5.1 Acids and Bases Acids and bases are very common. Acids and bases can be very dangerous and corrosive! NEVER try to identify an acid or base by taste or touch!

pH Scale The strength of acids and bases is measured on the pH scale pH below 7 = acidic pH 7 = neutral pH above 7 = basic 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acids Neutral Bases If the pH of a solution drops from 7 to 6, it’s concentration changes by a factor of 10. If the pH of a solution drops from 8 to 6, it’s concentration changes by a factor of 102 = 100

pH Indicators The pH of acids and bases cannot be determined by sight. pH indicators are chemicals that change colour depending on the pH of the solution they are placed in. Litmus paper is the most common indictor. Two colours of litmus paper: Blue = basic (>7) and Red = acidic (<7). A universal indicator contains a number of indicators that turn different colors.

pH Indicators A digital pH meter or probe measures an electrical property of the solution and uses this to determine the pH.

Acids In food and drink, taste sour. Are caustic (corrodes stuff). Named from their anions If you know a compound’s chemical formula, you may be able to identify it as an acid. Acids often behave like acids only when dissolved in water. Therefore, acids are often written with subscript (aq) = aqueous = water

Acids The chemical formula of an acid usually starts with Hydrogen (H). HCl(aq) = hydrochloric acid HNO3(aq) = nitric acid Acids with a carbon usually have the C written first. CH3COOH(aq) = acetic acid

How to Name Acids 3 simple rules: 1. If the anions name ends in –ide, the corresponding acid is named “Hydro________ic acid” For example, Formula: HCL Name: Hydrogen chloride Hydrochloric acid

How to Name Acids 2. If the anions name ends in –ate, the corresponding acid is named “________ic acid” For example, Formula: HNO3 Name: Hydrogen nitrate Nitric acid

How to Name Acids 3. If the anions name ends in –ite, the corresponding acid is named “________ous acid” For example, Formula: H2SO3 Name: Hydrogen sulfite Sulfurous acid

Name them! HI HNO2 H2CrO4 HNO3 H2S H2SO4

ACIDS pH of 0 to 6.9 Contribute H+ ions into a solution Turn litmus paper RED Conduct ELECTRICITY Produce H+ gas (when added to some metals)

Bases If you know a compound’s chemical formula, you may be able to identify it as a base. Bases, like acids, often behave like bases only when dissolved in water Therefore, bases are often written with subscript (aq) = aqueous = water

Bases The chemical formula of a base usually ends with hydroxide (-OH). Examples of common bases: NaOH(aq) Mg(OH)2(aq) Ca(OH)2(aq) NH4OH(aq)

How to Name Bases Easier than acids The cation (metal) goes first. Add “hydroxide” to it. For example: NaOH Ca(OH)2 Fe(OH)3

BASES pH of 7.1 to 14 Donate [OH]- ions into a solution The hydroxide [OH-] group is neutralized by a hydrogen ion to make water. Turns litmus paper BLUE Conducts ELECTRICITY Are Slippery Are also CAUSTIC

Production of Ions Acids and bases can conduct electricity because they release ions in solution. Acids release hydrogen ions, H+(aq) Bases release hydroxide ions OH–(aq)

The pH of a solution refers to the concentration of ions it has. Square brackets are used to signify concentration, [H+(aq)], [OH–(aq)] High [H+(aq)] = low pH, very acidic High [OH–(aq)] = high pH, very basic

H+(aq) + OH–(aq)  H2O(l) A solution cannot have BOTH high [H+(aq)] and [OH–(aq)] they cancel each other out and form water. This process is called neutralization. H+(aq) + OH–(aq)  H2O(l)

neutralization animations Litmus paper, pH paper, & neutralization animations http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks3/science/acids/index.htm