# STATICTICS FOR ANALYTICAL CHEMISTRY Essay Example

• Category:
Chemistry
• Document type:
Assignment
• Level:
Masters
• Page:
1
• Words:
437

Equation for the variance of e

The variance e is the absorbance which largely depends on the concentration of the solution, a plotting a line of best fit will enable us to know the absorptivity of the solution

Therefore, Y= mx + c

Y in this equation is the absorbance whereas the x is the concentration

e=A.V/l.m

e=l.mx + A.V

x is the slope of the plotted graph

Equation 2

A =log10 (lo/l)

A=ln (I)-In (Io)

=-In (l/lo)

Standard Deviation of Absorbance (SDA) As indicated in the curve above, the relative standard deviation of the absorbance is variable since the absorptivity increases as theconcentration of the solution increases.

Therefore, the optional choice of range should be increased abit so as to be able to deduce the most accurate absorptivity level in the solution

Q5 Determination of manganese in steels

1.18* (0.35/1.15)=0.359

1.17* (0.35/1.15)=0.356

1.21*(0.35/1.15)=0.368

1.19*(0.35/1.15)=0.362

Sample Absorbance Manganese(ww/Mn)

1 0.359 1.18

2 0.356 1.17

3 0.368 1.21

4 0.362 1.19 Slope=∆Y/∆X

Slope=(0.359-0.356)/(1.18-1.17)

1.18=0.3(1.17) + C

C=-0.829

Y= 0.3(0) -0.829

Y intercept=-0.829

The concentration of manganese from the solution is equivalent to the absolute value of the x-intercept

X intercept=(-0.829/0.3)=-2.7633

The manganese in the sample is equivalent -2.7633 ww/Mn

The contents in the solution 2.7633 *(0.35/1.15)= 0.8409 mg of Manganese in the sample

Therefore, both the lowest and highest estimated values falls within the range of the Manganese concentration.

t-Test Statistics

t=[│r│√(n-2)]/√(1-r2)

t2=r2(n-2)/(1-r2)

t2(1-r2)=r2(n-2)

t2-t2r2=nr2-2r2

nr2-2r2+t2r2=t2

r2(n-2+t2)=t2

=t/(√(t2+n-2)

3 2.85 0.312

1. 2.43 0.307

2. 2.23 0.280

3. 2.09 0.250

4. 1.95 0.222

5. 1.90 0.198

6. 1.87 0.178

7. 1.84 0.162

11 1.80 0.147 As indicated indicated in the graph above, there is significantyly linear correlation between the confidence level of the two variables hence the null hypothesis should be rejected

Determination of the concentrationof HCI in a solution

Indicator Mean HCI concentration(SD)/mol L-1 Number of titration experiment

Bromothymol 0.09656(0.00023) 28

Methyl red 0.08686(0.00098) 18

 SUMMARY OUTPUT Regression Statistics Multiple R Adjusted R Square Standard Error 0 Observations Significance F Regression Residual 0 0 Coefficients Standard Error Lower 95% Upper 95% Lower 90.0% Upper 90.0% Intercept 0 X Variable 1 0
1. In relation to the summary output above, the the standard deviation of the two variables do not significantly differ from each other since they are positively correlated with a correlation coeffiecient of 0.0694

2. The difference between Indicator 1 and Indicator 2 is insignificant based on the fact that the significant F is zero and the Lower and upper limit of confidence level 90% is 0.0694

Q12 The Absorbance,A of a solution A=- log10 (T) where T is the transmittance

A=- log10 (T)

=0.501 +0.001

A=-log10(0.502)

A=-(-0.2993)

A=0.2993

Absorbance 0.299

Standard deviation 0.0003