Furthermore, figures (5 & 6) shows the 95% confidence intervals and standard error (S. E). Using titration method to determine the end points. Phenolphthalein indicator (cm3) Methyl orange indicator (cm3) Table (1) volume of 0. 1MHCl titrated against the carbonate/bicarbonate mixture Calculation (1) Determination of carbonates (CO3-2) levels using the titration and pH indicator methods, values obtained from the table (1) and the derivative curve. CO3-2 + 2HCl H2O + CO2 + 2Cl- (1. 1) From the above equation; 1 mole carbonate (CO3-2) = 2 moles HCl step (1).
1 mole 0. 1MHCl = 1x 10-4 mole HCl = 1/2 x 10-4 mole CO3-2 step (2) Note; 1/2 used is because CO3-2 is half reaction. Therefore, 1ml 0. 1MHCl = 1/2 x 10-4 x 60 = 3mg CO3-2 step (3) (Relative molecular mass of CO3-2 = 60) 1ml 0. 1MHCl = 3mg CO3-2 step (4) Equivalence point for CO3-2 using the titration method = 2. 53ml (2. 53ml is the average value from table (1) phenolphthalein indicator) this means that half CO3-2 = 2. 53 complete CO3-2 used up = 2 x 2. 53 =5. 067ml step (5) Therefore, 3mg x 5. 067ml = 15. 2g CO3-2 in sample step (6) In 1000ml; 15. 2 x 1000/25 = 608mg/l.
Therefore, the value of CO3-2 present = 608mg/l (1. 2) Using the derivative curve value from figure (4); Taking from step (4) above 1ml 0. 1MHCl = 3mg CO3-2 step (4) from the derivative curve, the equivalence point for CO3-2 = 2. 0ml (1/2 CO3-2 reaction) for full reaction CO3-2 = 2 x 2 = 4. 0ml step (7) Therefore, CO3-2 = 3mg x 4. 0ml = 12mg CO3-2 in sample In 1000ml; CO3-2 = 12 x 1000/25 = 480mg/l Therefore, CO3-2 present = 480mg/l (2) Determination of bicarbonate (HCO3-) levels present in the reaction using the titration and pH methods, values obtained from table (1) and the derivative curve.
HCO3- + HCl H2O + CO2 + 2Cl- (2. 1) From the above equation 1ml 0. 1MHCl = 1x 10-4 mole HCl step (1. 1) Therefore, 1x 10-4 mole HCl = 1 x 10-4 x 61 = 6. 1mg HCO3- step (2. 1) The equivalence point using the titration method = 9. 567ml (9. 567ml is the average value from table (1) methyl orange indicator) full amount used up is given by this equation; Y – 2X Where; Y = HCO3- equivalence point = 9. 567ml 2X = full CO3-2 equivalence point = 5. 067ml Therefore, the full amount used = 9. 567 – 5. 067 = 4. 5ml Therefore, 6. 1 x 4. 5 = 27. 45mg HCO3- in sample In 1000ml; HCO3- = 27. 45 x 1000/25 = 1098mg/l.
Therefore, HCO3- present = 1098mg/l (2. 1) Using the derivative curve value from figure (4); Taking the values from st.ep .(2. 1) 1x 10-4 mole HCl = 1 x 10-4 x 61 = 6. 1mg HCO3- step (2. 1) the equivalence point from the derivative curve = 9. 3ml full amount used up is given by this equation; Y – 2X Where; Y = HCO3- equivalence point = 9. 3ml 2X = full CO3-2 equivalence point = 4. 0ml Therefore, the full amount used = 9. 3 – 4. 0 = 5. 3ml We then have; 6. 1 x 5. 3 = 32. 33mg HCO3- in sample In 1000ml; HCO3- = 32. 33 x 1000/25 = 1293. 2mg/l Therefore, HCO3- present = 1293. 2mg/l Derivative curve values.
CO3-2 (Phenolphthalein indicator) mg/l 608 480 HCO3- (Methyl orange indicator) mg/l 1098 1293. 2 One-Sample T: pH Test of mu = 95 vs not = 95 Variable N Mean StDev SE Mean 95% CI T P pH 38 6. 10395 2. 29270 0. 37192 (5. 35036, 6. 85754) -239. 02 0. 000 Descriptive Statistics: pH X, pH Y Variable meter N N* Mean SE Mean StDev Minimum Q1 Median Q3 pH X A 5 Variable meter Maximum pH X A 2.
800 D 2. 700 pH Y A 9. 200 Discussion Carbonate – bicarbonate system is the most significant in buffering of rivers, lake and ocean. The experiment looked at the measurement of alkalinity using the titration and pH indicator methods, figure (1), shows the relationship between the volumes of acid used (0. 1MHCl) against measured pH values. An increase in the volume of 0. 1MHCl, there is a corresponding decrease in H+ in the solution. Points A – B is the carbonate (CO3-2 ) buffer zone, points C – D is the bicarbonate (HCO3- ) buffer zone and points E – F is where carbon dioxide (CO2 (g)).
The highest peaks in figure (2) indicates the equivalence point, figure (1) was superimposed on figure (2) to give figure (3), with these relationship the actual equivalent point was determined. From several literatures, phenolphthalein colour change occurs at pH 8. 3 – 10; the experiment was able to show the colour change at this range. The same also was for methyl orange indicator (pH 3. 5 – 4. 5). However, point G in figure (1) is as a result of the pH meter, this could be attributed to interferences. At 95% confidence interval, figure was clearly from the same source.
The equivalence point, pH of the titration was within the transition range of the indicators. However, the values obtained from the class in table (4) by group 3 is different from the actual points from figure (3), this is as a result of rough extrapolation. Comparison of the titration and pH indicator methods. Both methods are a good measure of alkalinity in an aqueous medium, the titration method deals with colour change to determine the end point, this could be disadvantageous to someone who is colour blind. Methyl orange changes from yellow to but this change is not very clear to eye easily.
Titration method involves carrying out the process repeatedly so as to get a concordant result, many factors can affect such reading, for instance, sample transfer to beakers will affect the quality of result obtained. However, the pH indicator method gives a more accurate and consistent result when used appropriately. This method gives a wider spread of values compared to titration method. Comparing class values. From the descriptive statistic, it can be seen that the mean values of both meters are not different, therefore, both meters are equal in performance. There is 95% confidence interval that the samples are probably from the source.
Conclusion and Recommendation The alkalinity of the water sample was monitored using the titration and pH indicator methods for the determination of equivalence point. The end point value was used to determine the amount of carbonates and bicarbonates present in the water sample. Compared the class results to obtain a 95 % confidence interval that the sample was not from the same source. The following recommendation was made; > Further investigation should be carried out using a different methyl orange indicator, for instance, a mixed bromocresol methyl red indicator.
> Digital/automatic titrator should be used instead of the manual titration. References Andrew D. Eaton, Lenore S. Clesceri and Arnold E. Greenberg (1995) Standard Methods for The Examination of and wastewater. 19 edition America Public Office. Akintola T. Environment degradation in Nigeria Niger Delta. www. africaconservation. org Clair N. Sawyer, Perry L. McCarty and Gene F. Parkin Chemistry for Environmental Engineering. pp 473 – 483 McGraw – Hill International Edition Donald W. Hood (1971) Impingement of Man on The Ocean Willey – Interscience Frank N.
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