Which of the following statements is true about sodium glycinate?

• A. It is insoluble in water due to its ionic nature.
• B. It contains a carboxylic acid group that remains protonated in basic solution.
• C. It is the sodium salt of glycine and acts as a weak base in aqueous solution.
• D. It is a strong acid and completely dissociates in water.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the structure of sodium glycinate. Sodium glycinate is the sodium salt of glycine, which means glycine has lost a proton (H⁺) from its carboxylic acid group, forming a carboxylate ion (–COO⁻), and this negative charge is balanced by a sodium ion (Na⁺).
2. Step 2: Analyze the solubility in water. Since sodium glycinate is an ionic compound composed of Na⁺ and the glycinate ion (the conjugate base of glycine), it is generally soluble in water due to the strong ion-dipole interactions with water molecules, so the statement about it being insoluble is incorrect.
3. Step 3: Consider the behavior of the carboxylic acid group in basic solution. In sodium glycinate, the carboxylic acid group is already deprotonated (as –COO⁻), so it does not remain protonated in basic solution; instead, it stays as the carboxylate ion.
4. Step 4: Evaluate the acid-base properties. Sodium glycinate acts as a weak base in aqueous solution because the glycinate ion can accept a proton (H⁺) to reform glycine, making it a conjugate base of a weak acid (glycine). It is not a strong acid and does not completely dissociate in water.
5. Step 5: Summarize the correct statement. The correct description is that sodium glycinate is the sodium salt of glycine and acts as a weak base in aqueous solution, consistent with its chemical nature and behavior in water.