Question

{"given":"Four different mixtures of compounds in specific mole ratios are provided. We need to identify which combinations can form buffer solutions. A buffer requires both a weak acid or weak base and its conjugate species to be present simultaneously in significant amounts.","key_observation":"A buffer solution contains a weak acid-base conjugate pair in appreciable concentrations. When mixing compounds, we must consider the chemical reactions that occur and whether the final mixture contains both components of a conjugate acid-base pair. The stoichiometry of the reaction determines the final composition.","option_analysis":[{"label":"(A)","text":"$\\text{NH}_4\\text{Cl}$ and $\\text{NaOH}$ in $2:1$ mole ratio","verdict":"correct","explanation":"The reaction is $\\text{NH}_4\\text{Cl} + \\text{NaOH} \\rightarrow \\text{NH}_4\\text{OH} + \\text{NaCl}$. With 2 mol $\\text{NH}_4\\text{Cl}$ and 1 mol $\\text{NaOH}$, we get 1 mol $\\text{NH}_4\\text{OH}$ (weak base) and 1 mol unreacted $\\text{NH}_4\\text{Cl}$ (conjugate acid). This forms a buffer system."},{"label":"(B)","text":"$\\text{CH}_3\\text{COONa}$ and $\\text{HCl}$ in $1:1$ mole ratio","verdict":"incorrect","explanation":"The reaction is $\\text{CH}_3\\text{COONa} + \\text{HCl} \\rightarrow \\text{CH}_3\\text{COOH} + \\text{NaCl}$. With equal moles, all acetate is converted to acetic acid with no conjugate base remaining. Only weak acid is present, not a buffer."},{"label":"(C)","text":"$\\text{CH}_3\\text{COONa}$ and $\\text{HCl}$ in $2:1$ mole ratio","verdict":"correct","explanation":"With 2 mol $\\text{CH}_3\\text{COONa}$ and 1 mol $\\text{HCl}$, we get 1 mol $\\text{CH}_3\\text{COOH}$ (weak acid) and 1 mol unreacted $\\text{CH}_3\\text{COONa}$ (conjugate base). This creates an acetic acid-acetate buffer system."},{"label":"(D)","text":"$\\text{CH}_3\\text{COONa}$ and $\\text{HCl}$ in $1:2$ mole ratio","verdict":"incorrect","explanation":"With 1 mol $\\text{CH}_3\\text{COONa}$ and 2 mol $\\text{HCl}$, we get 1 mol $\\text{CH}_3\\text{COOH}$ and 1 mol excess $\\text{HCl}$ (strong acid). The presence of strong acid prevents buffer action, making this not a buffer solution."}],"answer":"(A) and (C)","formula_steps":[]}