carboxylic acid (carboxyl; carboxyl group)

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A carboxylic acid is an organic molecule with a -(C=O)-OH group. The group is also written as -COOH and is called a carboxyl group. The hydrogen on the -COOH group ionizes in water; carboxylic acids are weak acids. The simplest carboxylic acids are formic acid (H-COOH) and acetic acid (CH3-COOH).