1. General: The water alkalinity refers to the amount of substance contained in water that can accept hydrogen ions. Such as hydroxyl, acid and alkali salt, phosphate, hydrophosphate, silicate, silicate salt, hydrogen sulfite, humic acid salts and ammonia, etc., which are common alkaline substances in water, they can react with acid. Therefore, the appropriate indicator can be used for titration with standard solution. 

Alkalinity includes two kinds: phenolphthalein alkalinity and total alkalinity. Phenolphthalein alkalinity is the amount measured with phenolphthalein as indicator, its end point PH value is 8.3; total alkalinity is the mount measured with methyl orange as indicator, its end point PH value is about 4.2. 

2. The reagent:  

(1) 1% phenolphthalein indicator (ethanol solution). 

(2) 0.1% methyl orange indicator (weight/volume). 

(3) C (1/2 - h2so4) = 0.1 mol/L or C (1/2 - h2so4) = 0.01 mol/L sulfuric acid standard solution. 

3. Measuring method:

(1) Measure water sample of 100 ml to injection into the conical flask of 250ml. (2) Add 2-3 drops of phenolphthalein indicator, at this moment if the solution is red, use 0.05 mol/L (or 0.1 mol/L) sulfate solution for titration until the solution is colorless, record the acid elimination a.

(3) Add 2 drops of methyl orange indicator in the conical flask above mentioned, continue to use sulfuric acid standard solution for titration until the solution is orange red, recording the second time of acid consumption b (a is  not included). 

Alkalinity of water sample (JD) is calculated according to the following methods: (JD) phenolphthalein alkalinity = c.a. / V x 103 tendency/L. 

(JD) total alkalinity=C (a + b) /V x 103 / L. 

Where: C --- the hydrogen ion concentration of the standard solution of sulfuric acid mol/L. 

a and b --- The volume of the consumed sulfuric acid standard solution for titration of basicity, ml. 

V - --the volume of water sample, mL.