Acid–base equivalent concept: For the reaction Na2CO3 + HCl → NaHCO3 + NaCl, what is the equivalent weight of Na2CO3 in this reaction?

Introduction / Context:
Sodium carbonate is a diprotic base (carbonate ion CO3^2− can accept two protons). Its equivalent weight depends on the specific reaction step: full neutralization to carbonic acid or partial neutralization to bicarbonate. Understanding n-factor for the actual stoichiometry is key in titration and industry-scale neutralization calculations.

Given Data / Assumptions:

• Reaction: Na2CO3 + HCl → NaHCO3 + NaCl.
• Only one mole of HCl reacts per mole of Na2CO3 (partial neutralization).
• Molar mass of Na2CO3 = 106 g/mol.

Concept / Approach:
Equivalent weight = molar mass / n, where n is the number of equivalents reacted per mole in the given reaction. Here, carbonate is converted to bicarbonate, consuming one mole of H+ per mole of Na2CO3 (n = 1). If the reaction proceeded to Na2CO3 + 2 HCl → H2CO3 + 2 NaCl, then n would be 2, but that is not the reaction specified in the stem.

Step-by-Step Solution:

Verification / Alternative check:
Charge balance: CO3^2− + H+ → HCO3^− consumes one equivalent of acid per mole of carbonate, confirming n = 1 for this stepwise neutralization.

Why Other Options Are Wrong:

• Values like 53 or 10.6 correspond to dividing by 2 or by 10, not applicable here.
• 5.3 and 26.5 are off by orders of magnitude.

Common Pitfalls:
Using the full-neutralization n = 2 when the reaction explicitly shows only one proton transfer; always match n to the actual reaction stoichiometry.

Final Answer:
106