Problem 25 - Chemistry: The Central Science

Question

(a) Which of the following is the stronger BrønstedLowry acid, \(\mathrm{HBrO}\) or \(\mathrm{HBr}\) ? (b) Which is the stronger Brønsted-Lowry base, \(\mathrm{F}^{-}\) or \(\mathrm{Cl}^{-} ?\) Briefly explain your choices.

Step-by-Step Solution

Answer

The stronger Brønsted-Lowry acid is \(\mathrm{HBr}\), as its conjugate base, \(\mathrm{Br^-}\), is less stable than the conjugate base of \(\mathrm{HBrO}\), \(\mathrm{BrO^-}\). The stronger Brønsted-Lowry base is \(\mathrm{F^-}\), as its conjugate acid, \(\mathrm{HF}\), is less stable than the conjugate acid of \(\mathrm{Cl^-}\), \(\mathrm{HCl}\). This is due to the high electronegativity of fluorine making it less likely to donate a proton.

Step 1: A Brønsted-Lowry acid is a substance that can donate a proton (H+) to another substance. The strength of the acid depends on its ability to donate a proton. #Step 2: Analyze the stability of the conjugate base#

The stronger the acid, the more stable its conjugate base (the species formed after the acid loses a proton) is. We will compare the stability of the conjugate bases of \(\mathrm{HBrO}\) and \(\mathrm{HBr}\) to determine which acid is stronger. #Step 3: Compare conjugate bases of HBrO and HBr#

Step 2: The conjugate base of \(\mathrm{HBrO}\) is \(\mathrm{BrO^-}\) and the conjugate base of \(\mathrm{HBr}\) is \(\mathrm{Br^-}\). The \(\mathrm{BrO^-}\) ion has a stronger electron withdrawing group (oxygen) compared to the \(\mathrm{Br^-}\) ion. This makes \(\mathrm{BrO^-}\) more stable and thus, \(\mathrm{HBrO}\) a weaker acid than \(\mathrm{HBr}\). So, the stronger Brønsted-Lowry acid is \(\mathrm{HBr}\). #b) Comparing base strength: F- vs Cl-# #Step 1: Understand Brønsted-Lowry base definition#

A Brønsted-Lowry base is a substance that can accept a proton (H+) from another substance. The strength of the base depends on its ability to accept a proton. #Step 2: Analyze the stability of the conjugate acids#

Step 3: The stronger the base, the less stable its conjugate acid (the species formed after the base gains a proton) is. We will compare the stability of the conjugate acids of \(\mathrm{F^-}\) and \(\mathrm{Cl^-}\) to determine which base is stronger. #Step 3: Compare conjugate acids of F- and Cl-#

The conjugate acid of \(\mathrm{F^-}\) is \(\mathrm{HF}\) and the conjugate acid of \(\mathrm{Cl^-}\) is \(\mathrm{HCl}\). The \(\mathrm{HF}\) molecule is a weaker acid compared to \(\mathrm{HCl}\) due to the high electronegativity of fluorine, making it less likely to donate a proton. Hence, its conjugate base \(\mathrm{F^-}\) is a stronger base compared to \(\mathrm{Cl^-}\). So, the stronger Brønsted-Lowry base is \(\mathrm{F^-}\).