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Author Topic: HSC Chemistry Question Thread  (Read 1040647 times)  Share 

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jakesilove

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Re: Chemistry Question Thread
« Reply #1530 on: January 17, 2017, 08:54:04 am »
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For the following outcome, do we ever need to address oxides of metals in the Acidic Environment syllabus?

Identify oxides of non-metals which act as acids and describe the conditions under which they act as acids

The 'condition' they're talking about here is the reaction between the acidic oxide and water. If you walked into a room of sulfur dioxide, you wouldn't fizzle up from all the acid. The acid needs to become an aqueous solution (ie. sulfuric acid etc.) before it displays acidic properties.
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Iminschool

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Re: Chemistry Question Thread
« Reply #1531 on: January 17, 2017, 04:17:58 pm »
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Question here:

HF(aq)  + H2O(l) <---> F-(aq) + H3O+(aq)
 When added to this equilibrium, which one of the following soluble chemicals will least affect its position?
(A) Copper(II)fluoride
(B) Hydrogen chloride
(C) Sodium hydroxide
(D) Copper(II)nitrate

I am having trouble applying Le Chatlier's principle for some of the possible answers listed, and no i don't have the solution to this question.
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sweetcheeks

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Re: Chemistry Question Thread
« Reply #1532 on: January 17, 2017, 05:32:47 pm »
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Question here:

HF(aq)  + H2O(l) <---> F-(aq) + H3O+(aq)
 When added to this equilibrium, which one of the following soluble chemicals will least affect its position?
(A) Copper(II)fluoride
(B) Hydrogen chloride
(C) Sodium hydroxide
(D) Copper(II)nitrate

I am having trouble applying Le Chatlier's principle for some of the possible answers listed, and no i don't have the solution to this question.
A system will attempt to correct/oppose any change that is made, this includes adding more reactants or products as increasing the concentration of a substance will take the system out of equilibrium. If we add CuF2 to the solution it dissociates into Cu2+ and F-, resulting in an increase in the F- concentration which will disrupt equilibrium, causing the system to favour the backwards reaction. Hydrogen chloride is more easily identified as HCl, which when added to water will form H3O+ ions, again this will disrupt equilibrium. Sodium hydroxide, NaOH will dissociate into Na+ and OH-, the OH- ions will react with the H3O+, reducing its concentration again disrupting equilibrium. Finally adding Cu(NO3)3 will result in Cu2+ and NO3- ions entering the solution, the reaction doesn't involve either ions (and neither will result in precipitation) therefore it won't interfere with the position of equilibrium.

Iminschool

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Re: Chemistry Question Thread
« Reply #1533 on: January 17, 2017, 06:08:41 pm »
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A system will attempt to correct/oppose any change that is made, this includes adding more reactants or products as increasing the concentration of a substance will take the system out of equilibrium. If we add CuF2 to the solution it dissociates into Cu2+ and F-, resulting in an increase in the F- concentration which will disrupt equilibrium, causing the system to favour the backwards reaction. Hydrogen chloride is more easily identified as HCl, which when added to water will form H3O+ ions, again this will disrupt equilibrium. Sodium hydroxide, NaOH will dissociate into Na+ and OH-, the OH- ions will react with the H3O+, reducing its concentration again disrupting equilibrium. Finally adding Cu(NO3)3 will result in Cu2+ and NO3- ions entering the solution, the reaction doesn't involve either ions (and neither will result in precipitation) therefore it won't interfere with the position of equilibrium.

Thank you :)
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Iminschool

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Re: Chemistry Question Thread
« Reply #1534 on: January 17, 2017, 09:09:56 pm »
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I know how to do this question and i get my answer as (D) as i get a degree of ionisation of 100% which is the absolute highest. So the problem i'm having is that the answers say the answer is (C), plus this question is from a CSSA paper. Is this an error in the answers? Or is there a trick that i am not aware of?
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RuiAce

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Re: Chemistry Question Thread
« Reply #1535 on: January 17, 2017, 09:15:23 pm »
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I know how to do this question and i get my answer as (D) as i get a degree of ionisation of 100% which is the absolute highest. So the problem i'm having is that the answers say the answer is (C), plus this question is from a CSSA paper. Is this an error in the answers? Or is there a trick that i am not aware of?
Very inclined to say D is correct.

Iminschool

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Re: Chemistry Question Thread
« Reply #1536 on: January 17, 2017, 09:35:05 pm »
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Very inclined to say D is correct.

Awesome, must be an error then
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bsdfjnlkasn

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Re: Chemistry Question Thread
« Reply #1537 on: January 20, 2017, 04:56:09 pm »
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Question 1
Why don't neutral oxides react with either acidic or basic oxides?

Question 2
•   Metal oxides on the left side of Periodic Table are generally basic

Why is this the case? What makes them basic? Could someone please explain this with an equation or something? I just don't understand what property of metal oxides causes them to form bases. Same goes for non-metal oxides generally being acidic.

Question 3
Hey there,

I just wanted to clarify some things just quickly:

If an equilibrium is said to be "moving away", does this mean it is favouring the backwards reaction?

Also, If the concentration of ions increases in the products, does the system (going by Le Chatelier's principle) want to oppose that change by going to a state with less ions (which inevitably decreases the concentration of ions to a more stable level)? Does it do this by favouring the backwards reaction?

Thank you!! 

Question 4
How are oxidation states useful in determining whether an element (or specifically, a metalloid) will be amphoteric?

Question 5
I was just reading through a study guide online and it says:

"The left side of the periodic table generally consists of acidic oxides, while the right side is generally made of basic oxides."

Is this correct? Because I thought that metals form basic oxides. Metals are found on the LHS of the Periodic Table. Also, doesn't acidity follow the same trends as electronegativity, i.e. increases towards F? Further disproving the first half of the statement?

Or am I missing a crucial point somewhere in my above questions?

Thank you!  ;D

Question 6
For the outcome "Describe the solubility of carbon dioxide in water under various conditions as an equilibrium process and explain in terms of Le Chatelier’s principle"

Why is Le Chaterlier's principle applied differently for an increase in concentration and volume of CO2?

"An increase in the concentration of CO2 (g) will shift the equilibrium to the right, converting carbon dioxide and water into carbonic acid in order to reduce the concentration of carbon dioxide."

I understand how this works for concentration, but for:

"An increase in the volume of CO2 (g) will shift the equilibrium to the right, converting carbon dioxide and water into carbonic acid in order to reduce the volume of carbon dioxide. Thus the system will attempt to counteract this change by favouring the backwards reaction."

it almost seems to me that LC's principle has been applied twice in the instance of increased volume (inferred in the first sentence then applied in the second). Why is this the case?

Thank you!

Mod Edit: Posts merged. Use the Modify button to add questions to your initial post to avoid chain posting.
« Last Edit: January 20, 2017, 05:19:15 pm by jamonwindeyer »

bholenath125

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Re: Chemistry Question Thread
« Reply #1538 on: January 20, 2017, 04:57:04 pm »
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For Production of Materials,

Im having a lot of trouble understanding how to label Hydrocarbons like 3,4 Dibromoethene

Is there a site I could use?

RuiAce

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Re: Chemistry Question Thread
« Reply #1539 on: January 20, 2017, 11:41:15 pm »
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Question 1
Why don't neutral oxides react with either acidic or basic oxides?

Question 2
•   Metal oxides on the left side of Periodic Table are generally basic

Why is this the case? What makes them basic? Could someone please explain this with an equation or something? I just don't understand what property of metal oxides causes them to form bases. Same goes for non-metal oxides generally being acidic.

Question 3
Hey there,

I just wanted to clarify some things just quickly:

If an equilibrium is said to be "moving away", does this mean it is favouring the backwards reaction?

Also, If the concentration of ions increases in the products, does the system (going by Le Chatelier's principle) want to oppose that change by going to a state with less ions (which inevitably decreases the concentration of ions to a more stable level)? Does it do this by favouring the backwards reaction?

Thank you!! 

Question 4
How are oxidation states useful in determining whether an element (or specifically, a metalloid) will be amphoteric?

Question 5
I was just reading through a study guide online and it says:

"The left side of the periodic table generally consists of acidic oxides, while the right side is generally made of basic oxides."

Is this correct? Because I thought that metals form basic oxides. Metals are found on the LHS of the Periodic Table. Also, doesn't acidity follow the same trends as electronegativity, i.e. increases towards F? Further disproving the first half of the statement?

Or am I missing a crucial point somewhere in my above questions?

Thank you!  ;D

Question 6
For the outcome "Describe the solubility of carbon dioxide in water under various conditions as an equilibrium process and explain in terms of Le Chatelier’s principle"

Why is Le Chaterlier's principle applied differently for an increase in concentration and volume of CO2?

"An increase in the concentration of CO2 (g) will shift the equilibrium to the right, converting carbon dioxide and water into carbonic acid in order to reduce the concentration of carbon dioxide."

I understand how this works for concentration, but for:

"An increase in the volume of CO2 (g) will shift the equilibrium to the right, converting carbon dioxide and water into carbonic acid in order to reduce the volume of carbon dioxide. Thus the system will attempt to counteract this change by favouring the backwards reaction."

it almost seems to me that LC's principle has been applied twice in the instance of increased volume (inferred in the first sentence then applied in the second). Why is this the case?

Thank you!

Mod Edit: Posts merged. Use the Modify button to add questions to your initial post to avoid chain posting.
1. A substance is acidic if it reacts an actual acid/base in aqueous solution. Not with other oxides.
Acidic oxides like SO2 don't react with basic oxides like MgO

2. The fact that an oxide is basic if it reacts with an acid. As it so stands, in general they ALWAYS react with acids. So just know it.

3. "moving away" needs more context. Could just mean the equilibrium being disturbed. Because that's NOT common chemistry terminology

And simply put yes

4. Provide a question. I can see how they might be useful but I cannot give a concrete answer

5. That quote looks like it is in the complete wrong order

I want to get back to 6 later (unless Jake beats me). That one needs a more comprehensive answer and right now I am really tired

For Production of Materials,

Im having a lot of trouble understanding how to label Hydrocarbons like 3,4 Dibromoethene

Is there a site I could use?
Try providing an example for things like these. It's easier to illustrate thought processes.

(However, I think the Jacaranda textbook addresses it decently well.)

bsdfjnlkasn

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Re: Chemistry Question Thread
« Reply #1540 on: January 23, 2017, 12:53:49 pm »
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All the following questions relate to The Acidic Environment topic:

How important is it that we know how to name acids?

Do we need to know the following indicators: Alizarine yellow and bromoscresol green?

« Last Edit: January 23, 2017, 02:10:00 pm by bsdfjn;lkasn »

ellipse

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Re: Chemistry Question Thread
« Reply #1541 on: January 23, 2017, 01:59:16 pm »
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How important is it that we know how to name acids in The Acidic Environment topic?


Must we know the following indicators: Alizarine yellow and bromoscresol green?

It may be important, but just to be safe, make sure you know how to name the alkanoic acids, and there's a dot point in acidic environment that requires you to know the systematic and the common name for, iirc, HCl, H2SO4, ethanoic and citric acid, so try your best and memorise that as well. Learn the other acid names as you go through the course too, it may be useful.

As for the indicators, I'm pretty sure the syllabus doesn't require you to know them
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bsdfjnlkasn

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Re: Chemistry Question Thread
« Reply #1542 on: January 23, 2017, 02:10:49 pm »
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It may be important, but just to be safe, make sure you know how to name the alkanoic acids, and there's a dot point in acidic environment that requires you to know the systematic and the common name for, iirc, HCl, H2SO4, ethanoic and citric acid, so try your best and memorise that as well. Learn the other acid names as you go through the course too, it may be useful.

As for the indicators, I'm pretty sure the syllabus doesn't require you to know them

Perfect! I guess it's better to know than not to know  ;)

bsdfjnlkasn

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Re: Chemistry Question Thread
« Reply #1543 on: January 23, 2017, 02:12:59 pm »
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More questions on The Acidic Environment  :D :D:

Question 1.
Spoiler
Is interpreting equilibrium graphs an important/necessary skill for the course?

Question 2.

Spoiler
For the outcome "Describe the solubility of carbon dioxide in water under various conditions as an equilibrium process and explain in terms of Le Chatelier’s principle"

Why is Le Chaterlier's principle applied differently for an increase in concentration and volume of CO2?

"An increase in the concentration of CO2 (g) will shift the equilibrium to the right, converting carbon dioxide and water into carbonic acid in order to reduce the concentration of carbon dioxide."

I understand how this works for concentration, but for:

"An increase in the volume of CO2 (g) will shift the equilibrium to the right, converting carbon dioxide and water into carbonic acid in order to reduce the volume of carbon dioxide. Thus the system will attempt to counteract this change by favouring the backwards reaction."

It almost seems to me that LC's principle has been applied twice in the instance of increased volume (inferred in the first sentence then applied in the second). Why is this the case?

Question 2a. (Same outcome)

Spoiler
For the dissolution of CO2 in water, given by:
CO2 (g) +H2O (l) ⇌ H2CO3 (aq)

Will the rate of the forward reaction increase if the concentration of either reactant is increased?

Question 3

Spoiler
How is C6H8O7 (citric acid) triprotic if there are 8 Hydrogen's that will ionise not 3? (Taking that H+ ions are essentially protons) I could easily be misunderstanding what this means though.

« Last Edit: January 23, 2017, 02:56:08 pm by bsdfjn;lkasn »

ellipse

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Re: Chemistry Question Thread
« Reply #1544 on: January 23, 2017, 02:47:36 pm »
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More questions on The Acidic Environment  :D :D:

Question 1.
Spoiler
Is interpreting equilibrium graphs an important/necessary skill for the course?

Question 2.

Spoiler
For the outcome "Describe the solubility of carbon dioxide in water under various conditions as an equilibrium process and explain in terms of Le Chatelier’s principle"

Why is Le Chaterlier's principle applied differently for an increase in concentration and volume of CO2?

"An increase in the concentration of CO2 (g) will shift the equilibrium to the right, converting carbon dioxide and water into carbonic acid in order to reduce the concentration of carbon dioxide."

I understand how this works for concentration, but for:

"An increase in the volume of CO2 (g) will shift the equilibrium to the right, converting carbon dioxide and water into carbonic acid in order to reduce the volume of carbon dioxide. Thus the system will attempt to counteract this change by favouring the backwards reaction."

It almost seems to me that LC's principle has been applied twice in the instance of increased volume (inferred in the first sentence then applied in the second). Why is this the case?

Question 2a. (Same outcome)

Spoiler
For the dissolution of CO2 in water, given by:
CO2 (g) +H2O (l) ⇌ H2CO3 (aq)

Will the rate of the forward reaction increase if the concentration of either reactant is increased?

1. I think equilibrium graphs are very important. Take for instance q12 from 2012 HSC, which is a multiple choice with equilibrium graphs. I also remember there was another long response on equilibrium graphs, which requires you to explain all 3 factors (temperature, pressure and concentration). So yes, I think it is very important and try your best to master it

2. Im not really sure if quote thing is right (increasing volume doesn't really 'shift' it to the right, I may be wrong though). concentration is given by the formula c=n/v. So by increasing the volume, you're basically decreasing the concentration of the gases. So by LCP, the system will try to increase the concentration, and this is the backwards reaction. Another way to think about this is that volume is inversely proportional to the pressure. And pressure is directly proportional the amount of gaseous moles. Thus, by increasing the volume, the pressure is decreased. So to increase the pressure, the equilibrium shifts to the side with the most GAS moles, and this is the backwards reaction. This explanation might be really confusing, so I hope someone else is able to clearly explain this

2a. Recall that LCP is not applied to pure solids and liquids, ie they do not affect the equilibrium at all. So increasing/decreasing the concentration of water has no effect on the equilibrium. So the rate of forward reaction will only increase if the concentration of CO2 is increased.

3. Basically, its not necessary for all the hydrogen in a molecule to be 'removable'. eg in ethnaoic, the H's bonded to the carbon won't ionise, only the one that is bonded with the oxygen. Similarly, If you look at the structure of citric acid, only the 3 hydrogens sticking out of the carboxylic acid groups are able to ionise, hence its tri-protic.
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