\(R_f\) value

To analyse paper chromatography results, we determine the retention factor, Rf, where

R_f=\frac{distance\: travelled\: by\: substance\, from\: origin}{distance\: travelled\: by\: solvent\: front\: from \: origin}


For example (with reference to the above diagram),

R_{f,orange\: substance}=\frac{a}{c}

R_{f,yellow\: substance}=\frac{b}{c}


    1. Based on the diagram below, what are the Rf values for samples x and y?
    2. With reference to the calculated Rf values, describe the likely solubilities of samples x and y in the mobile and/or stationary phases.
    3. What could be the composition of sample z?

    1. Rf,x = 11.2/13.4 = 0.84; Rf,y = 3.1/13.4 = 0.23
    2. Since Rf,x Rf,y , sample x is relatively more soluble in the mobile phase than sample y (or sample y is relatively more soluble in the stationary phase than sample x), assuming partitioning is the main mechanism of separation.
    3. Sample z could be a mixture of x and y.


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