[Rutherford]

Which of the apparatuses shown in the figures is the best one for the synthesis of bromethane from potassium bromide, concentrated sulphuric acid and ethanol?


The product is separated by distillation, so B and D are incorrect (unknown processes). In A, the thermometer is too high positioned. Why is E correct and C isn't?

[billnotgatez]

coolant direction?

[Rutherford]

How so?

[UG]

In C your cooling water won't be filling up the condenser coils unless the flow rate is really high. There will be lots of air in there

[Rutherford]

Okay. Thanks for the explanation.

[DrCMS]

I think A is a better set up than E for a distillation.  In A the thermometer bulb is about inline with the vapour entering the condensor while in E it is too low.

[Rutherford]

Why can't it be so low?

[curiouscat]

How so?

Countercurrent cooling is more efficient than co-current cooling. Larger ΔT across tube walls.

[curiouscat]

Why can't it be so low?

I think too low a thermometer may give a bad reading because of entrainment / splashing / foaming etc.

[Rutherford]

Thanks for the reply. This would be solved now.

[billnotgatez]

@Raderford

Why is E correct and C isn't?

Why did you state this if A is correct?

@DrCMS
I do not doubt you
but in A the bulb seems above condenser inlet
  advocate

[curiouscat]

@DrCMS
I do not doubt you
but in A the bulb seems above condenser inlet

Very slightly. Between having it too low and too high I'd rather it be too high.

[Rutherford]

@Raderford

Why is E correct and C isn't?

Why did you state this if A is correct?

@DrCMS
I do not doubt you
but in A the bulb seems above condenser inlet
  advocate

Sorry, I thought it was E  .

[Arkcon]

I really thought it was A too, at the start, but everyone else was so sure it wasn't I just second guessed myself.  Actually, I thought, since this was a reaction, and not a simple distillation, that the water bath was necessary.  But DrCMS: is straight on -- the bulb of the thermometer must be in the vapor at the point it escapes the flask, in order to measure the real temperature.

[Big-Daddy]

Since the main question has been answered I thought I'd ask one of my own: why do we need the thermometer to measure temperature here? Aren't we just performing a synthesis?