ACIDS and BASES

Why ‘acids and bases’? Scientists like to classify things and donating them as acids or bases is one way to do that. If a solution is not an acid or a base, it is half way between the two and known as a neutral solution.

What are some properties of Acids? The word acid comes from the Latin word acere, which means "sour." All acids taste sour. Well known from ancient times were vinegar, sour milk and lemon juice. By the 1884s acids defined by Svante Arrhenius (Sweden), as a material that can release hydrogen ions (H + ). Acids turn litmus paper red. Acids are corrosive.

Some Common Acids NameChemical formula Uses Hydrochloric acid HCl Cleaning brickwork Sulfuric acid H 2 SO 4 Car batteries Nitric acid HNO 3 Fertiliser and dyes Acetic acid CH 3 COOH Vinegar Carbonic acid H 2 CO 3 Carbonated drinks Citric acid C6H8O7C6H8O7 Citrus fruits Lactic acid C3H6O3C3H6O3 Milk products

What are some properties of Bases? All bases taste bitter. Mustard tastes bitter. Many medicines such as cough syrup taste bitter. Cough syrups are advertised as having a great taste. This is because sweeteners are added in order to cover the bitterness of the active ingredient in cough syrup. Many bases are cleaning products and they have a slippery feel to them. Bases release OH- ions into solution. Bases turn litmus blue. Bases are corrosive.

Some Common Bases NameChemical FormulaUses Sodium hydroxide NaOH Soap-making, oven cleaners Potassium hydroxide KOH Soft soap making Calcium hydroxide Ca(OH) 2 Cement, plaster Ammonium hydroxide NH 4 OH Household cleaners Magnesium hydroxide Mg(OH) 2 Indigestion cleaners Sodium carbonate Na 2 CO 3 Glass-making Sodium hydrogen carbonate NaHCO 3 Baking soda

The pH of a solution This scale is logarithmic : It means that every time you go down 1 level on the scale, the solution is 10x stronger. For example an acid of pH 1 is 10 times more acidic than an acid with pH 2 and 100 times more acidic than an acid of pH 3. It also means that a base of pH 11 is 10 times more basic (stronger basicity) than a base of pH 10 and 100 times more basic than a base of pH More acid, strong acid Less acid, Weak acid Less basic, Weak base More basic, strong base Neutral The pH scale enables us to classify acids and bases

The pH scale pHExample Acids 0HCl : Hydrochloric acid 1Stomach acid 2 Lemon juice 3 Vinegar 4Soda, tomato juice 5Black coffee 6Milk, rain water Neutral7Pure water Bases 8Egg whites 9Baking Soda 10Limewater / antacid 11Ammonia 12Mineral Lime - Ca(OH) 2 13 Drano ® 14NaOH : sodium hydroxide 10X less acidic 100x more acidic

Indicators Indicators are substances that undergo colour changes in either acids or bases or in both Because of these properties, scientists can identify whether a solution is an acid or a base by noting the colour change Some popular indicators are: phenolpthalene, litmus paper, universal, methyl blue

Indicators 7014 More acid, strong acid Less acid, Weak acid Less basic, Weak base More basic, strong base Neutral

What does a neutral solution look like? HH O H O - H The glass of pure water is neutral (pH=7). There are as many “H+” ions as there are “OH-” ions. When a water molecule splits into hydrogen and hydroxide ions it is said to be dissociated. Water molecules in a glass jar Some water molecules have a natural tendency to split into OH- and H+ ions (see inside red oval shape)

What does an acid look like in solution? Add some acid to the water H+ OH- The acid dissociates leaving more H+ than OH-. The liquid is therefore Acidic H+ OH- H+ Hydrochloric Acid (HCl) H+ Cl- Start with a neutral solution of water

What does a base look like in solution? H+ OH- Base: Sodium Hydroxide (NaOH) The base dissociates leaving more OH- than H+ : the liquid is therefore Basic Add some base to the water OH- Na+ H+ OH- Start with a neutral solution of water

When there are as many OH- as H+, the solution becomes neutral as the acid has been neutralised by the base. Base: NaOH OH- Na+ H+ OH- H+ Cl- H+ OH- H+ Na+ Cl- Neutralisation Start with an acid solution i.e. HCl: more H+ than OH- Add a base i.e. NaOH The OH- from the base associates with the H+ from the dissociated acid

When there are as many H+ as OH-, the solution becomes neutral as the base has been neutralised by the acid. Acid: HCl H+ OH- Na+ H+ OH- H+ Na+ H+ Cl- Neutralisation Start with a Basic solution i.e.NaOH: more OH- than H+ Add some acid i.e.HCl The H+ from the acid associates with the OH- from the dissociated base

Some Common Salts Acid + BaseSalt + Water BaseAcidSaltUse Sodium hydroxide Hydrochloric acid Sodium chloride Table salt Potassium hydroxide Nitric acid Potassium nitrate Explosives, fertilisers Calcium hydroxide Sulfuric acid Calcium sulfate Plaster

Salts What is a salt? A salt is an ionic compound made up of a metal and a non metal Non metal Metal

H+ Cl- H+ Cl- HH Hydrogen Gas Fe+ Metal and acid reactions Fe e- A metal lattice of iron with many electrons HCl is added and dissociated The H+ ions join to form Hydrogen gas The chloride joins with the metal to make iron chloride Overall reaction for metals and acids: Metal + Acid Hydrogen + Salt

Metal and acid reactions Metal + Acid Hydrogen + Salt When sulfuric acid forms a salt it is a sulfate salt When nitric acid forms a salt it is a nitrate salt When acetic acid forms a salt it is an acetate salt When hydrochloric acid forms a salt it is a chloride salt Sulfuric acid + magnesiumMagnesium sulfate + hydrogen Nitric acid + zincZinc nitrate + hydrogen Acetic acid + potassium Potassium acetate + hydrogen Hydrochloric acid + sodiumSodium chloride + hydrogen

ACIDS and BASES The End