Problem 2: Chemical Equation Balancing The dissolution of copper sulfide in aque

Question

Problem 2: Chemical Equation Balancing The dissolution of copper sulfide in aqueous nitric acid is described by the following chemical reaction equation: where the coefficients a through g are the numbers of the various molecules participating in the reaction and are unknown. Balancing each atom in the reaction between the left and right sides of the reaction equation, and the ionic charge results in the following system of equations: a=d b=f 3b = 4e + f + g c=29 -b+c 2d -2e Since there is one more unknown than equations, a solution can be found through an iterative approach because we know that all of the coefficients must be positive integers. Start by assigning a-1 and solving the system, if the calculated coefficients are all positive integers you have a solution, if there is either a negative value or decimal/fraction then re-assign a 2 and continue until you find all positive integer coefficients, or find the scalar multiple to create all coefficients to be integers.

Explanation / Answer

The best way to balance redox reactions is via:

REDOX balancing

First, define the “ACIDIC” solution/conditions as H+ presence and

Basic solution implies OH- once it is balanced.

Also; note that ALL species must be balanced, as well as charges

Typical steps:

1) split half redox cells

2) balance atoms other than O,H

3) balance O by adding H2O

4) balance H by adding H+

5) balance charge by adding e-

6) balance e- by multiplying by the Greatest common divisor

7) Add both equations

8) simplify repeating elements, H+, H2O, and e- typically

9) add OH- if we need basic media, otherwise this is done.

10) Simplify again

then

split

CuS = Cu+2 + SO4-2

NO3- = NO

balance O adding H2O

4H2O + CuS = Cu+2 + SO4-2

NO3- = NO + 2H2O

balance H

4H2O + CuS = Cu+2 + SO4-2 + 8h+

4H+ + NO3- = NO + 2H2O

balance charge

4H2O + CuS = Cu+2 + SO4-2 + 8H+ + 8e-

3e- + 4H+ + NO3- = NO + 2H2O

balance e-

12H2O + 3CuS =3 Cu+2 + 3SO4-2 + 24H+ + 24e-

24e- + 32H+ + 8NO3- = 8NO + 16H2O

add all

24e- + 32H+ + 8NO3- + 12H2O + 3CuS =3 Cu+2 + 3SO4-2 + 24H+ + 24e- + 8NO + 16H2O

cancel common terms

8H+ + 8NO3- + 3CuS =3 Cu+2 + 3SO4-2 + 8NO + 4H2O

add phases

8H+(aq) + 8NO3-(aq) + 3CuS(s) =3Cu+2(aq) + 3SO4-2(aq) + 8NO(g) + 4H2O(l)

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