A specific polyhydric alcohol with the molecular formula is reacted completely with an excess of ace — Alcohols Phenols and Ethers Chemistry Question
Question
A specific polyhydric alcohol with the molecular formula $C_4H_{10}O_3$ is reacted completely with an excess of acetyl chloride. The resulting fully acetylated compound is found to have a molecular mass of $190 \text{ g/mol}$. Based on this mass increase, how many hydroxyl ($-OH$) groups were present in the original alcohol?
💡 Solution & Explanation
The molecular mass of the original compound $C_4H_{10}O_3$ is $(4 \times 12) + (10 \times 1) + (3 \times 16) = 106 \text{ g/mol}$. The mass of the acetylated product is $190 \text{ g/mol}$. The total mass increase is $190 - 106 = 84 \text{ g/mol}$. Each acetylation reaction replaces an $H$ atom (mass 1) with an acetyl group ($-COCH_3$, mass 43), yielding a net mass increase of $42 \text{ g/mol}$ per hydroxyl group. Therefore, $84 / 42 = 2$ hydroxyl groups.