Tartrate is potassium sodium 2,3-dihydroxybutanedioate. Write a partial structural formula.
$Na^+$ $^-OOC(CHOH)_2COO^-$ $K^+$ . We subsequently call this substance $cpx$
What is the formula of a of copper(II) sulfate solution ?
$Cu^{2+}$ $+$ $SO_4^{2-}$.
Adding tartrate, forms a dark blue chelate (the Fehling reagent) which we shall write $[Cu(cpx)_2]^{2+}$. Simplified equation?
$Cu^{2+}$ $+$ $2cpx$ $\rightarrow$ $ [Cu(cpx)_2]^{2+}$.
An aldehyde is converted into carboxylic acid by oxidation. Oxidation equation ?
$RCHO$ $-$ $2e^-$ $+$ $H_2O$ $\rightarrow$ $RCOOH$ $+$ $2H^+$
This reaction proceeds under basic conditions here and in addition the carboxylic acid is converted to carboxylate ion. Oxidation equation ?
$RCHO$ $-$ $2e^-$ $+$ $3OH^-$ $\rightarrow$ $RCOO^-$ $+$ $2H_2O$
The complexed $Cu^{2+}$ ion is reduced to copper(I) oxide (brick red precipitate) by releasing the complexing agent. Reduction equation in basic medium?
$2Cu(cpx)_2^{2+}$ $+$ $2e^-$ $+$ $2OH^-$ $\rightarrow$ $Cu_2O$ $ +$ $H_2O$ $ +$ $2cpx$
Establish the complete redox system!
$RCHO$ $-$ $2e^-$ $+ $ $3OH^-$ $\rightarrow$ $RCOO^-$ $ +$ $2H_2O$
$2Cu(cpx)_2^{2+}$ $+$ $2e^-$ $+$ $2OH^-$ $\rightarrow$ $RCOO^-$ $+Cu_2O$ $ +$ $H_2O$ $ +$ $2cpx$
$2Cu(cpx)_2^{2+}$ $+$ $RCHO$ $+$ $5OH^-$ $\rightarrow$ $Cu_2O$ $+$ $2cpx$ $+$ $RCOO^-$ $ +$ $3H_2O$