Answer to Question #328862 in General Chemistry for Tesha

Question

1. Why does the Department of Health (DOH) recommends the use of 70% rubbing alcohol than 40% as a precautionary measure against corona virus?

2. Why does the Department of Environment and Natural Resources, (DENR) concern on the cauliform level, in parts per million, during the rehabilitation of beaches in Boracay? Research on the tolerable level of cauliform.

Answer 1

As a disinfectant, the higher the concentration of alcohol, the less effective it is at killing pathogens. The Centers for Disease Control and Prevention (CDC) did research on disinfecting and sanitizing methods and published the Guideline for Disinfection and Sterilization in Healthcare Facilities.

Use of the more concentrated solutions (99%) will result in almost immediate coagulation of surface or cell wall proteins and prevent passage of the alcohol into the cell. When the outer membrane is coagulated, it protects the virus or bacteria from letting through the isopropyl (Widmer and Frei, 2011). Thus the stronger solution of isopropyl is creating a protection for the germ from the antiseptic properties of isopropyl, rendering the virus or bacteria more resilient against the isopropyl alcohol. To put it simply, higher concentrations cause an external injury that forms a protective wall and shields the organism. Furthermore, 99% isopropanol evaporates very quickly which does not allow it to penetrate cell walls and kill bacteria, and therefore isn’t as good for disinfecting surfaces. In other words, it breaks down the outside of the cell before it can penetrate the pathogen.

In comparison, a 70% isopropyl alcohol can effectiveness cross over the cell membrane, thereby attacking the entire cell and killing the bacteria (CDC, 2020). The benefits of using 70% alcohol are

Coagulation of surface proteins proceeds at a slower pace, thereby allowing the alcohol to enter the cell.

70% alcohol, being a dilution of absolute alcohol, contains water which is essential in the denaturing process of proteins.

Due to the concentration difference of water and alcohol on either side of the cell wall, 70% alcohol enters the cell to denature both enzymatic and structural proteins. This increases the potency of its antimicrobial properties.

The CDC recommends 70% for disinfecting one’s household and routine cleaning (CDC, 2020)