How much is needed to neutralize?

Question

1) How many mL of 0.715 M HCl is required to neutralize 1.25 grams of sodium carbonate? (producing carbonic acid)

the sample?

2) How many grams of oxalic acid (H₂C₂O₄) are required for a titration of 10.0 mL of 0.135 M NaOH?

Answer 1

2HCl + Na₂CO₃ ==> H₂CO₃ + 2NaCl ... balanced equation

1). 1.25 g Na2CO3 x 1 mol Na2CO3 / 106 g = 0.01179 mols Na2CO3

0.01179 mols Na2CO3 x 2 mol HCl / mol Na2CO3 = 0.02358 mols HCl

mls HCl = 0.02358 mols HCl x 1 L / 0.715 mols = 0.0330 L = 33.0 mls (3 sig. figs.)

2). molar mass H₂C₂O₄ = 90.03 g/mol (it is a dicarboxylic acid HOOC-COOH)

HOOC-COOH + 2NaOH ==> NaOOC-COONa + 2H₂O ... balanced equation

mols NaOH present = 10.0 mls x 1 L / 1000 ml x 0.135 mol/L = 0.00135 mols NaOH

mols H₂C₂O₄ needed = 0.00135 mols NaOH x 1 mol H₂C₂O₄ / 2 mol NaOH = 0.000675 mol H₂C₂O₄

grams H₂C₂O₄ = 0.000675 mols H₂C₂O₄ x 90.03 g / mol = 0.0608 g H₂C₂O₄ (3 sig. figs.)