Chapter 20: pH Measurement

indicator electrode

sensitive to hydrogen

Buffer Solution

· Required for calibrating pH meters and electrodes.

Glass electrode

-Most popular of all indicator electrodes -used for the determination of the pH of a solution -consists of an outer glass tube containing about 0.1 N HCl which makes contact with a silver, silver chloride electrode (with a sealed internal element)

Quinhydrone electrode

-is a cost-effective hydrogen ion-sensitive electrode. Comprises an equimolar mixture of quinone and hydroquinone with a platinum foil electrode. Requires additional equipment: calomel electrode, student-type potentiometer, 1.5-V batteries, standard cell, and a galvanometer.

3

Potential developed at junction varies depending upon the hydrogen-ion concentration and is responsible for producing the needle deflection on the pH meter

1, 2 & 5

Potentials at junctions remain constant for all measurements

(1) Hydrochloric Acid Buffer (2) Acid Phthalate Buffer (3) Neutralized Phthalate Buffer (4) Phosphate Buffer (5) Alkaline Borate Buffer

Standard Buffer Solutions

Potential hydrogen

abbreviation pH stands for

liquid-junction potentia

arises when two solutions with varying compositions meet. This occurs due to the different speeds at which cations and anions, which carry current in opposite directions at the interface, migrate through the solution.

-Cannot be for pH measurements in the range of 8 to 9. -Unsuitable for use in the presence of strong oxidizing or reducing agents.

limitation of quinhydrone electrode

reference electrode

maintains a constant potential.

reference electrode

o forming the core of pH measurement

indicator electrode

that varies its potential with hydrogen-ion activity (or concentration)

Saturated Calomel Electrode (SCE)

the most practical choice for reference electrode for all-around use and is the most popular

Saturated Calomel Electrode (SCE)

this calomel (Hg2Cl2) and mercury in a protective inner tube (inner element) and the outer body of the electrode contains a saturated potassium chloride solution (electrolyte solution).

Hydrogen Gas Electrode

® Ultimate standard of reference.

(1) Hydrochloric Acid (2) Potassium Biphtalate (3) Potassium Phosphate, Monobasic (4) Boric Acid and Potassium Chlloride (5) Potasium Chloride

Five stock solutions

(1) Hydrogen gas electrode (2) Quinhydrone electrode (3) Antimony electrode (4) Glass electrode

Hydrogen-ion responsive electrode