For a homologous series of compounds (that is, compounds of similar structure th

Question

For a homologous series of compounds (that is, compounds of similar structure that differ in the number of CH_2 groups in a chain) the log of the adjusted retention time usually a linear function of the number of carbon atoms. A compound was known to be a member of the family (CH_3)_2CH(CH_2)_nCH_2OSi(CH_3)_3. For the following gas chromatographic adjusted retention times, prepare a graph of log t_r' versus n and perform a least squares analysis using Excel to find the equation of the best-fit line. What are the values of the slope and intercept of this line? (Round your answer to 3 significant figures. The values do not have units.) What is the value for n in the chemical formula of an unknown compound whose retention time is 56.10 minutes? What would the retention time in minutes be for a compound in the same homologous series where n = (Round your answer to the nearest 0.1 minute).

Explanation / Answer

The data will be

1.940018

The graph will be

1) the equation comes out is

y = 0.19 x -0.9105

Which is linear equation like

y = mx + c

So m = slope = 0.19

Intercept = c = -0.9105 = -0.911

2) given retention time = 56.10

So we will put the value in the obtained equation as

log 56.10 = y = 1.749

so y = 0.19 x -0.9105 = 1.749

0.19 x = 1.749 + 0.9105 = 2.6595

x = 13.99 = 14 (so n = 14)

3) now we will put n= x = 4

y = log tr = 0.19 x -0.9105 = 0.19 X 4 - 0.9105 = -0.1505

taking antilog

tr = 0.707 min = 0.7 min

n tr log tr 8 4.07 0.609594 9 6.31 0.800029 15 87.1

1.940018

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