Ionic Equations, Acid-Base Reactions, and Stoichiometry in General Chemistry

Full and Net Ionic Equations

Introduction to Ionic Equations

Chemical reactions in aqueous solutions can be represented in three ways: molecular, full ionic, and net ionic equations. These representations help identify the actual chemical changes occurring, especially in precipitation and acid-base reactions.

• Molecular Equation: Shows all reactants and products as compounds.

• Full Ionic Equation: Shows all strong electrolytes as dissociated ions.

• Net Ionic Equation: Shows only the species that undergo change, omitting spectator ions.

Examples of Ionic Equations

Consider the reaction between potassium hydroxide and barium carbonate:

• Molecular: $2KOH(aq) + BaCO_3(s) \rightarrow 2K^+(aq) + 2OH^-(aq) + BaCO_3(s)$

• Full Ionic: $2K^+(aq) + 2OH^-(aq) + Ba^{2+}(aq) + CO_3^{2-}(aq) \rightarrow 2K^+(aq) + 2OH^-(aq) + BaCO_3(s)$

• Net Ionic: $Ba^{2+}(aq) + CO_3^{2-}(aq) \rightarrow BaCO_3(s)$

For the reaction of lead(II) sulfate and nitric acid:

• Molecular: $PbSO_4(aq) + 2HNO_3(aq) \rightarrow PbSO_4(s) + 2NO_3^-(aq)$

• Full Ionic: $Pb^{2+}(aq) + SO_4^{2-}(aq) + 2H^+(aq) + 2NO_3^-(aq) \rightarrow PbSO_4(s) + 2H^+(aq) + 2NO_3^-(aq)$

• Net Ionic: $Pb^{2+}(aq) + SO_4^{2-}(aq) \rightarrow PbSO_4(s)$

Types of Reactions in Aqueous Solution

Precipitation Reactions

Precipitation reactions occur when two soluble salts are mixed and an insoluble product (precipitate) forms.

• Example: $Na_2SO_4(aq) + MgCl_2(aq) \rightarrow NaCl(aq) + MgSO_4(aq)$

• Net Ionic: If no precipitate forms, there is no net ionic equation.

Gas-Forming Reactions

Some reactions produce a gas as a product, such as carbon dioxide or sulfur dioxide.

• Example: $Na_2SO_3(aq) + 2HCl(aq) \rightarrow 2NaCl(aq) + H_2SO_3(aq)$

• H_2SO_3(aq)$decomposes to$H_2O(l) + SO_2(g)$

• Net Ionic: $SO_3^{2-}(aq) + 2H^+(aq) \rightarrow H_2O(l) + SO_2(g)$

Acid-Base Reactions

Definition of Acids and Bases

An acid is a substance that dissolves in water to produce hydronium ions ($H_3O^+$). A base is a substance that dissolves in water to produce hydroxide ions ($OH^-$).

• Strong Acids: Fully ionize in water (e.g., $HNO_3$, $HClO_4$, $H_2SO_4$).

• Weak Acids: Partially ionize (e.g., acetic acid, citric acid).

• Strong Bases: Ionic compounds of group 1 and 2 metals with $OH^-$ (e.g., $NaOH$, $KOH$).

• Weak Bases: Compounds like ammonia ($NH_3$) that partially ionize.

Examples of Acid and Base Dissociation

• Strong Acid: $HCl(aq) + H_2O(l) \rightarrow Cl^-(aq) + H_3O^+(aq)$

• Weak Acid: $CH_3CO_2H(aq) + H_2O(l) \rightleftharpoons CH_3CO_2^-(aq) + H_3O^+(aq)$

• Strong Base: $NaOH(s) \rightarrow Na^+(aq) + OH^-(aq)$

• Weak Base: $NH_3(aq) + H_2O(l) \rightleftharpoons NH_4^+(aq) + OH^-(aq)$

Neutralization Reactions

A neutralization reaction occurs when an acid reacts with a base to form water and a salt. This is a type of double-displacement reaction.

• Example: $Mg(OH)_2(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + 2H_2O(l)$

• Net Ionic: $2OH^-(aq) + 2H^+(aq) \rightarrow 2H_2O(l)$

Stoichiometry and Chemical Equations

Introduction to Stoichiometry

Stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction. Balanced chemical equations provide the mole ratios needed for calculations.

• Example: $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$

• Mole Ratio: $1:3:2$ (N$_2$:H$_2$:NH$_3$)

Stoichiometric Calculations

• How many moles of ammonia from 6.0 moles of hydrogen? $6.0 \text{ mol } H_2 \times \frac{2 \text{ mol } NH_3}{3 \text{ mol } H_2} = 4.0 \text{ mol } NH_3$

• How many moles of nitrogen needed for 10.0 moles of ammonia? $10.0 \text{ mol } NH_3 \times \frac{1 \text{ mol } N_2}{2 \text{ mol } NH_3} = 5.0 \text{ mol } N_2$

Conversion Factors in Equations

Conversion factors are derived from the coefficients in balanced equations and can be used to convert between moles of different substances.

• Mole-to-mole: $\frac{5 \text{ mol } O_2}{1 \text{ mol } C_3H_8}$

• Gram-to-mole: Use molar mass as conversion factor.

Summary Table: Types of Chemical Equations

Type	Definition	Example
Molecular	All reactants and products as compounds	$Na_2SO_4(aq) + BaCl_2(aq) \rightarrow 2NaCl(aq) + BaSO_4(s)$
Full Ionic	All strong electrolytes as ions	$2Na^+(aq) + SO_4^{2-}(aq) + Ba^{2+}(aq) + 2Cl^-(aq) \rightarrow 2Na^+(aq) + 2Cl^-(aq) + BaSO_4(s)$
Net Ionic	Only species undergoing change	$Ba^{2+}(aq) + SO_4^{2-}(aq) \rightarrow BaSO_4(s)$

Additional info:

• Citric acid (found in fruits) and acetic acid (found in vinegar) are examples of weak acids.

• Strong acids and bases are completely ionized in water, while weak acids and bases are only partially ionized.

• Stoichiometry is essential for predicting the amounts of products and reactants in chemical reactions.