AQA Chemistry Unit 1 - [23rd May 2014]AM

June 2010 - question 1e hellppppp

why is the denominator 438 and not 618???

Reply 84

MissC123

3

Original post by LxH

Anyone know how to immediately tell that a coordinate bond is formed between atoms? Say if a question asks you what type of bond is formed, then what is a sure-fire way of knowing that it is coordinate? This has always bugged me.

Usually the coordinate bonds happen when there is an atom with a lone pair bonded to another atom. You can find lone pairs by quickly drawing a dot and cross diagram. Usually they also ask for the name of the bond and how it is formed- hint that it's not just an ordinary covalent bond.

Reply 85

Original post by Danny__Kidoo

help! i really don't know how to work out percentage purity! does anyone know the method you work it out by?

What you got / what you should have got x 100

usually what you got will be given to you.

use molar ratio to calculate what you should have got, they'll have given the info to calculate moles somewhere else in the question.

hard to explain without an example.

Reply 86

Also for 2e - why does Ne have the highest 1t ionisation energy and not Li?

Reply 87

MissC123

3

Original post by Rooroo96

It was a ridiculous paper, I did it last year, I'm predicted A*s in my subjects this year, i have medicine offers, I got a really high A in unit 2 (130/140ums) yet somehowwww managed to get a C in that paper

Not too sure how tomorrow will go D:

Posted from TSR Mobile

hey, I know this is totally irrelevant to this thread, but could you share your stats/work experience? Wanna apply for medicine next year as well :smile:

Reply 88

Original post by Barney098

June 2010 - question 1e hellppppp

why is the denominator 438 and not 618???

C = 12, F = 19, H = 1

C4F10 + 10HF

In total - 4C 20F 10H

4 x 12 = 48
20 x 19 = 380
10 x 1 = 10

48 + 380 + 10 = 438

Reply 89

Original post by nope..

hey! was just wondering if i could get some clarification in this question!

Zinc chloride can be prepared in the laboratory by the reaction between zinc oxide and
hydrochloric acid.
The equation for the reaction is
ZnO + 2HCl ZnCl2 + H2O
A 0.0830 mol sample of pure zinc oxide was added to 100 cm3 of 1.20 mol dm–3
hydrochloric acid.

Calculate the maximum mass of anhydrous zinc chloride that could be obtained from
the products of this reaction.

in this question i've worked out the moles of HCl to be 0.12, would i use this or the moles of zinc oxide to work out moles of zinc chloride to enable me to work out mass?
and would the same idea apply to similar calculations?

I would use the HCl one, halve it and then you have 0.06, the moles of ZnCl2 (you can then work out the mass or what ever). I think the reason we use this one is because maybe not all the zinc reacted as this was the one they were adding. I have no idea if this is correct, I just know you use the HCl one. :smile:

Sorry if this wasn't much help. How are you feeling about tomorrow?

Reply 90

Original post by Barney098

Also for 2e - why does Ne have the highest 1t ionisation energy and not Li?

Think about it? Why does IE increase across a period?

similar shielding - no effect
increased nuclear charge - has an effect

essentially Ne has a full energy level, and it has the highest IE due to an increased nuclear charge.

Reply 91

Original post by Barney098

Also for 2e - why does Ne have the highest 1t ionisation energy and not Li?

Neon has a full outer shell of electrons so it really doesn't want to lose one as it is pretty stable as it is. Lithium however is trying to attain a full outer shell and currently has one electron in its outer shell, the easiest way for it to get a full outer shell is to lose that one electron so it really wants to lose it.

Also, neon has more protons than lithium but similar shielding (same period, same number of shells) so it has a smaller atomic radius and the electrons are closer to the positive nucleus, making them harder to remove.

Reply 92

skizzle

6

Original post by Barney098

June 2010 - question 1e hellppppp

why is the denominator 438 and not 618???

Denominator should be everything on the left.

So

C4H10- ((12X4)+10) =58
10F2- ((19X2)x10))= 380

Add the two together gives 438

Reply 93

Original post by d.jackson95

C = 12, F = 19, H = 1

C4F10 + 10HF

In total - 4C 20F 10H

4 x 12 = 48
20 x 19 = 380
10 x 1 = 10

48 + 380 + 10 = 438

Ahhh -didn't read the question properly thank you!

Reply 94

Original post by _Caz_

Neon has a full outer shell of electrons so it really doesn't want to lose one as it is pretty stable as it is. Lithium however is trying to attain a full outer shell and currently has one electron in its outer shell, the easiest way for it to get a full outer shell is to lose that one electron so it really wants to lose it.

Also, neon has more protons than lithium but similar shielding (same period, same number of shells) so it has a smaller atomic radius and the electrons are closer to the positive nucleus, making them harder to remove.

Of course ! Ionisation energy increases across a period - I don't know what I was thinking

Thank you :smile:

Reply 95

Original post by Barney098

Of course ! Ionisation energy increases across a period - I don't know what I was thinking

Thank you :smile:

No problem, and don't worry about it - I have my moments sometimes and then I kind of just click and am like - oh that was obvious!

Reply 96

Original post by skizzle

Denominator should be everything on the left.

So

C4H10- ((12X4)+10) =58
10F2- ((19X2)x10))= 380

Add the two together gives 438

My advice in response to your post.. Just add up everything else on the product side.. This way, saves you having to all up all in atoms in the product again.. But whatever floats your boat.

Reply 97

nope..

1

Original post by _Caz_

I would use the HCl one, halve it and then you have 0.06, the moles of ZnCl2 (you can then work out the mass or what ever). I think the reason we use this one is because maybe not all the zinc reacted as this was the one they were adding. I have no idea if this is correct, I just know you use the HCl one. :smile:

Sorry if this wasn't much help. How are you feeling about tomorrow?

thank you! would you always use the reactant in excess then?
and i think i've put the work in so hopefully it goes well! how about you?

Reply 98