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Edexcel Chemistry Unit 1 (23/05/2013) Watch

1. has everyone finished there revision
3. (Original post by ayat94)
ppm is another way of measuring concentration

its the mass of something/ the volume its dissolved in x 1x10^6
4. Anyone has the Jan 2013 mark scheme for unit 1 please?? I can't find it anywhere
5. Can someone help me with http://www.edexcel.com/migrationdocu...e_20120307.pdf

(January 2012)Question 13 please a and b, I don't really understand. Thank you in advance!
6. why does atomic radius increase down the group
7. IN QUESTION 13A)
use this formula
charge of the positive(cation ) x charge of negative
example in LIF
charge of Li is +1 and F is -1
so you times +1 by -1 divide it by ionic radius if the anion +cation
the more negative the more exothermic

13b)just calculate difference of ionic radii
the greater the difference will give the answer

from my working out i have got the following answers
13a)c
13b)d
8. help on jan 13 tick box queations: Q3, 5,7, thanks
9. (Original post by ayat94)
why does atomic radius increase down the group
the addition of new shells mean that the outer electrons are further away from the nucleus, thus resulting in being less attracted. Therefore the protons are not pulling on the electrons as tightly.

The atomic radii decreases as you go along the period because the the number of protons in the nucleus of the atoms increase therefore this increase in positive charge means the outer electrons are being pulled in more tightly.

I hope that helps
10. Q3.
(Original post by SophieL1996)
help on jan 13 tick box queations: *Q3, 5,7, * thanks

Mass/Mr = 16g divided by 32 (which is the Mr of O2) as Oxygen is diatomic gives you 0.5
Do 0.5 x 6.02 x 1023 = 3.0 x 1023 which is D

Q5, Ionic equations are based on the ions involved in a reaction. So the charge particles in a reaction
This reaction is making a salt.
You know that Copper forms ions (most commonly of Cu2+) so it can't be B or C.
In all the reactions you form a silver precipitate. It's D because D is fully balanced and forms the right copper ion.
Ag just doesn't form 2[SUP]+[SUP] ions, it's just some charges that you have to learn.

Like, Carbonates are CO32-, Nitrates are NO3-, Aluminium ions are Al3+, Zinc are Zn2+ etc
It's just things that you just learn by rote I guess.

Q7 is C because the sign of all endothermic enthalpy changes is always going to be positive.
When a substance dissolves, you're making bonds between solvent and solute.
If the energy change is greater for breaking bonds than making them, temperature will increase,
vice versa for energy change for making bonds being greater than energy change for breaking them, temp decreases in solution.
11. (Original post by Mollymod)
I'm a resitter, simply to boost up my grade for A2.
I'm doing Unit 5 in a month too, so Unit 1 is a good like memory jogger.
I really need full UMS in this if I want an A, so it's a tight margin.
Any questions, you can ask me and I'll do my best to try and answer them
Can you please help me, i don't understand question17)b)vi) from the 2013 Jan pastpaper, Suggest the formula of another metal ion which could form an alum, in combination with potassium and sulfate ions. ( The answer in the markscheme is Cr3+/ Fe3+/ Sc3+ / Ga3+Accept any feasible triply positive metal ion) but i don't really understand why we have to choose a metal with a +3 charge.). Thank you
12. (Original post by ayat94)
IN QUESTION 13A)
use this formula
charge of the positive(cation ) x charge of negative
example in LIF
charge of Li is +1 and F is -1
so you times +1 by -1 divide it by ionic radius if the anion +cation
the more negative the more exothermic

13b)just calculate difference of ionic radii
the greater the difference will give the answer

from my working out i have got the following answers
13a)c
13b)d
could you please explain question 13b further?
13. how do you do q6 on jan 10?, the first ionisation energies of 4 elements with consecutive atomic numbers are shown: A 1680, B 2080, C 496 D 738, which element could be an inert gas, which element could be x in a covalent compound with formula HX and which element could be y in an ionic compound with formula YH2?
14. (Original post by maryam1996)
Can you please help me, i don't understand question17)b)vi) from the 2013 Jan pastpaper, Suggest the formula of another metal ion which could form an alum, in combination with potassium and sulfate ions. ( The answer in the markscheme is Cr3+/ Fe3+/ Sc3+ / Ga3+Accept any feasible triply positive metal ion) but i don't really understand why we have to choose a metal with a +3 charge.). Thank you
Read the information back at the top of Question 17.
It gives you a hint. An alum is Potassium Aluminium Sulphate.
So you've got the Sulphate, and you've got the Potassium. Obviously you can't pick Aluminium again.
What do all elements in Group 3 have in common? Three outer shell electrons on their structure. Therefore they'll react similar chemically, so you need something similar to Aluminium, and the only way you'll find that, is if you pick something in the same group or with the same charge. So if you know metal ions, such as chromium ions or iron ions, Gallium works here too, we're talking about something that will react the same as Aluminium chemically and ionically. So it's the 3+ charge that they want.
15. (Original post by rainerised)
how do you do q6 on jan 10?, the first ionisation energies of 4 elements with consecutive atomic numbers are shown: A 1680, B 2080, C 496 D 738, which element could be an inert gas, which element could be x in a covalent compound with formula HX and which element could be y in an ionic compound with formula YH2?

Inert gas will have highest Ionisation energy of the bunch, as it's stable and doesn't react, so it'll take loads of energy to remove its outer electron and get it to 'lose' its' 'happy/stable' state.

A is the answer to the second part because it's a covalent compound with 7 electrons in its outer shell, so the ionisation energy will be high (as it's nearly a full outer shell and would rather gain an electron than lose one as it's closer to being more stable that way) but it won't be as high as the inert gas one, so I chose the next-highest ionisation energy from the list.

6 electrons in its outer shell, so I'd say D because it's the third-highest ionisation energy for the same reason I gave above, but by process of elimination it's between C and D, and C is too low an ionisation energy for something that nearly has a full outer shell.
16. I'm still getting confused during calculations involving diatomic molecules...when am I supposed to double the molecular mass and when am I not supposed to?
17. I have another question, can someone please help me. Why does the electron affinity become less exothermic as you go down group 7?
Thank you
18. (Original post by Mollymod)
Inert gas will have highest Ionisation energy of the bunch, as it's stable and doesn't react, so it'll take loads of energy to remove its outer electron and get it to 'lose' its' 'happy/stable' state.

A is the answer to the second part because it's a covalent compound with 7 electrons in its outer shell, so the ionisation energy will be high (as it's nearly a full outer shell and would rather gain an electron than lose one as it's closer to being more stable that way) but it won't be as high as the inert gas one, so I chose the next-highest ionisation energy from the list.

6 electrons in its outer shell, so I'd say D because it's the third-highest ionisation energy for the same reason I gave above, but by process of elimination it's between C and D, and C is too low an ionisation energy for something that nearly has a full outer shell.
thanks
19. (Original post by maryam1996)
I have another question, can someone please help me. Why does the electron affinity become less exothermic as you go down group 7?
Thank you
The first time you add an electron to a halogen, you're forming a more stable ion so the reaction is exothermic. After that, you're just trying to add electrons to a stable ion, and that requires energy, so subsequent electron affinities are endothermic. These then become more endothermic, because you keep trying to add negative electrons to a negative ion, which is increasingly difficult
20. also how do you do q7 jan 10, it shows you a graph of second ionisation energies of a series of elements with consecutive atomic numbers and asks which could be lithium, the graph goes up from a-b then down from b-c then up from c-d?
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