ATAR Notes: Forum
Archived Discussion => 2010 => End-of-year exams => Exam Discussion => Victoria => Chemistry => Topic started by: amimery on November 12, 2010, 05:17:06 pm
-
people have been saying that the answer was that the conc of the conjugate acid was negligible etc... buttt would another appropriate response for the assumption be that the [H+] = [ch3ch(oh)coo -] ...? thoughts?
-
That is an assumption, so I suppose it should be a valid response. Don't know how they'd mark it though. It is a fairly important assumption for the calculation.. It assumes that the H+ from the self-ionisation of water is negligible. I expect there will be a wide variety of accepted answers. So you should be fine.
-
I said the exact same thing but apparentally its wrong? reason was that this is not an assumption. its a FACT
-
I said the exact same thing but apparentally its wrong? reason was that this is not an assumption. its a FACT
its not a fact...
-
that the concentration of the acid at equilibrium was the same as the initial concentration?
-
I said the exact same thing but apparentally its wrong? reason was that this is not an assumption. its a FACT
its not a fact...
So that assumption is correct? If so then I just went one higher than my estimation :D
-
that the concentration of the acid at equilibrium was the same as the initial concentration?
yeah, this is what i said.
assumed that [lactic acid] had not changed when in fact it has decreased by a very small amount.
-
I said the exact same thing but apparentally its wrong? reason was that this is not an assumption. its a FACT
its not a fact...
So that assumption is correct? If so then I just went one higher than my estimation :D
I dont think that is an assumption. If one molecule of lactic acid dissapates one H+ ion will be formed and one CH3.....- ion will be made..... t
-
I said the exact same thing but apparentally its wrong? reason was that this is not an assumption. its a FACT
its not a fact...
So that assumption is correct? If so then I just went one higher than my estimation :D
I dont think that is an assumption. If one molecule of lactic acid dissapates one H+ ion will be formed and one CH3.....- ion will be made..... t
However what if the container is contaminated and there are traces of CH3CH(OH)COO- already inside, hence we are assuming that [H+] is exactly equal to [CH3CH(OH)COO-] after ionisation. Just thinking..
-
Um I said that the temp is 25 degrees..wrong right :(
-
I said the exact same thing but apparentally its wrong? reason was that this is not an assumption. its a FACT
its not a fact...
So that assumption is correct? If so then I just went one higher than my estimation :D
I dont think that is an assumption. If one molecule of lactic acid dissapates one H+ ion will be formed and one CH3.....- ion will be made..... t
However what if the container is contaminated and there are traces of CH3CH(OH)COO- already inside, hence we are assuming that [H+] is exactly equal to [CH3CH(OH)COO-] after ionisation. Just thinking..
I dont think you're just thinking..you're just ASSUMING.
get it ? i lol'ed
-
IMO, there are two good correct responses to this question. The first is to assume that there are no traces of lactic acid already in the container (and yes, there could be), and the second is to assume that it's a very weak acid and that [A] does not change even what it deionises. It said write ONE assumption, but the reality is that you would've made more than one assumption. Personally, I wrote the first one, because I actually didn't use the 2nd assumption in a past paper and I still received the same answer to the correct number of significant figures.
-
that is a fact, not an assumption theyre in the same mol to mol ratio as theyre produced
-
that is a fact, not an assumption theyre in the same mol to mol ratio as theyre produced
but really, is anything in this world a fact? its all an illusion.
-
vcaa will probs accept a range of answers.
What OP has said should be fine, in fact in my text book it in fact gives little step by step thing on how to do these question and its exact wording is something like 'we must make the assumption that H+ = acid'
-
Did it specify that it was added to completely pure/deionised water in a container that had been cleaned properly? If not, it's not a fact. They do react in a 1 to 1 molar ratio, but we make the assumption that there wasn't any of the substance/ions initially in the container. We also assume that the [H+] ions don't react with anything else, so there are definitely a range of assumptions being made. This is certainly correct. The question said ONE assumption; it didn't say THE assumption.
-
Actually, it's never a fact. There is always going to be some H+ from the self-ionisation of water. So in saying that the only H+ in solution is coming from the acid you're assuming that the ionisation of water is negligible. At very high temperatures it becomes important..
-
I said the exact same thing but apparentally its wrong? reason was that this is not an assumption. its a FACT
its not a fact...
So that assumption is correct? If so then I just went one higher than my estimation :D
I dont think that is an assumption. If one molecule of lactic acid dissapates one H+ ion will be formed and one CH3.....- ion will be made..... t
However what if the container is contaminated and there are traces of CH3CH(OH)COO- already inside, hence we are assuming that [H+] is exactly equal to [CH3CH(OH)COO-] after ionisation. Just thinking..
i agree becca, you should be right in assuming that these two exactly equal each other, this assumption is needed for the calculation - so clearly it is a correct assumption to make.
-
YES VEXX THATS WAHT I PUT. :D LOVE YOU BUDDY
-
YES VEXX THATS WAHT I PUT. :D LOVE YOU BUDDY
hahah yayy :D you are going to smash this chem exam!!!
well done brooooooo.
-
assuming that temp = 25 degrees is acceptable
assuming that ATM = 1 is also acceptable
they are the conditions under which the K values are empirically determined.
U can also assume that all the solid 4.5 grams of lactic acid dissolves. U can assume there is no lactic acid already in the container etc.
-
can you say assume that no strong base was added coz that would change the results also.
-
can you say assume that no strong base was added coz that would change the results also.
sorry I dont get this assumption?
why would a strong base be added?
-
Nah, I don't think that would be accepted.. It's kinda .. irrelevant.
A valid assumption is also that there was not a meteorite strike which spilled the entire solution. Or that no one urinated in the beaker.. But they too are irrelevant..
Valid assumptions, but they wouldn't be accepted.
-
Nah, I don't think that would be accepted.. It's kinda .. irrelevant.
A valid assumption is also that there was not a meteorite strike which spilled the entire solution. Or that no one urinated in the beaker.. But they too are irrelevant..
Valid assumptions, but they wouldn't be accepted.
lol
-
can you say assume that no strong base was added coz that would change the results also.
sorry I dont get this assumption?
why would a strong base be added?
lol i was playing and somehow matty came up with funnier ones LOL