Chem

What is the effect of a non-volatile impurity on the boiling point of a substance? of a volatile impurity?
A non volatile impurity which is added to the volatile liquid, it's boiling point will increase. It is due to some of effective surface area which is available for evoperation is occupied by non volatile substance. If another volatile impurity is added then
1) if it does not chemically react with given liquid then boiling point will decreade due to increase in vapour pressure.
2) if it chemically react or combine then it will deviate from ideal behaviour and it may increase or may decrease the boiling point of solution in coparision with boiling point of pure solvent.
The presence of a non-volatile solute in a solution increases its boiling point. The amount of the elevation of the boiling point depends only on the number of molecules of solute present, and not on their identity.
Why is the thermometer bulb positioned near the sidearm of the distillation flask instead of being dipped in the solution?
Had you did it in the solution, the thermometer would have measured the temperature of the direct heat from the flame. However, what we want is the temperature at which a substance boils. Hence, by positioning the thermometer near the sidearm of the distillation flask measures the temperature of the vapour which is also the boiling point of that substance. what are the limitations of simple distillation?how to overcome these difficulties you can't purify completely a component only using distillation.
If you try to seperate 2 components who have very close temperatures of ebulition, then you won't be able to get a lot more than a 50%-55% concentration with a simple distillation.
To get better concentrations, use fractional distillation.
If this still isn't enough, then you'll have to use other methods (chemical reaction to change the properties of your component, then distillation, then another chemical reaction to get your original component back. - or separation using other physical properties such as density, or solubility... anything you like.) a problem with distilling may arise if the liquid has a somewhat high boiling point. decomposition may occur before distillation. Distillation under reduced pressure can overcome this problem, but that requires special glassware and equipment.
Why should the water inlet be at the lower end of the condenser?
The cooling water should enter the outflow end of the condenser because the apparatus is more efficient when it is operated that way. The difference in temperature between the cooling water and the substance to be distilled is what drives the heat exchange. But we need a good difference of temperature (temperature gradient) between the cooling water and the distillate all the way along the condenser, and not just a big one at the start and a wimpy one at the outflow end (which is what will happen if cooling water is routed in at the inflow end of the condenser).
Certainly by routing the cooling water into the inflow end of the condenser, the distillate will be cooled more quickly - at least in the first part of the condenser. But the distillate is moving, and heat transfer takes a finite amount of time. But routing the cooling fluid (the water) into the outflow of the condenser, there will be more dramatic cooling throughout the length of the condenser. Remember that the distillate is cooler toward the outflow end of the condenser, and it takes cooler water at this end to drive the heat exchange process.