JEE Main levelOne or more correct optionsDifficulty 2 of 3eq136
Choose the correct statements about indicator choice in acid-base titrations (phenolphthalein: pH range about 8.3-10; methyl orange: about 3.1-4.4).
APhenolphthalein is suitable for titrating acetic acid against NaOH
BMethyl orange is suitable for titrating aqueous ammonia against HCl
CIn titrating NaX2COX3 with HCl, the volume from start to the phenolphthalein end point equals the further volume from there to the methyl orange end point
DIn titrating NaHCOX3 with HCl, the phenolphthalein end point volume is half of the methyl orange volume
Answer: A, B, C
Weak acid/strong base gives a basic equivalence point, so phenolphthalein fits; strong acid/weak base gives an acidic one, so methyl orange fits. For carbonate, COX3X2−HCOX3X− and HCOX3X−HX2COX3 each need one mole of HCl, so the two volumes are equal. NaHCOX3 alone is already past the phenolphthalein stage (pH about 8.3), so its phenolphthalein volume is essentially zero, not half.