The Formation of Bromine in Manufacturing: How Does It Work?

[Kushal]

Homework Statement

Bromine is obtained from the sodium bromide dissolved in sea water by:

I passing chlorine into sea water at pH 3.5

II blowing out the bromine with air and absorbing it in aqueous sodium carbonate

III acidifying the solution and distilling out the bromine.

(i) Write an equation for step I.

(ii) Step II produces a solution of sodium bromate(V), NaBrO₃ in the molar ratio 1:5.

Construct an equation for the formation of the bromine in step III.

The Attempt at a Solution

(i) Cl₂ + NaBr ----> NaCl + Br₂

(ii) i have no idea how to interpret the information provided in this part. how can the mole ratio help me?

thnks

 

[Borek]

Google disproportionation.

 

[Kushal]

i didn't think of the disproportionation of bromine into bromide Br^- and bromate BrO₃^-.

thnks

but how does either of the products give bromine upon acidification?

is it a similar reaction as acid + carbonate?

 

[Borek]

I would call it "pH dependent equilbrium".

 

[Kushal]

i tried googling pH dependent equilibrium but i couldn't find something specific to the bromine extraction reaction.
sodium carbonate is alkaline. the pH would be around 9-10. acidifying the solution would decrease the pH...

i'm lost...

 

[Borek]

You are close. Just write balanced reaction equation Br2 + OH- and you will see that it is pH dependent. LeChetelier's priniciple is enough to explain what is going on.

 

[Kushal]

3Br₂ + 6OH^- ----> 5Br^- + BrO3^- + 3H₂O

ahhh... now i get why the ratio is 1:5...

is the reaction reversible?

if this is the case, as you add H⁺, the concentration of OH^- decrease. according to LCP the backward reaction is favoured, producing more Br₂