【Daily Question】Chemical Analysis Edition, 3/19/2021
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This post was last edited by zjp on 2021-3-19 08:18. Multiple-choice question: Select the appropriate indicator for the titrations in examples ①~④ below ( ). ①① Titrating Fe2+ with Ce4+ ② Standardizing Na2S2O3 with KBrO3 ③ Titrating H2C2O4 with KMnO4 ④ Titrating vitamin C with I2 A. Starch B. Methyl orange C. Sodium diphenylamine sulfonate D. Self-indicator Answer: C, B, D, A
①Titrating Fe2+ with Ce4+ C, sodium diphenylamine sulfonate ②Standardizing Na2S2O3 with KBrO3 A, starch ③Titrating H2C2O4 with KMnO4 D, self-indicator ④Titrating vitamin C with I2 A, starch CADA
Generally, potassium dichromate is used to standardize sodium thiosulfate; potassium bromate can also be used in the same way (indirect iodometry). Therefore, it is considered that starch can be used as an indicator. If each type of indicator in this problem can only be used once, then under appropriate analytical conditions, potassium bromate should also be able to oxidize methyl orange. This has not been done before, so perhaps this method is not very commonly used. If the problem states that each indicator can only be used once, then it is a sequential selection of CBDA.