Introduction to Alkalinity Test and Standard Solutions By Douglas Rittmann, Ph.D., P.E. Water/Wastewater Consultant Presented to CE 4153 On February 7, 2006

General Considerations 1. Its capacity to neutralize acids or its buffering capacity major classes of materials A. Bicarbonates, HCO ≤ pH 8.3 B. Carbonates, CO >pH 8.3 < pH 10 C. Hydroxide, OH - - > pH 10.0

Sanitary Significance 1. Lime/Soda Ash Softening 2. Effects on Coagulant Dosing 3. Total Dissolved Solids compliance 4. Industrial Wastes Discharges 5. Calcium Carbonate Stability

Method of Analysis 1. Phenolphthalein Alkalinity A. Phenolphthalein indicator B. pH 8.3 endpoint of titration 2. Total Alkalinity C. Measures Carbonates and Hydroxide ions A. Bromcresol green or Methyl Orange indicator B. pH 4.5 endpoint of titration C. Measures Bicarbonates

Methods of Expressing 1. Phenolphthalein Alkalinity as CaCO 3 P. Alk. = ml 0.02N sulfuric acid (1000/ml sample) = mg/L as CaCO 3 2. Total Alkalinity as CaCO 3 T. Alk. = ml 0.02N sulfuric acid X (1000/ml sample) = mg/L as CaCO 3 3. Hydroxide, Carbonate, and Bicarbonate Alkalinity as CaCO 3

Alkalinity Relationships Titration Result OH - Alkalinity as CaCO 3 CO 3 - Alkalinity as CaCO 3 HCO 3 - Alkalinity as CaCO3 P = 0 00T P<1/2 T 02PT-2P P=1/2 T 02P0 P>1/2 T 2P – T 2(T- P) 0 P = T T00

Standard Solutions General Considerations General Considerations 1. Saves Time in calculating results 2. Selection of Proper Normality is convenient * 1 mg/ml or 1000mg solution * 1/eq.wt., example: Alkalinity as CaCO3 = 0.02 N 3. Preparation of Solution of Proper Normality * Material of Known purity is weighed & transferred to volumetric flask * Purchase Solutions of known Normality * Purchase Solutions of known Normality

Preparation of 1N Acid Solution * Sulfuric acid used for Alkalinity Test 1 GMW = 98 g pure H 2 SO 4 = g H + 1 GMW/2 = 49 g pure H 2 SO 4 = g H + Acid is 96% pure, then 49/0.96 = 51 g = g H + Make 5% stronger = 51 X 1.05 = 53.5 g Procedure: Weigh about 53g of conc. acid into a small beaker on Trip balance. Place 500 ml of distilled water in 1-liter graduated cylinder And add the acid to it. Rinse the contents of the beaker into the cylinder With distilled water, and add water to the 1-liter mark. Mix by pouring Back and forth from the cylinder into a large beaker. Cool to room temp.

Primary Standard * Sodium Carbonate is a convenient primary standard MW = 106 of Na 2 CO 3 1EW or 1N = 53g/L when reacting with H 2 SO 4 to pH 4.5, T. Alk endpoint Preparation of 0.02 N Acid or N/50 can be made from 1N based on ml X N = ml X N Example: ml X 1.0 = 1000 X 0.02 ml = 20