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HSC Chemistry Question Thread
keltingmeith:
--- Quote from: Hawraa on November 06, 2019, 01:35:43 pm ---Hi everyone,
Just regarding this graph question from ATAR Notes chemistry topic test. So it says that the trend line(line of best fit) should not be linear but should go near most points. For me it looks like the dotted line has been connected by hand. Is it wrong to draw it with a ruler ( like I did, if you can see the line in the middle) because I'm confused. My teacher said it should be linear but the answer here says it should not. So do we connect the dots or just draw a line approximately through them.
Can someone please explain this to me? Thanks.
--- End quote ---
Would help if we could see the question
--- Quote from: Hawraa on November 06, 2019, 09:31:15 pm ---Hi everyone,
Urgent question please.
Ethanol is widely used fuel that can be made from both renewable and non renewable resources. Using relevant chemical equations, outline two methods that can be used to produce Ethanol.
The methods I would use are fermentation (equation of glucose turning into Ethanol and CO2) and hydration of ethene. Is the second method wrong? Because the answer I have talks about fermentation and the substitution of halogenated alkanes with water? Are they both correct?
Any help would be appreciated guys, thanks.
--- End quote ---
No need to worry, hydration of ethene is still a correct answer
mani.s_:
Hi, how would I find the pH of 0.020 mol/L citric acid without using Ka values??? Thanks
louisaaa01:
--- Quote from: mani.s_ on November 22, 2019, 07:48:30 pm ---Hi, how would I find the pH of 0.020 mol/L citric acid without using Ka values??? Thanks
--- End quote ---
Hi,
Citric acid is a weak triprotic acid, so to accurately find pH you would have to use Ka. However, if Ka isn't provided, the question could be solved (though somewhat erroneously) relying on the assumption that citric acid is a strong acid.
Since citric acid is triprotic, assuming it is strong and thus completely dissociates, a 0.020 mol/L solution of citric acid will have [H+] = 3 x 0.020 = 0.060 mol/L. You can then use the formula, pH = -log[H+] to determine pH.
Hope this helps!
milie10:
Hi!
I tried doing some of the past HSC questions on acids and bases, and I'm having a bit of trouble doing these two.
For this, I tried using c1v1=c2v2 but ended up with 10L :( Is this the right method to use here?
I'm still confused about limiting reagent type questions- in this question, when I use n=cxv, does this find n(2HCl), or does it only find n(HCl)? Also, is there a quicker way to do this question?
Thanks so much! :D
r1ckworthy:
Hey!
--- Quote from: milie10 on January 30, 2020, 06:22:37 pm ---Hi!
I tried doing some of the past HSC questions on acids and bases, and I'm having a bit of trouble doing these two.
(Image removed from quote.)
For this, I tried using c1v1=c2v2 but ended up with 10L :( Is this the right method to use here?
--- End quote ---
You are right! 10L is the answer, so you choose the answer that is closest to this value, which is C!
--- Quote from: milie10 on January 30, 2020, 06:22:37 pm ---(Image removed from quote.)
I'm still confused about limiting reagent type questions- in this question, when I use n=cxv, does this find n(2HCl), or does it only find n(HCl)? Also, is there a quicker way to do this question?
Thanks so much! :D
--- End quote ---
Here is my working out of the question (click on the image to make it larger):
When you use \( n=c \times v \), it only finds n(HCl). I find limiting reagent questions confusing, so I like to write statements as I did in my working. In those statements, I calculated how many moles a substance will react with/ use up (according to stoichiometric ratios). I compare the two statements and pretty quickly find out which substance is the limiting reagent.
I am not sure of a quicker way to do this question (hopefully someone can chip in!).
Let me know if you need any more help!
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