Chapter 23, Problem 77A

Interpretation Introduction

Interpretation : To determine the alcohols that act as moistening agents in the toothpaste and to establish their structures.

Concept Introduction : Toothpaste has many active ingredients like fluoride, sorbitol, hydrated silica, polyethylene glycol, Sodium Lauryl Sulfate, Ethanol or grain alcohol, Cellulose gum, etc., The ingredients may differ for each toothpaste and the ingredients listed above correspond to Pepsodent.

Answer to Problem 77A

Sorbitol. The number of hydroxyl groups present is 6. The structure of Sorbitol is

  

Explanation of Solution

Sorbitol is a sugar alcohol. It acts as a humectant that is it draws moisture from the air and will help in maintaining the toothpaste moist. It also can hold the water that is used during the manufacture of toothpaste. This clearly shows that if sorbitol is absent the toothpaste may convert into dry hard powder.

Conclusion

All the ingredients present in the toothpaste will have different functions, but sorbitol will be used as a moistening agent that helps in maintaining the toothpaste moist. There is another alcohol like ethanol present but this ethanol is not used as a moistening agent but used to decrease the viscosity.