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Chemistry Unit 2 Edexcel, Exam- 23rd May 2012

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Original post by Arusa01
HAA! Princess?


Princess jajajajaja
Yolo
LOL Scrib
Reply 1001
Original post by Future Medics
Princess jajajajaja
Yolo
LOL Scrib


PM :smile:
Hey, how would u know if you need to use silver nitrate or hexane if u want to test halogen/halide?
why does NH3 have a lower boiling point than HF and H2O have a higher boiling point than HF? Help, someone!!
Reply 1004
Original post by VRS
Explain why the thermal stability increases with nitrates and carbonated down group 1 and 2

Also what are the trends we have to know for group 1,2,7 and across the period? Just trends


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from group 1 NaC03 downwards ,the carbonates don't decompose when heated
only the nitrates of group 1 from Na downwards decompose
so the thermal stability increases down group 2 meaning the carbonates and nitrates become more stable to heat as the ionic radius of the positive ion increases down the group ie the positive ion becomes larger so polarisation of the carbonated electron cloud

i think the only trends you need to know are :
solubility of group 2 hydroxides and sulfates
thermal stabilities of group 1 and 2
and with group 7 there isnt a trend you need to learn except that the ionization energy decrease and the electro negativity also decreases down the group
the main things you need to know about group 7 are its reactions
and the test for halides
also someone explain steric inheritance!!
Original post by Pandamojia
Hey, how would u know if you need to use silver nitrate or hexane if u want to test halogen/halide?


Silver Nitrate for Chloride, Bromide, Iodide ions
Hexane for Chlorine, Bromine, Iodine
Original post by Arusa01
HAA! Princess?


lol.
meant bride. what your name means in arabic.
Reply 1008
Original post by Exams v__v
why does NH3 have a lower boiling point than HF and H2O have a higher boiling point than HF? Help, someone!!


as HF can form hydrogen bonding so more energy needed and H2O has greater b.p then HF as it can from up to 2 hydrogen bonds with one molecule so much stronger
Original post by fiza_1
as HF can form hydrogen bonding so more energy needed and H2O has greater b.p then HF as it can from up to 2 hydrogen bonds with one molecule so much stronger


Even NH3 can form H.B, but still why is it's boiling point lower than that of HF?
Original post by Exams v__v
why does NH3 have a lower boiling point than HF and H2O have a higher boiling point than HF? Help, someone!!


H2O has a higher boiling point than HF because it can form 2 hydrogen bonds as there are 2 electron lone pairs on the oxygen while HF forms 1 hydrogen bond. So more energy required to break the intermolecular forces in H2O than in HF.

Not sure about why NH3 has a lower boiling point than HF
Original post by The Doggfather
Silver Nitrate for Chloride, Bromide, Iodide ions
Hexane for Chlorine, Bromine, Iodine


Yh but isn't it Chlorine from CH3CH2CH2Cl an atom? Yet...we used silver nitrate?
Reply 1012
Original post by fiza_1
from group 1 NaC03 downwards ,the carbonates don't decompose when heated
only the nitrates of group 1 from Na downwards decompose
so the thermal stability increases down group 2 meaning the carbonates and nitrates become more stable to heat as the ionic radius of the positive ion increases down the group ie the positive ion becomes larger so polarisation of the carbonated electron cloud

i think the only trends you need to know are :
solubility of group 2 hydroxides and sulfates
thermal stabilities of group 1 and 2
and with group 7 there isnt a trend you need to learn except that the ionization energy decrease and the electro negativity also decreases down the group
the main things you need to know about group 7 are its reactions
and the test for halides


Thank you so much - appreciate it!


This was posted from The Student Room's iPhone/iPad App
Original post by The Doggfather
H2O has a higher boiling point than HF because it can form 2 hydrogen bonds as there are 2 electron lone pairs on the oxygen while HF forms 1 hydrogen bond. So more energy required to break the intermolecular forces in H2O than in HF.

Not sure about why NH3 has a lower boiling point than HF


Cant the delta positive 2 hydrogens also form hydrogen bonds? So in all, 4 hydrogen bonds in water molecules?
Reply 1014
Original post by Exams v__v
Even NH3 can form H.B, but still why is it's boiling point lower than that of HF?


as HF has higher electro negativity
Cant the delta positive 2 hydrogens in water molecule also form hydrogen bonds? So in all, 4 hydrogen bonds in water molecules?
Original post by Pandamojia
And how would u know to use hexane or silver nitrate to test halide?


Add Silver Nitrate and Dilute Nitric Acid
Chloride - White ppt
Bromide - Cream ppt
Iodide - Yellow ppt

In Hexane
Chlorine - Colourless
Bromine - Orange-Red
Iodine - Pink-Violet

In Water
Chlorine - Colourless
Bromine - Yellow-Orange
Iodine - Brown

If the Halogen is not bonded to another atom, then add to Hexane or Water. Otherwise add Silver Nitrate and Dilute Nitric acid e.g. KCl, KBr
(edited 11 years ago)
Original post by Exams v__v
Cant the delta positive 2 hydrogens in water molecule also form hydrogen bonds? So in all, 4 hydrogen bonds in water molecules?


They can form hydrogen bonds with the oxygen on another water molecule but that's the same as when the oxygen forms hydrogen bonds with hydrogen's if you know what I mean. So don't include them, it's 2 hydrogen bonds per water molecule because of 2 electron lone pairs.
Reply 1018
Original post by Exams v__v
Cant the delta positive 2 hydrogens in water molecule also form hydrogen bonds? So in all, 4 hydrogen bonds in water molecules?

In H2O the O only has 2 pair of lone electrons so only 2 hydrogen bonds can occur.
Original post by The Doggfather
They can form hydrogen bonds with the oxygen on another water molecule but that's the same as when the oxygen forms hydrogen bonds with hydrogen's if you know what I mean. So don't include them, it's 2 hydrogen bonds per water molecule because of 2 electron lone pairs.


Thank you so much.

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