Question: why is phenolphthalein usually used in titration experiments rather than bromothymol blue

title: Phenolphthalein
text: A reduced form of phenolphthalein , phenolphthalin , which is colorless , is used in a test to identify substances thought to contain blood , commonly known as the Kastle - Meyer test . A dry sample is collected with a swab or filter paper . A few drops of alcohol , then a few drops of phenolphthalin , and finally a few drops of hydrogen peroxide are dripped onto the sample . If the sample contains hemoglobin , it will turn pink immediately upon addition of the peroxide , because of the generation of phenolphthalein . A positive test indicates the sample contains hemoglobin and , therefore , is likely blood . A false positive can result from the presence of substances with catalytic activity similar to heme . This test is not destructive to the sample ; it can be kept and used in further tests . This test has the same reaction with blood from any animal , so further testing would be required to determine whether it originates from a human .