Double Replacement Rxn - Neutralization Rxn

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As you know, one of three products (form a solid, water or gas) must be produced in a double chemical reaction for the reaction to occur. Here, we will explain formation of one of these products: the formation of water.

As with all double replacement reactions, you have two reactants that are aqueous (compounds that break-up into their ions in water). In other words, you have a bucket of ions before the reaction occurs. The task is to rearrange the ions into new compounds (cpds) knowing that like charged ions can't create cpds.

Even though water (H₂O) is a molecular cpd, we often think of it as made up of two ions, hydronium ion (H⁺¹) and hydroxide ion (OH^-1). It would look like HOH if written as a cpd. Therefore, one of our reactants must contain the hydroxide ion (OH^-1) and one must contain the hydronium ion (H⁺¹). If you place these two reactants into a bucket, you product water (H₂O). See example below.

These types of reactions are very common place to the point that we give the reactants and chemical reaction special names:

Acid - a compound that breaks up into ions in water where one of the ions is hydronium ion (H⁺¹). Acids look like ionic cpd that has H as the cation. Example#1, HNO₃ breaks up into 1 H⁺¹ and 1 NO₃^-1. Example#2, H₂SO₄ breaks up into 2 H⁺¹ and 1 SO₄^-2.
Base - a compound that breaks up into ions in water where one of the ions is the hydroxide ion (OH^-1).
Neutralization Rxn - a double replacement reaction that produces water (H₂O) as one of its products. The two reactants are an acid & a base.

Examples of Neutralization Reaction

1 NaOH_(aq) + 1 HCl_(aq) ==> 1 H₂O_(l) (or 1 HOH_(l)) + NaCl_(aq)

1 Ca(OH)_{2 (aq)} + 2 HCl_(aq) ==> 2 H₂O_(l) (or 2 HOH_(l)) + CaCl_{2 (aq)}

Net Ionic Reaction for Neutralization Reactions

To determine any Net Ionic Reaction, you must follow the directions stated in (NetIonicReactions).

Example of Determining Net Ionic Reactions for Neutralization Reaction

Step 1: 1 Ca(OH)_{2 (aq)} + 2 HCl_(aq) ==> 2 H₂O_(l) + CaCl_{2 (aq)} (Balanced Molecular Equation)

Step2 : 1 Ca⁺² + 2 OH⁺¹ + 2 H⁺¹ + 2 Cl^-1 --> 2 H₂O_(l) + 1 Ca⁺² + 2 Cl^-1

Step 3: I can't show on this webpage cancel out of spectator ions. You can do it right on work above. The spectator ions are Ca⁺² and 2 Cl^-1 since they are the same on both side of arrow.

Step 4: 2 OH^-1 + 2 H⁺¹ --> 2 H₂O_(l)
- But you can cancel out a "2" in each of the coefficient so the actual Net Ionic Reaction is

1 OH^-1 + 1 H⁺¹ --> 1 H₂O_(l)

(The Special Condition for Net Ionic Reactions of Neutralization is that all neutralization reactions have the same Net Ionic Reaction: the one above)