Acids, Bases, Indicators

Acids

• All acids produce hydrogen ions, in aqueous solution. (Hydrogen ions must be present) Hydrogen Ions (H+)
• HYDROGEN IONS (H+) MUST BE PRESENT TO BE CALLED AN ACID  Thus, for example Hydrochloric acid is not an acid in gaseous form, only in aqueous solution.
• Acids have a sour taste. 
• Acids dissolve in water to form solutions which conduct electricity. 
• Acid turns blue litmus paper red. 
• Acids have a pH < 7
• Acids react with reactive metals to form hydrogen and a salt. However, there are some acid and metal reactions that do not give hydrogen. 
• Acids only show the properties of acids when the are dissolved in water. This is because acids dissociate in water to produce hydrogen ions which are responsible for acidic properties.

Examples:

• Hydrochloric acid, HCl (gaseous) -> (dissolved in water) H+(aq) + Cl-(aq)
• Sulfuric acid, H₂SO₄(gaseous) -> (dissolved in water) 2H+(aq) + SO₄^2-
• Nitric acid, HNO₃
• Ethanoic acid, CH₃COOH -> (dissolved in water) CH₃COO^-(aq) + H⁺(aq)
• Carbonic acid, H₂CO₃ (gaseous) -> (dissolved in water) 2H⁺(aq) + CO₃^2-(aq)

Strong Acids	Weak Acids
Hydrochloric acid	Ethanoic acid
Sulfuric acid	Carbonic acid
Nitric acid

Bases and Alkalis
A base is any metal oxide or hydroxide. We can also define base as a substance that reacts with an acid to give a salt and water only. An alkalis is a bass that is soluble in water (most bases are insoluble in water) Alkalis have a bitter taste and soapy feel. Alkalis turn red litmus paper blue. An alkalis produce hydroxide ions when dissolved in water. All alkalis can react with acids to form a salt and water only. This reaction is called neutralisation. Alkalis heated with ammonium salts give off ammonia gas.
Concentration and Strengths
The term concentration tells us how much a substance is dissolved in 1 dm3 of the solution. The term strength refers to how easily an acid or an alkali dissociates when dissolved in water. A strong acid dissociates easily in water, while a weak acid does not fully dissociate when dissolved in water.The strength of an acid or alkali cannot be changed.
The PH Scale
The pH scale is a set of numbers used to indicate whether a solution is acidic, neutral or alkaline. Acids have pH values less than 7, alkalis have pH values greater than 7, and a neutral solution has a pH value of exactly 7. 
Types of Oxides
Many acids and alkalis are formes by dissolving oxides in water. An oxide is a compound of oxygen and another element. 
Acidic Oxides
Non-Metals may form acidic oxides. Most acidic oxides dissolve in water to form an acid. Acid oxides do not react with acids. However, they react with alkalis to form a salt and water. 
Basic Oxides
The oxides of metals are basic oxides. Most basic oxides are insoluble in water. A few oxides, however, dissolve readily in water. They are called alkalis.
Amphoteric Oxides
Amphoteric Oxides are metallic oxides that react with both acids and bases to form salt and water.
Neutral Oxides
Some non- metals form oxides that show neither basic nor acidic properties. These oxides are called neutral oxeds and they are insoluble in water.