Question: Balance the following reactions by the oxidation number method.
a) I2 + HNO3 --> HIO3 + NO2 + H2O
b) MnO4- + H+ + Cl- --> Mn2+ + Cl2 + H2O
I know how to give each atom oxidation number but after i don't know how to apply the method.
http://www.mpcfaculty.net/mark_bishop/redox_balance_oxidation.htm
To balance reactions using the oxidation number method, follow these steps:
Step 1: Write down the balanced chemical equation.
In this case, we have:
a) I2 + HNO3 --> HIO3 + NO2 + H2O
b) MnO4- + H+ + Cl- --> Mn2+ + Cl2 + H2O
Step 2: Assign oxidation numbers.
Assign oxidation numbers to each atom in the equation. This helps you track the transfer of electrons in the reaction.
Step 3: Identify the atoms that undergo changes in oxidation number.
Look for atoms whose oxidation numbers change from one side of the equation to the other. These are the atoms involved in redox (reduction-oxidation) reactions.
Step 4: Determine the change in oxidation number.
Calculate the change in oxidation number for each atom that undergoes a change. This is done by subtracting the oxidation number on one side of the equation from the other side.
Step 5: Balance the atoms undergoing changes.
Balance the atoms undergoing changes using coefficients. Start with the elements whose oxidation numbers change the most and use coefficients to make the numbers of atoms equal on both sides.
Step 6: Check that the number of each type of atom is the same on both sides of the equation.
Make sure that all the atoms are balanced by checking the number of each type of atom on both sides of the equation.
Step 7: Balance the rest of the atoms.
Balance the remaining atoms (those not involved in redox reactions) by placing coefficients in front of the appropriate compounds.
Step 8: Check the charge balance.
Add a net charge to check if the charges of the reactants and products are balanced.
NOTE: Balancing redox reactions can sometimes be complicated. It may require additional steps, such as balancing hydrogen or oxygen atoms by adding H2O or H+ ions. In some cases, you may need to use half-reactions to balance the reaction.
Applying these steps to the given reactions, here's how you can balance them:
a) I2 + HNO3 --> HIO3 + NO2 + H2O
First, assign the oxidation numbers:
I2: 0
HNO3: H(+1), N(+5), O(-2)
HIO3: H(+1), I(+5), O(-2)
NO2: N(+4), O(-2)
H2O: H(+1), O(-2)
It is clear that iodine (I) is undergoing a change in oxidation number. The oxidation number of iodine increases from 0 in I2 to +5 in HIO3.
Balance iodine (I):
I2 + 10HNO3 --> 2HIO3 + 5NO2 + 4H2O
The iodine atoms are now balanced, so we can proceed to the next step.
Next, check if all the other atoms are balanced:
10 Nitrogen (N) atoms on both sides
30 Hydrogen (H) atoms on both sides
36 Oxygen (O) atoms on both sides
The reaction is now balanced.
b) MnO4- + H+ + Cl- --> Mn2+ + Cl2 + H2O
Assign the oxidation numbers:
MnO4-: Mn(+7), O(-2)
H+: H(+1)
Cl-: Cl(-1)
Mn2+: Mn(+2)
Cl2: Cl(0)
H2O: H(+1), O(-2)
Notice that manganese (Mn) undergoes a change in oxidation number. The oxidation number of manganese decreases from +7 in MnO4- to +2 in Mn2+.
Balance manganese (Mn):
MnO4- + 8H+ + 5Cl- --> Mn2+ + 5Cl2 + 4H2O
Check other atoms:
8 Hydrogen (H) atoms on both sides
5 Chlorine (Cl) atoms on both sides
9 Oxygen (O) atoms on both sides
The reaction is now balanced.
Remember, balancing redox reactions can sometimes be complex, so in some cases, additional steps or half-reactions may be necessary.