What is produced when a carboxylic acid reacts with magnesium metal?

• A. A salt (carboxylate) and hydrogen gas
• B. Water and carbon dioxide
• C. An alcohol and carbon dioxide
• D. A metal oxide and hydrogen

Answer: (A)

When a carboxylic acid meets a reactive metal like magnesium, an acid–metal reaction occurs. The acid donates a proton, while magnesium is oxidized and the hydrogen is released as diatomic hydrogen gas. At the same time, the carboxylate anion formed from the acid combines with Mg2+ to make a metal carboxylate salt. Since two carboxylate ions balance the +2 charge of magnesium, the typical product is a magnesium carboxylate salt and hydrogen gas, expressed as (RCOO)2Mg + H2. The other possibilities would require different reactants or reaction pathways, not simply a carboxylic acid with magnesium.