Chemical Reactions & Solubility: Types and Examples

Displacement/Substitution Reactions (#R = #P)

In these reactions, one element replaces another in a compound (single replacement) or two compounds exchange components (double replacement).

Combination/Addition/Synthesis Reactions (#R > #P)

Multiple reactants combine to form fewer products.

Decomposition Reactions (#R < #P)

One reactant breaks down into multiple products.

Precipitation Reactions

Two aqueous solutions react to form a solid (precipitate) and another aqueous product.

Acid-Base/Neutralization Reactions

An acid reacts with a base to form water and a salt.

Oxidation-Reduction (Redox) Reactions

Electrons are transferred between species, leading to changes in oxidation states.

Single Replacement (Displacement/Substitution)

Mg (s) + HCl (aq) → MgCl2 (aq) + H2 (g)

Double Replacement (Displacement/Substitution)

KI (aq) + Pb(NO3)2 (aq) → KNO3 (aq) + PbI2 (s)

Two Elements Combining (Combination/Addition/Synthesis)

I2 (s) + 3 Cl2 (g) → I2Cl6 (s)

Compound + Element (Combination/Addition/Synthesis)

2 SO2 (g) + O2 (g) → 2 SO3 (g)

Two Compounds Forming One (Combination/Addition/Synthesis)

CO2 (g) + H2O (l) → H2CO3 (aq)

Thermal Decomposition (Decomposition)

CaCO3 (s) → CaO (s) + CO2 (g)

Electrolytic Decomposition (Decomposition)

2 NaCl (l) → 2 Na (l) + Cl2 (g)

Precipitation Reaction (Precipitation)

KI (aq) + Pb(NO3)2 (aq) → KNO3 (aq) + PbI2 (s)

Acid-Base Reaction (Acid-Base/Neutralization)

HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)

Redox Reaction (Oxidation-Reduction)

5 Fe2+ (aq) + 8 H+ (aq) + MnO4- (aq) → 5 Fe3+ (aq) + Mn2+ (aq) + 4 H2O (l)

Solvent-Solute Compatibility Rule

"Like dissolves like" — polar solvents (like water) dissolve polar or ionic solutes (like sugar or salt), while nonpolar solvents dissolve nonpolar solutes.

Salt Dissolution Mechanism

Salt dissolves due to strong ion-dipole interactions between the ions and water molecules.

Solubility Principle

Nonpolar substances like oil dissolve in nonpolar solvents, while polar substances like water dissolve polar or ionic solutes.

Dual-Solubility Characteristics

Substances with both polar and nonpolar regions (like ethanol) can dissolve in both water and oil, making them versatile solvents.

Nonpolar Chain Influence on Solubility

As the nonpolar part of a molecule increases, it becomes more soluble in nonpolar solvents like oil and less soluble in polar solvents like water.

Methanol's Solubility in Water

Methanol is a small, highly polar molecule, so it dissolves best in water, which is also polar, due to hydrogen bonding.

Ethanol's Dual Solubility Preference

Ethanol is soluble in both water and oil, but it is more soluble in water because the polar −OH group allows stronger interactions with water molecules.

What salts are always soluble?

Salts with group 1 metal cations (Li⁺, Na⁺, K⁺, etc.) and ammonium ion (NH₄⁺).

What nitrates, ethanoates, chlorates, and perchlorates are soluble?

Nitrates (NO₃⁻), ethanoates (acetates) (CH₃COO⁻), chlorates (ClO₃⁻), and perchlorates (ClO₄⁻) are soluble.

What salts are generally insoluble?

Ag⁺, Pb²⁺, and Hg₂²⁺ salts are insoluble.

What halides are generally soluble?

Chlorides (Cl⁻), bromides (Br⁻), and iodides (I⁻) are generally soluble.

What sulfates are soluble, except?

Sulfates (SO₄²⁻) are soluble, except those containing Ca²⁺, Sr²⁺, or Ba²⁺.

What compounds are generally insoluble?

Carbonates (CO₃²⁻), hydroxides (OH⁻), oxides (O₂²⁻), phosphates (PO₄³⁻), and sulfides (S²⁻) are generally insoluble.