23.98 mL of 0.100 M HCl. An additional 0.700 mL of 0.100 M HCl is required to re

Question

23.98 mL of 0.100 M HCl. An additional 0.700 mL of 0.100 M HCl is required to reach the methyl orange endpoint. What is the percentage of Na_2Co_3 by mass in the sample? Carbonic acid (H_2CO_3) is a weak diprotic acid with K_a1 = 4.43 times 10^-7 and K_a2 = 4.73 times 10^-11. When sodium bicarbonate (NaHCo_3) is titrated with hydrochloric acid (HCl), it acts as a weak base according to the equation NaHCo_3(aq) + HCl(aq) right arrow H_2Co_3(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 p^K a values. Suitable indicators for use in titrating carbonic acid or carbonate solutions are methyl orange and phenolphthalein. What volume of 0.150 M HCl is required for the complete neutralization of 1.70 g of NaHCo_3 (sodium bicarbonate)? Express your answer to three significant figures and include the appropriate units. What volume of 0.170 M HCl is required for the complete neutralization of 1.70 g of Na_2Co_3 (sodium carbonate)? Express your answer to three significant figures and include the appropriate units. A sample of NaOH (sodium hydroxide) contains a small amount of Na_2Co_3 (sodium carbonate). For titration to the phenolphthalein endpoint, 0.200 g of this sample requires

Explanation / Answer

2NaHCO3 + 2HCl ----> NaCl + H2O + 2CO2

no of mol of NaHCO3 = 1.7/84.007 = 0.02 mol

No of mol of HCl required = 0.02 mol

volume of HCl required = 0.02/0.15 = 0.133 L

   = 133 ml

Na2CO3 + 2HCl ----> 2NaCl+ H2O + CO2

no of mol of Na2CO3 = 1.7/105.9888 = 0.016 mol

No of mol of HCl required = 0.016*2 = 0.032 mol

volume of HCl required = 0.032/0.17 = 0.188 L

   = 188 ml

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