***2013 LC Chemistry Before/After***

Well turns out adding Mg to ethanol also allows H2 gas to form so my method of distinguishing was wrong.

yoppo

Deleted User wrote: »

Well turns out adding Mg to ethanol also allows H2 gas to form so my method of distinguishing was wrong.

They said simple so I said ethanoic turns blue litmus red.

simons545

TheChosenOne wrote: »

First time I hear of "iodoform", but it seems right Maybe just different book or something.

Idoform test is from biology haha I put that down too!
Its a test for an alcohol using potassium iodide and sodium hypochlorite. Think we might be cheating slightly...

TheChosenOne

simons545 wrote: »

Idoform test is from biology haha I put that down too!
Its a test for an alcohol using potassium iodide and sodium hypochlorite. Think we might be cheating slightly...

Haha, the applied maths crowd are the biggest cheaters when it comes to the mechanics question in Physics

But do you reckon adding sodium carbonate causing CO2 won't do?

yoppo

yoppo wrote: »

They said simple so I said ethanoic turns blue litmus red.

I know! I slip up on the simple questions :rolleyes:

KildareKing

Deleted User wrote: »

Thanks but then the initial temp was 14 and it reached 20.9 so should the heat change not be 6.9? Not around 4?

6.9 was temperature change not heat change, you plug in that number to MC(delta)T. (Delta)T=6.9, M=mass in kg so (75cm^3+75cm^3)multiplied by density which was 1. This will give you mass in grams convert to Kg and the plug it into the formula above. C is the no. given in the question 4.3.

your answer will be heat change for 0.075 moles, you need to find the answer for 1mole. so you divide what ever you got by 0.075. that will get you the answer.

KildareKing

Deleted User wrote: »

Well turns out adding Mg to ethanol also allows H2 gas to form so my method of distinguishing was wrong.

noooo are you serious...

yoppo

Deleted User wrote: »

I know! I slip up on the simple questions :rolleyes:

I made some simple mistakes in it myself... To make it even worse I have a degree in chemistry

Here's hoping for the A1!

KildareKing

KildareKing wrote: »

6.9 was temperature change not heat change, you plug in that number to MC(delta)T. (Delta)T=6.9, M=mass in kg so (75cm^3+75cm^3)multiplied by density which was 1. This will give you mass in grams convert to Kg and the plug it into the formula above. C is the no. given in the question 4.3.

your answer will be heat change for 0.075 moles, you need to find the answer for 1mole. so you divide what ever you got by 0.075. that will get you the answer.

Sounds familiar anyway!

KildareKing

KildareKing wrote: »

noooo are you serious...

Yup :rolleyes: Ah well, it's only 5 marks..

KildareKing

TheChosenOne wrote: »

No, the diagram was right in this regard. Water should always flow in from the bottom so it moves slowly around the tube

damn it I hope the 2 extra questions will cover me then.

KildareKing

KildareKing wrote: »

noooo are you serious...

Although I looked up the curriculum there and we are not required to know the reaction of ethanol with Mg so maybe they might give it to us?

yoppo

Deleted User wrote: »

Although I looked up the curriculum there and we are not required to know the reaction of ethanol with Mg so maybe they might give it to us?

Are you sure? We done it in class. It forms sodium ethoxide :cool:

SecondMan

yoppo wrote: »

Are you sure? We done it in class. It forms sodium ethoxide :cool:

Same as us

xJEx

What were the ansers for question 3?
ike the burette - i said it would measure a more accurate volume but that it would be slow to add it so would affect accuracy in measuring the temp rise.
and then i said to measure it as accurately as possibe add quickly plus a lid to avoid heat loss?

oh and for the last bit i said a the lower concentrations would have given a slower reaction so more time for heat losses

MarieCurie22

Deleted User wrote: »

Sounds familiar anyway!

F*ck so hang on I took it as the molarity and didnt divide anything at the end? Ii got 4.3kj/mol?

a sure look i did all 3 experiments and an extra question my a** is safe in the A2 and probably A1

Glee_GG

xJEx wrote: »

What were the ansers for question 3?
ike the burette - i said it would measure a more accurate volume but that it would be slow to add it so would affect accuracy in measuring the temp rise.
and then i said to measure it as accurately as possibe add quickly plus a lid to avoid heat loss?

oh and for the last bit i said a the lower concentrations would have given a slower reaction so more time for heat losses

I remember at some stage our teacher told us that you don't put a base in the burette because it tends to jam the tap and the opening over time so I just wrote that down, couldn't really think of anything else!

yoppo

xJEx wrote: »

What were the ansers for question 3?
ike the burette - i said it would measure a more accurate volume but that it would be slow to add it so would affect accuracy in measuring the temp rise.
and then i said to measure it as accurately as possibe add quickly plus a lid to avoid heat loss?

oh and for the last bit i said a the lower concentrations would have given a slower reaction so more time for heat losses

A) Definition
Polystyrene
C) More accurate, bases cause the tap to stick
D) Use digital thermometer and use a lid to minimize heat loss
E) Basic calculation
F) Corrosive, burn your skin. Triangle symbol with the test tube and hand.

MarieCurie22

yoppo wrote: »

A) Definition
Polystyrene
C) More accurate, bases cause the tap to stick
D) Use digital thermometer and use a lid to minimize heat loss
E) Basic calculation
F) Corrosive, burn your skin. Triangle symbol with the test tube and hand.

For disadvantage would they accept takes longer to accurately measure?

And what about stirring and using a standard mercury thermometer with more graduations on it and of a low specific heat capacity?

yoppo

yoppo wrote: »

Are you sure? We done it in class. It forms sodium ethoxide :cool:

We didnt do it :0

yoppo

MarieCurie22 wrote: »

For disadvantage would they accept takes longer to accurately measure?

And what about stirring and using a standard mercury thermometer with more graduations on it and of a low specific heat capacity?

Longer yeah but its still accurate!

Stirring is alright, more graduations I dunno. Human error still could mess that up. In fairness the marking scheme could say anything!

MarieCurie22

yoppo wrote: »

Longer yeah but its still accurate!

Stirring is alright, more graduations I dunno. Human error still could mess that up. In fairness the marking scheme could say anything!

yeah is it just me or was this a "harder" paper....you know some years there like and then last year it was:):P ?

xJEx

Is adding quickly alright for a way of ensuring accuracy?

And can you not say the burette would take longer to add so thats a disadvantage? like the burette takes soooo long to empty so the heat rise would be totally inaccurate cause you'd loose loads of heat to surrounding by the time you had added it all?

MarieCurie22

Is it ok for q 5 when dealing with bohrs theory being modified to talk about the exsistance of sublevels??

Glee_GG

Actually for Q6 the bit on benzene what did ye write for the two parts? We had a paragraph on benzene in general but I wasn't too sure about how to go about splitting it up?

yoppo

MarieCurie22 wrote: »

yeah is it just me or was this a "harder" paper....you know some years there like and then last year it was:):P ?

I want the A1 so I had some nerves going in. Bits of it were sticky but overall is was no more difficult. I messed up the calculations slightly in one bit but its not like maths where it carries on. It's one mark for each maths slip! The main theory was easy enough. I'll find out in August!

MarieCurie22

yoppo wrote: »

I want the A1 so I had some nerves going in. Bits of it were sticky but overall is was no more difficult. I messed up the calculations slightly in one bit but its not like maths where it carries on. It's one mark for each maths slip! The main theory was easy enough. I'll find out in August!

Im pretty sure I nabbed my A1....did extra qs to be sure...girls left early in mine in tears so youre lucky

yoppo

Glee_GG wrote: »

Actually for Q6 the bit on benzene what did ye write for the two parts? We had a paragraph on benzene in general but I wasn't too sure about how to go about splitting it up?

I wrote carbon has 3sp2 hybridized orbitals which is uses to form two sigma bonds to two other carbons and one hydrogen.

for part (ii) i wrote carbon then uses its p orbitals which are above and below the plane of the ring to form pi bonds with carbon using its 6 pi electrons. These 6 pi electrons are delocalised in the ring inferring extra stability which means it has resonance structures. Then I drew benzene.

MarieCurie22

Yo yoppo did you do the moles per litre of I2 AND O2 did you see that? Also is the steam trap the flaw? cause tbh the taps are fine to me?

yoppo

MarieCurie22 wrote: »

Yo yoppo did you do the moles per litre of I2 AND O2 did you see that? Also is the steam trap the flaw? cause tbh the taps are fine to me?

it was: 200 x Mol I2/1 = 9.4 x .02/2

Because it's 2:1 (said in ques), divide answer above by 2 to get moles/L

Then x32 to get g/L
Then x1000 to get mg/L
Thats your answer in ppm