Butan-2-ol and 2-methylpropan-2-ol can be distinguished by

Butan-2-ol, a secondary alcohol, is oxidised and turns orange $\mathrm{Cr}{}_2\mathrm{O}{}_7{}^{2-}$ to green $\mathrm{Cr}{}^{3+}$; the tertiary alcohol is not oxidised under these conditions. Both alcohols release hydrogen with sodium, and neither responds to neutral $\mathrm{FeCl}{}_3$ or Tollens reagent.