The steps in the analysis for Ni2+ in the complex are listed below but not in th

Question

The steps in the analysis for Ni2+ in the complex are listed below but not in the correct order. Arrange them in the correct order by placing a number from 1 to 10 in the blank to the left of the step. divide by the slope divide by mass of weighed sample divide by the atomic weight of nickel determine slope of B-L plot dissolve accurately weighed mass of compound in known volume of acid prepare Ni2+ standard solutions correct for the volume of the acid solution measure absorbance of the acid solution read the procedure determine absorbance of Ni2+ standards (continues)

Explanation / Answer

1.  Read the procedure. You also need to identify risks associated with the experiments and decide what protective measures you have to take while performing the experiment.

2.  Prepare Ni2+ standard solutions: You would need minimum 5 standard solutions in order to construct a Beer-Lambert plot

3.   Determine absorbance of the Ni2+ standards: You will have to adjust the spectrometer first. This is done by filling a clean, dry cuvette three-fourth full with deionized water and adjusting the instrument. For measuring absorbance of each standard, the cuvette must be clean and dry.

4. Dissolve accurately weighed mass of compound in known volume of acid:

5. Measure absorbance of the acid solution:

6.   Determine the slope of the B-L plot: This is done by plotting the concentration on the x-axis, and absorbance on the y-axis. If the data exhibits a linear relationship, then the standard curve will be a straight line. A slope is calculated by the equation y = mx + b. The y variable can be expressed in terms of a constant (b) and a slope (m) times the x variable.

7.   Divide by slope: The data is analysed by locating the measurement on the y-axis that corresponds to the absorbance of the acidic solution and the x-axis that corresponds to the unknown Ni2+ concentration. The unknown Ni2+ concentration can be found by dividing the difference of Absorbance and constant (b) by the slope. The simplification for this calculation is given as follows:

y = absorbance (A) and it has no unit

x = concentration (C) and has unit of M or mol/L

m = (m) = slope or the molar extinction coefficient in B-L law and has unit of M1 cm1

A = mC +b

Then C = (A-b)/m

8. Correct for volume of the acid solution: This step helps in determining the number of moles of unknown Ni2+ and is calculated using the formula: number of moles of the Ni2+ (n) = concentration of Ni2+ from the plot X Volume of the solution.

9. Divide by atomic weight of Ni: This step is used to determine the mass of unknown Ni. The mass of Ni = number of moles of Ni2+ X Atomic mass of Ni. Please note that Atomic mass of Ni and Ni2+ will be nearly same.

10. Divide by the mass of weighed sample: This will give % yield of the reaction.

% yield = (measured mass) 100 / actual mass

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