HSC 2012-2015 Chemistry Marathon (archive) (1 Viewer)

[abdog]

re: HSC Chemistry Marathon Archive

look at the equation for every 1 mole of SO2 used, 2 moles of H2S is consumed, so in the end 4 moles of SO2 will be in excess

Oh I see! They both started with the same amount but when H2S is finished only half of S02 is used, so H2S is limited. Is this correct?

 

[babberz]

re: HSC Chemistry Marathon Archive

Oh I see! They both started with the same amount but when H2S is finished only half of S02 is used, so H2S is limited. Is this correct?

yep

 

[abdog]

re: HSC Chemistry Marathon Archive

A certain solution has 10 times the hydrogen ion concentration of a solution of pH 8. What is the pH of the MORE acidic solution? (This is the whole question, no diagrams,no continuation etc)

A) 0.8
B) 4
C) 7
D) 9

The answer is given as D, which makes no sense to me as that means the solution is more basic(less H+), rather than acidic(more H+). Am I missing something?

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

A certain solution has 10 times the hydrogen ion concentration of a solution of pH 8. What is the pH of the MORE acidic solution? (This is the whole question, no diagrams,no continuation etc)

A) 0.8
B) 4
C) 7
D) 9

The answer is given as D, which makes no sense to me as that means the solution is more basic(less H+), rather than acidic(more H+). Am I missing something?

LOL (d) is definitely wrong
I would go for (c)

 

[khoavo12]

re: HSC Chemistry Marathon Archive

Yea D is wrong by just looking. Because the question asked you for the pH of the MORE acidic solution, hence it has lower pH than 8 so can't be D. You can work out the concentration of the initial solution, which is 10^-8 then multiply by 10. That gives 10^-7 then -log(10^-7) = 7 --> C

 

[AB940]

re: HSC Chemistry Marathon Archive

A certain solution has 10 times the hydrogen ion concentration of a solution of pH 8. What is the pH of the MORE acidic solution? (This is the whole question, no diagrams,no continuation etc)

A) 0.8
B) 4
C) 7
D) 9

The answer is given as D, which makes no sense to me as that means the solution is more basic(less H+), rather than acidic(more H+). Am I missing something?

10x more acidic means 10x more H+ ions (in mol/L) and since the pH is a negative logarithmic scale, an increase in the concentration of H+ decreases the numerical pH value. Acids have pH values lower than 7 while bases' are higher.

 

[Frie]

re: HSC Chemistry Marathon Archive

Will Copper metal dissolve in 1.0 M HCl (aq)? Give your reasions for why or why not.

 

[bangladesh]

re: HSC Chemistry Marathon Archive

Will Copper metal dissolve in 1.0 M HCl (aq)? Give your reasions for why or why not.

Copper is less reactive than Hydrogen, Therefor it cannot displace the Hydrogen ions in HCL and hence will not dissolve in HCL.

 

[girlworld_club]

re: HSC Chemistry Marathon Archive

A few drops of methyl orange indicator were added to 10ml of water in a beaker. The mixture appeared yellow. Drops of dilute acetic acid were then added until the mixture just turned red. Identify the change that can be made to turn the indicator colour back to yellow:

Ch3cooh + h20 <--> Ch3coo- + h30+

a) Add drops of HCL
b) Remove acetate ions by precipitation.
c) Reduce the volume of the vessel by half.
d) Add sodium acetate crystals with stirring.

what is the answer, giving reasons.

 

[AB940]

re: HSC Chemistry Marathon Archive

A few drops of methyl orange indicator were added to 10ml of water in a beaker. The mixture appeared yellow. Drops of dilute acetic acid were then added until the mixture just turned red. Identify the change that can be made to turn the indicator colour back to yellow:

Ch3cooh + h20 <--> Ch3coo- + h30+

a) Add drops of HCL
b) Remove acetate ions by precipitation.
c) Reduce the volume of the vessel by half.
d) Add sodium acetate crystals with stirring.

what is the answer, giving reasons.

Add sodium acetate crystals.
the formula is CH3COO-Na so when it dissolves in water this will increase the concentration of CH3COO- ions. According to Le Chatelier's Principle, this will shift the equilibrium position so that there will be more of the reagents, and consequently the concentration of H3O+ will decrease.

 

[Frie]

re: HSC Chemistry Marathon Archive

Add sodium acetate crystals.
the formula is CH3COO-Na so when it dissolves in water this will increase the concentration of CH3COO- ions. According to Le Chatelier's Principle, this will shift the equilibrium position so that there will be more of the products, and consequently the concentration of H3O+ will decrease.

Is this also a reasonable explanation?

Since adding an acidic solution caused the indicator to change from yellow to red, adding a basic substance/alkaline solution will change it back. Sodium acetate is basic, as it is produced from strong base (NaOH) and weak acid (acetic acid).
Also basic because in solution it produces OH- ions
CH3COO- + H2O <-> CH3COOH + OH-

I think you messed up your explanation, as the equilibrium shifts to the left due to excess CH3COO- ions (on product side). This causes decrease in H3O+ which makes the mixture less acidic and revert back to original indicator colour (yellow)

 

[AB940]

re: HSC Chemistry Marathon Archive

Is this also a reasonable explanation?

Since adding an acidic solution caused the indicator to change from yellow to red, adding a basic substance/alkaline solution will change it back. Sodium acetate is basic, as it is produced from strong base (NaOH) and weak acid (acetic acid).
Also basic because in solution it produces OH- ions
CH3COO- + H2O <-> CH3COOH + OH-

I think you messed up your explanation, as the equilibrium shifts to the left due to excess CH3COO- ions (on product side). This causes decrease in H3O+ which makes the mixture less acidic and revert back to original indicator colour (yellow)

Yeah I meant reagents, sorry.

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

Question 1:
(a) What is a buffer solution?
(b) Can a solution comprised of KCH₃COO and CH₃COOH act as a buffer? Justify your reasoning

Question 2: A student decided to construct a galvanic cell to zap himself. One half cell containing copper metal (as an electrode), and copper nitrate electrolyte, the other half cell containing lead metal (as an electrode) and lead nitrate electrolyte
(a) Identify the anode and include an explanation
(b) Describe FIVE quantitative changes that could be observed during the operation of this cell
(c) The student has a flame and wants to attempt suicidal. What is the best way to suicide? (without using the flame to hurt yourself)

 

[AnimeX]

re: HSC Chemistry Marathon Archive

Question 1:
(a) What is a buffer solution?
(b) Can a solution comprised of KCH₃COO and CH₃COOH act as a buffer? Justify your reasoning

Question 2: A student decided to construct a galvanic cell to zap himself. One half cell containing copper metal (as an electrode), and copper nitrate electrolyte, the other half cell containing lead metal (as an electrode) and lead nitrate electrolyte
(a) Identify the anode and include an explanation
(b) Describe FIVE quantitative changes that could be observed during the operation of this cell
(c) The student has a flame and wants to attempt suicidal. What is the best way to suicide? (without using the flame to hurt yourself)

I haven't done ANY revision since trials , but I'll give this a go. (please correct my errors)

Q1: a) a buffer solution consists of a weak acid and its conjugate base, a buffer is a solution that resists a change in pH to a certain extent.
b) yes, it can because CH3COOH (acetic acid) is a weak acid and CH3COO- is it's conjugate base, which comes out from the KCH3COO when put into water. thus it can act as a buffer.


Q2: a) the anode is copper because it is the more reactive element

b) (assuming there is a salt bridge) 1, the copper metal will erode as there is a loss of Cu2+ ions, the copper metal will have looked like some of it has disappeared. 2, the lead would look more chunky (idk how to word this) as more Pb2+ ions displace onto the lead electrode. 3, the electrons will flow from the anode to the cathode. 4, the nitrate ions will flow from the cathode to the anode. 5, the copper solution will look more blue as there are more copper 2+ ions in the solution

c) [lol attempt suicidal haha] blend the lead cathode into small pieces, cook it with the flame, eat the lead while it's hot

 

[AnimeX]

re: HSC Chemistry Marathon Archive

Question 1:
a) discuss the reason why ethylene is considered carbon neutral (3 marks)
b) write a balanced equation (with states) showing the process of the polymerisation of ethylene (1 mark)
c) outline the steps of the polymerisation of ethylene (3 marks)

Question 2:
a) what are the systematic names of: [3 marks]
i) vinyl chloride ii) polystyrene iii) ethylene

b) outline three uses of: (including the reasons for the uses) [4 marks]
i) poly vinyl chloride ii) polystyrene

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

I haven't done ANY revision since trials , but I'll give this a go. (please correct my errors)

Q1: a) a buffer solution consists of a weak acid and its conjugate base, a buffer is a solution that resists a change in pH to a certain extent.
b) yes, it can because CH3COOH (acetic acid) is a weak acid and CH3COO- is it's conjugate base, which comes out from the KCH3COO when put into water. thus it can act as a buffer.


Q2: a) the anode is copper because it is the more reactive element

b) (assuming there is a salt bridge) 1, the copper metal will erode as there is a loss of Cu2+ ions, the copper metal will have looked like some of it has disappeared. 2, the lead would look more chunky (idk how to word this) as more Pb2+ ions displace onto the lead electrode. 3, the electrons will flow from the anode to the cathode. 4, the nitrate ions will flow from the cathode to the anode. 5, the copper solution will look more blue as there are more copper 2+ ions in the solution

c) [lol attempt suicidal haha] blend the lead cathode into small pieces, cook it with the flame, eat the lead while it's hot

Good work for question 1 but u made a small mistake in Q2 (a) which costed u the rest of the question
1 (b) i would say potassium acetate ionises to form acetate ions instead of "which comes out from the KCH3COO when put into water"

2 (a) Lead is more reactive

(b) only '3' is correct

(c) He could heat the lead nitrate and then sniff it in lol

 

[Dementured]

re: HSC Chemistry Marathon Archive

Question 1:
a) discuss the reason why ethylene is considered carbon neutral (3 marks)
b) write a balanced equation (with states) showing the process of the polymerisation of ethylene (1 mark)
c) outline the steps of the polymerisation of ethylene (3 marks)

Question 1:
a) what are the systematic names of: [3 marks]
i) vinyl chloride ii) polystyrene iii) ethylene

b) outline three uses of: (including the reasons for the uses) [4 marks]
i) poly vinyl chloride ii) polystyrene

a) The raw material that is used to produce ethylene, sugar cane, is a renewable material. However, the processes used to create the ethylene from sugar cane result in the emission of CO2, as well as the emissions produced from the transportation of the ethylene. However, the process of photosynthesis requires CO2, so in effect, the growing of sugar cane results in the entire process being 'carbon neutral'.

b) CH2=CH2 (g) -> -CH2-CH2-n (s)

c) Sugar cane (extraction) -> Glucose (fermentation) -> Ethanol (distillation) -> Ethylene

Question 2:

a)
i) Chloroethene
ii) Poly..ethenylbenzene?
iii) Ethenylbenzene

b)
(i) polyvinylchloride: (1) flexible raincoats (due to water resistance), (2) pipes and gutters (water resistant, rigid), (3) cable insulation (through plasticisers)
(ii) polystyrene: (1) foam/insulated cups (addition of air in molten state), (2) protective packaging (hard, brittle, transparent), (3) disposable cutlery (hard, brittle)

 

[mahmoudali]

re: HSC Chemistry Marathon Archive

I haven't done ANY revision since trials , but I'll give this a go. (please correct my errors)

Q1: a) a buffer solution consists of a weak acid and its conjugate base, a buffer is a solution that resists a change in pH to a certain extent.
b) yes, it can because CH3COOH (acetic acid) is a weak acid and CH3COO- is it's conjugate base, which comes out from the KCH3COO when put into water. thus it can act as a buffer.


Q2: a) the anode is copper because it is the more reactive element

b) (assuming there is a salt bridge) 1, the copper metal will erode as there is a loss of Cu2+ ions, the copper metal will have looked like some of it has disappeared. 2, the lead would look more chunky (idk how to word this) as more Pb2+ ions displace onto the lead electrode. 3, the electrons will flow from the anode to the cathode. 4, the nitrate ions will flow from the cathode to the anode. 5, the copper solution will look more blue as there are more copper 2+ ions in the solution

c) [lol attempt suicidal haha] blend the lead cathode into small pieces, cook it with the flame, eat the lead while it's hot

+1 for that
would heating the galvanic cell increase in the voltage drop then can he zap himself to death
or does heat not affect the voltage

 

[babberz]

re: HSC Chemistry Marathon Archive

Question 1:
(a) What is a buffer solution?
(b) Can a solution comprised of KCH₃COO and CH₃COOH act as a buffer? Justify your reasoning

Question 2: A student decided to construct a galvanic cell to zap himself. One half cell containing copper metal (as an electrode), and copper nitrate electrolyte, the other half cell containing lead metal (as an electrode) and lead nitrate electrolyte
(a) Identify the anode and include an explanation
(b) Describe FIVE quantitative changes that could be observed during the operation of this cell
(c) The student has a flame and wants to attempt suicidal. What is the best way to suicide? (without using the flame to hurt yourself)

carbon monoxide? lol

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

carbon monoxide? lol

forget about it, it was to troll