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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Dolphinsiu on January 20, 2007, 02:15:02 PM

Title: Simple distillation
Post by: Dolphinsiu on January 20, 2007, 02:15:02 PM

I am preparing an experiment about simple distillation of methanol/water mixture

Boiling point(1 atm)              pure methanol : 64.7 Degree Celsius
of                                      pure water: 100 Degree Celsius

1.Measure 40ml of the given methanol/water misxture into pear-shaped flask
2.Put in a few pieces of anti-bumping granules
3.Set up the apparatus for simple distillation (10 ml measuring cylinder as receiving vessel)
4.Place the cylinder in ice bath and plug it loosely with cotton
  (Why we need to do this step??)
5.Heat the flask gently
6.Record the temperature when distillate start dripping off into condenser
7.Replace vessel with clean dry test tube to collect the first few drops(about 5 drops)
  of distillate for refractive index measurement (RI measurement)
8.Reconnect the vessel again

9.After 5 ml of distillate is collected, repeat step7 - 8
10. Repeat this for every 5 ml of distillate collected and Record the temperature at every 5ml interval.

When I need to plot the boiling curve (temperature vs mole fraction),

Take an example,

Volume of Distillate(ml)             0           5         10          15         20          25     
Mole fraction of methanol         ?            ?          ?            ?           ?            ?
Mole fraction of water              ?            ?          ?            ?           ?            ?
Boiling point(Degree Celsius)   65.5       77.5      90.0     120.0     117.5     110.0

How to calculate the mole fraction of methanol and water respectively?
If we plot the boiling curve, we get only the vapour curve only!
Do we need to plot the liquid curve also?


Please help me to answer THREE bold questions! Thanks a lot!



     

Title: Re: Simple distillation
Post by: chiralic on January 20, 2007, 05:37:15 PM

Quote

Replace vessel with clean dry test tube to collect the first few drops(about 5 drops) of distillate for refractive index measurement (RI measurement)

Did you measurement refractive index of yours distillates? Could you post these data?

Title: Re: Simple distillation
Post by: Dolphinsiu on January 21, 2007, 02:31:37 PM

Is the measurement in refractive index really important for calculation in mole fraction of methanol and water?

I haven't done the experiment yet! (I am just preparing for!)

My lab manual just says

Refractive index of (20 degree Celsius): Pure methanol :1.329
                                                       Pure water: 1.333

Are they useful??