Question

To determine the % of
fe in the given ferrous alloy by kmno4 method.

Answer 1

Percentage composition

Answer 2

"KMnO4 is the titrant and it is burette liquid.

        $Fe^{2+}$ readily oxidized by oxygen in the air, before titration ensure that all iron is in the form of $Fe^{2+}$. It is possible to reduce iron 3+ using Jones redactor.

                                       $2FeCl_3 + SnCl_2 \rightarrow 2FeCl_2 + SnCl_4$

       To be sure reaction was complete small excess of the $SnCl_2$ is added, and then solution is treated with mercury(II) chloride:

                                     $SnCl_2 + 2HgCl_2 \rightarrow SnCl_4 + Hg_2Cl_2(s)$

       White precipitate of mercury (I) chloride is not easily oxidized by permanganate.The solution was prepared by dissolving iron sample in concentrated hydrochloric it contains high concentration of chlorides.

        First, iron (III) chloride complexes are yellow, and they can make it difficult to spot end point. To avoid the problem, we can add phosphoric acid to the solution. Phosphate complex has higher stability constant and is colorless.

        Second, permanganate is strong enough to oxidize chlorides to free chlorine. To avoid the problem, we can add $Mn^{2+}$to the solution to lower redox potential of the permanganate to the point where chloride oxidation is impossible.

        To simplify titration procedure, we can use so called Reinhardt-Zimmermann solution, which combines concentrated sulfuric acid, $MnSO_4$ cations and phosphoric acid.

Reaction taking place during titration is

                        $5Fe^{2+} + MnO_4^- + 8H^+ \rightarrow 5Fe^{3+} + Mn^{2+} + 4H_2O$

        End point is the appearance of pale pink color permanently.

Short Procedure $KMnO_4 Vs Fe^{2+}$

•        Bring iron solution (acidified with hydrochloric acid to pH around 0.5) almost to boil.

•        Add drop wise $SnCl_2$solution to agitated iron solution till the yellow color disappears and then one drop of excess.

•        Cool the solution.

•        Add fast 10 mL of mercury (II) chloride solution.

•        If the precipitate is gray, don't titrate sample.

•        In the separate flask mix 400 mL water with 25 mL of Reinhardt-Zimmermann solution. Don't forget to add mixture to water!

•        Add reduced sample to the flask.

•        Titrate with permanganate solution until a faint pink color persists for 30 seconds.

Final result calculation

         According to the reaction equation given above 1 mole of permanganate reacts with 5 moles of iron and this ratio have to be used for titration result calculation.

                                 The percentage of Fe =$Mass \quad of \quad iron \times 100/mass \quad of \quad the \quad sample \quad taken$

By applying values in the above equation, the percentage of Iron is the given sample is calculated ."