Why did we need to add acid to the FAS in step B4? In step C4, where does the pa

Question

Why did we need to add acid to the FAS in step B4? In step C4, where does the pale pink color from that shows the endpoint has been reached? Another common analysis for iron is titration of iron(II) with potassium dichromate. Divide the reaction below into its two half-reactions, balance the half-reactions, and then recombine the balanced half-reactions into the balanced overall equation for the reaction. Fe^2+(aq) + Cr_2O_7^2-(aq) + H^+(aq) rightarrow Fe^3+(aq) + Cr^3+(aq) + H_2O(l) If 26.23 mL of potassium permanganate solution is required to titrate 1.041 grams of ferrous ammonium sulfate hexahydrate, calculate the Molarity of the KMnO_4 solution. If a 2.893 gram sample of an unknown containing iron requires 28.45 mL of the permanganate solution described in the previous question to reach the endpoint, calculate the percent iron in the unknown.

Explanation / Answer

Q2..

Typically, we add acids, strong acids, in order to increase the kenetics of reaction, they typically favour since they are able to donate protons/electron flow

Q3.

The pale pink color comes from the color of permangante ion which is formed

Q4.

reduction must containt the species REDUCING, i.e. gaining electrons

this is clearly Cr, since it goes form +6 to +3

The oxidation is for the species being oxidized so, Fe goes form +2 to +3, it loses electrons

OXIDATION Fe+2(aq) ---> Fe+3 + e-

REDUCTION CrO72- --> Cr+3

Note that H+ is actually not being reduced/oxidized since it remains in H+ form

Oxygen also remains in -2 state

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