Atoms, Molecules, Acids, and Bases

• An atom is the smallest unit of matter retaining an element's properties.
• An element cannot be broken down into simpler substances chemically.
• A molecule consists of two or more bonded atoms.
• A compound consists of two or more different types of atoms chemically bonded.
• All compounds are molecules, but not all molecules are compounds.

Acids

• Acids have a pH lower than 7 and donate protons.
• Acids taste sour, and concentrated acids can be corrosive.
• When dissolved in water, acids release hydrogen ions (H+) or hydronium ions (H3O+).
• Examples of acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), acetic acid (CH₃COOH), nitric acid (HNO₃), citric acid (C₆H₈O₇), vinegar and lemon juice.

Bases

• Bases have a pH higher than 7 and accept protons.
• Water-soluble bases are called alkali; strong alkalis can be dangerous.
• When dissolved in water, bases release hydroxide ions (OH-).
• Examples of bases include sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium carbonate (CaCO₃), baking soda, soap, and bleach.

Metal and Non-Metal Oxides

• An oxide contains at least one oxygen atom and one other element atom.
• Metal oxides are always bases.
• Non-metal oxides are always acids.

Indicators

• Indicators determine if a substance is an acid or alkali and can sometimes indicate pH.
• Universal Indicator: shows pH levels by changing color.
• Litmus Paper: turns red for acid and blue for alkali.
• Methyl Orange: turns red for acidic and yellow for basic or neutral substances.
• Phenolphthalein: turns colorless in acids and pink in alkalis.

Equations

• Metal + Acid → Salt + Hydrogen gas
• Metal Carbonate + Acid → Salt + Water + Carbon Dioxide
• Acid + Base → Salt + Water

Precipitation

• Precipitation is the formation of an insoluble solid (precipitate) in a chemical reaction.
• The remaining liquid is called a supernate or supernatant.
• Example: Potassium iodide + Lead nitrate → Lead iodide (precipitate) + Potassium nitrate (solution)

Preparing Crystals from Neutralisation Reaction

• Add nickel(II) carbonate to dilute sulfuric acid, stir until no more dissolves.
• Filter out excess nickel(II) carbonate and pour the filtrate into an evaporating dish.
• Boil the filtrate to about half its original volume, then cool.
• Leave the evaporating dish overnight to form crystals of pure nickel(II) sulfate.
• Filter out the crystals and let them dry.

Strength and Concentration

• Strength or concentration indicates the amount of solute in a volume.
• It can be expressed in molarities (M), mass concentration, etc.

Reactants

• Reactants are substances that undergo a chemical reaction and are consumed during the reaction.
• Reactions involve breaking and forming chemical bonds.

Neutralisation

• Neutralization is when an acid and a base react to form a neutral solution.
• Acid + Base → Salt + Water

Products

• Products are substances formed from a chemical reaction.
• Reactants undergo chemical changes to form products.

Collecting Hydrogen Gas

• Place diluted hydrochloric acid in a test tube, add magnesium, and test with a glowing splint.
• The presence of hydrogen gas is indicated by a 'pop' sound.
• Metals and dilute acids: acid + metal → salt + hydrogen
• Metal carbonates and dilute acids: acid + carbonate → salt + water + carbon dioxide

Ions

• Positively charged ions are called cations and are formed when an atom loses electrons.
• Examples of cations: Sodium (Na+), Magnesium (Mg2+)
• Negatively charged ions are called anions and are formed when an atom gains electrons.
• Examples of anions: Chloride (Cl-), Sulfate (SO42-)

Words

• Electrolytes: solutions that conduct electricity.