Electrochemistry
LEC 06
06.15 pH measurement What you can learn about Potentiometric determination of pH Glass electrode pH indicators Acid-base titrations
Principle and tasks The most important and common method to determine the pH value is to measure the potential of an electrode which is sensitive to hydrogen ion activity. Typically, an electrochemical cell is constructed from a pH sensitive electrode and a suitable reference electrode. The cell is then calibrated by measuring its e.m.f. in a series of solutions of known pH. A glass electrode, an antimony electrode and a quinhydrone electrode are calibrated in buffer solutions and after that used to measure the pH of an unknown solution.
What you need: Digital pH-meter pH electrode, glass Reference electrode, AgCl Storage flask for pH-electrodes Platinum electrode in protective tube Antimony electrode Temperature probe, Pt1000 Magnetic stirrer, mini Magnetic stirrer bar, l = 30 mm Retort stand, h = 750 mm Right angle clamp Universal clamp Support for two electrodes Spring balance holder Universal clamp Burette clamp, roller mounting Connecting cord, l = 500 mm, black Burette, 50 ml, lateral stopcock Silver nitrate, crystalline, 15 g Precision balance CPA 623S (620 g/0.001 g), set with software Weighing dishes, 80 50 14 mm Glass beaker, 150 ml, tall Graduated cylinder, 100 ml Volumetric flask, 1000 ml Volumetric pipette, 10 ml Volumetric pipette, 50 ml Graduated pipette, 25 ml Pipettor Pipette dish Pasteur pipettes Rubber bulbs Funnel, glass, do = 55 mm Funnel, glass, do = 80 mm Spoon Microspoon Wash bottle, 500 ml 86 Laboratory Experiments Chemistry
13702.93 18452.00 18475.00 18481.20 45206.00 18477.01 13702.01 47334.93 46299.02 37694.00 37697.00 37715.00 45284.01 03065.20 37715.00 37720.00 07361.05 36513.01 30222.00
1 1 1 2 1 1 1 1 1 1 2 1 1 2 1 1 1 2 1
49224.88 1 45019.25 1 36003.00 17 36629.00 1 36552.00 1 36578.00 2 36581.00 4 36602.00 2 36592.00 1 36589.00 1 36590.00 1 39275.03 1 34457.00 2 34459.00 1 33398.00 1 33393.00 1 33931.00 1
Calibration curves for the antimony (o) and quinhydrone (x) electrode. The cell e.m.f. E is measured using a Ag(S) AgCl(S) Cl–(aq.) reference electrode.
Quinhydrone, 100 g Methyl orange solution, 0.1%, 250 ml Bromthymol blue, 1 g Phenolphthalein solution, 1%, 100 ml Citric acid, 250 g Hydrochloric acid, 1 M, 1000 ml Sodium hydroxide solution, 1 M, 1000 ml Buffer solution, pH 4.62, 1000 ml Buffer solution, pH 7.01, 1000 ml Buffer solution, pH 9.00, 1000 ml Ethyl alcohol, absolute, 500 ml Water, distilled, 5 l
pH measurement PHYWE Systeme GmbH & Co. KG · D - 37070 Göttingen
31195.10 31573.25 31138.01 31714.10 30063.25 48454.70 48329.70 30280.70 46271.12 30289.70 30008.50 31246.81
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P3061501