Acids, Bases, and Salts

• Acids, bases, and salts are important chemical compounds.

Terminology

• An atom is the simplest particle of an element.
• A molecule consists of two or more chemically bonded atoms.
• An element includes only one type of substance, examples include gold (Au), carbon (C), and oxygen (O).
• A compound is a substance of two or more chemically bonded elements, for example, water (H₂O), which is a compound of hydrogen (H) and oxygen (O).
• A mixture is a combination of two or more elements that are NOT chemically bonded, for example, air is a mixture of many gases.
• A solution is a homogenous mixture of two or more substances, usually in liquid form.

pH Scale & Universal Indicator

• The pH scale represents the strength of an acid or an alkali.
• An indicator shows if a solution is acidic or alkaline and includes universal indicator, litmus paper, methyl orange, and phenolphthalein.
• A universal indicator can indicate the pH of a solution.
• Solutions with a pH of 0-6 are acids, pH of 7 is neutral, and pH of 8-14 are alkalis.
• Solutions with pH of 0-2 include Gastric acid and Lemon juice.
• Solutions with pH of 3-5 include Orange juice, Tomato juice and Black coffee.
• Solutions with a pH of 6-8 include Urine, Distilled Water, and Sea Water.
• Solutions with pH of 9-12 include Baking Soda, Milk of Magnesia, and Ammonia Solution,.
• Solutions with pH of 13-14 include Soapy Water and Bleach.

Experimental Setup

• The amount of carbon dioxide produced by chemical reactions using acids can be measured using the water displacement method.

Acids

• Acids taste sour and are corrosive in concentrated form.
• Acids have a pH number less than 7.
• Examples of acids include vinegar, lemon juice, sulphuric acid (used in car batteries), and hydrochloric acid (helps digest proteins in the stomach).
• An acid is a solution with an excess of hydrogen (H⁺) ions, meaning that a stronger acid has a higher concentration of H⁺ ions.

Bases / Alkalis

• Bases are the chemical opposite of acids.
• Strong alkalis are as dangerous as strong acids.
• Alkalis have a pH number greater than 7.
• Bases that dissolve in water are called alkalis.
• Bases are found in many household items like baking soda, soap, washing machine liquid, and toothpaste.
• An alkali is a soluble base that has an excess of hydroxide (OH¯) ions, meaning a stronger alkali has a higher concentration of hydroxide (OH¯) ions.
• A neutral solution has equal concentrations of H⁺ and OH¯ ions.
• H⁺ + OH¯ → H₂O is water.
• Oxides of metals are always bases, and examples of metal oxides include copper oxide and sodium oxide in solid form.
• Oxides of non-metals are always acids, and examples of non-metal oxides include sulphur dioxide and carbon dioxide as acidic gases.

Reactants and Products in a Chemical Reaction:

• Reactants are substances that go into a chemical reaction.
• Products are substances produced by a chemical reaction.

Chemical Reactions of Acids:

• Acid + Metal → Salt + Hydrogen, for example, Calcium + Hydrochloric acid → Calcium chloride + Hydrogen gas (Ca + 2HCl → CaCl₂ + H₂).
• Acid + Metal Carbonate → Salt + Carbon Dioxide + Water, for example, Sulphuric acid + Magnesium carbonate → Magnesium sulphate + Carbon dioxide + Water (MgCO₃ + H₂SO₄ → MgSO₄ + CO₂ + H₂O).
• Acid + Base → Salt + Water, for example, Hydrochloric acid + Sodium hydroxide → Sodium Chloride + Water (HCl + NaOH → NaCl + H₂O) where NaCl is salt water. Sulphuric acid + Sodium hydroxide → Sodium Sulphate + Water (H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O)

Neutralization Reactions:

• Acid + Base → Salt + Water
• Acids and bases are chemical 'opposites' that cancel each other out when they react together, which is called a neutralization reaction.
• A neutralization reaction is a solution with pH 7 (neither acidic nor alkali) if the concentrations and quantities of hydrochloric acid and sodium hydroxide are precisely balanced.
• Measured neutralization experiments are called titration.

Balancing Equations:

• Hydrogen + Oxygen → Water : 2 H₂ + O₂ → 2 H₂O
• Two molecules of hydrogen react with one molecule of water to produce two molecules of water.
• Subscript numbers indicate how many atoms there are of each element in a single molecule of the compound.
• Balancing a chemical equation makes sure that the number of atoms of each element is the same for the products (right side of the equation) and the reactants (left side of the equation).
• Balanced equations include: 2 H₂ + O₂ → 2 H₂O, 2 Al + 3 Cl₂ → 2 AlCl₃, and 3 Mg + 2 S → Mg₃S₂

Salts:

• A salt is a substance produced by the neutralisation of an acid and a base.
• Salt solutions are always neutral.
• The name of the metal reactant is the first word in the name of the salt.
• The name of the acid reactant is where the second word in the name of the salt is derived from.
• Metal + Acid → Salt + Hydrogen, for example, Magnesium + Hydrochloric acid → Magnesium chloride + Hydrogen
• Common acids and their corresponding salt names: Hydrochloric Acid (Chloride), Sulphuric Acid (Sulphate), and Nitric Acid (Nitrate).

This lesson covers acids, bases, and salts, fundamental chemical compounds. It explains related terminology such as atoms, molecules, elements, compounds, mixtures, and solutions. It also explains the pH scale and universal indicators.