A mixture of two compounds, I and II, is separated by column chromatography. The extent of adsorptio — Qualitative and Quantitative Analysis Chemistry Question
Question
A mixture of two compounds, I and II, is separated by column chromatography. The extent of adsorption of I onto the stationary phase is strictly greater than the adsorption of II. If $R_{f(I)}$ and $R_{f(II)}$ represent their respective retardation factors, and $v_I$ and $v_{II}$ represent their respective vertical elution velocities down the column, consider the following four mathematical inequalities: 1. $R_{f(I)} > R_{f(II)}$ 2. $R_{f(I)} < R_{f(II)}$ 3. $v_I > v_{II}$ 4. $v_I < v_{II}$. How many of these four inequalities are factually correct?
💡 Solution & Explanation
Since compound I is adsorbed more strongly than II, it interacts more with the stationary phase and is retained longer. Therefore, it travels slower down the column ($v_I < v_{II}$) and covers less distance relative to the solvent front, resulting in a lower $R_f$ value ($R_{f(I)} < R_{f(II)}$). Thus, exactly 2 inequalities (numbers 2 and 4) are correct.