Acids, Bases and Salts Mrs Teocc

Acids Acids Strong acids Weak acids man-made mineral acids corrosive e.g. sulphuric acid hydrochloric acid nitric acid Weak acids found in plants and animals, used in food organic acid not very corrosive e.g. ethanoic acid citric acid malic acid

Physical Properties of Acids 1. Acids have a taste. sour Lemons, limes, oranges, grapefruits - citric acid Grapes – tartaric acid

Physical Properties of Acids 2. Acids can the colour of indicators change Indicator Colour in acid Blue Litmus Phenolphthalein Methyl orange Red Colourless Red

Chemical Properties of Acids An acid reacts with a metal to form a salt and hydrogen acid + metal  salt + hydrogen e.g 1. zinc + hydrochloric  acid 2. Magnesium + sulphuric  acid zinc + hydrogen chloride Zn + 2 HCl  ZnCl2 + H2 zinc + hydrogen sulphate Mg + H2SO4 MgSO4 + H2

Chemical Properties of Acids acid + metal  salt + hydrogen

Chemical Properties of Acids acid + metal  salt + hydrogen Note: 1. Different metals have different rates of reaction with dilute acids. 2. Sodium , potassium, lithium react explosively with dilute acids. 3. Copper, silver, gold do not react with dilute acids.

Chemical Properties of Acids a salt + water 2. An acid reacts with a base to form acid + base  salt + water e.g. (a) copper(II) + sulphuric  oxide acid (b) sodium + hydrochloric  hydroxide acid copper(II) + water sulphate CuO + H2SO4  CuSO4 + H2O sodium + water chloride HCl + NaOH  NaCl + H2O

Chemical Properties of Acids The reaction between a base and an acid to produce a salt and water is called neutralisation.

Chemical Properties of Acids 3. An acid reacts with a carbonate to produce a salt, water and carbon dioxide acid + carbonate  salt + water + carbon dioxide eg. (a)magnesium +hydrochloric  carbonate acid magnesium + water + carbon chloride dioxide MgCO3 + 2HCl  MgCl2 + H2O + CO2

Chemical Properties of Acids carbonate + acid  salt + water + carbon dioxide White precipitate is formed

Properties of Acids Summary 1. Acids have a sour taste. 2. Acids change the colour of indicators 3. acid + metal  4. acid + base  5. acid + carbonate  salt + hydrogen salt + water salt + water +carbon dioxide

Explanation for Properties 1. When an acid dissolves in water, it undergoes ionisation. H+ ions and the corresponding acid polyatomic ions are formed. The properties of an acid are due to the presence of hydrogen ions.

Hydrogen ions and Acids citric acid + water (hydrogen citrate) sulphuric acid + water (hydrogen sulphate) hydrochloric acid + water (hydrogen chloride) H+ ion + citrate ion H+ ion + sulphate ion H+ ion + chloride ion When acid dissolves in water, H+ ions are formed

Hydrogen ions and Acids An acid is a substance that produces hydrogen ions in water

Strength of Acids Acids Strong acids Weak acids all the acid molecules ionise to become ions Weak acids most molecules remained unchanged

Some Uses of Acids Hydrochloric acid Sulphuric acid Nitric acid Cleaning metallic surfaces before they are painted or coated with other metals Used as an in car batteries, making fertilisers, and plastics Making fertilisers and explosives Preserving food and cooking Making health salts Hydrochloric acid Sulphuric acid Nitric acid Ethanoic acid Citric acid

Bases and Alkalis Bases * aqueous ammonia * metal oxides and metal hydroxides e.g. copper (II) oxide, zinc oxide, magnesium oxide, sodium oxide, zinc hydroxide, potassium hydroxide Alkalis * aqueous ammonia * metal hydroxides which are soluble in water e.g. calcium hydroxide, sodium hydroxide, potassium hydroxide

Bases and Alkalis BASES ALKALIS e.g. NaOH e.g.CuO ALKALIS e.g. NaOH Alkalis are bases but not all bases are alkalis

Physical of Properties of Alkalis Alkalis feel Alkalis taste soapy. bitter.

Physical of Properties of Alkalis 3. Alkalis change the colour of indicators Indicator Colour in Alkali Red litmus Blue Phenolphthalein Pink Methyl Orange Yellow

Chemical Properties of Alkalis 1. An alkali reacts with an acid to produce a salt and water only. acid + alkali  salt + water e.g. (a) copper(II) + sulphuric  oxide acid (b) sodium + hydrochloric  hydroxide acid copper(II) +water sulphate CuO + H2SO4  CuSO4 + H2O sodium + water chloride HCl + NaOH  NaCl + H2O

The reaction between an alkali (base) and an acid to produce a salt and water is called neutralisation.

Chemical Properties of Alkalis 2. An alkali reacts with an ammonium aalt to produce a salt, water and ammonia gas. alkali + ammonium salt  salt + water + ammonia gas e.g. ammonium chloride + sodium hydroxide  sodium chloride + water + ammonia NH4Cl + NaOH  NaCl + H2O + NH3

Chemical Properties of Alkalis 3. An alkali reacts with a solution of metal salt to form a metal hydroxide. e.g. FeCl3 + 3NaOH  Fe(OH)3 + 3NaCl (red-brown ppt) CuSO4 + 2NaOH Cu(OH)2 + Na2SO4 (blue ppt)

salt + water + ammonia gas. Properties of Alkalis Summary 1. Alkalis feel soapy. 2. Alkalis change the colour of indicators 3. alkali + acid  4. alkali + ammonium salt  5. alkali + solution of metal salt  salt + water. salt + water + ammonia gas. metal hydroxide + salt

Hydroxide ions and Alkalis When an alkali dissolves in water hydroxide ions (OH-) ions are produced. e.g. NaOH  Na+ + OH- KOH  K+ + OH- * Properties of alkalis are due to the presence of hydroxide ions.

Strength of Alkalis Alkalis Strong alkalis Weak alkalis when the alkali is dissolved in water, all the ions are dissociated Weak alkalis most molecules remained unchanged

Strength of Alkalis Strong alkalis e.g. NaOH  Na+ + OH- KOH  K+ + OH-

Strength of Alkalis Strong alkalis e.g. NaOH  Na+ + OH- KOH  K+ + OH- OH- Na+ OH- Na+ Na+ OH- OH- Na+

Strength of Alkalis Weak alkalis e.g. NH3 + H2O NH4+ + OH- - Only a small fraction of ammonia molecules form OH- - Most of molecules remained unchanged

Strength of Alkalis Weak alkalis e.g. NH3 + H2O NH4+ + OH- - Only a small fraction of ammonia molecules form OH- - Most of molecules remained unchanged NH3 NH3

Uses of bases/alkalis mainly for 2 reasons neutralise acids e.g. toothpaste (magnesium hydroxide) antacid (aluminium hydroxide, magnesium hydroxide) remove grease e.g. soap, floor cleaners (strong alkali-sodium hydroxide) cleaners for glass windows (weak alkali/ /ammonia)

Uses of Alkalis Alkalis Common names Uses Sodium hydroxide caustic soda Making soap, washing powder, drain cleaner Potassium hydroxide caustic potash Making paint removers dyes for fabric Calcium hydroxide slaked lime Reducing acidity of soil and making mortar Aqueous ammonia Making fertilisers and (Ammonia solution) household cleaning liquids