Acids & Bases

• two classes of chemicals that play an important role in everyday life

• classified based on their properties:

Property Acids Bases

molecular or ionic? molecular ionic

aqueous solution conducts electricity? yes yes

feel slippery

taste sour bitter

Acids• produce hydrogen ions (H+) when dissolved in water (aq)• e.g. HCl splits into H+ and Cl- ions in water • react with substances in characteristic ways:

Reaction with Metalsacid + metal hydrogen gas + ionic compound

Example: hydrochloric acid with zincHCl(aq) + Zn(s) H2(g) + ZnCl2(aq)

Reaction with Carbonatesacid + carbonate carbon dioxide + water + ionic compound

Example: vinegar with baking sodaHC2H3O2(aq) + NaHCO3(aq) CO2(g) + H2O(l) + NaC2H3O2(aq)

• acid chemical formulas typically begin with an H, and followed by (aq)

• acids show their properties only when dissolved in water

Naming Acids

• first group of acids are called binary – only 2 elements

Acid name Chemical formula Use

Hydrofluoric acid HF(aq) Etching glass

Hydrochloric acid HCl(aq) Cleaning concrete

Hydrobromic acid HBr(aq) To make cleaning compounds

Hydrosulfuric acid H2S(aq) Purifying metals

• second group are oxyacids • contain polyatomic ions• more commonly encountered

Acid Chemical formula Related polyatomic ion Polyatomic ion name

Acetic acid HC2H3O2 (aq) C2H3O2−(aq) acetate

nitric acid HNO3(aq) NO3−(aq) nitrate

carbonic acid H2CO3(aq) CO32–(aq) carbonate

sulfuric acid H2SO4(aq) SO42−(aq) sulfate

phosphoric acid H3PO4(aq) PO43−(aq) phosphate

Bases

• also known as alkaline• many are ionic• a substance that produces hydroxide (OH-) ions

when dissolved in water • e.g. NaOH splits into Na+ and OH- ions in water

Naming BasesBase Chemical formula Uses

Sodium hydroxide NaOH(aq) Making paper

calcium hydroxide Ca(OH)2(aq) decreasing the acidity of lakes and soil

ammonium hydroxide NH4OH(aq) window cleaners

magnesium hydroxide Mg(OH) 2(aq) antacids

aluminum hydroxide Al(OH)3(aq) heartburn medications

sodium hydrogen

carbonate (baking soda)

NaHCO3(aq) making baked goods rise

an abrasive cleaner

pH• related to the number of hydrogen ions (H+) in

a solution• power (or potential) of hydrogen• pH scale indicates how acidic or basic a

solution is• ranges from 0 (very acidic) to 14 (very basic)• pH of 7 is neutral

Acid-Base Indicators

• any substance that changes colour if an acid or a base is present

Indicator Colour in Acid Colour in Base

bromothymol blue yellow blue

phenolphthalein colourless pink

phenol red yellow red/pink

litmus red blue

methyl orange red orange/yellow