Balancing Chemical Equations



Atoms can neither be destroyed nor created during a simple chemical reaction. Therefore, in a chemical reaction

The sum of atoms before reaction = the sum of atoms after reaction

In this lesson, we will look at some examples of
Balancing chemical equations containing polyatomic ions

Related Topics: More lessons on Chemistry

General Rules for balancing chemical equations – Polyatomic Ions

Balancing chemical equations may require some trial and error. There are some general rules that could be helpful, but they may not work all the time.

Rule 1 Balancing chemical equations using the one’s and two’s technique Rule 2 Balancing chemical equations using the two’s and three’s technique
Rule 3 Balancing chemical equations using the CHO technique Rule 4 Balancing chemical equations using the even technique
Rule 5 Balancing chemical equations containing polyatomic ions  




Case 1: If the polyatomic ion remains the same before and after the reaction, then treat it as “a single element” for ease of calculation. Try to start with the most complicated-looking group.

Example:

Balance the equation

Ca + HNO3 → H2 + Ca(NO3)2

Solution:

  • The nitrate ion NO3 is unchanged before and after the reaction.
  • Start with Ca(NO3)2 since it looks most complicated.
  • There is one NO3 on the left and two on the left.
  • Using the one’s and two’s technique, the equation is balanced by placing the coefficient of 2 for HNO3

    Ca + 2HNO3 → H2 + Ca(NO3)2

  • We test the other atoms and we find that we already have a balanced equation.
  • Check to make sure that all coefficients are in the lowest-possible ratio





The following videos show some examples of balancing chemical equations containing polyatomic ions.








This video shows how to balance chemical equations containing polyatomic ions.






Case 2: If the polyatomic ion is changed after the reaction then it would be necessary to consider each atom individually.

Example:

Balance the chemical equation

Ba(OH)2 + H3PO4 → BaHPO4 + H2O

Solution:

  • Use the CHO technique. Since we don't have carbon, we could try to balance the hydrogen first.
  • We have five hydrogen atoms on the left and three hydrogen atoms on the right.
  • To balance the hydrogen, we can place the coefficient of 2 at H2O

    Ba(OH)2 + H3PO4 → BaHPO4 + 2H2O

  • We test the other atoms and we find that we already have a balanced equation.
  • Check to make sure that all coefficients are in the lowest-possible ratio.





This video show how to balance chemical equations with polyatomic ions by rewriting H2O as H(OH)



This lesson shows three helpful tips and tricks that make Balancing Chemical Equations easier.






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