Question

Which chemical group is most likely to be responsible for an organic molecule behaving as a base (see Concept 3.3)

1. hydroxyl

2. carbonyl

3. amino

4. phosphate

Short answer

1. The option “hydroxyl” isfalse.

2. The option “carboxyl” isfalse.

3. The option “amino” is true.

4. The option “phosphate” is false.

Step-by-step solution

Organic molecules

Certain molecules are primarily made of carbon atoms. The carbon atoms in these molecules are bonded to other carbon atoms or other elements. These molecules are called organic molecules.

Organic molecules are classified as acids and bases. Acid is a substance that donates a proton (H+) and thereby increases the hydrogen ion concentration of a solution. On the contrary, a base is a substance that accepts protons and thereby decreases the hydrogen ion concentration of a solution.

Explanation of option (A)

The hydroxyl group is a functional group that consists of one oxygen atom covalently bound to one hydrogen atom and has the chemical formula -OH. Thehydroxyl (-OH) group donates its hydrogen in a solution.

Thus, an organic molecule containing a hydroxyl group would behave as an acid. It would increase a solution’s hydrogen ion concentration.

Therefore, the given option is false.

Explanation of option (B)

A carbonyl group is a functional group that consists of one carbon atom that is double-bonded to an oxygen atom and has the chemical formula C=O.The carbonyl group has hydrogen on its alpha carbon that can donate a proton (H+) and is considered acidic.

Thus, an organic molecule containing the carbonyl group would behave as an acid. The carbonyl group donates a proton and does not accept a proton.

Therefore, the given option is false.

Explanation of option (C)

The amino group is a functional group that consists of a nitrogen atom and two hydrogen atoms and has the chemical formula NH2.The amino group accepts protons to form ammonium ions (NH3+), which means it removes protons from the solutions and acts as a base.

Thus, an organic molecule containing an amino group would behave as a base as it accepts hydrogen ions. A molecule that accepts proton is a base.

Therefore, the given option is true.

Explanation of option (D)

A phosphate group is a functional group that consists of a phosphorus atom and four oxygen atoms and has the chemical formula –PO4.Phosphate groups release hydrogen ions into solutions and are thereby considered acidic.

Thus, an organic molecule containing a phosphate group would behave as acid as it donates hydrogen ions. A molecule that accepts hydrogen ions is a base.

Therefore, the given option is false.