The glycerol sample was titrated with HCl or NaOH standard solution using phenolphthalein as indicator, and the volume of HCl or NaOH standard solution consumption was calculated. The determination method is as follows.
(1)Reagent distilled water does not contain carbon dioxide
- NaOH standard solution: 0.01mol/L
- HCl standard solution: 0.01mol/L
- Phenolphthalein indicator: dissolve 1 g of phenolphthalein in 95% (volume ratio) ethanol, dilute to 100 mL;
- Add 0.Qmol/L NaOH solution until pink appears.
(2)Instruments, general laboratory instruments and microtitrators (acidic and basic), with a scale of 0.01 mL
(3)In the determination step, about 30g (accurate to 0.001g) of the sample was taken in a 250 mL conical bottle, 100 mL of water was added, and 3 drops of phenolphthalein indicator were added to shake well. When the solution is colorless, the acidity is titrated with NaOH standard solution until a persistent pink color appears. When the solution is red, the alkalinity is titrated with HC1 standard solution, and it just fades to red.
(4)Calculate the acidity and basicity of glycerol, expressed as the amount of substance (mmol) consumed by 100g sample. The calculation formula is as follows:
pH degree of acid and alkali: c×V÷m×100=100cV/m
V – The volume of hydrochloric acid or NaOH standard solution, mL.
C – The concentration of hydrochloric acid or NaOH standard solution for titration, mol/L;
m- The quality of the test sample, g.
The difference between the two parallel analysis results should be no more than 0.01.