Question

How would the net charge on an amino acid affect its Rf value?

Answer 1

Amino acid is polar. The stationary phase of TLC plate is also polar. Rf value depends on the relative strength of attractive forces between (1) amino acid and stationary phase and (2) amino acid and mobile phase.

Any factor that increases the polarity of amino acid, will increase the strength of the attractive forces between amino acid and stationary phase and will decrease the Rf value.

When an amino acid has a net charge, then it is more polar than amino acid with zero net charge.