I have read the test for chloride ions (chromyl chloride test). The reaction is: $$\ce{K2Cr2O7 + 4NaCl + 6H2SO4 -> 2CrO2Cl2 + 2KHSO4 + 4NaHSO4 +3H2O}$$ My doubt here is if chlorine gas is evolved in a side reaction. Is it evolved in detectable amount? The side reaction is: $$\ce{6Cl- + (Cr2O7)^{2-} + 14 H+ → 3Cl2 + 2Cr^{3+} + 7H2O}$$ Can someone please confirm this?
Answer
If you write the ionic equation, it seems that chlorine gas will produce. However, we see their half equation and standard potential.
$$\ce{ Cr_2O_7 ^2- + 14H^+ + 6e^- -> 2Cr^3+ + 7H_20}$$ Standard potential = +1.33V
$$\ce{ 6Cl^- -> 3Cl_2 + 6e^-}$$ Standard potential = -1.36V
Thus, the standard potential cell for this ionic you say is equal to $$\ce{+1.33V + (-1.36V) = -0.03V}$$ Because the standard potential cell is negative, so, it is call not energetically feasible or this reaction will not happen.
P.S The explanation only work under standard conditions.
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