In this experiment students will prepare a reaction mixture

In this experiment, students will prepare a reaction mixture containing the solutions of iron (III) nitrate, potassium thiocyanate and distilled water inside a beaker. What indication of chemical change will be used to study the equilibrium constant of the reaction in this experiment? (0.025 pt.) (b) Why is Beer\'s law applicable in measuring the concentration of products in the reaction mixtures in this experiment? (0.05 pt.) (c) What the the optimum time range when to obtain/record the absorbance reading of the reaction? (0.025 pt.) Why it is necessary to strictly follow this time range when observing the absorbance readings at 470 nm wavelength.

Solution

Fe(NO3)2 + 3KSCN <==> FeSCN2+ + 3KNO3

(a) the formation of FeSCN2+ (blood red color) compound is detected by colorimetry experiment. The intensity of color formed is directly related to the amount of complex formed in the solution. Therefore, absorbance readings are taken to follow the reaction.

(b) Beer\'s law is applicable here as the solution concentration is kept at a value which gives accurate measurements for the complex formed and the absorbance readings therefore. At no points the concentration of complex goes too high.

(c) Optimum time range for the experiment is above 10 minutes and below 30 minutes as all the complexation reaction is done by then.

(d) The time range is important to get accurate mesurements for the complex at 470 nm (lambda max) value for the complex found by running the experiment at regular time intervals and plotting to get the time when maximum amount of complex is formed in solution.