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chem doubt....

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cashem'up:
hey guys this is very interesting question
In a past paper they said that when a halogen reacts with water an oxidising agent is formed BUT
1) when chlorine dissolves it forms HCL and HOCl......so how does this act as an oxidising agent bcos arent these ions......and halides are reducing agents whereas halogens are oxidising agents
2) or is it that when halogen reacts with water it remains as halogen and not turn into halide???

please help Thanks
 :)

girl_92:
im not sure but i guess they are talking abt hypochlorate HOCL oxidation state of chlorine is +1 in it so i guess it will gain an electron adn reduce itslef to chlorine
By the way which year paper it is scan it nd post it here if its a old paper

cashem'up:

--- Quote from: libra_92 on May 29, 2010, 08:51:36 am ---im not sure but i guess they are talking abt hypochlorate HOCL oxidation state of chlorine is +1 in it so i guess it will gain an electron adn reduce itslef to chlorine
By the way which year paper it is scan it nd post it here if its a old paper

--- End quote ---
it was a w06 ppr i think 3rd question last part where they give periodic table..........

Chingoo:
Since we do not consider Fluorine and Astatine in our reactions, we'll exclude them from this explanation. Hence, the remainder is chlorine, bromine and iodine. Down the group, the bond energy between the halogen atoms increases.
Cl2<Br2<I2
Also, the electron affinity decreases down the group:
Cl2>Br2>I2Hence, Chlorine is the most electronegative whilst Iodine is the least. As a rule, the most electronegative element has the most oxidising power as it will readily accept an electron from a reductant.

When Chlorine dissolves in water, a disproportionation reaction occurs to form HCl and HOCl. HOCl is an unstable species and it decomposes to form HCl and O (reactive oxygen atoms), which is why it is important as bleach and in germicides in swimming pools. Hence, the actual halide in this reaction is only HCl.

However, in hydrogen halides there is a similar problem of oxidising ability reducing down the group. Hence, HCl is a weak reducing agent and strong oxidising agent. When it reacts as a metal halide with H2SO4, only HCl is formed (as an acid breaks up the salt) but it will not be oxidised by H2SO4, whilst that is not true for Br2 and I2.

When a metal bromide reacts with H2SO4, it also forms HBr initially. However, as it is not as strong as HCl when it comes to oxidising ability, it is oxidised by H2SO4 to Br2 and hence the following reactions take place:
NaBr + H2SO4 ----> HBr + NaHSO4
HBr + H2SO4 ----> Br2 + H2O + SO2 (not balanced)In case of metal iodide, the same mechanism occurs but instead of just stopping at SO2, it is able to reduce H2SO4 to H2S, with the lowest oxidation state of Sulphur:
NaI + H2SO4 ----> HI + NaHSO4
HI + H2SO4 ----> I2 + H2S + H2O (not balanced)
This trend in the halides is due to the decreasing bond enthalpies of the H-X bond, which means each progressive halide is more unstable and hence is a better reducing agent, more willing to 'get rid' of the hydrogen.

IGCSE nightmare:
When KMnO4 being acidified oxidises an alkene, what are the conditions?
And how do we know if it's going to oxidise an alcohol or an alkene?

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