A sample of material contains for its active components NaOH, Na2CO3, NaHCO3 or compatible mixtures of these. Two samples, each weighing 1.000 g, are dissolved in H2O. To one sample phenolphthalein is added and the solution is titrated cold with 1.038 M HCl, of which, 17.96 mL is required. The other sample is titrated cold, with methyl orange as indicator, and 21.17 mL of the same acid is required. What alkalis are present, and what is the percentage of each in the original sample?

What is the % Na2CO3? (Correct: 13.37)

What is the % NaHCO3? (Incorrect: 16.84)

What is the % NaOH? (Incorrect: 69.79)

What is the % inert material?

NaHCO3(aq)+HCl(aq)→H2CO3(aq)+NaCl(aq)

Suitable indicators are those that change color within the pH range for the equivalence point of a specific titration. The expected pH at the equivalence point can be calculated using pKa values. Suitable indicators for use in titrating carbonic acid or carbonate solutions are methyl orange and phenolphthalein.

Part A

What volume of 0.130 M HCl is required for the complete neutralization of 2.00 g of NaHCO3(sodium bicarbonate)?

What volume of 0.170 M HCl is required for the complete neutralization of 1.50 g of Na2CO3(sodium carbonate)?

A sample of NaOH (sodium hydroxide) contains a small amount of Na2CO3 (sodium carbonate). For titration to the phenolphthalein endpoint, 0.190 g of this sample requires 23.98 mL of 0.100 MHCl. An additional 0.700 mL of 0.100 M HCl is required to reach the methyl orange endpoint. What is the percentage of Na2CO3 by mass in the sample?