For which trial(s) is phenophthalein a good indicator? For which trial(s) was it a poor indicator? For those trials in which it was a poor indicator, suggeest a better indicator and indicate its pH range on the titration curve.
So for phenophthalein the equivalence point has to be from 8.3 to 10 right?
Trial 1: 7.29 pH so bromothymol blue indicator
trial 2: 8.14 so phenol red indicator
Trial 3: 9.21 falls between 8.3 and so that's good
trial 4: 7.01 so bromothymol blue
So much of this depends upon how steep the curve is at the equivalence point AND for how large a range. But if we have short ranges and the curve is not too steep, then I would pick phenol red for trial 1. My text lists that as changing from 6.8-8.4 and 7.29 seems closer to mid-range for phenol red than for bromothymol blue (6.2-7.6....here 7.29 is so close to the high end). Trial 2 at 8.14 is so close to the high end of phenol red (6.8-8.4); it appears cresol purple (7.6-9.4) might be more in the middle. Trial 3 looks good for phenolphthalein. Trial 4 looks good. Actually, all of those you picked will work if the curve is steep enough and the range is high enough.
Phenolphthalein is a good indicator for trials where the equivalence point falls within its pH range of 8.3 to 10.
In Trial 1, with a pH of 7.29, phenolphthalein would be a poor indicator. Instead, a better indicator to use would be bromothymol blue, which has a pH range between 6.0 and 7.6 on the titration curve.
In Trial 2, with a pH of 8.14, phenolphthalein can still be used as it falls within its pH range of 8.3 to 10. Therefore, phenolphthalein is suitable for this trial.
In Trial 3, with a pH of 9.21, phenolphthalein would be a good indicator since it falls within its pH range.
In Trial 4, with a pH of 7.01, phenolphthalein would again be a poor indicator. A better alternative in this case would be bromothymol blue, which has a pH range of 6.0 to 7.6.
To summarize:
- For Trial 1 (pH 7.29), bromothymol blue is a better indicator.
- For Trial 2 (pH 8.14), phenolphthalein can be used.
- For Trial 3 (pH 9.21), phenolphthalein is suitable.
- For Trial 4 (pH 7.01), bromothymol blue is a better indicator.