Distilled water should be boiled at least 10min to remove carbon dioxide.
sodium hydroxide GB/T629),c(NaOH)=0.01mol/L Standard titration According to 4.1 solution Preparation and standard of QB/T2739-2005
hydrochloric acid (GB/T 622), c(HC L)=0.01mol/L Standard titration solution, According to 4.3 solution Preparation and standard of QB/T2739-2005
95% ethanol (GB/T 679)
Phenolphthalein (GB/T 10729) indicator solution: Dissolved phenolphthalein 1.0g in 95% ethanol, 100mL solution, dropping. 0.01mol/L sodium hydroxide solution until pink appears.
Commonly used laboratory instruments and plug and plug micro burette, indexing 0.01mL
The sample is about 30g (nominal to 0.001g) in the 250mL cone bottle. Add distilled water (12.2.1) 100mL, add 3 drops of phenol. Phthalate indicator, shake well. Observe the colour of the solution. When colorless, titrate the acidity with sodium hydroxide standard solution (12.2.2) until just a persistent pink color appears. When red, titrate the alkalinity with hydrochloric acid standard solution (12.2.3) until the pink just fades away.
x=c x V/m×100…………………………………………………………………………….(8)
The acidity or alkalinity of glycerol (X) is expressed in the form of a molar ratio of 100g (mmol/100g), according to formula (8).
x=c x V/m×100…………………………………………………………………………….(8)
c一The concentration of sodium hydroxide or hydrochloric acid standard titration solution used for titration is mol per liter (mol/L)
v一The volume of the standard solution of sodium hydroxide or hydrochloric acid is determined to be milliliter [ml].
m一The quality of the test unit is g. Acidity or alkalinity is represented by the arithmetic mean of the results of two parallel measurements to two digits.
Precision, the absolute difference between the two independent test results obtained under repeated conditions is no more than 0.01, with the precondition that the absolute difference between the two independent test results is no more than 5% when the precision is greater than 0.01.
Determination of saponification equivalent
Neutralizing and saponification of acids and esters in glycerol with excessive alkali, titrating the excess base with acid standard titration solution.
sodium hydroxide (GB/T 629),c(NaOH)=0.2mo/L solution, According to 4.1 of QB/T 2739-2005 Confecting
sulphuric acid (GB/T 625). c=(H2SO4)=0.2mo/L Standard titration solution, According to 4.4 of QB/T 2739-2005 Confecting
Phenolphthalein (GB/T 10729) Indicator fluid, 10g/L Ethanol solution, according to 5.1 of QB/T 2739-2005 confecting
Commonly used laboratory instrument
Conical flask, 500mL, has a grinding glass interface.
Cooler, water-cooled, with grinding glass joint and conical flask match.
Plug and plug burette, 50mL
The sample is weighed about 100g (weighed to 0.1g) in a conical flask (13.3,1) and added with 100 mL of hot water and phenol without carbon dioxide. Phthalein indicator 1mL. If the solution is alkaline, the standard sulfuric acid titration solution (13.2.2) is used to adjust it to just neutral, and then the stopperless burette is used.
Add sodium hydroxide solution (132.1) 20.00mL, connect the flask with the condensate (13.3.2), heat it to boiling and keep it.
Micro cooling, rinse the condenser tube with a small amount of water, remove the flask, seal and cool the bottle with a soda lime stopper. Titration with standard sulfuric acid titration solution (13.2.2) and blank test with 140mL water instead of sample.
13.5.1 saponification equivalent (Y) of glycerol was expressed in formula (9) with a molar ratio of 100g (mmol/100g).
C 一 The concentration of sulfuric acid standard titration solution is mol per liter (mol/L).
一The volume of standard titration solution consumed by blank test is mL (milliliter).
m一The volume of standard titration solution consumed by titration sample solution is mL (milliliter).
The absolute difference between the two independent test results obtained under repeated conditions is not greater than 0.05, with the precondition that the absolute difference is not more than 5% when the precision is greater than 0.05.
Limit test of arsenic
Trivalent arsenic was reduced to trivalent arsenic by potassium iodide and stannous chloride in the test solution, and then hydrogen arsenide was formed with the new ecological hydrogen produced by zinc particles and acid, and then yellow to orange spots were formed with brominated test paper. The samples were compared with standard arsenic spots to make a judgment.
hydrochloric acid (GB/T622),P3≈1,19g/mL,
Potassium iodide (GB/T1272), 165g/L solutionHydrochloric acid solution of stannous chloride (GB/T638): dissolved stannous chloride 8g in 500 mL hydrochloric acid (14.2.1), stored in a stoppered Brown reagent bottle, effective for three months, granular, particle size 08mm ~ 1.8mm
Sodium hydroxide (GB/T629), 200g/L solution
Sulfuric acid (GB/T625), (60 to 1000) dilute solution (by volume).
Lead acetate absorbs cotton: dissolve lead acetate three hydrate 9.5g in water, dilute to 100mL, store in glass bottle. Degreased cotton is immersed in the mixture of lead acetate solution and water of equal volume. After immersion, excessive solution is leached and dried below 80 C. Stored in stopper bottle for reserve.
Mercuric bromide (GB1398 test paper was used to dissolve the mercuric bromide 5.5G in 95% ethanol and diluted it to 100mL. Cut the arsenic-free filter paper into 2 cm diameter discs or 2 cm edge-length squares. Soak it in mercury bromide solution for more than 1 hour. Store it in the refrigerator and remove the filter paper when it is ready for use. Leave it in the dark for drying.
arsenic trioxide (GB/T1256)
Arsenic standard solution: dry arsenic trioxide (14.2.9) in sulfuric acid dryer until constant weight, weigh 0.1320g in 100 mL beaker, dissolve in sodium hydroxide solution (14.2.5) 5mL, neutralize with sulfuric acid (14.2.6), add sulfuric acid 10mL, transfer water to 1000mL volumetric flask and dilute to scale, mix well. This solution is an arsenic standard reserve solution containing arsenic 0.1mg/mL.
Accurate removal of arsenic standard solution, 1.0 ml to 100 ml volumetric flask, add 1 ml sulphuric acid (14.2.6), dilute to the scale with water, mix, this solution is arsenic standard solution, containing arsenic 1 mg / ml, need to be prepared when in use.
Commonly used laboratory Instrument
Measuring cylinder, 25mL