Read TECH 338, Visible Absorption Measurements, and TECH 325, Volume Measurement

Question

Read TECH 338, Visible Absorption Measurements, and TECH 325, Volume Measurements of Liquids, in this series or another authoritative source for a discussion of a techniques to be used in this experiment. Why is it so important that you avoid any loss of solutions when transferring and measuring solutions in this experiment If the % T of a solution is 82.7, What is the absorbance of that solution A student mixed 4.00 mL of 1.02 x 10^-1M HNO_3 as the solvent for both solutions, and found the absorbance of the resulting equilibrium mixture to be 0.253. Given these data, calculate the following. [Fe*] [SCN*]

Explanation / Answer

1) You may read that

2) It is important to avoid loss of solution , as the absrobance is directly proportional to concentration so it will decrease the absrobance and will deviate the whole results

3) Absorbance = A = 2 - log %T

%T = 82.7

A = 2- log 82.7 = 2 - 1.917 = 0.083

4) Absorbance = e.c.l

The reaction will be

Fe+3 + NCS– ---> FeNCS+2 (red coloured)

Moles of Fe+3 used = Molarity X volume in litres = 0.102 X 0.004 = 4.08 X10^-4

Moles of SCN- = 1.98 X 10^-4 X 0.1 = 0.198 X 10^-4

From absrobance we can calculate concentration of FeNCS+2 formed by using Beer Lambert's law

Absorbance = e. concentration X length

now we need the values of extinction coeffecient and length from instrument.

So let the concentration of FeNCS+2 = x mole / L

So

[Fe+3] = Initial concentration - concentration of FeNCS+2

Initial concentration = Moles of Fe+3 / Total volume

Similarly [SCN-] = Concentration of SCN- - Concentration of FeNCS+2

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