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March 29, 2024, 07:58:25 am

Author Topic: VCE Chemistry Question Thread  (Read 2313398 times)  Share 

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keltingmeith

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Re: VCE Chemistry Question Thread
« Reply #8655 on: July 15, 2020, 09:47:24 pm »
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Hi newcomer here,
I'm having trouble about what types of experiments I should do for Unit 2 Chem. Does anyone have any past experiments relating to water?

Thanks!

Feel free to get creative! What's a question you always wanted the answer to? Not knowing what you're limited to, here's some random thoughts off the top of my head:

-What can and can't be dissolved by water?
-What happens when you give different types of water to plants?
-How does water vary based on place to place?
-What colour is water?
-How does pH affect solubility?
-How long does it take for water to fill a container at different hardnesses, pH, etc.
-How much water does it take for someone to trip over?

And there can be so many more. What's something, maybe not related to water, that you're really interested in and want to know more about, and how can you include water in that study? Or maybe just something silly you've always wanted to know?

HYANA

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Re: VCE Chemistry Question Thread
« Reply #8656 on: July 26, 2020, 04:29:44 pm »
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Hello people, so I just did a little quiz and I don't know how to get the correct answer. Here is the question.

What is the concentration, in mol/L, of a solution that contains 2.00g of silver nitrate, AgNO3, dissolved in 300ml od solution?

The answer was meant to be 0.0392 mol/L but i have no idea how to get to that point. Can someone help? Thanks.

whys

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Re: VCE Chemistry Question Thread
« Reply #8657 on: July 26, 2020, 04:34:35 pm »
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Hello people, so I just did a little quiz and I don't know how to get the correct answer. Here is the question.

What is the concentration, in mol/L, of a solution that contains 2.00g of silver nitrate, AgNO3, dissolved in 300ml od solution?

The answer was meant to be 0.0392 mol/L but i have no idea how to get to that point. Can someone help? Thanks.
If you want to find the concentration in mol/L, you want to find the amount of AgNO3 in moles - can you think of a certain formula you can use? (hint: you've already been given the information of the grams of silver nitrate, is there any other info you can also use that you know about AgNO3 that you could plug into a formula to find the mol?) Since it's asking for mol/L, you'd need to find the amount of solution in litres too. Try and recall the formula to calculate concentration (hint: it involves moles and volume).

Hope this set you on the right path to finding the answer!
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zhouzhennan

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Re: VCE Chemistry Question Thread
« Reply #8658 on: July 29, 2020, 06:58:32 pm »
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Hey there im wondering how relevant is pH and acid and base stuff(and indicator) in Year 12 VCE? Is it possible that there will be questions on them in the exam?

colline

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Re: VCE Chemistry Question Thread
« Reply #8659 on: July 30, 2020, 08:04:24 am »
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Hey there im wondering how relevant is pH and acid and base stuff(and indicator) in Year 12 VCE? Is it possible that there will be questions on them in the exam?

Nope, they're not on the 3/4 study design. Doesn't hurt to still learn it though ;)

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Coolgalbornin03Lo

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Re: VCE Chemistry Question Thread
« Reply #8660 on: August 01, 2020, 09:13:22 am »
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1. In a chromatogram is it peak height or peak area which tells you about concentration of components? I thought it was area but now I’m not so sure.....

2. And is it necessary to know about the theory of NMR and IR? I know about nucleons spinning and changing the vibrational energy of covalent bonds but anything else?
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IThinkIFailed

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Re: VCE Chemistry Question Thread
« Reply #8661 on: August 01, 2020, 10:23:00 am »
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1. In a chromatogram is it peak height or peak area which tells you about concentration of components? I thought it was area but now I’m not so sure.....

2. And is it necessary to know about the theory of NMR and IR? I know about nucleons spinning and changing the vibrational energy of covalent bonds but anything else?

1: Peak area tells you about the concentration of components. Generally though, you’d need to compare the peak areas to peak areas produced by standard solutions ran through the same conditions to determine concentration.

2:
Yea I don’t know about this either lol, the study design is kinda vague and just says “general principles”, but it does state specifically you need to know about spin energy levels regarding NMR.
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sweetcheeks

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Re: VCE Chemistry Question Thread
« Reply #8662 on: August 01, 2020, 12:51:32 pm »
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For HPLC both peak height and peak area are able to be used for concentration. Peak area is generally better, as the area doesn't vary as much as height does if parameters slightly change during the run (slight fluctuations in flow rate, temperature etc. ). Sometimes peak height needs to be used if there are two species that elute close to each-other (in this case, the peak area will be overlapping between the two and differentiating the two is nearly impossible).

Of course, you need some sort of reference to compare to. For the purpose of VCE, you just need to know about the calibration curve method.

Coolgalbornin03Lo

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Re: VCE Chemistry Question Thread
« Reply #8663 on: August 01, 2020, 08:37:26 pm »
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1. Because isomers are the same compound does that mean their fingerprint regions are the same?

2. Why does decreasing particle size of stationary phase increase retention time? I thought because SA has increased THERES more chances for the components to adsorb and desorb quicker into the mobile phase?

Sorry for posting so much today!
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sweetcheeks

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Re: VCE Chemistry Question Thread
« Reply #8664 on: August 01, 2020, 10:47:04 pm »
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1. Because isomers are the same compound does that mean their fingerprint regions are the same?

2. Why does decreasing particle size of stationary phase increase retention time? I thought because SA has increased THERES more chances for the components to adsorb and desorb quicker into the mobile phase?

Sorry for posting so much today!

1. Do you mean isomers or enantiomers? If you mean enantiomers, than yes, their fingerprint regions will be the same. For isomeric species (those that are not enantiomers), their fingerprint regions will differ.

2. I'm not sure why you think it would be quicker. Molecules are initially in the mobile phase and as they move through the column they will adsorb to the stationary phase, desorb back into the mobile phase and continue this cycle throughout the column. If you have a higher surface area, there is more chance for these molecules to absorb onto the stationary phase and this will increase the overall time they are in the stationary phase, resulting in them remaining in the column longer. You can assume that each adsorption/desorption process takes the same amount of time, so increasing the amount of events will increase the amount of time the molecule spends in the column.

Coolgalbornin03Lo

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Re: VCE Chemistry Question Thread
« Reply #8665 on: August 03, 2020, 09:39:49 pm »
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Why is the volume of [insert standard solution] added to neutralise (reach equivalence point) the same for a strong base and weak acid? I thought the strong acid would need more as it’s pH is much lower?
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Re: VCE Chemistry Question Thread
« Reply #8666 on: August 03, 2020, 11:20:04 pm »
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Why is the volume of [insert standard solution] added to neutralise (reach equivalence point) the same for a strong base and weak acid? I thought the strong acid would need more as it’s pH is much lower?
Strong acid and weak acid, assuming all other factors constant, still have the same moles of acid. The only difference is how much of the acid in question is dissociated pH is a measure of the acid dissociation in a solution, and since weak acids dissociate less, their recorded pH is higher in a solution compared to an identical strong acid solution.

Coolgalbornin03Lo

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Re: VCE Chemistry Question Thread
« Reply #8667 on: August 05, 2020, 08:55:11 pm »
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Why is NaOH not a good primary standard? I know it reacts readily with oxygen and CO2 in atmosphere but the solutions also say it needs to have a known Formula mass? I know this is a requirement for a primary standard but isn’t sodium hydroxides formula mass already known.
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keltingmeith

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Re: VCE Chemistry Question Thread
« Reply #8668 on: August 05, 2020, 09:42:11 pm »
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Why is NaOH not a good primary standard? I know it reacts readily with oxygen and CO2 in atmosphere but the solutions also say it needs to have a known Formula mass? I know this is a requirement for a primary standard but isn’t sodium hydroxides formula mass already known.

It would have a known formula mass if all of it was NaOH, but as you said - NaOH reacts with oxygen and CO2. So some of it reacts with oxygen to make sodium oxide and water, and the CO2 will make sodium carbonate and water

So what if 5% of your NaOH ISN'T NaOH? Then your molar mass is no longer 40 g/mol, it's 38 g/mol. Or maybe you only have 80% of your NaOH, so it would have a molar mass of 32 g/mol. And that's before we even know what that other 5% and 20% ACTUALLY is - if it's all sodium carbonate, then it would be 5.3 g/mol and 21 g/mol, and if it's all sodium oxide, then it would be 3.4 g/mol and 14 g/mol. If you've gotten lost in numbers, that's kinda my point here - when we don't know how much of the NaOH IS ACTUALLY NaOH, we end up becoming lost in numbers

So you see, because we don't know how much of the NaOH has reacted with the environment, it's not a good primary standard

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Re: VCE Chemistry Question Thread
« Reply #8669 on: August 12, 2020, 10:55:40 pm »
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Hello
would this be right