1.a) Boiling Point ranges Fraction1 Fraction 2 Fraction 3 42-45 40-43 43-50 39-4
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Question
1.a) Boiling Point ranges Fraction1 Fraction 2 Fraction 3 42-45 40-43 43-50 39-40 Observed 41-48 38-39 Calibrated b) Boiling point of pure ethyl acetate Boiling point of pure butyl acetate c) What do the boiling point data indicate about the quality of your separation? 2. a) Refractive Indices and the temperature at the time they were taken: Pure ethyl acetate Pure butyl acetate Fraction 1 Fraction 2 Fraction 3 RI 1.3700 1.3920 1.3710 1.3750 1.3750 Temp 70.4 70.4 41-48 40-43 38-39 b) Show your calculations the mole fraction of ethyl acetate and butyl acetate in: Fraction 1 Fraction 2 Fraction 3Explanation / Answer
1) b. Boiling point of pure ethyl acetate is 77.1oC. Boiling point of pure butyl acetate is 126oC.
c. The boiling point data clearly indicates that the quality of separation is very poor. The data given in the table is not even near to the boiling point of pure compounds. This mean that your separation is very poor and whatever fractions you got are mixtures only. You need do the separation again. The boiling point of ethyl acetate should be in the range of 74.5oC-79.5cC and that of butyl acetate should be in the range of 123.5oC-128.5oC.
2) b
The relation between the mole fraction and refractive indices of components in a mixture is given below. The mixture contains two components ethyl acetate (EA) and butyl acetate (BA),
Refractive index of the mixture, nmixture = (xEA X nEA) + (xBA X nBA) -----------equation 1
Where xEA - mole fraction of ethyl acetate
XBA – mole fraction of butyl acetate
nEA– refractive index of pure ethyl acetate
nBA– refractive index of pure butyl acetate
Sum of mole fractions of all components in a mixture is equal to 1.
Thus,
mole fraction of ethyl acetate (xEA) + mole fraction of butyl acetate (xBA) = 1
xBA = 1- xEA substitute this in equation 1.
nmixture = (xEA X nEA) + ((1- xEA) X nBA)
nmixture = (xEA X nEA) + nBA – xEA X nBA
nmixture - nBA = xEA (nEA - nBA )
xEA = (nmixture - nBA )/ (nEA - nBA )--------------equation 2
You can use this equation to find out mole fractions of each component by using the given data.
Fraction 1
xEA = (nmixture - nBA )/ (nEA - nBA )
= (1.3710 – 1.3920)/(1.3700-1.3920)
= 0.9545
xBA = 1- xEA
= 1- 0.9545
= 0.0454
Fraction 2
xEA = (nmixture - nBA )/ (nEA - nBA )
= (1.3750 – 1.3920)/(1.3700-1.3920)
= 0.7727
xBA = 1- xEA
= 1- 0.7727
= 0.2272
Fraction 3
xEA = (nmixture - nBA )/ (nEA - nBA )
= (1.3750 – 1.3920)/(1.3700-1.3920)
= 0.7727
xBA = 1- xEA
= 1- 0.7727
= 0.2272
c. The refractive index data indicates that your separation is not good. You got only mixture of butyl acetate and ethyl acetate. This you can directly understand from mole fractions as well.
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