Final answer:
70% ethyl alcohol is generally more effective as a disinfectant than 99% isopropyl alcohol because high alcohol concentrations can prevent proper penetration of the cells due to rapid protein coagulation on the cell surface. The optimal effectiveness is achieved in alcoholic solutions that are around 70% concentration.
Step-by-step explanation:
When comparing 70% ethyl alcohol and 99% isopropyl alcohol as disinfectants, it is important to understand how these substances interact with microbial cells. Alcohols, including both ethyl alcohol (ethanol) and isopropyl alcohol (isopropanol), are commonly used antiseptics that work by denaturing proteins and disrupting membranes. These actions lead to cell metabolism inhibition and cell lysis, effectively killing bacteria and viruses.
While a higher percentage may seem more effective, alcohols actually work better in aqueous solutions of about 70% rather than at higher concentrations. This is because in higher concentrations, such as 99%, rapid coagulation of proteins occurs on the surface of the microbes, which can actually prevent the alcohol from effectively penetrating and killing the cells. Thus, a 70% ethyl alcohol solution is generally more effective at inhibiting microbial growth than a 100% solution.
In the case of hand sanitizers, they often contain between 60% to 80% alcohol, with the remainder being substances such as ethylene glycol or glycerin, which serve to keep the skin soft. Ethanol is volatile and flammable, so caution is required when using sanitizers based on this chemical.