Chemistry

Seite 1

Acids and Bases

Chapter 11 Pages 148 – 165 in text book

Chapter 12 Pages 84 – 91 in revision guide

As a solution, an acid

contains H⁺ ions (protonated

hydrogen). An example is hydrochloric acid HCL (aqueous). As a solution, it

dissociates its ions into H⁺ and Cl⁻.

Every formula for acid must

have hydrogen in it. Strong acids dissociate fully and all its molecules turn

into ions (strong concentration of H⁺ ions) and weak acids dissociate a little,

so some of its molecules become ions. Strong acids therefore also conduct

better.

Strong

acids: Weak acids:

Hydrochloric acid HCl Ethanoic

acid CH₃COOH

Sulfuric acid H₂SO₄ Methanoic

acid HCOOH

Nitric acid HNO₃ Citric

acid C₆H₈O₇

A base neutralizes an acid, and is metal hydroxides and metal oxides.

An

alkali is a soluble base.

Solutions of alkalis contain OH⁻ ions

(hydroxide ions). Stronger alkalis conduct better. Some examples of alkalis (as

aqueous solutions) are:

Sodium hydroxide NaOH

Potassium hydroxide KOH

Calcium hydroxide Ca(OH)₂

Ammonia NH₃ (weak

alkali)

The pH (protonated hydrogen) scale is used to show how acidic or

alkaline a solution is (measures H⁺ concentration). Numbers 0 – 6 are acid solutions; the lower the

number, the more acidic the solution (the

higher concentration of H⁺ ions). Number 7 is neutral (e.g. pure water). Numbers 8 – 14 are alkaline solutions; the higher the number, the more

alkaline in the solution (the higher

concentration of OH⁻ ions).

An indicator indicates whether something is an acid or an alkali.

Litmus, phenolphthalein and methyl orange are all indicators:

Litmus turns red in acid, and

blue in alkali.

Phenolphthalein turns

colourless in acid and pink in alkali.

Methyl orange turns red in

acid and yellow in alkali.

Universal

indicator is

a mixture of dyes. It is used to find the pH of a solution. It can be used as a

solution or paper strip. See page 149TB for chart

Acid + Base →

Salt + Water

Acid + Metal →

Salt + Hydrogen

Acid + Carbonate →

Salt + Water + Carbon Dioxide

Hydrochloric acid salt ends with chloride

Sulfuric acid salt ends with sulphate

Nitric acid salt ends with

nitrate

A neutralisation reaction is a

reaction with acid that gives water as well as salt, and neutralises the acid.

Acid reactions with bases and carbonates are neutralisations.

When strong bases are heated

with ammonium compounds ammonia gas if given off.

It is important to control

acidity in soil because if the soil is too acidic, the crops don’t grow.

Neutralisation is used to reduce the acidity in soil. The soil is treated with

crushed limestone, lime or slaked lime.

Acids and bases