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Worksheet 1 - Putting Ions Together and Taking Them Apart Again

  1. Writing formulas for ionic compounds - Table 1 contains a list of cations and anions. In the box where the row of a cation intersects with the column of an anion, write the correct formula for the compound formed between them.
Table 1 
  Br1- N3- NO3 1- PO4 3- OH- C2H3O2 1- S2-
K 1+              
NH4 1+              
Fe 2+              
Ba 2+              
Fe 3+              
Al 3+              
    Each of the following ionic compounds dissolves in water; each dissociates into its constituent ions. Following the examples below, complete the equations for this dissociation.

Examples: CaCl2 ® Ca2+ + 2Cl1-Note: The crystal lattice of CaCl2 contains two separate and distinct Cl1- ions. When the compound dissociates, it does so giving two separate and distinct Cl1- ions. This is indicated by 2Cl1- . To write Cl2 2- would indicate that the two Cl1- actually bond together. This is incorrect! Two negative Cl1- ions find each other repulsive - they will not be close to each other, much less bonded together.

Fe2(SO4)3 ® ? Recognize SO4 2- as a polyatomic ion; look up its charge: -2 [ SO4 2-]. The total negative charge is –6. (3 ions x –2 charge/ion.) Therefore, the total positive charge is +6. Two ions: each of charge +6/2 = +3

Fe2(SO4)3 ® 2 Fe 3+ + 3 SO4 2-

1. Na2S ®

2. KNO3 ®

3. K3PO4 ®

4. Ba(OH)2 ®

 5. Al(NO3)3 ®

6. (NH4)2 SO4 ®

7. (NH4)3PO4 ®

8. CuSO4 ®

Check your answers here.