Answer:
The unknown acid is citric acid.
Explanation:
Based on the reactions:
Citric acid: H3C6H5O7(aq) + 3NaOH (aq) → 3H2O (l) + Na2C6H5O7 (aq)
Tartaric acid: H2C4H4O6 (aq) + 2NaOH (aq) → 2H2O (l) + Na2C4H4O6 (aq)
0.956g of sample if tartaric acid requires:
0.956g × (1mol / 150,087 g) = 0.006370 moles of tartaric acid. As 1 mole reacts with 2 moles of NaOH:
0.006370 moles of tartaric acid × (2 mol NaOH / 1 moles tartaric acid) = 0.0127 moles of NaOH. As the concentration of the NaOH is 0.513M:
0.0127 moles of NaOH × (1L / 0.513mol) = 0.0248L ≡ <em>24.8mL</em>
Now, 0.956g of citric acid requires:
0.956g × (1mol / 192,124g) = 0.004976 moles of citric acid. As 1 mole reacts with 3 moles of NaOH:
0.004976 moles of citric acid × (3 mol NaOH / 1 moles tartaric acid) = 0.0149 moles of NaOH. As the concentration of the NaOH is 0.513M:
0.0149 moles of NaOH × (1L / 0.513mol) = 0.0291L ≡ <em>29.1mL</em>
As the titration requires 29.1mL of the base, the unknown acid is <em>citric acid.</em>
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