PH Titration Lab Report Example | Topics and Well Written Essays - 1500 words

PH Titration - Lab Report Example The paper describes the experiment. During titration, it is essential to figure out the ‘equivalence point’ where moles of acid and moles of base added become equivalent. To aid an experimenter in this situation, a halochromic organic compound known as ‘indicator’ (s.a. phenolphthalein, methyl red, methyl orange, and bromothymol blue) is incorporated where appearance of color change from clear solution signifies the ‘end point’ or the point assumed to be nearest the point of equivalence. At this stage, the volume of reading from the burette is noted down the instant the indicator changes color. With experimental outcomes comprising known molar concentrations and volumes of acid and base used, pH is calculated. In place of an indicator, glass electrode is utilized so that multiple pHs may be read and graphed from which to determine the pH at the equivalence point. For the neutralization reaction occurring between HCl (aq) and NaOH (aq): For the n eutralization reaction occurring between CH3COOH (aq) and NaOH (aq): Hypothesis: The equivalence point is achieved once the titration has gone to the extent when the acid (analyte) and the base (titrant) are in equimolar amounts which takes place on yielding a neutral pH along a steep region in the titration curve Aim: To locate the ‘equivalence point’ through the measure of pH based on the titrant volume vs. pH-titration curve obtained in the experiment and identify the remaining species (in excess) as well as find the pH of the resulting solution after each titration attempt Method: The burette was filled with 1.0 NaOH to the zero mark. A 250- conical flask was rinsed with distilled water, emptying the flask and refilling it with about 50 of deionised water, after which, a 25 of 0.1 HCl was poured into the flask via pipette and the flask was placed on the magnetic stirrer. With the stirrer bar dropped in the flask, the glass electrode was immersed in the flask then th e burette was positioned over the flask’s mouth such that the NaOH would be added into it without obstruction from the glass electrode. The magnetic stirrer was turned on and the flask was adjusted in the manner that would enable the stirrer bar to move freely, having no obstructive contact with the glass electrode throughout the titration process. Measuring of the pH prior to titration was initiated then successive additions of the base titrant were carried out starting with 1 until the equivalent point was arrived at, followed by 0.2-additions that sum up to approximately 8 of NaOH. Final addition of two consecutive 1- titrant amounts was made, taking into account the pH reading for each addition from the onset of titration to this point. Another trial (using the same analyte -- HCl) was performed, then titration was repeated, this time using a different analyte (0.1 CH3COOH) and applying the same quantity (50 ) of deionised water and of 1.0 NaOH. As conducted for HCl, pHs of neutralization reaction between HOAc (analyte) and the titrant (NaOH) were correspondingly read after each base addition. Results and calculations: Note: ( 1 cm3 ? 1 mL ; 1 mol / dm3 ? 1 M ) pH @ equivalence point is about 6.8 based on the graph. This corresponds to NaOH volume of about 5.5 mL. mmoles NaOH = (1.0 M) (9.00 mL) = 9.0 mmoles NaOH mmoles HCl = (0.1 M) (25.00 mL) = 2.5 mmoles HCl Upon neutralization, 9.00 mmoles - 2.5 mmoles = 6.5 mmoles NaOH left total volume = 50 + 25 + 9 = 84 mL [OH-] = = 0.07738 M ---? pOH = -log (0.07738) pOH = 1.11 so that pH = 14 - 1.11 ---? pH = 12.89 Since NaOH and HCl are strong base and strong acid, respectively, pH