
« Reply #8794 on: September 24, 2020, 08:13:37 pm »
0
This may be a naïve question but do you include the amount of sig figs in a temperature figure given on a question?
2021-2025: BMedSci/M.D @ Monash

ArtyDreams

  • MOTM: Jan 20
  • Victorian Moderator
  • Forum Leader
  • *****
  • Posts: 518
  • Fly against the wind. Not with it.
  • Respect: +599
Re: VCE Chemistry Question Thread
« Reply #8795 on: September 24, 2020, 08:48:46 pm »
+4
This may be a naïve question but do you include the amount of sig figs in a temperature figure given on a question?

Correct me if I'm wrong but if you've used the value in the calculation, then yes.

Coolgalbornin03Lo

  • Forum Leader
  • ****
  • Posts: 542
  • Respect: +132
Re: VCE Chemistry Question Thread
« Reply #8796 on: September 25, 2020, 03:49:40 pm »
0
What would be the easiest way to write the half Equation in a fuel cell which involves ethanol and produces carbon dioxide in alkaline cell?

I tried this question for 15 minutes but could not get and I have the answer but the it was hard! The way I go about balancing is C——>H——>O and I balanced the O with water and the H with OH- because it’s alkaline conditions
My avatar sums up life.
“I’m free to be the greatest one alive” ~ Sia
╔══════════════════════════════╗
2020: English | Methods | Biology | Chemistry |              Psychology | ATAR: 0
╚══════════════════════════════╝

Chocolatepistachio

  • Science Games: Silver
  • Forum Obsessive
  • ***
  • Posts: 470
  • Respect: +51
Re: VCE Chemistry Question Thread
« Reply #8797 on: September 25, 2020, 04:58:37 pm »
0
For this question
When a reaction is at equilibrium and more reactant is added which of the following changes is the immediate result?
A the forward reaction rate remains the same
B the forward reaction and the reverse reaction remain the same
C the reverse reaction rate increases
D the forward reaction rate increases

Would it be D

keltingmeith

  • Honorary Moderator
  • Great Wonder of ATAR Notes
  • *******
  • Posts: 5493
  • he/him - they is also fine
  • Respect: +1292
Re: VCE Chemistry Question Thread
« Reply #8798 on: September 25, 2020, 05:30:09 pm »
+4
holy crap this is like a gauntlet

i need help with this question

and is this reaction exothermic or endothermic because i thought it was exothermic

Thanks!

Well, why do you think it's exothermic?

Hey guys I need help with redox reaction questions, I still find it quite hard.

Sure, what do you find so hard about them? Where do your problems lie?

i need help urgently. pls

how do you work out solution 5 has the highest pH

Well, pH is inversely proportional to the concentration of hydronium ions in solution - so the solution with the highest pH will have the lowest concentration of hydronium ions. This is a picture, not a number, so you need to think about this conceptually. If you look at the equation:



How do you make this number, C, smaller? Either by making the numerator smaller, or the denominator bigger (if this confuses you, think about what happens to the decimal form of 2/3 if you make 3 a bigger number or 2 a smaller number). So, which picture has the smallest n but the biggest V?

LOL I love how you actually did it - soz I don't exactly check every question that's ever been asked. So we don't need to know anything about Ka? Also would we need to know about the concentration fraction? (I'm just seeing all these terms in past VCAA exams and want to know if they're still assessable)
I've attached a picture of a question from the 2013 VCAA exam

Thank you.

I mean, theoretically, you could still be given an equation like this in your exam:



Then asked to calculate the equilibrium constant, asked to find the concentration of hydronium ions, etc., but you wouldn't be expected to recall any of this by yourself - you'd have to be guided through the material, just like you would be on any other equilibrium question.

Yeah, in this case, they're using %ionisation as an acid-base term, you don't need to know how to calculate it (sidenote: this was the exam I did and I don't remember that question or how to calculate it, oops). If you see a term in a past exam that you don't recognise, and it's at all related to something you know is removed from the study design, tbh you're better off just assuming that you don't need to know how to calculate it - there are still PLENTY of exams relating to this study design that will tell you if something's worth remembering or not. Typically, VCAA will have covered every type of concept they might ask about in a span of two years. A new year's exam might seem different in the way they've "dressed up" the questions, but the core concepts (including equations you should need) should be the same.

This may be a naïve question but do you include the amount of sig figs in a temperature figure given on a question?

See ArtyDreams. +1. All sig figs are real sig figs.

What would be the easiest way to write the half Equation in a fuel cell which involves ethanol and produces carbon dioxide in alkaline cell?

I tried this question for 15 minutes but could not get and I have the answer but the it was hard! The way I go about balancing is C——>H——>O and I balanced the O with water and the H with OH- because it’s alkaline conditions

Yeah, so alkaline cells are difficult in that way because adding in hydroxide ALSO adds in H, not just O. The easiest way to do these types of questions is to balance them out the same way you would for acidic conditions. Then, whichever side has the free protons, add in the same amount of hydroxide on BOTH sides of the equation. Eg, let's say we have:



We have 8 free protons on the left side of the equation, so let's add 8 hydroxides to both sides:



Any free protons and hydroxide ions will combine to make water:



Cancel out the excess water:



And you're done! A balanced electrochemical reaction in alkaline medium. Why don't you try this for your question, now?

For this question
When a reaction is at equilibrium and more reactant is added which of the following changes is the immediate result?
A the forward reaction rate remains the same
B the forward reaction and the reverse reaction remain the same
C the reverse reaction rate increases
D the forward reaction rate increases

Would it be D

Why do you think D would be correct?

Chocolatepistachio

  • Science Games: Silver
  • Forum Obsessive
  • ***
  • Posts: 470
  • Respect: +51
Re: VCE Chemistry Question Thread
« Reply #8799 on: September 25, 2020, 05:46:25 pm »
0
It is exothermic because heat is on the products side

D because more reactant is added so you need to use it up in the forward direction then the rate of the forward increases


I’m confused how do you work out the concentration of hydronium ions from the percentage ionisation
« Last Edit: September 25, 2020, 05:57:10 pm by Chocolatepistachio »

keltingmeith

  • Honorary Moderator
  • Great Wonder of ATAR Notes
  • *******
  • Posts: 5493
  • he/him - they is also fine
  • Respect: +1292
Re: VCE Chemistry Question Thread
« Reply #8800 on: September 25, 2020, 05:57:02 pm »
0
It is exothermic because heat is on the products side

D because more reactant is added so you need to use it up in the forward direction then the rate of the forward increases

Sounds like you don't need us to check your answers for you ;)

Chocolatepistachio

  • Science Games: Silver
  • Forum Obsessive
  • ***
  • Posts: 470
  • Respect: +51
Re: VCE Chemistry Question Thread
« Reply #8801 on: September 25, 2020, 06:24:28 pm »
0
for this question would e be right

keltingmeith

  • Honorary Moderator
  • Great Wonder of ATAR Notes
  • *******
  • Posts: 5493
  • he/him - they is also fine
  • Respect: +1292
Re: VCE Chemistry Question Thread
« Reply #8802 on: September 25, 2020, 06:26:37 pm »
0
for this question would e be right

Again - why do you think e would be right?

Chocolatepistachio

  • Science Games: Silver
  • Forum Obsessive
  • ***
  • Posts: 470
  • Respect: +51
Re: VCE Chemistry Question Thread
« Reply #8803 on: September 25, 2020, 06:30:28 pm »
0
Because the concentration of the product increased but the reactants decreased an increase in temperature favours the products

keltingmeith

  • Honorary Moderator
  • Great Wonder of ATAR Notes
  • *******
  • Posts: 5493
  • he/him - they is also fine
  • Respect: +1292
Re: VCE Chemistry Question Thread
« Reply #8804 on: September 25, 2020, 06:35:38 pm »
0
Because the concentration of the product increased but the reactants decreased an increase in temperature favours the products

See? You don't need our help, you know exactly what you're doing! ;)