Soap making:

Question:

We have not had much luck with the Preparation and properties of soap, STAWA Chemistry Lab Manual Experiment 68.
Do you have any hints on how to make it work, or other recipes please?

Answer:

1. The product made in this exercise bears little resemblance to a bar of Dove but, as long as reasonably fresh oil is used, students can observe the saponification reaction.

triglyceride + sodium hydroxide produces sodium salt of carboxylic acid + glycerol

The soap will probably be crumbly and not suitable for personal use!
Note: The STAWA method is simpler than the Heinemann Science 2 (2.8/Expt 5) and we use it for Year 9.
2. Our classes have had quite good results using the soap recipe from the TEE Physical Science Materials book. There are just a few slight differences to the one in the STAWA Lab Manual
3. We make soap the STAWA way in Year 9 as well as in Year 11 or 12. It works, in the sense that the reaction produces the desired product (following reactants and method exactly as in the manual). The product however, is not creamy Lux, rather a crumbly, harsh version, not recommended for the face!
4. We have varied results, some very good, some not even vaguely similar to soap. The only change we made was to use VERY FRESH castor oil bought the previous day. All other things seem to point to operator error.
5. You need to have Watsonia lard (from pigs), not fat.
Its very different to the STAWA method. It can be done in a 60 minute lesson.
Technician melts lard on hot plate in beaker. Then mixes together well equal amounts of lard and olive oil. Reduce temperature down to 50 to 60 degrees C and control on the hot plate.
Student: in 250 ml beaker;
To 100ml of distilled water, add 30 gm of sodium hydroxide stirring constantly, to prevent a lump. Reduce heat of sodium hydroxide solution in a cold-water bath until about 40 degrees C. In 600ml or litre beaker, mix 200ml of oil and lard mixture with 100ml sodium hydroxide solution.
Stir continuously until the mix starts to solidify. Pour into moulds- we use cake moulds.
6. Using Copha (solidified coconut oil), as an alternative to lard is reasonably successful. (Thank you to KH of Queensland for this idea).

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