Module 4.2 Balancing Redox Equations

Question 1

Oxidation Numbers

Answer 1

The charge on an atom within a molecule

Question 2

What is the charge of

O₂

Answer 2

Zero (per rule 2)

Question 3

Rule 1

Answer 3

The sum of the total charges in a compound is equal to zero

Question 4

Rule 2

Answer 4

The charge of an element zero (an element is an atom that is not combined with any other element) ex. O₂

Question 5

Rule 3

Answer 5

The normal charge of H is +1

Question 6

Rule 4

Answer 6

The normal charge of O is -2

Question 7

Rule 5

Answer 7

The charge of a group 1, 2, or 3 metal atom is positive (+) and equal to its periodic table group number

Ex. K = +1, Ca = +2, Al = +3

Question 8

Rule 6

Answer 8

The charge of a transition metal Adam cannot be determined from its periodic table position since it has no group number
The charge of this item is determined by knowing the total charges of the other atoms or polyatomic groups with which it is combined and use a rule 1
Ex. Mn = +7 in KMnO₄ since K = +1, 4 O = (4*-2) sum charges = 0

Question 9

Rule 7

Answer 9

The charge of a nonmetal which is combined only with a metal is negative and equal to its group number - 8

Ex. S = -2 in Na₂S (S group is 6 - 8 = -2)

Question 10

Rule 8

Answer 10

The charge of a nonmetal which is part of a polyatomic group is determined by knowing the total charges of the other atoms with which it is combined and the use of rule 1

Ex. N = +5 in KNO₃ Since K= +1, 3 O = (3*-2) sum charge = O


Question 11

Oxidation Number on

KNO₃

Answer 11

K= ( Rule 5) +1
N= ( Rule 8 ) +5 (to balance to zero (Rule 1)
O= ( Rule 4 ) -2 * 3 = -6

K= +1
N= +5
O= -2

Question 12

Oxidation Number on

Na₂ Sn O₃

Answer 12

Na= (Rule 5) +1*2= +2
Sn= (Rule 6) & (Rule 1) +4
O= (Rule 4) -2*3= -6

Na= +1
Sn= +4
O= -2

Question 13

Oxidation Number on

Mn (NO₃)₂

Answer 13

Mn= (Rule 6) +2
NO₃ = (Polyatomic group Nitrate has -1 charge) -1*2= -2
N= (Rule 8) +2 ? -12 = 0 ( ? = +10) 
O= (Rule 4) -2*6= -12

Mn= +2
N= +5 (+10 / 2)
O= -2

Question 14

Step 1

Answer 14

determine the charge of each atom including those in a polyatomic group and determine which two atoms charges are changing and what the changes are

Question 15

Step 2

Answer 15

equate the changes multiply the changes by numbers to produce two products results of each multiplications which are equal the numbers by which the changes were multiplied become the coefficient of them compounds containing the changing atoms on both sides of the equation

Question 16

Step 3

Answer 16

balance the remainder of the atoms in the equation by making use of the coefficients determine and step 2

Question 17

Balance the Redox Equation

Zn + KNO₃ + HCl ———> ZnCl₂ + KCl + NH₄Cl + H₂O

Answer 17

First layout charges (Step 1)
Zn = 0 charge
K= +1 charge
N= +5 charge (Polyatomic group need to know K&O, K is +1 & O is -2*3= -6, to balance to 0 N = +5
O= -2 charge
H= +1charge
Cl= -1 charge (to balance to zero with H)

v Right Side v
Zn = +2 charge Need to know Cl, (Rule 7 metal (Zn & nonmetal Cl) 
Cl= -1 charge Group 7 -8 = -1 * 2 = -2
K= +1 charge 
Cl= -1 charge(to balance with K +1 to get 0) 
N= -3 charge 
H= +1 charge ( * 4= +4 to get N) 
Cl= -1 charge
H= +1 charge 
O= -2 charge 

Then Layout all changes from left to right

Zn from 0 to + 2 change of 2
N from +5 to -3 change of 8

Then Equate the changes (Step 2)

Take the change and multiply by a number that will result in the same answer (4 & 8) these numbers will become the coefficient for the respected substance
Zn change of 2 * 4 = 8
N change if 8 * 1 = 8

Becomes
4Zn + 1KNO₃ + HCl ———> 4ZnCl₂ + KCl + 1NH₄Cl + H₂O

Then balance the remaining atoms
to find the other coefficients

4Zn + 1KNO₃ + 10HCl ———> 4ZnCl₂ + 1KCl + 1NH₄Cl + 3H₂O