What was that for ? The actual mass of I2 you would get? What was the percentage yield? I Got something around 37 but lots of people said it was around 75?

Reply 4

warkan

OP

3

Original post by El Nin0

what did you get as the concentration in g dm-3? i think I got something like 3.45

I don't remember what I got for the answer. But I remember doing number of moles /volume and then times this answer with the formula mass given .

What did you get for the formula in the first question B part? I got Nh3 as gas and cation I put Nh4+ and anion I got so4(2-) . So my formula read something like NH4twiceso4(Ammonium sulfate)

And for the burette question I Said 1.) Make sure read from eye level to avoid parallax error and 2.) Make sure the tip below the tap is filled in burette because it is a part of accuracy of the burette . Read it somewhere lol

For the Graph question when it said write down the maximum temperature it goes up to . Did you just read it off the graph where the extrapolated lines met?

What did you guys write for why is iodine added slowly and in small amounts? All i could think off was 'The reaction is exothermic , So to prevent vigorous reactions .'
Any other questions you guys remember?

Reply 5

5araol

It was one of the easiest papers if not the easiest one!!

guys for the % error question do we have to do answer X 2 or not?

Reply 6

Machimbawe

its was really easy but i did sooo manny stupid mistakes !

and yes, its answer*2
(i got that one wrong)
and for percentage it was 75% , i got 36.5 % ( or something) because we forgot to multiply the mass of idione by 2 to get I2

Reply 7

warkan

OP

3

The percentage question was just 1 mark right ? Grade boundaries for an A ?? 38/50 for an A ? last year was 33 I think..

Reply 8

xstrawberryswingx

Yeah for the concentration one I got sumthing like 3 point something as well.

I got 75% for percentage yield and yea you have to times the molar mass of I2 by 2.

For the first question I got NH4twiceSO4 as well. And the first was KBr?

The burette I wrote read at eye level and lower meniscus. And the last point was completely random so I wrote take at room temperature so glass of burette has not contracted or anything =/

For adding iodine is small amounts.. I saw that question in a past paper for bromine and the answer was coz it’s a vigorous reaction. So I just re wrote tht.

For percentage error you were NOT meant to x2. It’s a pipette reading. You only x2 for temperature and measures that you take TWICE. So it was just like 0.06 or whatever divided by 25. So I THINk it was 0.24 percent or whtever.

I had a question =/ I wasn’t sure for the enthalpy question when we had to calculate energy produced… the mass that we had to take.. was it 50 + volume from neutralization point OR 50 + 50.. coz I put 50 + 50.. coz I remember reading somewhere that the mass in the enthalpy of neutralization reactions is the TOTAL volume of liquidS added… which one is right ? =/

Reply 9

warkan

OP

3

Original post by Machimbawe

its was really easy but i did sooo manny stupid mistakes !

and yes, its answer*2
(i got that one wrong)
and for percentage it was 75% , i got 36.5 % ( or something) because we forgot to multiply the mass of idione by 2 to get I2

What other mistakes did you make ? Seems like I am on the same boat :/

Reply 10

warkan

OP

3

Original post by xstrawberryswingx

Yeah for the concentration one I got sumthing like 3 point something as well.

I got 75% for percentage yield and yea you have to times the molar mass of I2 by 2.

For the first question I got NH4twiceSO4 as well. And the first was KBr?

The burette I wrote read at eye level and lower meniscus. And the last point was completely random so I wrote take at room temperature so glass of burette has not contracted or anything =/

For adding iodine is small amounts.. I saw that question in a past paper for bromine and the answer was coz it’s a vigorous reaction. So I just re wrote tht.

For percentage error you were NOT meant to x2. It’s a pipette reading. You only x2 for temperature and measures that you take TWICE. So it was just like 0.06 or whatever divided by 25. So I THINk it was 0.24 percent or whtever.

I had a question =/ I wasn’t sure for the enthalpy question when we had to calculate energy produced… the mass that we had to take.. was it 50 + volume from neutralization point OR 50 + 50.. coz I put 50 + 50.. coz I remember reading somewhere that the mass in the enthalpy of neutralization reactions is the TOTAL volume of liquidS added… which one is right ? =/

I missed out on the percentage question !! I would still be awarded for the previous one where we had to calculate the actual mass right ? cuz it looks like for the percentage i got exactly half of what was required.

Yup the first question was KBR .

For the burette first point is valid but not really sure about second though..

Yup for pipette no x2 !

For the enthalpy question i added the 50 + 26.5 or whatever volume we calculated from graph for neutralization. This one should be the right method.

How did u calculate the maximum temperature of the experiment reached in the (a) part of 3rd question ?

Reply 11

BilalArshad

I got maximum temperature as 29.8 something....with temperature difference as something like 7.6..

Reply 12

Vampire diaries

ya 1st question's answer was KBr but wat did u guys get for the 2nd thing???

Reply 13

nich_k94

For the second I got ammonium sulphate? (NH3)2 SO4 ... I guessed, but quite a few people I asked put the same thing :s
For percentage error I got 0.48% and enthalpy change question I got -47 kJ/mol.. last one was 75% and that's all the answers that I remember putting :tongue:

Reply 14

5araol

Original post by nich_k94

For the second I got ammonium sulphate? (NH3)2 SO4 ... I guessed, but quite a few people I asked put the same thing :s
For percentage error I got 0.48% and enthalpy change question I got -47 kJ/mol.. last one was 75% and that's all the answers that I remember putting :tongue:

Isnt Ammonium NH4?

other than that i got the same answers except for the enthalpy change where i got -48.

Reply 15

nich_k94

sorry! that's what I meant :colondollar:

Reply 16

El Nin0

Yeh I got KBr and (NH4)2SO4

For max temp I got 29.9 and the temp change 6.7 or something around that.
I got concentration of HCl as 1.98 mol/dm3
For the energy change i did 50+23.5 and then calculated it.
For the last enthalpy bit I got -43 kJ mol-1 or -40something (cant remember)

For burette one i said take reading which is at bottom of meniscus and removed any trapped are prior to doing experiment.

Yeh for the yield I got 70% something I did it wrong first then realised you had to do 127*2. The concentration was 3.45 or something.

For organic question i said becuase reaction is exothermic.
Water bath is used becuase both of them were flammable

Cant remember what the other questions were but prob remember what I put down if anyone can remember question.

(edited 12 years ago)

Reply 17

usamakhanlodhi

1

Are you guys talking about the unit 3 chem where you do b.c and d ...2 out of 14 one out of 12
If so why is it out out of 50 when it adds up to 40
What are the grade boundaries and if they were 33 is that just out of 40 or is that out of 50..very confused as need to know if ive done well enough in my unit 3 to balance out unit 2