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Appendix
B Net Ionic Equations
Introduction For reactions which occur in aqueous solution, the net ionic equation is particularly useful since only those species which participate in the reaction, i.e. reacting species , are included. The principal step in writing the net ionic equation is to determine which molecular species or salts are strong electrolytes in aqueous solution. Therefore, it is necessary to have a complete understanding of strong electrolytes before proceeding to the writing of net ionic equations.
Strong Electrolytes In aqueous solution, strong electrolytes dissolve and dissociate (separate) 100% to form ions. Thus, an aqueous solution of a strong electrolyte contains a relatively high concentration of ions. For example, when dissolved in water, the ionic compound NaCl is classified as a strong electrolyte. As a result, NaCl(aq) really exists in solution as dissociated and separated ions of Na (aq) and Cl+ G(aq). Neutral formula units of NaCl do not exist dissolved in solution. Strong acids , strong bases , and soluble ionic compounds are classified as strong electrolytes in aqueous solution. Most general chemistry books agree that the seven compounds given below are strong acids (ergo strong electrolytes) when dissolved in water. Consequently, an aqueous solution of the
Strong Acids HCl(aq) HClO (aq) 4 H SO (aq) 2 4 HBr(aq) HClO (aq) 3 HNO (aq) 3 HI(aq)
strong acid perchloric acid, HClO (aq), actually consists of dissociated and separated ions of 4 H (aq) and ClO+ 4 G (aq). Neutral molecules of HClO do not exist dissolved in solution. 4 Likewise, an aqueous solution of the strong acid hydrochloric acid, HCl(aq), really consists of H (aq) and+ ClG(aq). Neutral molecules of HCl do not exist dissolved in solution. The dissolution equations for HClO 4 and HCl are represented as shown below. When dissolved in water, any other acid,
H O 2 HClO 4 ˇ H (aq) + ClO+ 4 G(aq) ∆»« 100% ∆--------»---------« 0% dissolved as 100% dissociated and dissolved neutral molecules as separate ions
Appendix B Net Ionic Equations
H O 2 HCl ˇ H (aq) + Cl+ G(aq) ∆»« 100% ∆------»------« 0% dissolved as 100% dissociated and dissolved neutral molecules as separate ions
e.g., HC H O , H CO , HF, H S, etc., is a 2 3 2 2 3 2 weak acid and therefore a weak electrolyte. Weak electrolytes dissolve but dissociate less than 100% to form ions. Thus, an aqueous solution of a weak electrolyte contains a relatively low concentration of ions. For example, the weak acid acetic acid, HC H O , readily dissolves in water. However, the majority of this acid (~99%) dissolves 2 3 2 as neutral molecules of HC H O. Only a small amount (~1%) dissociates and exists as separate 2 3 2 ions of H (aq) and C H O+ 2 3 2 G (aq). The dissolution equation for HC H O 2 3 2 is represented as shown below. H O 2 HC H O (aq) 2 3 2 ∫ H (aq) + C H O+ 2 3 2 G(aq) ∆--»---« ~1% ∆--------»---------« ~99% dissolved ~1% dissociated and dissolved as neutral molecules as separate ions
Most general chemistry books agree that the Group IA metal hydroxides and the heavier Group IIA metal hydroxides given below are strong bases (ergo strong electrolytes) when dissolved in water. Consequently, an aqueous solution of the strong base calcium hydroxide,
Strong Bases IA IIA LiOH(aq) RbOH(aq) Ca(OH) (aq) 2 NaOH(aq) CsOH(aq) Sr(OH) (aq) 2 KOH(aq) Ba(OH) (aq) 2
Ca(OH) (aq), really consists of dissociated and separated ions of Ca 2 +2(aq) and OHG(aq). Neutral formula units of Ca(OH) do not exist dissolved in solution. 2 However, if the solution is saturated with Ca +2and OHG ions, solid undissolved Ca(OH) may be present as a precipitate at the bottom 2 of the vessel. The dissolution equation for Ca(OH) 2 is represented as shown below. When dissolved in water, weak bases , such as ammonia and its derivatives,are classified as
H O 2 Ca(OH) (s) 2 ˇ Ca +2(aq) + 2 OHG(aq) ∆--»--« 100% ∆--------»---------« 0% dissolved as 100% dissociated and dissolved as neutral formula units as separate ions
weak electrolytes. For example, the weak base ammonia, NH , readily dissolves in water. 3 However, the majority of this base (~99%) dissolves as neutral molecules of NH. 3 A small amount (~1%) reacts with water to form separated ions of NH 4 +(aq) and OHG(aq), as shown
Appendix B Net Ionic Equations
EXAMPLE: Aqueous solutions of calcium chloride and sodium carbonate are mixed. Write the net ionic equation.
Step 1: A. Write correct chemical formulas for each compound given.
calcium chloride = CaCl 2 Reactants sodium carbonate = Na CO 2 3 A
B. If not given, predict products by allowing reactants to trade partners. Ca +2 ClG CaCO 3 Products Na +^ CO 3 G 2 NaCl A
C. Write the balanced molecular equation.
Balanced Molecular Equation: CaCl + Na CO 2 2 3 ˇ CaCO + 2 NaCl 3
Step 2: A. Identify strong electrolytes. Remember.....strong electrolytes are strong acids, strong bases, and soluble ionic compounds. Use Appendix C to determine whether an ionic compound is soluble or insoluble.
CaCl : 2 ionic compoundˇsoluble by Rule #3ˇ strong electrolyte Na CO : 2 3 ionic compoundˇsoluble by Rule #1ˇ strong electrolyte CaCO : 3 ionic compoundˇinsoluble by Rule #6ˇprecipitates NaCl: ionic compoundˇsoluble by Rule #1ˇ strong electrolyte
B. Write the full ionic equation by showing all species as they really exist in solution, i.e., strong electrolytes are shown dissociated into ions.
Balanced Full Ionic Equation: Ca +2^ + 2 ClG + 2 Na +^ + CO 3 G 2 ˇ CaCO (s) + 2 Na 3 + + 2 ClG
Step 3: A. Identify spectator ions. Spectator ions are ions that appear on both sides of the equation in exactly the same form.
Spectator Ions: Na +and ClG These ions are present on both sides of the equation in the same form (dissolved in solution) and with the same charge.
Appendix B Net Ionic Equations
Reacting Ions: Ca +2^ and CO 3 G^2 These ions are changing form. On the reactant side they are dissolved in solution; whereas, on the product side they are present in an insoluble precipitate.
B. Write the net ionic equation by removing spectator ions from the full ionic equation and balance (if the molecular equation was not previously balanced in Step 1C).
Balanced Net Ionic Equation: Ca +2^ + CO 3 G 2 ˇ CaCO (s) 3
EXAMPLE: Aqueous solutions of ammonium chloride and magnesium hydroxide are mixed. Write the net ionic equation if the products of this reaction are magnesium chloride, ammonia, and water.
Step 1: A. Write correct chemical formulas for each compound given.
ammonium chloride = NH Cl 4 Reactants magnesium hydroxide = Mg(OH) 2 A
magnesium chloride = MgCl 2 ammonia = NH 3 Products water = H O 2 A
B. Write the balanced molecular equation
Balanced Molecular Equation: 2 NH Cl + Mg(OH) 4 2 ˇ MgCl 2 + 2 NH 3 + 2 H O 2
Step 2: A. Identify strong electrolytes.
NH Cl: 4 ionic compoundˇsoluble by Rule #1ˇ strong electrolyte Mg(OH) : 2 ionic compoundˇinsoluble by Rule #6ˇsolid MgCl : 2 ionic compoundˇsoluble by Rule #3ˇ strong electrolyte NH : 3 molecular compoundˇweak baseˇweak electrolyte H O: 2 molecular compoundˇweak or non-electrolyte
B. Write the full ionic equation by showing all species as they really exist in solution, i.e., strong electrolytes are shown dissociated into ions.
Appendix B Net Ionic Equations Name:
Questions: Predict products and write the balanced net ionic equation for each of the following reactions. (Note: BaSO 3 is insoluble.)
- Zn(C H O ) 2 3 2 2 + Na S 2 ˇ
- Pb(NO )3 2 + NH Cl 4 ˇ
- Na PO 3 4 + MgCl 2 ˇ
- Cu(NO )3 2 + NaOH ˇ
- ZnSO 4 + BaS ˇ
- Na CO + HCl 2 3 ˇ (HINT: H CO (aq) normally decomposes to CO (g) and H O(l)) 2 3 2 2
- NiS + HCl ˇ
- BaCl + Na SO 2 2 3 ˇ
- Zn + HCl ˇ (HINT: This is a redox reaction. Zn is oxidized to Zn +2^ and H +^ is reduced to H (g)) 2
- Hg(NO )3 2 + (NH ) SO4 2 4 ˇ
Appendix B Net Ionic Equations
Questions: Write the balanced net ionic equation for each of the following reactions.
- barium acetate + ammonium sulfate ˇ
- calcium hydroxide + sodium carbonate ˇ
- iron(III) nitrate + barium hydroxide ˇ
- barium hydroxide + hydrochloric acid ˇ
- silver nitrate + magnesium bromide ˇ
- acetic acid + potassium hydroxide ˇ
- sodium chromate + silver nitrate ˇ
- calcium chlorate + sodium phosphate ˇ
- ammonium chloride + sodium hydroxide ˇ (HINT: NH OH(aq) does not exist and decomposes to NH (g or aq) and H O(l)) 4 3 2
- calcium carbonate + sulfuric acid ˇ (HINT: H CO (aq) normally decomposes to CO (g) and H O(l)) 2 3 2 2
