Acetic acid dissolved in benzene shows a molecular mass of:

Options

A. 1.62 and 98.3
B. 0.81 and 98.3
C. 0.5 and 86
D. 1 and 98.3

Answer

A

Explanation

`Delta T_(b) = 0.36`
Experimental molar mass ` = 117.8 g mol^(-1)`
`i= ("Normal molar mass")/("Experimental molar mass")`
` = (60)/(117.8) = 0.509`
`Delta T_(b) = ixx k_(b) xx m`
` m = (x xx 1000)/(60 xx 100) = (x)/(6)`
`therefore " " 0.3 = 0.509 xx 2.57 xx (x)/(6)`
or `" " x = (0.36 xx6)/(0.509 xx 2.57) = 1.65 g`
Acetic acid dimerizes as
` 2CH_(3) COOH hArr (CH_(3) COOH)_(2)`
If `alpha` is the degree of association.
`{:(,"Initial",1,0),(,"After association", 1-alpha,alpha//2):}`
Total moles of after association ` = 1 - alpha + (alpha)/(2) = 1 - alpha //2`
` i= (1-alpha//2)/(1) = 0.509`
` - alpha//2 = 0.509 -1 = - 0.491`
`alpha = 0.491 xx 2 = 0.982 or 98.2%`