Question

Calculate the %T of a solution that is measured in a 4.00cm cell and has a molar absorptivity of 431 M-1cm-1 , given that the solution is 0.02%w/v. The compound has a formula weight of 650.86 g/mol.

Answer #1

**consider 100 ml of soution**

**then**

**% w/v = mass of compound x 100 / volume of
solution**

**so**

**0.02 = mass of compound x 100 / 100**

**mass of compound = 0.02 g**

**now**

**moles = mass / formula mass**

**so**

**moles of compound = 0.02 / 650.86**

**moles of compound = 3.073 x 10-5**

**now**

**concentration = moles x 1000 / volume (ml)**

**so**

**concentration (C) = 3.073 x 10-5 x 1000 /
100**

**conc (C) = 3.073 x 10-4**

**now**

**according to Beers law**

**A = e x l x c**

**so**

**A = 431 x 4 x 3.073 x 10-4**

**A = 0.53**

**now**

**we know that**

**A = 2 - log %T**

**so**

**0.53 = 2 - log %T**

**%T = 29.53**

**so**

**%T of the solution is 29.53**

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