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A strong acid is a substance that completely ionizes or dissociates into its ions when dissolved in water. This means that all the molecules of the acid will break up into their constituent ions in the solution, leading to a high concentration of H+ ions.

Given the solution is 0.500 M HCl, we know that the concentration of the acid is 0.500 moles per liter. Since HCl is a strong acid, it will completely dissociate into its ions when dissolved in water: \[ \mathrm{HCl \rightarrow H^+ + Cl^-} \] In this case, the concentration of H+ ions will be equal to the concentration of HCl. Therefore, \( [\mathrm{H}^{+}] = 0.500 \,\mathrm{M} \).

Among the given acids, HF, HCl, HBr, and HI, we need to determine which are strong acids. The general rule of thumb is that the strength of a binary acid (an acid containing hydrogen and a halogen) increases as we move from left to right and top to bottom in the periodic table. Based on this rule: 1. HF - Hydrogen fluoride is a weak acid because it does not dissociate completely in water. The F- ion forms a strong bond with the H+ ions, making it difficult for the acid to release these ions. 2. HCl - Hydrogen chloride is a strong acid because it dissociates completely in water, releasing a high concentration of H+ ions. 3. HBr - Hydrogen bromide is a strong acid because it also dissociates completely in water, releasing a high concentration of H+ ions. 4. HI - Hydrogen iodide is a strong acid because it dissociates completely in water, releasing a high concentration of H+ ions as well. In conclusion, HCl, HBr, and HI are strong acids, while HF is a weak acid.