Module 8.1 Chemical Reactions

Precipitation Reaction

A reaction that forms a solid or precipitate when two aqueous solutions are mixed. ● Reactions that form solid substances in water. ● Also used to remove dissolved toxic metals in industrial waste. Example: ◦ Precipitation reactions occur when positive ions (cations) and negative ions (anions) in aqueous solution combine/react to form an insoluble ionic solid called a precipitate. ◦ Whether or not such a reaction occurs can be determined by using the solubility rules for common ionic solids.

Precipitate

An insoluble product formed through the reaction of two solutions containing soluble compounds.

Combustion Reactions; - a subcategory of Oxidation-reduction reactions

Combustion Reactions are a subcategory of Oxidation-reduction reactions. ● In Oxidation-reduction reactions electrons are transferred from one substance to another. ● Oxidation; the substance that 'Oxidises' loses electrons (by giving them away). ● Reduction; the substance that 'reduces' gains electrons (receives electrons thus, reducing its charge)

Combustion Reaction: Driving a Car

Hydrocarbons such as Octane (C₈H₁₈) from gasoline combine with Oxygen (O₂) from the air and react to form Carbon Dioxide Gas (CO₂) and Water (H₂O). ● Substance (Octane) reacts with Oxygen, emits heat (exothermic reaction), forms one or more Oxygen-containing compounds. (expands gasses in car's cylinders, thus accelerating it forward) ● Octane & Oxygen go into the cars engine (engine is hot), they react and transform into Carbon Dioxide (CO₂) and Water (H₂O).

Dissociation

In aqueous solution, the process by which a solid ionic compound separates into its ions. Example: ● Laundry detergents contain Sodium Carbonate (Na₂CO₃) which removes Calcium and magnesium ions from the water. ●Sodium Carbonate (Na₂CO₃) dissolved in water 'dissociates', or separates into Sodium ions (Na⁺) and Carbonate ions (CO₃⁻²).

Reactions of Soap

Pure water: Soap forms suds (foams up) Hard Water: ● Contains dissolved Calcium (Ca²⁺) and Magnesium (Mg²⁺) ions. ・ Soap reacts with the ions to form a grey residue that adheres to clothes. ・ This grey slimy substance iscalled curd, or soap scum.

Gas Evolution Reactions

Reactions that occur in liquids and form a gas. When liquids react to form gas. Example: ● Baking soda volcano experiment; Sodium Bicarbonate reacts with Acetic Acid in vinegar to form Carbon Dioxide Gas, Water, and Sodium Acetate. ➢ Carbon dioxide bubbles out

Combustion Reactions

● Reactions in which a substance reacts with Oxygen, emitting heat and forming one or more oxygen-containing compounds ● Combustion Reactions are a subcategory of Oxidation-reaction reactions, in which electrons are transferred from one substance to another.

Oxidation-reduction Reaction: Example

● The formation of 'rust' ● Dulling of car paint

Chemical Reaction

● Transformation of one of more substances into different substances ● In all cases, chemical reactions produce change in the arrangements of the molecules and atoms that compose matter. ◦ Often molecular changes (microscopic) cause macroscopic changes , that are visible to the naked eye. ● Can be as simple as combustion, or as complex and protein synthesis.