Chemistry $1120$ Pre$-$lab Exercise

Experiment $1$

Exercise Number $267$

The concentration of a solution of iron $($II$)$ sulfate, $FeS{O}_4,$ can be determined through a redox titration. A $50\mathrm{.}00mL$ sample of the solution is diluted to $250\mathrm{.}00mL$ with deionized water. A $25\mathrm{.}00mL$ aliquot is then pipetted into an Erlenmeyer where it is acidified with sulfuric acid and then titrated with a standard solution of potassium dichromate, $K_{2}C{r}_2{O}_7.$ The reactants and products of the reaction $($unbalanced$)$ are:

Question $($a$)$ Write the balanced half$-$reactions $($state whether oxidation or reduction halfreaction$),$ and the overall balanced redox equation for the reaction between dichromate ion and iron$($II$)$ ion in acidic solution.

Reduction half

$6e^{-}+14H^{+}+C{r}_2{O}_7^{2-}2C{r}^{3+}+7H_{2}O,6[C{r}^{3+}F{e}^{2+}F{e}^{3+}F{e}^{3+}+e^{-}]$

$6C+14H^{+}+C{r}_2{O}_7^{-}+6F{e}^{2+}$Longrightarrow$2C{r}^{3+}+7H_{2}O+6F{e}^{3t}+6t-$

$14H^{+}+CrO{n}^{2-}(aq)+6F{e}^{2+}(aq)2C{r}^{3+}(a{q}_1)+7H_{2}O+6F{e}^{3+}(aq)$

Question $($b$)$ From the data given above and the following data, calculate the molarity of the original iron sulfate solution. Show your reasoning$/$calculations$.$

DATA:

Volume of original sample $=$

Volume of diluted solution $=$

Volume of diluted sample titrated $=,25\mathrm{.}00mL$

Standard dichromate solution: $[C{r}_2{O}_7^{2-}]=0\mathrm{.}04310M$

Initial burette reading $=$

Final burette reading $=$

$50\mathrm{.}00mL$

$250\mathrm{.}00mL$

$25\mathrm{.}00mL$

$0\mathrm{.}04310M$

$0\mathrm{.}05mL$

$22\mathrm{.}88mL$