Question

The most acidic hydrogen atoms are present in:
A.ethane
B.ethene
C.ethyne
D.Benzene

Answer 1

We know that the acidic property of a compound can be calculated by the presence of its s-character. Therefore, we must understand that the s-character is the contribution of a sigma type of bond in a process of formation of orbitals called hybridization. Hence, different hybrid orbitals have different percentage of s-character such as: $sp^3$ have 25% s-character and 75% p-character, $sp^2$ have 33% s-character and 66% p-character whereas $sp$ has 50% s-character and 50% p-character. As mentioned above, the more s-character present in a bond, the shorter and stronger is the bond with the most acidic properties. So, a $sp - sp$ bond is the strongest bond and $sp^3$ is the weakest bond.

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Complete step by step solution :

We can understand that ethyne has the highest percentage of s-character. As the s-character increases, the electronegativity of carbon increases. Hence, carbon attracts strongly bond pair electrons of $C - H$ bond towards itself, and $H +$ is quickly set free. Therefore, ethyne acts as an acid. And in the given problem ethyne possesses the most acidic hydrogen atom.

Hybridisation of ${C_2H_2}$

Ethyne is built from hydrogen and carbon atoms. These carbon atoms do not have enough unpaired electrons to form a bond (1 to the hydrogen atom and three to the other carbon atom), so it needs to promote one of the $2{s^2}$ pair into the empty $pz$ orbitals during the process.

And, hence option C is the correct answer.

Note:**** We must understand that the diamond is the hardest substance known on earth due to its tetrahedron structure. In graphite due to the presence of delocalized electrons, it becomes a good conductor of electricity.