40 g NaOH, 106 g Na₂CO₃ and 84 g NaHCO₃, are dissolved in water and the solution is made 1 litre. 20 mL of this stock solution is titrated with 1N HCl, hence which of the following statements are correct.

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The tire reading of HCl will be 80mL, if methyl orange is used as indicator from the very beginning

The titre reading of HCl will be 40mL if methyl orange is used indicator after 1^st end point

The titre reading of HCl will be 40 mL, if phenolphthalein is used indicator from the very beginning

The titre reading of HCl will be 60mL if phenolphthalein is used indicator from the very beginning

answer is A, D.

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Detailed Solution

When phenolphthalein is used from the beginning then,
$Milliequivalents of Acid = Milliequivalents of (NaOH + \frac{1}{2} {Na}_{2} {CO}_{3}) 1 \times 1 \times V (in mL) = (1 \times 20 \times 1) + \frac{(1 \times 20 \times 2)}{2} V (in mL) = 40 mL$
Similarly, after I^st end point, using methyl orange: