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Paper discussion
by ddp.cronin Leaving Cert Chemistry — 23/06/16 36

I personally thought that was the hardest Chem so far. Usually titration is simple and straight forward. Found this one hard. Anyone get 4.8% for w/v


36 Comments
Chris241197 — 21/06/16
yes whooooo got 4.8
shannon8 — 21/06/16
I got that too! I thought the paper was so hard, I was hoping for an A, got a B2 in the DEB, I'll be lucky to get that after that paper
ddp.cronin — 21/06/16
What did you get for instanteneous rate at 4min
MAYYAMIMI — 21/06/16
I got something like 7. .... I don't clearly remember but it was in the sevens
Bengee — 21/06/16
What did you get for the Kc?
Insa333 — 21/06/16
Guys I got 48%. I reanalysed the paper and I don't think I'm wrong because they mentioned ORIIGINAL vinegar as opposed to DILUTED vinegar!!
Chris241197 — 21/06/16
pretty sure you'd be dead with 48% v/w in vinegar :) , but maybe you are right time will tell
shannon8 — 21/06/16
I think 8.something for the instantaneous rate. I think they asked for the diluted vinegar no?
Chris241197 — 21/06/16
no its original
Bengee — 21/06/16
Googled it ... "optimum amount of acetic acid in vinegar is between 4 and 5 percent by weight." 4.8% sounds right
ddp.cronin — 21/06/16
its 4.8%. Its 48% in the orginal but thats per L. You have to write it per 100cm
1282 — 21/06/16
4.8%
conor6842 — 21/06/16
w/v is per litre and i got 4.8% were we suppose to know the makeup of arsine?
ddp.cronin — 21/06/16
it gave it in the question. As with 3 hydrogen atoms
conor6842 — 21/06/16
ahh fuck i couldent find it in the peroidic table too late now
Longbottoms — 21/06/16
What did people get for the KC value in question 7?
Aisling21 — 21/06/16
For Kc I got 12.25 but think it's wrong.. I got loads of different answers and wasn't sure which to put down, went with this in the end
Aisling21 — 21/06/16
Which titrations are used to standardise sodium hydroxide?
ddp.cronin — 21/06/16
I said anhydrous sodium carbonate to standardise HCl and then HCL to standardise sodium hydroxide ?
Aisling21 — 21/06/16
Ah yeah thanks that sounds right
Fjfj — 21/06/16
I got something like 3920 for the Kc definitely wrong lol
Longbottoms — 21/06/16
I got 196000
Longbottoms — 21/06/16
for the KC
what.the.matter.is.the — 21/06/16
KC was 196000
what.the.matter.is.the — 21/06/16
I got like 7.5 or something in the instantaneous rate.
what.the.matter.is.the — 21/06/16
I got around 7.5 in the instantaneous rate.
Aisling21 — 21/06/16
Agh I originally got that for Kc but thought it was wrong as there was a two at the start of the equation
Sinott — 21/06/16
Different values of Kc probably came from whether moles were divided by the 50Litre volume of the container, which I believe was to be divided before subbing into the Kc expression.
orlaithdd — 21/06/16
There was a misprint on the ordinary paper, HCL titration had the wrong chemical equation I think?
laylalushni — 21/06/16
the kc i got had 4 numbers, but i converted the grams to moles, found the moles at equilibrium and divided by 50 then I used the formula to find the kc
Insa333 — 22/06/16
If 4.8% is the answer then I messed up in a place where I wrote 0.8 instead of 0.08. This meant my other answers further down were also affected by this. How many marks will I lose for this? Will I only be marked down for the initial slip or will marks be taken away from the other answers as well?
michael.ryan.712714 — 22/06/16
I am hoping that they will account for slips. They would hardly be that cruel
michael.ryan.712714 — 22/06/16
to take off marks for the remainder for the question
momo5478 — 23/06/16
Having done LC would you advise getting grinds if one only gets 74% in their summer house exam
Insa333 — 23/06/16
I am a firm believer, when it comes to subjects like chemistry and biology, that one will only waste money on grinds. Let alone the fact that I had great teachers in these subjects, I feel that the textbooks are so comprehensive and easy to follow. Working hard on each chapter and understanding the material is vital and this is made easy by the great layout of information in the textbooks.
maria.pachowicz — 23/06/16
I got 4.8% for the concentration too, and 196,000 for Kc. My instantaneous rate was somewhere around 8 or 9 but they generally accept a range of values for that! Regarding grinds, I agree with Insa333 - I don't think any grinds teacher could explain the material better than the textbooks do! It takes time and work but it all clicks eventually
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