Part II
Do not reuse test tubes. Use the commercial indicators directly on the 21 substances remaining in the cups.
Follow the instructions for using the pH kits
Devise a second data table (on the back of this sheet, or separately). Record your findings (color and pH) for each substance.
Delegate your assignment to our experts and they will do the rest.
Part III
Test each of the 5 unknowns , as well as the HCL and NaOH with Bromothymol Blue.
Record your results (on the back of this sheet, or separately). The colors should range between yellow to blue. Bromothymol Blue is not as sensitive to pH as are other indicators, and is typically used to determine if a liquid is either acidic or basic.
Conclusions :
Which household items are bases?
Answer: The household items that are said to be bases are bleach, ajax, ammonia, laundry detergent, syrup and Drano.
Which are acids?
Answer: The household items which are considered acids are vinegar, ginger ale, lemon juice, and vegetable oil.
Does the cabbage indicator agree with the commercial pH kit? If it differs, how does it differ?
Answer: Generally, the trend of acidity and basicity of the substances using cabbage indicator conforms with the result in using the commercial pH kit. However, there are some erroneous results like that of lemon juice which showed to be acidic in commercial pH kit while when used with cabbage indicator, it showed to be basic. This can be attributed to human error or errors in the preparation of the substance. It might be that the test substance or the indicators used are contaminated hence giving erroneous result.
Based on your results for the cabbage juice, determine what colors for the Bromothymol Blue in solution correspond (roughly) to what pH. For example, if the cabbage indicator turns a sample blue, that substance would have a pH of 8. If the same substance treated with bromothymol blue turns a deep blue, what is the substance’s pH? Record those results (for clear, yellow, green and blue for bromothymol blue) below:
Answer: The change in color of the substance to yellow indicates a pH of 1-6; green indicates pH of 7 while blue indicates pH 8-14. However, the substance may turn clear if the pH becomes to high.
Critical thinking (the answer is not in the book): In a very high pH solution (think drain cleaner), the cabbage indicator could turn not yellow, but instead, completely colorless. Why might this happen? Hint: the second paragraph of this report states that at a very high pH, an anthocyanin will be completely reduced . What does the word “reduced” mean in chemistry? Anthocyanin is a pigment (which is a protein ). What happens when a protein is degraded (for example, by drain cleaner)? Why does this protein (in the cabbage juice) turn completely colorless when mixed with a strong base (pH 13-14)? Use a the back of this page or a separate sheet (Preferably typed) to answer this question.
Answer:
Reduced in chemistry means that a certain atoms involved in a chemical reaction have gained electrons. The pigment anthocyanin, once degraded, will loose its physiologic function. The rate of degradation increases as the pH increases. In the experiment, the cabbage juice might turn completely colorless when mixed with a strong base because as pH is increased, the molecule become deprotonated and at higher pH, the molecule forms a negative ion or anion resulting into a colorless substance. As the pH increases, kinetic and thermodynamic competition occurs between the hydration reaction of flavylium cation and the proton transfer reactions related to it’s acidic hydroxyl group.
