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

_LilyRose_

ahmdoda wrote: »

i was going to write uv light but i wondered how is uv light a reagent! it would be a condition to carry out the reaction and if that what he wanted the other two answer would of both been nickle catalyst at 200 degree so had cl2 instead

Yeah the 'reagent' threw me I was trying to think of chemicals! But is the nickel catalyst not for turning aldehydes, ketones into alcohols? And what's the 200 degree thingy?!

ahmdoda

_LilyRose_ wrote: »

Yeah the 'reagent' threw me I was trying to think of chemicals! But is the nickel catalyst not for turning aldehydes, ketones into alcohols? And what's the 200 degree thingy?!

yes im confused now my self dont bother with the 200 degree i just remember my teacher saying that the nickle has to be at 200 degrees but its never required

xJEx

xJEx wrote: »

But why, what am I leaving out?
i said air contains oxygen so it would affect the ppm result in the end...

They could specify that they want it mentioned that atmospheric O2 dissolves into the sample. Like I said, I would give you the marks but it will depend on the marking scheme.

ahmdoda

Deleted User wrote: »

They could specify that they want it mentioned that atmospheric O2 dissolves into the sample. Like I said, I would give you the marks but it will depend on the marking scheme.

im not sure if their going to be thats specific about it all that it says in my book is to prevent air bubbles containing oxygen from affecting the result but if they do i guess ur safe good thinking though

MarieCurie22

What were your dissolved oxygen in ppm??? I got 7.52

Also heat of neutralization....4.3kj?

And anyone do the oxidation q with the masses of Al and Fe??

xJEx

Deleted User wrote: »

They could specify that they want it mentioned that atmospheric O2 dissolves into the sample. Like I said, I would give you the marks but it will depend on the marking scheme.

Ok. for the reagent I said 'MnSo4 - manganese sulfate'' instead of manganese (II) sulfate - would i lose a mark or would it be okay cause i had the formula correct?
And what was the last bit, about it having to be done immediately?

mocker2012

xJEx wrote: »

Ok. for the reagent I said 'MnSo4 - manganese sulfate'' instead of manganese (II) sulfate - would i lose a mark or would it be okay cause i had the formula correct?
And what was the last bit, about it having to be done immediately?

Photosynthesis/Respiration by organisms in water change dissolved o2 levels in water over

MarieCurie22

xJEx wrote: »

Ok. for the reagent I said 'MnSo4 - manganese sulfate'' instead of manganese (II) sulfate - would i lose a mark or would it be okay cause i had the formula correct?
And what was the last bit, about it having to be done immediately?

I wrote the two as well id say it was a hard paper so theyd give you the marks....

xJEx

mocker2012 wrote: »

Photosynthesis/Respiration by organisms in water change dissolved o2 levels in water over

Hmm i didnt really know so I said the amount os dissolved oxygen can change when the sample is exposed to air and light?

ynwa14

The ordinary paper was HORRIBLE I thought gah. I dont care anymore. Never looking at this subject again.

MarieCurie22

xJEx wrote: »

Hmm i didnt really know so I said the amount os dissolved oxygen can change when the sample is exposed to air and light?

It was only three marks, so the dissolved O2 value doesnt change will probably give it to you

MarieCurie22

What did you guys get for your dissolved O2???In ppm....and did you guys notice we had to find the I2 in moles/litre AND O2!!!!!!!!!!

xJEx

Can anyone explain how to do the pH Q? Getting so confused!
OH and for the ionisation was it Helium, oxygen and then x = 653?

ahmdoda

MarieCurie22 wrote: »

What did you guys get for your dissolved O2???In ppm....and did you guys notice we had to find the I2 in moles/litre AND O2!!!!!!!!!!

fip totaly missed that!! here goes another 6 marks

MarieCurie22

xJEx wrote: »

Can anyone explain how to do the pH Q? Getting so confused!
OH and for the ionisation was it Helium, oxygen and then x = 653?

No Helium and Sulfur...
x=900?

How did you get 635?

MarieCurie22

xJEx wrote: »

Can anyone explain how to do the pH Q? Getting so confused!
OH and for the ionisation was it Helium, oxygen and then x = 653?

PH q you had to divide 7 by 35 (mr of the chemical) to get in moles per litre ie molarity....
Then you had to multiply the molarity by the Kb and square root that....
Then put that into the -log10(x)
Then that gave you POH and we needed PH so we had to take our answer from 14

BTW does ph have to be a whole number??

MarieCurie22

MarieCurie22 wrote: »

PH q you had to divide 7 by 35 (mr of the chemical) to get in moles per litre ie molarity....
Then you had to multiply the molarity by the Kb and square root that....
Then put that into the -log10(x)
Then that gave you POH and we needed PH so we had to take our answer from 14

BTW does ph have to be a whole number??

Not necessarily I did all questions by the way (I saw you ask) so just PM me if you have any questions cause I might miss them on the forum
I'm not saying I have all the answers but we can discuss something if you PM me (goes for everyone )

AndyMc

It wasnt helium. Noble gasses arnt included in ionisation energy as they have no tendency to loose electrons what so ever.

SecondMan

MarieCurie22 wrote: »

No Helium and Sulfur...
x=900?

How did you get 635?

I got 900 as well and I also got Sulfur. Really confusing question though, nevertheless.

AndyMc

AndyMc wrote: »

It wasnt helium. Noble gasses arnt included in ionisation energy as they have no tendency to loose electrons what so ever.

Noble gases do have ionisation energies. They are just really high because of their lose tendency to lose electrons.

AndyMc

Deleted User wrote: »

Noble gases do have ionisation energies. They are just really high because of their lose tendency to lose electrons.

But they arnt given in the log tables which the graph said refer to. The graph would have had constant blanks

xJEx

MarieCurie22 wrote: »

No Helium and Sulfur...
x=900?

How did you get 635?

**** why the hell did i say oxygen.. cause the mass of oxygen is 16 ugh! oops... I didn't even notice late while i was saying H was oxygen haaha!
But i got 653, it was chromium ?
And to whoever said it wasn't helium, it twas my friend

AndyMc

AndyMc wrote: »

But they arnt given in the log tables which the graph said refer to. The graph would have had constant blanks

That's electronegativity values.

SecondMan

AndyMc wrote: »

It wasnt helium. Noble gasses arnt included in ionisation energy as they have no tendency to loose electrons what so ever.

If noble gases aren't included in ionisation energy then why do they have values in the tables? And the question stated that the graph included ionisation values of the first 31 elements, if helium had not been included then they would not have said that.

xJEx

AndyMc wrote: »

But they arnt given in the log tables which the graph said refer to. The graph would have had constant blanks

They are given. They have really high energies. You're thinking of electronegativities, they cant have electronegativities because they cant form bonds

xJEx

Ugh my revision book is the stupidest thing ever.. it said when the acid/base has more than one proton (H) you mulitply by the number of H's to get the concentration before you get the pH. So basically for the pH when subbing in for (OH-) i put 5(0.2) = 1 ....but i followed the formula and got the moles bit beforehand out so how many marks our of 12 would i get do you think?

TheChosenOne

Just to add to the confusion:

Did everyone get:

7.52 ppm in Q1?

In Q2 (a) to confirm it's ethanoic acid and not ethanol, could you have added sodium carbonate, with fizzing that turns lime water milky observed?

In Q2 (b), did you have to shake the test tube or put in warm bath or both?

In the same question, (e), I talked about the steam trap and also said that the liebeg condenser should be reversed, i.e. the left arm should point up.

Then in Q5 (a), what was Boyle's understanding of the "element"?

Did everyone get -126.4 for the heat of reaction in Q6 (c) ?

In Q8 (b) (i), was it Cl2 and u.v. light?

In Q11 (b), did you get 11.28 for the pH?

Thanks so much

TheChosenOne

TheChosenOne wrote: »

Just to add to the confusion:

Did everyone get:

7.52 ppm in Q1? Yes

In Q2 (a) to confirm it's ethanoic acid and not ethanol, could you have added sodium carbonate, with fizzing that turns lime water milky observed? I'm sure that this would be fine however I used the Mg and evolution of H2 gas.

In Q2 (b), did you have to shake the test tube or put in warm bath or both? Just shake it. No water bath

In the same question, (e), I talked about the steam trap and also said that the liebeg condenser should be reversed, i.e. the left arm should point up. I had the liebig condenser, didn't notice the steam trap was wrong.

Then in Q5 (a), what was Boyle's understanding of the "element"? A substance that cannot be broken down any further by chemical means.

Did everyone get -126.4 for the heat of reaction in Q6 (c) ? Yes.

In Q8 (b) (i), was it Cl2 and u.v. light? I think so because we need a Chlorine radical for the reaction to occur and u.v light does this.

In Q11 (b), did you get 11.28 for the pH? Yes.

Thanks so much

Answers in quote

MarieCurie22

TheChosenOne wrote: »

Just to add to the confusion:

Did everyone get:

7.52 ppm in Q1?

In Q2 (a) to confirm it's ethanoic acid and not ethanol, could you have added sodium carbonate, with fizzing that turns lime water milky observed?

In Q2 (b), did you have to shake the test tube or put in warm bath or both?

In the same question, (e), I talked about the steam trap and also said that the liebeg condenser should be reversed, i.e. the left arm should point up.

Then in Q5 (a), what was Boyle's understanding of the "element"?

Did everyone get -126.4 for the heat of reaction in Q6 (c) ?

In Q8 (b) (i), was it Cl2 and u.v. light?

In Q11 (b), did you get 11.28 for the pH?

Thanks so much

For q2 b i went through the motions of how bromine water decolorises....
An element is a simple substance that cannot be split into simpler substances by chemical means!

All calculations are parfait!

SecondMan

For the ethanoic acid and ethanol distinguishing test, I said add iodoform and if you get a negative result then use blue litmus paper in the sample and if it turns red then it's ethanoic acid?

TheChosenOne

Deleted User wrote: »

Answers in quote

You see, I think I lost a lot in that damn question 2... So I'm trying to calculate if I still have the A1.

KildareKing

SecondMan wrote: »

Yes. I drew a hand that resembled a side-view of a rabbit's head.

same and I put an arrow pointing towards it and wrote "this is hand"

MarieCurie22

I noticed the steam trap....the arms were ok? water was going against the flow essentially?

TheChosenOne

SecondMan wrote: »

For the ethanoic acid and ethanol distinguishing test, I said add iodoform and if you get a negative result then use blue litmus paper in the sample and if it turns red then it's ethanoic acid?

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

TheChosenOne

TheChosenOne wrote: »

You see, I think I lost a lot in that damn question 2... So I'm trying to calculate if I still have the A1.

Well like I said before you can lose up to 40 marks so you should be fine!

TheChosenOne

MarieCurie22 wrote: »

I noticed the steam trap....the arms were ok? water was going against the flow essentially?

Yeah, but I said it would have a poor thermal contact with the tube because it would only touch the bottom of it and then flow out? But if the "out" arm was upwards, it would force water to encircle all of the tube, if you know what I mean xD

SecondMan

TheChosenOne wrote: »

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

The iodoform test is used on the Biology course to detect the presence of alcohol

KildareKing

MarieCurie22 wrote: »

For q2 b i went through the motions of how bromine water decolorises....
An element is a simple substance that cannot be split into simpler substances by chemical means!

All calculations are parfait!

for leibig condenser you had to say water should be going in from the top, in the diagram water was coming out from the top of the condenser thats the error.

yoppo

KildareKing wrote: »

for leibig condenser you had to say water should be going in from the top, in the diagram water was coming out from the top of the condenser thats the error.

Other way round buddy. Water goes in the bottom, out the top.

TheChosenOne

KildareKing wrote: »

for leibig condenser you had to say water should be going in from the top, in the diagram water was coming out from the top of the condenser thats the error.

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

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..