Science Buddies: "Ask an Expert"

Hi there,

I'm stumped on how to fill in this part of the report:

4.2 Balanced equations for reactions of
4.2.1 potassium bromide with sulphuric acid
KBr + H2SO4 → HBr + KHSO4
4.2.2 hydrogen bromide with sulphuric acid
HBr + H2SO4 → H3SO4+ + Br –

the answers in italics are what i guessed, but i couldnt find anything in self-help books or the internet.

Pls help, thanks!!

This is the main equation for the reaction:

CH3CH2CH2CH2OH + KBr + H2SO4 → CH3CH2CH2CH2Br + KHSO4 + H2O

butanol + potassium bromide + sulphuric acid → 1-bromobutane + water + KHSO4.

Now, I haven't taken chemistry in a year, so you might want to double-check this with another Expert, but here is what I recall:

4.2.1. You almost have this one. The reaction will be a double-replacement, in which you are replacing K+ with H2 (or Br- with SO4(-2), whichever is easiest for you to think about). Make sure both sides of the equation are balanced when you are finished.

4.2.2. This would be a reaction I would take to a teacher. It might be an oxidation-reduction reaction. You can also try it writing H2SO4 as H2O + SO2. I think you are probably right that you will get Br- as a product.

Hope this helps!
Sonia

hi!

you practically have the answer, but I agree with Lise that you have to make sure your equations are balanced. The first is a double replacement so that equation will be:

2KBr + H2SO4 --> 2HBr + K2SO4

hope this helps!

Hi there

would liek to ask, i thot my eqn was balanced?? the first one?

4.2.1 potassium bromide with sulphuric acid
KBr + H2SO4 → HBr + KHSO4

but i'm so confused, i thot for eqn there shld only be one answer, but how come i got this, then jessica got 2HBr + K2SO4 but my fwen got another answer too??

Hi!

I believe in a double replacement you do not split up the hydrogens like that. The K bonds with the SO4, and the H2 bonds with the Br. You cannot split the H2 to make it bond with both the SO4 and the Br. That would not be how you do a double replacement.

I hope that makes sense to you!

Jessica is right. The reason is because of the charges of the ions. SO4 has a charge of (-2), so you need two H+ to balance this charge. When H2SO4 reacts with another substance, both H+ are stripped away and replaced with something different, in this case two K+ ions. The H+ ions then distribute themselves among the Br(-1) ions.

Post if you have more questions,
Sonia