Bromothymol blue (often mistakenly referred to as "bromathal blue") is a pH indicator. It changes color based on the pH of a solution, transitioning from yellow in acidic conditions (pH < 6.0) to green at neutral pH (around pH 6.0 - 7.6) and then to blue in basic conditions (pH > 7.6).
If you leave plastic wrap in a container with bromothymol blue for four days, a few possible outcomes might occur:
1. **No Reaction**: If the plastic wrap is inert and doesn't leach any chemicals into the solution, there may be no change in the color of the bromothymol blue.
2. **Change in pH**: If the plastic releases any acidic or basic substances into the solution, the color of the bromothymol blue may change accordingly. This could indicate some chemical interaction between the plastic wrap and the solution.
3. **Physical Changes to Plastic Wrap**: Depending on the nature and quality of the plastic wrap, it might become softer, more brittle, or undergo other physical changes if any components of the wrap are affected by the solution.
4. **Color Adhesion**: If the bromothymol blue solution is concentrated, it might stain the plastic wrap, causing it to take on a coloration (blue, green, or yellow depending on pH).
5. **Evaporation**: If the container isn't sealed, some of the solvent (usually water) in the bromothymol blue solution might evaporate over the four days, potentially concentrating the solution.
6. **Contamination**: If the setup isn't sterile, over four days, there's a potential for bacterial or fungal growth, especially if there are any nutrients in the solution. Some microorganisms can alter the pH of their environment, which would be indicated by a color change in the bromothymol blue.
The exact outcome will depend on various factors including the specific type of plastic wrap used, the concentration of the bromothymol blue solution, and the initial pH of the solution. If you're conducting this as an experiment, it would be interesting to observe and note any changes!