When water-cooled condensers are used for distillation or for refluxing a liquid
ID: 1003721 • Letter: W
Question
When water-cooled condensers are used for distillation or for refluxing a liquid, the water enters the condenser at the lowest point (i.e., water in) and leaves al the highest (i.e., water out) Briefly explain How many milliliters of boiling water are required to dissolve 36 gm of phthalic acid if the solution was cooled to 14 degree C? How many grams of phthalic acid would recrystallize out? Note, the solubility of phthalic acid at 14 degree C is 0.54g/100mL in water and at the boiling point (99 degree C) of water, the volubility of phthalic acid is 18.0g/100mL? "(Show all Calculations for Full Credit)".Explanation / Answer
1)
Water condenser is used if bp of the liquid is 130 C or below 130 C. If bp is above 130 then cooling by air is adequate. So an air condenser is used.
If a water condenser is used for a very high boiling liquid then there is a danger of cracking / breaking of condenser. For example, if bp of a liquid is 180 C than the temperature of the vapours will be obviously around 180. Then some portion of glass will be at 180 C temperature and water will be around 20 /25 C. There will be uneven temperature in the glassware and will break / crack. Air around air condenser will be at a higher temperature than water so difference of temperature will be less. Thus the arrangement will be safer.
Water is allowed to get in from the lower inlet and is made to come out from the upper outlet. So that all the time inner pipe of the condenser remain surrounded by water. If it is other way round then water will be at the lower end and may not surround all the length of inner pipe. Water will quickly leave the condenser without adequate cooling. In distillation the vapours which might escape from the lower end get the water at the lowest possible temperature. The upper part of the condenser gets comparitively hotter water (it is just about to leave the conderser after cooling vapours ( it is exhausted).. It is much like water moving in counter current direction. This makes effective use of water economically. Vapours of higher temperature get relatively hot water for cooling and colder vapours get colder water for cooling.
I hope this explanation will serve your pourpose. Even small things which we take it for granted are quite complicated and so many process are going on at the same time.
2)18 g phallic acid dissolves in 100 ml of water at 100 C. So 36 g would need 200 ml H20 at 100C.
.54g phallic acid dissolves at 14C so ppt = 36-0.54 = 35.46g
one mL of boiling water is needed to dissolve 25 g.
After cooling to 14 C, only 2.5 will still be in solution, thus the amount crystallizing out will be 36 - 2.5 or 34.5 g.
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