Calculating the Ligand/Metal Ratiohow

2021-05-19 13:27:11
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To calculate the ligand/metal ratio, graph plotted is absorbance against CL/CM values. After plotting the graph, a trend line equation for the two plots is set equal to one another and the value of X calculated.

X represents the ligand

MA = 0.2882/392.2/0.1000

= 0.00734

MB = MAVA/VB

7.34 (25)/2.50 = 7.34*10-4Y =0.2467x 0.0265

Y=4E-16x+0.699

0.2476x-0.0265 = 4E-16X+ 0.699

X = b/a

2.93/0.9 = 3

Part 2: Slope Ration Method

Slope Ratio Method: Absorbance versus Fe (11) ions

VL (mL) VM (mL) CL (M) CM (M) Transmittance (%) Absorbance

10.0 0.5 0.5 8.40E-04 1.40E-05 65.0 0.1871

10.0 1.0 1.0 8.40E-04 2.80E-05 43.0 0.3665

10.0 1.5 1.5 8.40E-04 4.20E-05 28.1 0.5513

10.0 2.0 2.0 8.40E-04 5.60E-05 19.0 0.7212

1.0 2.5 2.5 8.40E-04 7.00E-05 13.0 0.8861

Slope Ratio Method: Absorbance versus Ligand

VL (mL) VM (mL) CL (M) CM (M) Transmittance (%) Absorbance

1.0 5.0 2.80E-05 1.40E-04 78.0 0.1079

2.0 5.0 5.60E-05 1.40E-04 60.0 0.2218

3.0 5.0 8.40E-05 1.40E-04 46.0 0.3372

4.0 5.0 1.12E-04 1.40E-04 34.6 0.4609

5.0 5.0 1.40E-04 1.40E-04 26.0 0.5850

From the two tables shown above and using that data, two graphs are plotted: Absorbance versus Fe (11) ions and Absorbance versus Ligand

The calculation will be as follows:

Absorbance versus Ligand: y= 4261.8x 0.0154

M1 = 4261.8 M -1

Absorbance versus Fe (11) ions: y = 12519x + 0.0166

M2= 12519 M 1

The ligand/metal ratio is therefore calculated from the Beers Law equation.

Using the Slope Ratio Method together with the equation of the Beer Law, the molar absorptivity is thus calculated.

Mean = 12652 mol/cm

Jobs Method of Continuous Variations

A graph of absorbance versus volume (Fe (111)) is plotted. It is important to note that the tangents of the curve when the volume is 0 ml and 10 ml are calculated using the derivative of the equation.

Y = 0.0072*2 + 0.0713x + 0.0129

Y = 0.0144x + 0.0713

Using Jobs Technique

Fe (111) y * The Equations intercept

0.0y (0)=0.071318 y (x) = 0.071318x

10y (10) = 0.072867 0.728672 y2 (x) = -0.072867x + 0.72867

The ligand mole ratio is established though the intersection of the tangent lines.

0.0713x + 0 = -0.0729x + 0.729

x = 5.055 ml

Fraction of the mole = 0.5055

The value of X calculated in the above equation is used to calculate the value of y.

Y = 0.0713X + 0

Y = 0.0713 (5.055) + 0

Y= 0.360

The values of A (x) and A max are therefore

A (X) 0.071318X = -0.072867X + 0.72867

0.144186X = 0.728672

X= 5.055

A(X)= 0.07131 (5.055) = 0.36042

Amax y = -0.007209*2 + 0.07318x + 0.01294

Y = 0.01441X + 0.07131 = 0

X = 4.94638

Determination for the value of Kf

V (Fe 11) ml V (Ligand) ml Amax A CM CL A/Amax*Clim

4..6 0.28527 0.19033 3.20E-04 4.80E-04 2.14E-04

4.5 0.32093 0.19629 3.60E-04 4.40E-04 2.20E-04

5.5 0.35659 0.19864 4.00E-04 4.00E-04 2.23E-04

5.54.5 0.39228 0.19738 4.40E-04 3.60E-04 1.81E-04

6.4 0.42791 0.19252 4.80E-04 3.20E-04 1.44E-04

Through the application of the formula below, the value of Kf is thus calculated

CM (A/Amax)*Clim

CL- (A/Amax)* Clim Kf pKf

1.06E-04 2.66E-04 7.52E+03 3.88E+00

1.40E-04 2.20E-04 7.16E+03 3.86E+00

1.77E-04 1.77E-04 7.10E+03 3.85E+00

2.59E-04 1.79E-04 3.91E+03 3.59E+00

3.36E-04 1.76E-04 2.43E+03 3.39E+00

The mean is therefore 5.63 E+03, 3.75E +00

THEREFORE

Ligand/Metal Ratio from the three methods

Jobs method 1.01940/1 3.75

Slope Ration Method 2.9375/3 1265. 2

Mole Ratio Method 2.99 = 3

As can be seen from the above, the ratio is about 3. This figure, three, represents the stoichiometric ratio between the ligand and the metal in the solution.

Percentage ratio in the Mole Ratio Method = 1/3

Ligand/Metal Ratio (Slope Ratio Method) = 3

Percentage error 2.08%

Ligand/Metal Ratio (Jobs method) 1

Percentage error 1.9%

 

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