COOKING OIL QUALITY TESTS
IPT05
Last Revised: May 2015 1. PURPOSE This exercise determines the saponification and iodine value of a cooking oil sample. 2. REAGENTS & EQUIPMENT 2.1
Liquid vegetable oil sample (eg olive, castor, safflower, sunflower) 2.2
Wij’s reagent 2.3
Iodine bottles 2.4
Standardised 0.1 M sodium thiosulfate 2.5
15g/100 mL KI 2.6
Standardised 0.5 M HCl 2.7
Ethanolic 0.5 M KOH 2.8
Reflux apparatus 3. PROCEDURE Both these analyses must be set up at the end of your morning class, otherwise there will not be enough time to complete them. 3A. Saponification Value 3.1
In duplicate, weigh accurately 2 g of the sample into a 125mL Quickfit round bottom flask. 3.2
Pipette 50 mL of 0.5M ethanolic potassium hydroxide into each flask. 3.3
Grease the joints well with Silicone grease. 3.4
Add a boiling chip, attach a condenser and reflux gently for one hour. 3.5
Cool the flask, add distilled water (10 mL) and titrate in the same as 3.6. 3.6
To “standardise” the KOH solution, titrate a 50 mL aliquot of the 0.5 M alcoholic KOH with standardised 0.5 M hydrochloric acid to phenolphthalein endpoint. This will serve as the blank. 3B. Iodine value 3.7
Use the CRC Handbook (the table on fats and oils normally around D‐220) to find the typical iodine value for the oil type being tested. 3.8
Calculate the required sample weight according the following formula: sample weight (g) 
35
typical iodine value
3.9
3.10
3.11
3.12
In duplicate, weigh accurately about the required amount directly into the special iodine flasks. Pipette 25 mL of Wij’s solution into each flask. Stopper the flasks and half‐fill the reservoir with KI solution. Place the flasks in a cool, dark place for 1 hour. 3.13
3.14
3.15
3.16
Afterwards, remove the stopper and allow the KI to run into the flask. Add about 100 mL of water. Titrate each flask as in 3.15‐3.16. To “standardise” the Wij’s reagent, pipette 25 mL into a conical flask and titrate with standardised 0.1 M sodium thiosulfate solution to a pale straw colour. Add starch indicator and continue titrating until the blue colour has disappeared. This will serve as the blank. Reporting 
Use the equations to below to calculate the values for the duplicates 
Calculate the average values for SV and IV and record these on your Result Sheet Saponification value SV 
28.05 M (b  v )
w
Iodine value IV 
12.69 M (b  v )
w
where M is the molarity of the thiosulfate or HCl b is the blank titre in mL v is the sample titre in mL w is the sample weight in g IPT05 p2