ACIDS, BASES AND SALTS A guide for A level students 2008 SPECIFICATIONS KNOCKHARDY PUBLISHING.

ACIDS, BASESACIDS, BASESAND SALTSAND SALTSA guide for A level studentsA guide for A level students

2008 2008 SPECIFICATIONSSPECIFICATIONSKNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING

INTRODUCTION

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ACIDS, BASES AND SALTSACIDS, BASES AND SALTS

BRØNSTED-LOWRY THEORY

ACID proton donor HCl ——> H+(aq) + Cl¯(aq)

BASE proton acceptor NH3 (aq) + H+(aq) ——> NH4+(aq)

ACIDS AND BASESACIDS AND BASES




Conjugate systemsAcids are related to bases ACID PROTON + CONJUGATE BASE

Bases are related to acids BASE + PROTON CONJUGATE ACID





Conjugate systemsAcids are related to bases ACID PROTON + CONJUGATE BASE

Bases are related to acids BASE + PROTON CONJUGATE ACID

For an acid to behave as an acid, it must have a base present to accept a proton...

HA + B BH+ + A¯acid base conjugate conjugate

acid base

example CH3COO¯ + H2O CH3COOH + OH¯

base acid acid base


STRONGACIDS completely dissociate (split up) into ions in aqueous solution

e.g. HCl ——> H+(aq) + Cl¯(aq) MONOPROTIC 1 replaceable H

HNO3 ——> H+(aq) + NO3¯(aq)

H2SO4 ——> 2H+(aq) + SO42-(aq) DIPROTIC 2 replaceable H’s

STRONG ACIDS AND BASESSTRONG ACIDS AND BASES

STRONGACIDS completely dissociate (split up) into ions in aqueous solution

e.g. HCl ——> H+(aq) + Cl¯(aq) MONOPROTIC 1 replaceable H

HNO3 ——> H+(aq) + NO3¯(aq)

H2SO4 ——> 2H+(aq) + SO42-(aq) DIPROTIC 2 replaceable H’s

STRONGBASES completely dissociate into ions in aqueous solution

e.g. NaOH(aq) ——> Na+(aq) + OH¯(aq)

STRONG ACIDS AND BASESSTRONG ACIDS AND BASES

Weak acids partially dissociate into ions in aqueous solution

e.g. ethanoic acid CH3COOH(aq) CH3COO¯(aq) + H+(aq)

When a weak acid dissolves inwater an equilibrium is set up HA(aq) + H2O(l) A¯(aq) + H3O+(aq)

The water stabilises the ions

To make calculations easier the dissociation can be written... HA(aq) A¯(aq) + H+(aq)

WEAK ACIDSWEAK ACIDS

Weak acids partially dissociate into ions in aqueous solution

e.g. ethanoic acid CH3COOH(aq) CH3COO¯(aq) + H+(aq)

When a weak acid dissolves inwater an equilibrium is set up HA(aq) + H2O(l) A¯(aq) + H3O+(aq)

The water stabilises the ions

To make calculations easier the dissociation can be written... HA(aq) A¯(aq) + H+(aq)

The weaker the acid the less it dissociates the more the equilibrium lies to the left.

WEAK ACIDSWEAK ACIDS

Partially react with water to give ions in aqueous solution e.g. ammonia

When a weak base dissolves in water an equilibrium is set up

NH3 (aq) + H2O (l) NH4+ (aq) + OH¯ (aq)

as in the case of acids it is more simply written

NH3 (aq) + H+ (aq) NH4+ (aq)

WEAK BASESWEAK BASES

Partially react with water to give ions in aqueous solution e.g. ammonia

When a weak base dissolves in water an equilibrium is set up

NH3 (aq) + H2O (l) NH4+ (aq) + OH¯ (aq)

as in the case of acids it is more simply written

NH3 (aq) + H+ (aq) NH4+ (aq)

The weaker the base the less it dissociatesthe more the equilibrium lies to the left

The relative strengths of bases can be expressed as Kb or pKb values.

WEAK BASESWEAK BASES

Is a typical acid in dilute aqueous solution HCl ——> H+ (aq) + Cl¯(aq)

REACTIONS OF HYDROCHLORIC ACID REACTIONS OF HYDROCHLORIC ACID

Hydrogen chloride is a colourless covalent gas; it is a poor conductor of electricity because there are no free electrons or ions present. It has no action on dry litmus paper because there are no aqueous hydrogen ions present.




If the gas is passed into water, the hydrogen chloride molecules dissociate into ions. The solution now conducts electricity showing ions are present. For each hydrogen chloride molecule that dissociates one hydrogen ion and one chloride ion are produced. The solution turns litmus paper red because of the H+(aq) ions.



HYDROGEN CHLORIDE HYDROCHLORIC ACID

colourless gas Appearance colourless soln.covalent molecule Bonding aqueous ionsHCl(g) Formula HCl(aq) poor Conductivity goodno reaction Dry blue litmus goes red



Appearance Bonding and formula Conductivity Dry litmushydrogen chloride colourless gas covalent molecule HCl(g) poor no reactionhydrochloric acid colourless soln. aqueous ions HCl(aq) good goes red


If the gas is passed into water, the hydrogen chloride molecules dissociate into ions. The solution now conducts electricity showing ions are present. For each hydrogen chloride molecule that dissociates one hydrogen ion and one chloride ion are produced. The solution turns litmus paper red because of the H+(aq) ions.

Metals magnesium + dil. hydrochloric acid ——> magnesium chloride + hydrogen

Mg(s) + 2HCl(aq) ——> MgCl2(aq) + H2(g)


1. WRITE OUT THE BALANCED EQUATION FOR THE REACTION



Mg(s) + 2H+(aq) + 2Cl¯(aq) ——> Mg2+(aq) + 2Cl¯(aq) + H2(g)


1. WRITE OUT THE BALANCED EQUATION FOR THE REACTION2. DILUTE ACIDS AND SALTS CONTAIN IONS; WATER, HYDROGEN & CARBON DIOXIDE DON’T




cancel ions Mg(s) + 2H+(aq) ——> Mg2+(aq) + H2(g)


1. WRITE OUT THE BALANCED EQUATION FOR THE REACTION2. DILUTE ACIDS AND SALTS CONTAIN IONS; WATER, HYDROGEN & CARBON DIOXIDE DON’T3. CANCEL OUT THE IONS WHICH APPEAR ON BOTH SIDES OF THE EQUATION




cancel ions Mg(s) + 2H+(aq) ——> Mg2+(aq) + H2(g)

BasicOxides copper(II) oxide + dil. hydrochloric acid ——> copper(II) chloride + water

CuO(s) + 2HCl(aq) ——> CuCl2(aq) + H2O(l)

Cu2+O2-(s) + 2H+(aq) + 2Cl¯(aq) ——> Cu 2+ (aq) + 2Cl¯(aq) + H2O(l)

cancel ions O2- + 2H+(aq) ——> H2O(l)


Alkalis sodium hydroxide + dil. hydrochloric acid ——> sodium chloride + water

NaOH(aq) + HCl(aq) ——> NaCl(aq) + H2O(l)

Na+(aq) + OH¯(aq) + H+(aq) + Cl¯(aq) ——> Na+ (aq) + Cl¯(aq) + H2O(l)

cancel ions H+(aq) + OH¯(aq) ——> H2O(l)






Carbonates calcium carbonate + hydrochloric acid ——> calcium chloride + carbon dioxide + water

CaCO3(s) + 2HCl(aq) ——> CaCl2(aq) + CO2(g) + H2O(l)

Ca2+CO32-(s) + 2H+(aq) + 2Cl¯(aq) ——> Ca2+(aq) + 2Cl¯(aq) + CO2(g) + H2O(l)

cancel ions CO32- + 2H+(aq) ——> CO2(g) + H2O(l)






Carbonates calcium carbonate + hydrochloric acid ——> calcium chloride + carbon dioxide + water

CaCO3(s) + 2HCl(aq) ——> CaCl2(aq) + CO2(g) + H2O(l)

Ca2+CO32-(s) + 2H+(aq) + 2Cl¯(aq) ——> Ca2+(aq) + 2Cl¯(aq) + CO2(g) + H2O(l)

cancel ions CO32- + 2H+(aq) ——> CO2(g) + H2O(l)

Hydrogen carbonates H+(aq) + HCO3¯ ——> CO2(g) + H2O(l)


SUMMARY

METALS react to give a salt + hydrogen

METAL OXIDES react to give a salt + water

METAL HYDROXIDES react to give a salt + water

CARBONATES react to give a salt + water + carbon dioxide

HYDROGENCARBONATES react to give a salt + water + carbon dioxide

AMMONIA reacts to give an ammonium salt


© 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING© 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING

THE ENDTHE END

ACIDS, BASESACIDS, BASESAND SALTSAND SALTS

ACIDS, BASES AND SALTS A guide for A level students 2008 SPECIFICATIONS KNOCKHARDY PUBLISHING.

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