$9.$ Explain why no precipitate formed in K$2$Cr$2$O$7$ in Step $7$ of Part IV$,$ while some did form in Step $9.$

Part IV: Equilibrium Involving Chromate and Dichromate Ions

$2Cr{O}_4^{2-}(aq)+2H^{+}(aq)C{r}_2{O}_7^2(aq)+H_{2}O(l)$

Other Observations:

$Ba(N{O}_3{)}_2(aq)-$ Clear golourless solution