Explain why (a) acid strength increases as the oxidation...

Explain why (a) acid strength increases as the oxidation number of the central nonmetal atom increases. (b) nitrogen dioxide is paramagnetic. (c) the oxidizing strength of an oxoanion is inversely related to $\mathrm{pH}$. (d) sugar turns black when treated with concentrated sulfuric acid.

Explain why
(a) acid strength increases as the oxidation number of the central nonmetal atom increases.
(b) nitrogen dioxide is paramagnetic.
(c) the oxidizing strength of an oxoanion is inversely related to $\mathrm{pH}$.
(d) sugar turns black when treated with concentrated sulfuric acid.

Key Concepts

Oxidation State and Acid Strength

The oxidation number of the central atom is a measure of its electron deficiency, and as it increases, the atom becomes more electronegative. This increased electronegativity enhances its ability to stabilize the negative charge on the conjugate base after deprotonation by withdrawing electrons. Consequently, acids with higher oxidation states are stronger because they more readily release protons.

Molecular Orbital Theory and Paramagnetism

Paramagnetism in molecules arises from the presence of one or more unpaired electrons in molecular orbitals. In cases such as certain nitrogen oxides, an odd number of electrons results in at least one unpaired electron, making the molecule attracted to magnetic fields. This phenomenon is best explained using molecular orbital theory which accounts for electron distribution in bonding and antibonding orbitals.

pH Dependence in Redox Chemistry

The oxidizing strength of oxoanions often varies with pH because the redox potential is influenced by the concentration of hydrogen ions. In acidic environments, additional protons can drive redox reactions forward by stabilizing the reduced form of the species. In contrast, in alkaline conditions the lack of these protons reduces the oxidizing capability, establishing an inverse relationship between pH and oxidizing strength.

Dehydration and Carbonization Reactions

When sugar is treated with concentrated sulfuric acid, the acid acts as a strong dehydrating agent by removing water molecules from the sugar. This dehydration process leads to the breakdown of the sugar structure and the formation of elemental carbon, which appears black due to its charred, amorphous state, evidencing a transformation rather than a combustion reaction.

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