1、Field
Analytical methods for the concentration of the alkali in an alkaline solution

2、Abstract
With phenolphthalein as indicator, prepare a standard acid solution( known concentration of hydrochloric acid) for titration. According to the consumed volume of standard acid solution to calculate the alkali concentration.in the sample.

3、Reagents
Hydrochloric acid: analysis grade, prepare a 0.1 mol/L of the standard solution;
Phenolphthalein indicator: prepare in an ethanol solution of 10 g/L.

4、Materials
4.1 Conical flask: 150 ml.
4.2 Burette: 25 ml
4.3 Pipette: 5 ml

5、Procedures
Transfer certain volume V of alkaline sample with a pipette (5% alkali: take 5 ml, 10% alkali: take 3 ml, 30% alkali: take 1 ml) to the conical flask that has approx.10 ml of distilled water. Make up the total volume to approx. 50 to 60 ml with distilled water,. Then add 2 ~ 3 drops of phenolphthalein indicator, and take a titration with the standard acid solution.Complete the titrition once the red colour just disappeared. The red colour is the  end point of titration. Record the consumed volume of standard acid solution.

6、Notes
6.1 Be careful in handling the alkaline sample
6.2 Be careful in handling the Hydrochloric acid

7、Calculation
C1 Standard acid solution, 01 mol
V1 Consumed volume of the standard acid solution during the titrition, mL
V2 Volume of sample, mL

8、Report
Repeat the above analysis twice and take the average figure as the final result.