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March 29, 2024, 04:04:03 am

Author Topic: HSC Chemistry Question Thread  (Read 1040598 times)  Share 

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conic curve

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Re: Chemistry Question Thread
« Reply #540 on: July 31, 2016, 04:36:14 pm »
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For this extended response; why they are more metals available to use now than 200 yrs ago, what would I have to talk about other than "recently developed technology" which made it cheaper and easier for us to extract?

Sssssrr

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Re: Chemistry Question Thread
« Reply #541 on: August 01, 2016, 09:58:29 pm »
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hey, could some please explain what equilibrium constants actually are
many thanks

RuiAce

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Re: Chemistry Question Thread
« Reply #542 on: August 01, 2016, 10:00:43 pm »
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hey, could some please explain what equilibrium constants actually are
many thanks
What it actually is? Well it is a measure of just where exactly does the equilibrium lie for a reversible reaction. I.e. by how much the products or reactants dominate at equilibrium.

conic curve

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Re: Chemistry Question Thread
« Reply #543 on: August 01, 2016, 10:03:16 pm »
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hey, could some please explain what equilibrium constants actually are
many thanks

The equilibrium constant of a chemical reaction is the value of the reaction quotient when the reaction has reached equilibrium. An equilibrium constant value is independent of the analytical concentrations of the reactant and product species in a mixture, but depends on temperature and on ionic strength. Known equilibrium constant values can be used to determine the composition of a system at equilibrium.
« Last Edit: August 01, 2016, 10:09:43 pm by conic curve »

RuiAce

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Re: Chemistry Question Thread
« Reply #544 on: August 01, 2016, 10:04:22 pm »
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Equilibrium constants are separated into a homogenous equilibrium and heterogenous equilibrium

A homogeneous equilibrium has everything present in the same phase. The usual examples include reactions where everything is a gas, or everything is present in the same solution

A heterogeneous equilibrium has things present in more than one phase. The usual examples include reactions involving solids and gases, or solids and liquids.
All of this isn't actually a part of the syllabus, fyi.

jakesilove

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Re: Chemistry Question Thread
« Reply #545 on: August 01, 2016, 10:13:04 pm »
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All of this isn't actually a part of the syllabus, fyi.

I think maybe it's part of Industrial Chem? Not entirely sure
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RuiAce

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Re: Chemistry Question Thread
« Reply #546 on: August 01, 2016, 10:15:36 pm »
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I think maybe it's part of Industrial Chem? Not entirely sure
It's not. Relating heterogeneous/homogeneous isn't.

Source: Personal experience :P

jakesilove

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Re: Chemistry Question Thread
« Reply #547 on: August 01, 2016, 10:17:02 pm »
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It's not. Relating heterogeneous/homogeneous isn't.

Source: Personal experience :P

Ah sorry I see I see, I didn't actually see your definition post :)
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onepunchboy

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Re: Chemistry Question Thread
« Reply #548 on: August 02, 2016, 07:48:08 pm »
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Im not sure how to convert into ppm. Can someone crash course this q for me and maybe ppm in general? Thanks

RuiAce

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Re: Chemistry Question Thread
« Reply #549 on: August 02, 2016, 07:52:03 pm »
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(Image removed from quote.)
Im not sure how to convert into ppm. Can someone crash course this q for me and maybe ppm in general? Thanks
To say the least

The units "ppm" is decomposed to mg/kg or mg/L

I.e. 1 ppm = 1mg/1kg
OR 1 ppm = 1mg/1L

To determine concentration in ppm, convert the numerator into a mass in mills. Also convert the bottom to a mass in kilograms, or a mass in litres.

To go from molarity (moles per litre) you would leave the denominator the same (possibly equal to 1), and use m=nMM on the numerator and convert the grams to mills.

(Your question can't be done yet as I don't know what the actual precipitate is.)
« Last Edit: August 02, 2016, 07:53:41 pm by RuiAce »

onepunchboy

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Re: Chemistry Question Thread
« Reply #550 on: August 02, 2016, 07:58:45 pm »
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To say the least

The units "ppm" is decomposed to mg/kg or mg/L

I.e. 1 ppm = 1mg/1kg
OR 1 ppm = 1mg/1L

To determine concentration in ppm, convert the numerator into a mass in mills. Also convert the bottom to a mass in kilograms, or a mass in litres.

To go from molarity (moles per litre) you would leave the denominator the same (possibly equal to 1), and use m=nMM on the numerator and convert the grams to mills.

(Your question can't be done yet as I don't know what the actual precipitate is.)
Silver chloride hehe

RuiAce

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Re: Chemistry Question Thread
« Reply #551 on: August 02, 2016, 09:33:23 pm »
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Silver chloride hehe
The percentage composition of chloride ions in silver chloride (by molar masses) is

35.45/(107.9+35.45) * 100% = 24.7296826...%

Thus, the mass of chloride ions present in the sample is
mCl- = 3.65g * 24.7296826.../100 = 0.9026334147...g

Convert this mass into milligrams: 902.6334147... mg

The mass of the water is in mL. We want to convert this to L: 0.05 L

Concentration in ppm = 902.6334147...mg / (0.05 L) = 18052.66829... ppm = 1.80*104 ppm (3 s.f.)

That's quite a large concentration. Unsurprising because 3.65g precipitate out of 50mL is massive in the context of ppm but still dubious. Will let someone else check my working here.

jakesilove

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Re: Chemistry Question Thread
« Reply #552 on: August 02, 2016, 09:39:02 pm »
+1
The percentage composition of chloride ions in silver chloride (by molar masses) is

35.45/(107.9+35.45) * 100% = 24.7296826...%

Thus, the mass of chloride ions present in the sample is
mCl- = 3.65g * 24.7296826.../100 = 0.9026334147...g

Convert this mass into milligrams: 902.6334147... mg

The mass of the water is in mL. We want to convert this to L: 0.05 L

Concentration in ppm = 902.6334147...mg / (0.05 L) = 18052.66829... ppm = 1.80*104 ppm (3 s.f.)

That's quite a large concentration. Unsurprising because 3.65g precipitate out of 50mL is massive in the context of ppm but still dubious. Will let someone else check my working here.

Was just about to post my working, and got the same solution. Unless we're both doing the same thing wrong, pretty sure that checks out!
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conic curve

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Re: Chemistry Question Thread
« Reply #553 on: August 02, 2016, 09:47:39 pm »
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I'm not getting the idea of this question:

The concentration of mercury in a solution is 0.005g (% w/w). Express this concentration in ppm

jakesilove

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Re: Chemistry Question Thread
« Reply #554 on: August 02, 2016, 09:53:59 pm »
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I'm not getting the idea of this question:

The concentration of mercury in a solution is 0.005g (% w/w). Express this concentration in ppm

Assuming that this just means 0.005% of the solution was Mercury (I can't think of another way to answer this question), we can convert it straight to ppm. Parts per million are exactly that; if there were a million 'parts', how many would be Mercury? Well, 0.005% of them. You can plug this straight into a calculator, and find that the answer is 50ppm
ATAR: 99.80

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