Chapter 6, Problem 59E

Chromium(VI) forms two different oxyanions, the orangedichromate ion ${\text{(Cr}}_{\text{2}}{\text{O}}_{\text{7}}{}^{\text{2–}}\text{)}$ , and the yellow chromate ion ${\text{(CrO}}_{\text{4}}{}^{\text{2–}}\text{)}$ . (See the photos below.) The equilibriumreaction between the two ions is
${\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}{}^{\text{2–}}\text{(}aq{\text{)+H}}_{\text{2}}\text{O(}l\text{)}\rightleftharpoons 2{\text{CrO}}_{\text{4}}{\text{2}}^{\text{–}}\text{(}aq{\text{)+2H}}^{\text{+}}\text{(}aq\text{)}$
Explain why orange dichromate solutions turn yellowwhen sodium hydroxide is added.