Show work for all problems. Give corr significant figures for numerical answer b

Question

Show work for all problems. Give corr significant figures for numerical answer beta -carotene is a yellow hydrocarbon composed carbon and 10.5% hydrogen. It is found in plant chlorop as of the light collecting molecules for photosynthesis. A solution ma dissolving 0.805 g of beta-carotene in 12.1 g of carbon tetrachlori e reez -26.60 degree C. The freezing point of pure carbon tetrachloride is -22.90 degree C and i s freezing point constant is Kf = 29.9 degree C/m. What is the molecular formula of carotene?

Explanation / Answer

From the elemental analysis:

89.5/12 = 7.46

10.5/1 = 10.5

10.5/7.458= 1.41 = 7:5 (proportion H:C)

The proposed formula is (C5H7)x and the proposed molar mass M = 5x12 + 1x7= 67x

From the freezing point depression:

Depression dt = -22.90

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