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March 28, 2024, 11:34:17 pm

Author Topic: HSC Chemistry Question Thread  (Read 1040544 times)  Share 

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RuiAce

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Re: Chemistry Question Thread
« Reply #315 on: May 16, 2016, 09:35:27 pm »
+1
Hey guys!

I was learning about coordinate covalent bonds today and I was wondering how you can tell which pairs form a product that does contain a coordinate covalent bond? Sorry if this seems simple but here's an example of a question:

Which of the following pairs form a product containing a coordinate covalent bond?
a) Ca and 2H+
b) H2O and H+
c) Ag+ and Cl-
d) NH4+ and OH-

Thank you! you're all amazing :D

Neutron

The hydronium H3O+ is known to contain a coordinate covalent bond.

Otherwise, the process of elimination works as follows:
c) is definitely wrong as AgCl is an example of an ionic compound
a) is an impossibility.
d) is wrong because NH4+ and OH- will react in a neutralisation reaction to produce H2O and NH3
Therefore the answer must be b)

katherine123

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Re: Chemistry Question Thread
« Reply #316 on: May 17, 2016, 09:38:47 pm »
0
1. what is the method to identify that it's CaSO4(s)
the ans: include adding HNO3 and i dont get the purpose of that    isnt acid added just for like metal carbonates

don't we normally identify what ions are present in the solution rather than what type of compound it is

2. do we differentiate Fe(OH)2 and Fe(OH)3 because Fe(OH)2 goes from white to brown and then Fe(OH)3 stays consistently brown

3.the solubility rules differ across different sources
i got mine from the matrix website but i dont know if its a good idea

« Last Edit: May 17, 2016, 10:09:33 pm by katherine123 »

RuiAce

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Re: Chemistry Question Thread
« Reply #317 on: May 17, 2016, 10:06:21 pm »
0
1. what is the method to identify that it's CaSO4(s)
the ans: include adding HNO3 and i dont get the purpose of that    isnt acid added just for like metal carbonates

don't we normally identify what ions are present in the solution rather than what type of compound it is

2. why does Fe(OH)2 (s) turn from white to brown

Not enough info

If these are your cation/anion tests, you need to give the whole entire question.

(For Q1 however, if that IS the entire question, then CaSO4 can be VERIFIED by an acid test, but not IDENTIFIED.)

RuiAce

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Re: Chemistry Question Thread
« Reply #318 on: May 19, 2016, 10:36:38 pm »
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Still insufficient information after the edit for Q1. Nitric acid will react with both carbonates and sulfates. But it doesn't distinguish between which is what.

Q2: The hydroxide test to determine which iron ion (lol) is present is a bit ambiguous.

In the laboratory, sometimes what happens is that Fe2+ shows up in a colour it's not meant to show up. Fe3+ is technically meant to stay brown as you stated, but I think when I did the test for Fe2+ I actually ended up with green.

Q3: ALWAYS keep in mind that multiple cation have MORE THAN ONE acceptable test pathway to determine its nature. Some sources refer to "secondary tests" because they provide further evidence to what they call a "primary test"

Johny1234567

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Re: Chemistry Question Thread
« Reply #319 on: May 20, 2016, 11:09:44 pm »
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What is the half-equations illustrating the reaction between iodide ions and dilute sulfuric acid?
I know how to do it with concentrated sulfuric acid, but the aqueous symbol for dilute throws me off since I'm not quite sure about the oxidation half. Help appreciated :)

Sheikie

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Re: Chemistry Question Thread
« Reply #320 on: May 21, 2016, 04:31:21 pm »
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hey, I was wondering what is the best way to study for chemistry pracs?

RuiAce

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Re: Chemistry Question Thread
« Reply #321 on: May 21, 2016, 06:19:25 pm »
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What is the half-equations illustrating the reaction between iodide ions and dilute sulfuric acid?
I know how to do it with concentrated sulfuric acid, but the aqueous symbol for dilute throws me off since I'm not quite sure about the oxidation half. Help appreciated :)
This is a bit confusing. Which galvanic cell are you interested in? Or what's the full question.

Alternatively, give the half equations to concentrated sulfuric acid for a reference point for me

hey, I was wondering what is the best way to study for chemistry pracs?

Studying for pracs is a matter of:
- Knowing the aim
- Knowing the method
- Only knowing results if its relevant (however this is often more than not)
- Knowing limitations to the experiment
- Identifying controls/variables, as well as relating validity/reliability/discussion

jakesilove

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Re: Chemistry Question Thread
« Reply #322 on: May 21, 2016, 06:47:15 pm »
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hey, I was wondering what is the best way to study for chemistry pracs?

Hey!

I think that, generally, there is little to study when it comes to chemistry pracs. Most of the time, you aren't being assessed on specific, actual knowledge of the course; rather, on your analytical skills, your ability to form a discussion and sometimes your ability to do calculations.

Other than being comfortable with a titration, in case you are asked to do one, I think that the main this to worry about is being able to write balanced chemical formulas, use equations from throughout the course, and understanding what accuracy, reliability and validity are. This latter point is especially important, in case you are asked (as often occurs) to write out a discussion for your prac.

You need to be able to write a risk assessment (risk, precaution, response) and be able to graph any results you find.

I think that's about it; I didn't elaborate on each of the above notes because I figured that you probably understand most of them, but if there is any part of this answer that I can expand on (accuracy, reliability and validity for example) please let me know! Happy to help out however I can.

Jake
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RuiAce

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Re: Chemistry Question Thread
« Reply #323 on: May 21, 2016, 07:06:01 pm »
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Hey!

I think that, generally, there is little to study when it comes to chemistry pracs. Most of the time, you aren't being assessed on specific, actual knowledge of the course; rather, on your analytical skills, your ability to form a discussion and sometimes your ability to do calculations.

Other than being comfortable with a titration, in case you are asked to do one, I think that the main this to worry about is being able to write balanced chemical formulas, use equations from throughout the course, and understanding what accuracy, reliability and validity are. This latter point is especially important, in case you are asked (as often occurs) to write out a discussion for your prac.

You need to be able to write a risk assessment (risk, precaution, response) and be able to graph any results you find.

I think that's about it; I didn't elaborate on each of the above notes because I figured that you probably understand most of them, but if there is any part of this answer that I can expand on (accuracy, reliability and validity for example) please let me know! Happy to help out however I can.

Jake

Kinda need both in my opinion. I distinctively recall panicking when a past paper question said "outline a experiment to produce an ester in a laboratory"

jakesilove

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Re: Chemistry Question Thread
« Reply #324 on: May 21, 2016, 07:14:39 pm »
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Kinda need both in my opinion. I distinctively recall panicking when a past paper question said "outline a experiment to produce an ester in a laboratory"

I totally agree in terms of needing to know the actual pracs etc. when it comes to examination, but I assume the question was about an in-class practical task? A prac exam?

Jake
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RuiAce

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Re: Chemistry Question Thread
« Reply #325 on: May 21, 2016, 08:56:52 pm »
+1
I totally agree in terms of needing to know the actual pracs etc. when it comes to examination, but I assume the question was about an in-class practical task? A prac exam?

Jake

Oh touche. It does give off that vibe.

I generally just assume the final exam though because what you have to memorise for that overlaps into what you have to know for a practical exam anyway

therealqwerty

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Re: Chemistry Question Thread
« Reply #326 on: May 23, 2016, 08:13:22 pm »
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Can you explain how to do this question, thanks  :)

RuiAce

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Re: Chemistry Question Thread
« Reply #327 on: May 23, 2016, 08:52:51 pm »
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Can you explain how to do this question, thanks  :)
Should be Q and R I reckon.

Q is the most reactive because not only does it burn in oxygen and react with acid, but it even reacts with water. (It might be aluminium)

R is the least reactive because it just reacts slowly with oxygen

S is in the middle

So the difference in Eo values for Q and R should be the greatest

jakesilove

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Re: Chemistry Question Thread
« Reply #328 on: May 23, 2016, 09:19:41 pm »
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Should be Q and R I reckon.

Q is the most reactive because not only does it burn in oxygen and react with acid, but it even reacts with water. (It might be aluminium)

R is the least reactive because it just reacts slowly with oxygen

S is in the middle

So the difference in Eo values for Q and R should be the greatest

Yep I agree! You always want to look for a reaction between a substance highest on the standard reduction potential table, and a substance lowest on the standard reduction potential table. As this table is also a marker of reactivity, you want a substance that is very reactive, and a substance that is not very reactive, to make the best possible galvanic cell.

Jake
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therealqwerty

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Re: Chemistry Question Thread
« Reply #329 on: May 24, 2016, 07:48:01 am »
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Should be Q and R I reckon.

Q is the most reactive because not only does it burn in oxygen and react with acid, but it even reacts with water. (It might be aluminium)

R is the least reactive because it just reacts slowly with oxygen

S is in the middle

So the difference in Eo values for Q and R should be the greatest


Thanks :)