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Balancing Chemical Equations

Balancing Chemical Equations in Chemistry

Balancing chemical equations by ion-electron formula and change of oxidation number are uses to balance the oxidation-reduction process or redox reactions for learning chemistry. The ion-electron method set up for balancing partials equation of oxidant and reductant and balance the charges these partial equations in acid or base solution. Other hand oxidation numbers use for balancing chemical equations set up by change or calculation of the oxidation number of reactant and product atoms present in chemical elements, molecules, or ions.

Balancing Equations by Ion-electron Method

Balancing chemical equations by ion-electron formula and oxidation number balance method in chemistry

Balancing chemical equations by the ion-electron method has certain general rules or formulas which use for balance oxidation-reduction reaction or redox reactions. Therefore, we use rules for balancing equations by the ion-electron method are

  1. Certain the oxidizing agent and reducing agent, and their chemical formula for balancing chemical equations.
  2. Set up the partial balancing equations representing the reduction of the oxidant, and the oxidation of the reductant.
  3. If the reaction occurs in acid solution or low pH solution use a requisite number of hydrogen ion for balancing the number of the atom involved in the partial equations and for the alkaline solution or high pH solution we use hydroxyl ions.
  4. Balancing the changes of partial chemical equations by adding a suitable number of electrons. These electron particles involve balancing oxidation and reduction half-reactions.
  5. Multiply each partial equation by a suitable factor for balancing ionization chemicals. Therefore, each of the two partial equations involves the same number of electrons.
  6. Add the partial equations and cancel out similar species that appear on both sides of the balancing chemical reaction.

Examples for Balancing Chemical Equations

Balancing Iron in potassium permanganate solution

Potassium permanganate in dilute sulfuric acid oxidizes iron from the ferrous state to the ferric state by changing the electronic configuration of the iron atom. Therefore, permanganate ion is the oxidant and ferrous ion is the reductant in balancing chemical equations.

MnO4 + H+ + Fe+2 ⇆ Mn+2 + Fe+3 + H2O

The left-hand side of the ultimate equation will carry, MnO4, H+ ion, and Fe+2 ion, and the right-hand side will have Mn+2, water, and Fe+3. Therefore, the partial equation representing the reduction of the oxidant, MnO4 → Mn+2. This reaction occurs in an acid solution, thus we use hydrogen ion to balance the four oxygen atoms in permanganate ion.

MnO4 + 8H+ → Mn+2 + 4H2O

The above partial equation still unbalanced from the viewpoint of charges and the equation balancing by bringing in five electrons.

MnO4 + 8H+ + 5e ⇆ Mn+2 + 4H2O

The partial equation representing the oxidation of the reductant, Fe+2 ⇆ Fe+3 + e. This equation balancing with respect to charges and reacting elements. Therefore, to balancing charges of partial equations, this equation multiplies by 5 and then adding with the first equation.

MnO4 + 8H+ + 5e ⇆ Mn+2 + 4H2O
5×( Fe+2 ⇆ Fe+3 + e)
MnO4 + 8H++ 5Fe+2 → Mn+2 + 5Fe+3 + 4H2O

Balencing Potassium iodide in acid solution of dichromate

For balancing oxidation of potassium iodide in an acid solution of dichromate, chromium reduces from +6 state to +3 state and iodine ion oxidized to form the elementary iodine molecule. Therefore, the balancing partial equations of the dichromate side and iodine side are

Cr2O7-2 + 14H+ + 6e ⇆ 2Cr+3 + 7H2O
2I ⇆ I2 + 2e

For balancing overall equations iodine side multiplies by 3 and adding with dichromate side.

Cr2O7-2+14H++6e ⇆ 2Cr+3+7H2O
3 (2I ⇆ I2 + 2e)
Cr2O7-2 + 14H+ + 6I → 2Cr+3 + 3I2 + 7H2O

Balancing Permanganate ion in alkaline solution

Permanganate ion in alkaline solution oxidizes Na2SnO2 to Na2SnO3. Therefore, the partial equation representing the reduction of oxidant in alkaline solution and balancing the chemical equations with a requisite number of OH ion.

MnO4 + 2H2O → MnO2 + 4OH

The above partial equation still unbalanced from the viewpoint of charge, the equation balance by bringing in three electrons.

MnO4 + 2H2O + 3e → MnO2 + 4OH

Again the partial equation representing the oxidation of the reductant.

SnO2-2 + 2OH ⇆ SnO3-2 + H2O + 2e

Hence balancing these chemical equations, first partial equation multiplies 2 and the second partial equation multiplies 3 and adding to the given final balance chemical equation.

2MnO4 + 4H2O + 6e ⇆ 2MnO2 + 8OH
3SnO2-2 + 6OH ⇆ 3SnO3-2 + 3H2O + 6e
2MnO4 + 3SnO2-2 + H2O → 2MnO2 + 3SnO3-2 + 2OH

Problem: Balancing the chemical equation of permanganate to manganous by hydrogen peroxide in acid solution.

Solution: Balance partial equations for the above chemical reaction are

MnO4 + 8H+ + 5e ⇆ Mn+2 + 4H2O
H2O2 ⇆ 2H+ + O2 + 2e

Balancing the overall charges of the chemical equations multiplying by 2 and second by 5 and adding.

2MnO4 + 16H+ + 10e ⇆ 2Mn+2 + 8H2O
5H2O2 ⇆ 10H+ + 5O2 +10e
2MnO4 + 5H2O2 + 6H+ ⇆ 2Mn+2 + 8H2O + 5O2

Working Examples for Chemical Reactions

Balancing Mn+2 to MnO4 by acidic NaBiO3

NaBiO3 oxidizes Mn+2 to MnO4 in sulfuric acid solution with the formation of BiO+ ion. Balancing partial equations and overall chemical equation for the above chemical reaction are

2Mn+2 + 8H2O → 2MnO4 + 16H+ + 10e
5BiO3 + 20H+ + 10e → 5BiO+ + 10H2O
2Mn+2 + 5BiO3 + 4H+ → MnO4 + 5BiO+ + 2H2O

Problem: Balancing the chemical equation of reduction of nitrate ion to ammonia by aluminum in aqueous sodium hydroxide.

Answer: The Balance partials and overall equation for the reduction of nitrate ion to ammonia by aluminum in an aqueous sodium hydroxide are

3NO3 + 18H2O + 24e ⇆ 3NH3 + 27OH
8Al + 32OH ⇆ 8AlO2 + 16H2O + 24e
3NO3 + 8Al + 2H2O + 5OH → 3NH3 + 8AlO2

Chemical Equation Balanced by Oxidation Number

Balancing oxidation-reduction reactions by the change of oxidation number going hand to hand with ion-electron methods for balance chemical equations. Let us illustrate this equation balancing method by oxidation of iron by acidic permanganate solution.

MnO4 + H+ + Fe+2 → Mn+2 + Fe+3 + 4H2O

For balancing the oxidation number,  Mn in MnO4 decreases by 5 and iron increases by 1 in the above equations. Therefore, putting the right factors for balancing the decreases and increases in oxidation numbers and hydrogen ion (acid solution) and water molecules for balance chemical equations.

MnO4 + 8H+ + 5Fe+2 → Mn+2 + 5Fe+3 + 4H2O

Balancing iodide ion in acidic dichromate solution

Cr2O7-2 + I → 2Cr+3 + I2

The oxidation number of chromium decreases by 2 and the oxidation number of iodine increases by 1. Balancing the increase and decrease in oxidation number by putting the right factor on the above equations. Fourteen hydrogen ions and the requisite number of water molecules also added to balance the above equation.

Cr2O7-2 + 6I + 8H+ → 2Cr+3 + 3I2 + 7H2O

Balancing Sodium stannite to stannate in alkaline solution

MnO4 + SnO2-2 → MnO2 + SnO3-2

The oxidation number of manganese decreases by 3 and the oxidation number of tin increases by 2. Hence, equalizing the increase and decrease in oxidation number by putting the right factor and two hydroxyl ions and the requisite number of water molecules are added to balance the above chemical equation. Therefore, the balancing equation for the above reactions

2MnO4 + 3SnO2-2 + H2O → 2MnO2 + 3SnO3-2 + 2OH

Balancing Iodide ion and iodate ion in acid solution

Change of oxidation number of iodine in the above chemical bonding uses for balancing this chemical equation.

I (-1) + IO3 (+5) → I2 (0)

Therefore, the oxidation number of iodide increases by 1, and iodate ion decreases by 5. Putting the right factors for decrease and increase in oxidation number and balancing the above equation.

I- + IO3 + 6H+ → I2 + 3H2O

Balancing sulfurous acid in dichromate ion

Balancing chemical equations for the oxidation of sulfurous acid to sulfuric acid by potassium dichromate

3SO3-2 + Cr2O7-2 + 8H+ → 3SO4-2 + 2Cr+3 + 4H2O

For balancing equations, the oxidation number of two chromium atom decrease by 6, and the oxidation number of sulfur increases by 2. Therefore, we put the right factor and the requisite number of hydrogen ion and water to balance the above ionic equations.

Therefore, the above oxidation-reduction reactions discussion useful for balancing any chemical equations by ion-electron formula and oxidation number method. These balancing formula uses for only balances the chemical equations of oxidation-reduction or redox reaction reactions in learning chemistry or chemical science.