题目内容

Which of the following substances cannot be used as a reference substance?

A. Na2B4O7·10H2O
B. Na2CO3
C. KOH
D. H2C2O4·2H2O

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If the NaOH solution is not used for a long time, the concentration will change, so it should be re-calibrated before use.

Only results with high accuracy and high precision at the same time are reliable.

1H NMR spectrum of a compound (C5H10O) shows only two single peaks. The structural formula of the compound should be ( ).

A. CH3CH2CH2COCH3
B. (CH3)2CHCOCH3
C. (CH3)3CCHO
D. CH3CH2COCH2CH3

Among -OCH3, -CCH3, and -NCH3, -NCH3 displays the largest proton chemical shift in NMR spectrum.