Based on their compositions and structures and on conjugate acid–base relationships, select the stronger base in each of the following pairs: (a) BrO- or ClO- (c) HPO42- or H2PO4-

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Identify the conjugate acid for each base in the pair. For BrO- and ClO-, the conjugate acids are HBrO and HClO, respectively. For HPO4^2- and H2PO4^-, the conjugate acids are H2PO4^- and H3PO4, respectively.

Recall that the strength of a base is inversely related to the strength of its conjugate acid. A weaker conjugate acid corresponds to a stronger base.

Compare the acid dissociation constants (Ka) of the conjugate acids. The acid with the lower Ka value is the weaker acid, and thus its conjugate base is stronger.

For BrO- and ClO-, compare the Ka values of HBrO and HClO. The one with the lower Ka value will have the stronger conjugate base.

For HPO4^2- and H2PO4^-, compare the Ka values of H2PO4^- and H3PO4. The one with the lower Ka value will have the stronger conjugate base.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Conjugate Acid-Base Pairs

In acid-base chemistry, a conjugate acid-base pair consists of two species that differ by the presence or absence of a proton (H+). The strength of a base is often determined by its ability to accept protons, while the strength of an acid is determined by its ability to donate protons. Understanding these relationships helps in predicting which species will act as a stronger base in a given pair.

Electronegativity and Stability

Electronegativity refers to the tendency of an atom to attract electrons in a bond. In the context of conjugate bases, a more electronegative atom can stabilize the negative charge better, making the conjugate base weaker. Therefore, when comparing bases like BrO- and ClO-, the electronegativity of the central atom plays a crucial role in determining which base is stronger.

Acid-Base Strength Trends

The strength of acids and bases can be predicted based on their position in the periodic table and their molecular structure. Generally, as you move from left to right across a period, acid strength increases, while base strength decreases. Additionally, the presence of multiple acidic protons, as seen in HPO4^2- and H2PO4-, influences the overall basicity, with the more deprotonated species typically being the stronger base.

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Strength of Conjugate Acids and Bases

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