The Chemistry class is completing the acid-base lesson. I ordered several indicator solutions: phenol red, bromothymol blue (BTB), phenolphalein (PHTH), cabbage powder, universal indicator, and litmus. We had hydrochloric acid (HCl) and sodium hydroxide (NaOH) solutions. We had had issues with the acid dilutions when the kids did the titrations. I contacted the company because the acid stock solution was not within the concentration parameters on the bottle. So what pH are the acid and base? We measured the solutions with a pH meter. I wanted the kids to become familiar with a variety of pH indicator charts. First the class took the pH of a sample of the HCl and NaOH. Next they added a drop of indicator solution to the samples and compared the colors to the indicator charts. Next, the kids made dilutions, measured the pH, and repeated the test with a range of indicators. I wanted them to see if the colors matched up, reinforce the relationship between concentration and pH, and understand how the indicator charts are created. Below are pictures.
http://m.imgur.com/dWc6HXU,Ueg3Z8G
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