To make soap scum, gather together hard water, distilled water, Epsom salt, and bar soap that has been grated to form flakes. Although calcium and magnesium salts are known to occur in hard water, Epsom salt is added to ensure salt presence that is necessary to make soap scum. Add 1/8 to 1/4 teaspoon of Epsom salt to 1 to 2 cups (250 to 500mL) of hard water taken in a medium-sized glass bottle or jelly jar, and mix well before adding the powdered soap. Epsom salt contains water insoluble magnesium that clings to the soap to form insoluble soap scum. Take distilled water in another bottle labeled as control; distilled water is soft water with no minerals, and without addition of Epsom salt, this will not make soap scum. Add soap to both bottles and leave it aside after mixing well. Look for cloudy white scum layer in the hard water mixture. You can conclude from this experiment that salts present in water combine with soap to make soap scum.
This is a titration experiment performed in your chemistry lab. Automatic water softener removes the calcium and magnesium ions in water, and adds sodium, which does not affect the functions of detergent or soaps. Laundry softeners added to hard water also effectively soften it, preventing scum formation. In this experiment, combine hard water with a chelating agent such as EDTA, an ingredient in softeners, which binds to the calcium and magnesium salts in hard water and prevents salts from reacting with the soap (flakes or powdered bar soap) to form soap scums. Sodium and potassium salts of carboxylic acids are water soluble; EDTA binds to the calcium and magnesium salts in water and in turn, lends its sodium salts to water that do not react with soap to form soap scum. Add 10ml of hard water to a 250ml Erlenmeyer flask, then add 20ml ammonium buffer to keep PH constant, and add 6-8 drops of eriochrome Black T indicator; the indicator tells you how much EDTA is required to remove the calcium and magnesium salts from the water. Titrate it against 0.005M standard EDTA in burette and stop until the water in flask turns from red to blue. Add soap to the water in the titrated flask and compare it to soap added to untreated sample water in another flask, looking for dingy scum layer in the latter. This experiment proves that addition of water softener softens hard water and prevents formation of soap scum by removing the calcium and magnesium salts from hard water.
The calcium and magnesium ions of hard water make it difficult to form lather, and also lead to the creation of soap scum. In this experiment, 500mL hard water and 1 tsp. bar soap flakes are used in each of the four bottles. Treat 500mL (2 cups) hard water by adding 60-125mL washing soda or sodium carbonate which precipitates the calcium ions; the required amount of washing soda depends on the extent of hardness of the water. Transfer this treated water to a small bottle (glass jelly jars), add soap and check for soap scum formation. The temporary hardness of water can be removed by boiling. Boil 500mL hard water to break down the calcium ions, which form lime scale; transfer this boiled water to second glass bottle and add 1 tsp. soap to see if it forms scum. Add laundry softeners (5 drops) along with 1tsp. soap to the 500mL hard water in a third bottle; this would serve as negative control. 1 tsp. soap added to 500mL untreated hard water in a fourth bottle serves as positive control. Shake the bottles and compare the soap scum formation by looking for insoluble precipitates in all the four bottles to see how the presence of ions in hard water affects the formation of soap scums; scums make it difficult for the soap to produce lather, therefore the amount of bubbles is another measure of soap scum. Visible soap scum and no bubbles will be seen in the fourth bottle or positive control, while the other three bottles will have bubbles. Scum can be seen visibly floating after the lather subsides. The lather forms only when calcium ions are used up and stearate ions (of the soap) are left. This experiment concludes that the treatment of hard water influences scum formation.
In this experiment, you make suds by adding detergent to distilled water or soft water that contains no minerals; this serves as control. You then make "hard" water out of "soft" water by adding ¼ tsp. Epsom salt to 500mL distilled water see how scum affects suds formation in hard water. Take two bottles of distilled water and add Epsom salt or magnesium sulfate to one bottle and mix well before labeling it as hard water. The other bottle is labeled as soft water. Add 1 tsp. detergent to both the bottles and shake well to form bubbles. The hard water will look dingy as magnesium (Epsom salt) binds to the detergent molecules to form scum, and make detergent unavailable to hold the bubble structure; without detergent molecules, the bubbles collapse as soon as they form. Compare the amount of suds formed in hard water and soft water and see that scum affects suds formation in hard water.