the bisulfite ion (HSO,) becomes sulfurous acia addition of a proton. The bislfi

Question

the bisulfite ion (HSO,) becomes sulfurous acia addition of a proton. The bislfite ion is unchanged in the golution. In basic solution, the bisulfite ion becomes sulfite (H, So,) by neutral s on (so,) through the loss of a proton to OH forming water. Therefore, the containing species are: three balanced half reactions for the oxidation of the three sulfur- acidic: neutral: basic: HSO, + H,.., SO.. . + 3 H. + 2 e. 13) The manganese-containing producta of the reduction half reactións for the three pH conditions are: acidic: anganese (II) ion neutral: basic: very pale pink Mn2* Mno2 Mno.-green 1: Manganese dioxide brown Manganate ion The permanganate ion, Mno-, is violet in color. Under each of the three pH conditions, the product of the reduction of the permanganate ion is a different color than the original permanganate ion (as shown in the table above) Therefore, the manganese-containing species acts as its own indicator during the oxidation-reduction titration PRE-LAB QUESTIONS Write balanced halt reactions for the reduction of Mno the three pH conditions 1. for each of 2. Por each of the three pH conditions, write a balanced net ionic equation for the overal oxidation half reactions for the sodium bisulfite (given as equa tions 1, 2, and 3 above) each of the ction half reac- reduction half with the appropr tion for the permanganate ion (question 1). That is, add the acidic oxidation half reaction (equation 1) to the acidic reaction (from question 1), etc. Recall that, in order to add half reactions, the number of electrons given off in the oxidation process must equal the number of el trons taken up in the reduction process. EXPERIMENTAL PROCBDURE In this procedure, you will carry out titrations involving KMno and NaHsO, under acidic, neutral, and ba precision, three replicate titrations will be performed for each condition sic conditions. In order to improve pH the KMno4 solution and 100 mL of th inn in clean dry heakers, Record the concentration o 1. Obtain approximately 300 mL of

Explanation / Answer

Pre-lab

1. balanced half-reactions for the reduction of MnO4- for three conditions,

acidic : MnO4^– + 8 H+ + 5e- <==> Mn^2+ + 4 H2O

neutral : MnO4– + 4H+ + 3e- <==> MnO2 + 2H2O

basic : MnO4^– + e- <==> MnO4^2–

2. Overall equation,

acidic :

(MnO4^– + 8 H+ + 5e- <==> Mn^2+ + 4 H2O) x 2

(H2SO3 + H2O ---> HSO4- + 3H+ + 2e-) x 5

So,

2MnO4^– + 16H+ + 10e- <==> 2Mn^2+ + 8H2O

5H2SO3 + 5H2O ---> 5HSO4- + 15H+ + 10e-

-----------------------------------------------------------------------------

2MnO4- + 5H2SO3 + 16H+ ---> 2Mn2+ + 5HSO4- + 3H2O

Is overall reaction under acidic condition

Neutral,

MnO4– + 4H+ + 3e- <==> MnO2 + 2H2O

HSO3- + H2O --> SO4^2- + 3H+ + 2e-

-------------------------------------------------------------------

MnO4- + HSO3- + H+ ----> MnO2 + SO4^2- + H2O

Is the overall reaction under neutral condition

basic,

(MnO4^– + e- <==> MnO4^2–) x 2

SO3^2- + 2OH- --> SO4^2- + H2O + 2e-

------------------------------------------------------------

2MnO4- + SO3^2- + 2OH- ---> 2MnO4^2- + SO4^2- + H2O

Is the overall reaction under basic condition

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