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Topic: electrochemistry question i need help with  (Read 2385 times)

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Offline portugal

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electrochemistry question i need help with
« on: August 23, 2007, 06:06:43 AM »
1. When KBr reacts with conc. H2SO4 some bromine and SO2 are evident as well as the main product (HBr). The number of moles of KBr which reacts with one mole of conc. H2SO4 in this side reaction is:

 a. 1.33 mol

 b. 0.75 mol

 c. 1.00 mol

 d. 2.00 mol

 e. 0.50 mol




Offline Borek

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Re: electrochemistry question i need help with
« Reply #1 on: August 23, 2007, 06:08:52 AM »
Please read forum rules. Start with reaction equation.
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Offline portugal

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Re: electrochemistry question i need help with
« Reply #2 on: August 23, 2007, 07:00:54 AM »
thats exactly what i am having problems with establishing the equation and once someone can help me out with that i can do the rest

Offline Borek

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Re: electrochemistry question i need help with
« Reply #3 on: August 23, 2007, 07:09:01 AM »
You know reactants, you know products. Write skeletal reaction, then it is just a matter of balancing.
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Offline portugal

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Re: electrochemistry question i need help with
« Reply #4 on: August 25, 2007, 08:51:59 PM »
so would you say this is the correct answer then:

2 KBr + 2 H2SO4 = 4 HBr + -0 SO2 + -1 Br2 + 2 KSO4

Therefore the answer would be 1????

Offline Borek

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Re: electrochemistry question i need help with
« Reply #5 on: August 26, 2007, 03:45:04 AM »
1. No such thing as KSO4

2. You are looking for side reaction - so your skeletal should not contain main product (HBr)

3. You have two weird coefficients - one is negative (all should be positive) one is zero (which means there is no SO2 in products, yet you were specifically told it IS present, so your equation doesn't describe the reaction in question).

What you were told is that side reaction is between KBr + H2SO4 and it yields Br2 + SO2:

KBr + H2SO4 -> Br2 + SO2

However, this can't be right for an obvious reason - no K and H on the right side. The most logical guess is that K becomes K2SO4. What about hydrogen? Hmm, that's more complicated, however, you have hydrogen and at the same time SO42- gets converted to SO2 - so it looses oxygen. Hydrogen and oxygen means water, so your skeletal reaction should look like:

KBr + H2SO4 -> Br2 + SO2 + K2SO4 + H2O

And you should balance it now.
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