chemistry help Watch

jamesgillian123
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"Josie investigated the reactions that occur when chlorine,bromine or iodinme are added to different sodium halide solutions."
we are given a table
sodium chloride sodium bromide sodium iodide
cl water
bromine water
iodine water
they are all filled in with the colour or no reaction apart from bromine to sodium bromide. the answer is no reaction but im confused as to why there is no reaction? this is gcse level
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CasMom
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Because sodium bromide = NaBr (Sodium + Bromine), so if you add more bromine you'd still get NaBr (sodium bromide), so it looks like no reaction takes place. It's the same with if you add iodine to sodium iodide, or chlorine to sodium chloride
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jamesgillian123
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(Original post by CasMom)
Because sodium bromide = NaBr (Sodium + Bromine), so if you add more bromine you'd still get NaBr (sodium bromide), so it looks like no reaction takes place. It's the same with if you add iodine to sodium iodide, or chlorine to sodium chloride
ah ok, why is there no reaction with iodine + sodium bromide?
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Federerr
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When Halogens react, they gain an electron. Therefore they are oxidising agents. As you go down Group 7 the oxidising ability of the halogens decreases due to them becoming bigger atoms and there having their outer electrons further from the nucleus (Therefore ability of attract and gain an electron decreases)

Oxidising strengths of the halogens can be seen in the displacement reactions with the halide ions.

The Rule - A halogen will displace a halide from solution if the halide is below it in the periodic table (So chlorine can displace bromide ions but bromine cannot displace chloride ions)

Therefore bromine will not displace the bromide ions as if bromine was to gain an electron. It'd just produce bromide ions again and you already have this in solution. Therefore there is no reaction taking place.

However if you had Chlorine water and NaBr in solution. The chlorine atoms will become reduced by the bromide ions which will be oxidised and you'd form Br2 which is an orange solution (this colour change shows that a reaction has taken place)
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Federerr
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(Original post by jamesgillian123)
ah ok, why is there no reaction with iodine + sodium bromide?
Iodine isn't strong enough of an oxidising agent to take electrons from the bromide ions and oxidise them.

It's just a trend, all you have to do is memorise it.

Why are they weaker oxidising agent? What is oxidising agent - Power to gain an electron

So if you go down the halogen group, the atoms become larger with a bigger atomic radius. So the outer shell is further from the positive nucleus. Therefore power of the nucleus to attract electrons decreases.
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CasMom
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(Original post by jamesgillian123)
ah ok, why is there no reaction with iodine + sodium bromide?
Because bromine is more reactive than iodine. the halogen bound to sodium can only be displaced by a different halogen that is more reactive. Where iodine is the LEAST reactive (will get displaced by Chlorine AND Bromine), Chlorine can displace Iodine but is displaced by Bromine. And bromine can displace both iodine and chlorine
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jamesgillian123
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(Original post by CasMom)
Because bromine is more reactive than iodine. the halogen bound to sodium can only be displaced by a different halogen that is more reactive. Where iodine is the LEAST reactive (will get displaced by Chlorine AND Bromine), Chlorine can displace Iodine but is displaced by Bromine. And bromine can displace both iodine and chlorine
(Original post by Federerr)
Iodine isn't strong enough of an oxidising agent to take electrons from the bromide ions and oxidise them.

It's just a trend, all you have to do is memorise it.

Why are they weaker oxidising agent? What is oxidising agent - Power to gain an electron

So if you go down the halogen group, the atoms become larger with a bigger atomic radius. So the outer shell is further from the positive nucleus. Therefore power of the nucleus to attract electrons decreases.
so iodine bromide+ sodium = sodium bromide + iodine and its a displacement reaction because sodium is above iodine in the periodic table and is more reactive?
also how will i know that its sodium bromide + iodine and not sodium iodide + bromine ?
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Federerr
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(Original post by jamesgillian123)
so iodine bromide+ sodium = sodium bromide + iodine and its a displacement reaction because sodium is above iodine in the periodic table and is more reactive?
also how will i know that its sodium bromide + iodine and not sodium iodide + bromine ?
You're confusing yourself. Sodium is irrelevant in the situation. It's to do with the halogen and the halide ions.

Just learn this table:

Cl2 + NaCl = No Reaction
Cl2 + 2NaBr = 2NaCl + Br2 (Colourless Solution to Orange Solution)
Cl2 + 2NaI = 2NaCl + I2 (Colourless Solution to Brown Solution)

Br2 + NaCl = No Reaction
Br2 + NaBr = No Reaction
Br2 + 2NaI = 2NaBr + I2 (Colourless Solution to Brown Solution)

I2 + NaCl = No Reaction
I2 + NaBr = No Reaction
I2 + NaI = No Reaction
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