Question

7. The following reaction occurs in basic solution: H2O(aq) + MnO, (aq) + CIO (aq) - MnO (s) + CIO, (ag) + OH(aq) When the equation is properly balanced, what is the sum of the lowest whole number coefficients? a. 20 b. 9 c. 10 d. 6 e. 12 8. What is the molarity of an Nal solution that contains 7.0 g of Nal in 21.0 mL of solution? a. 2.2 M b. 0.046 M c. 0.003 M d. 0.00014 M e. 0.33 M 9. What minimum mass of iron (II) nitrate must be added to 10.0 of a 0.0699 M phosphate solution order to completely precipitate all of the phosphate as solid iron (II) phosphate? 2PO/(aq) + 3Fe(NO3)2(aq) Fe3(PO4)2(s) + 6NO3(aq) a. 0.125 g b. 0.377 g c. 0.0838 g d. 0.0419 g e. 0.188 g

Answer 1

7)

Mn in MnO4- has oxidation state of +7

Mn in MnO2 has oxidation state of +4

So, Mn in MnO4- is reduced to MnO2

Cl in ClO- has oxidation state of +1

Cl in ClO4- has oxidation state of +7

So, Cl in ClO- is oxidised to ClO4-

Reduction half cell:

MnO4- + 3e- --> MnO2

Oxidation half cell:

ClO- --> ClO4- + 6e-

Balance number of electrons to be same in both half reactions

Reduction half cell:

2 MnO4- + 6e- --> 2 MnO2

Oxidation half cell:

ClO- --> ClO4- + 6e-

Lets combine both the reactions.

2 MnO4- + ClO- --> 2 MnO2 + ClO4-

Balance Oxygen by adding water

2 MnO4- + ClO- --> 2 MnO2 + ClO4- + H2O

Balance Hydrogen by adding H+

2 MnO4- + ClO- + 2 H+ --> 2 MnO2 + ClO4- + H2O

Add equal number of OH- on both sides as the number of H+

2 MnO4- + ClO- + 2 H+ + 2 OH- --> 2 MnO2 + ClO4- + H2O + 2 OH-

Combine H+ and OH- to form water

2 MnO4- + ClO- + 2 H2O --> 2 MnO2 + ClO4- + H2O + 2 OH-

Remove common H2O from both sides

Balanced Eqn is

2 MnO4- + ClO- + H2O --> 2 MnO2 + ClO4- + 2 OH-

This is balanced chemical equation in basic medium

Sum of coefficient = 2 + 1 + 1 + 2 + 1 + 2 = 9

Answer: b

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