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

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