3. Colorimetry is a technique used to determine the concentration of many molecu

Question

3. Colorimetry is a technique used to determine the concentration of many molecules in solution that do not absorb visible light. One example is the detection of glucose in a sample. Glucose itself will not absorb visible light, but forms a blue-green complex when reacted with toluidine in acetic acid. The analytical wavelength for this complex is 635 nm. A student prepares the following Beer's Law plot. Use the plot to answer the following questions. Beers Law Plot of Absorbance vs. Glucose concentration at 635 nm 0,7 0.S 0.3 0.1 Concentration (M

Explanation / Answer

WL = 635 nm

Slope = 23.75

note that for beer'w law:

A = e*l*C

A: Absorbsivity, e = emission l = path length, C= concentation

so

A vs C then slope = e*l = 2375

a)

calculate e from complex... if l = 1 cm

so

m = e*l 23.75

e = m/l = 23.75/1 = 23.75 L/(g*cm)

b)

calculate C from unkown..

A = 0.732

then

A = e*l*C

C = A/(e*l)

C = 0.732 / (23.75 *1) = 0.03082 g/L

c)

number of moles in tablet

so..

V = 300 mL = 0.3 L so

mol= M*V = 0.03082*0.3 = 0.009246 mol of glucose

d)

mass of glucose from previous work

1 mol = 180.16 g/mol

mol = mass/MW = 0.009246*180.16 = 1.6657 gof glucose

e)

% mass = mass of glucose / total mass * 100%

1.6657/2.5 *100 = 66.628 %

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