Final answer:
Applying 70% alcohol to a strand for 5-7 minutes is used to remove a filler, which helps hair retain color before a treatment. Alcohol is not typically used for removing henna, shampoo, or a neutralizer.
Step-by-step explanation:
The use of 70% alcohol on a strand for 5-7 minutes is a technique commonly employed to remove a filler. In this context, a filler is a hair care product used to equalize porosity. Hair fillers are known to help hair retain color and are often applied before a color treatment. On the other hand, henna is a natural dye which can be difficult to remove, and typically alcohol is not effective for this purpose. Shampoo is a cleansing agent and is not removed with alcohol. A neutralizer is used to stop the chemical process of a perm or a relaxer and isn't typically something that alcohol is used to remove.
For reference, the effectiveness of chemical disinfectants like alcohol has historically been compared to that of phenol, which was once a standard for comparison.
When it comes to molecular techniques such as gel electrophoresis, a pre-run of the gel for 30 minutes at 15 watts helps to eliminate any unpolymerized acrylamide and free radicals that may have been produced during the polymerization process, ensuring clarity and accuracy of the electrophoresis results.