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ACIDS AND BASES 1.1.10

ACIDS AND BASES 1.1.10. Acid & Bases. CONTENTS The Arrhenius Theory of acids and bases Brønsted-Lowry theory of acids and bases LEWIS THEORY – this is A2 Strong acids and bases Weak acids Weak bases Hydrogen ion concentration and pH. Historic acid–base theories.

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ACIDS AND BASES 1.1.10

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  1. ACIDS AND BASES 1.1.10

  2. Acid & Bases • CONTENTS • The Arrhenius Theory of acids and bases • Brønsted-Lowry theory of acids and bases • LEWIS THEORY – this is A2 • Strong acids and bases • Weak acids • Weak bases • Hydrogen ion concentration and pH

  3. Historic acid–base theories • 1776 Lavoisier - he defined acids in terms of their containing oxygen • 1810 Sir Humphry Davy - proved the lack of oxygen - • "acidity does not depend upon any particular elementary substance, but upon peculiar arrangement of various substances". • Berzelius - stated “acids are oxides of nonmetals while bases are oxides of metals”. • 1838 Justus von Liebig – “an acid is a hydrogen-containing substance in which the hydrogen could be replaced by a metal” • 1884 Svante Arrhenius with Friedrich Wilhelm Ostwald established the presence of ions in aqueous solution • Arrhenius - Nobel Prize in Chemistry in 1903 for "recognition of the extraordinary services... rendered to the advancement of chemistry by his electrolytic theory of dissociation".

  4. THEORIES OF ACIDS AND BASES • The Arrhenius Theory of acids and bases • Acids are substances which produce hydrogen ions in solution. • Bases are substances which produce hydroxide ions in solution. • Neutralisation happens because hydrogen ions and hydroxide ions react to produce water. • hydrogen ions + hydroxide ions  Water H + (aq) + OH¯ (aq) H2O(l)

  5. NH4Cl(s) (g) g Limitations of the theory Hydrogen Chloride / Hydrochloric acid is neutralised by both sodium hydroxide solution and ammonia and a solution of ammonia. Word/symbol equations sodium hydroxide + hydrochloric acid  ammonia + hydrochloric acid  Ammonia dissolves in water HCl(aq)    +       NH4OH(aq)NH4Cl(aq)    +  H2O(l)

  6. The Bronsted-Lowry Theory of acids and bases • An acid is a proton (hydrogen ion) donor. • A base is a proton (hydrogen ion) acceptor. • Hydroxide ions are bases - they accept hydrogen ions from acids and form water. • An acid produces hydrogen ions in solution - it reacts with the water molecules by giving a proton to them. • hydrogen chloride gas dissolves in water to produce hydrochloric acid, • Hydroxonium ions, H3O+, are produced.

  7. Hydroxonium ions, H3O+, It is important to realise that hydrogen ions in solution, H+(aq) are hydroxonium ions.

  8. The hydrogen chloride / ammonia problem If it is in solution, the ammonia accepts a proton from a hydroxonium ion If the reaction is happening in the gas state, the ammonia accepts a proton directly from the hydrogen chloride: Either way, the ammonia acts as a base by accepting a hydrogen ion from an acid. NH3(aq) + H3O+(aq) ——> NH4+(aq) + H2O(aq) NH3(g) + HCl(g) ——> NH4+(s) + Cl-(s)

  9. ACIDS AND BASES BRØNSTED-LOWRY THEORY ACIDproton donor HCl ——> H+(aq) + Cl¯(aq) BASEproton acceptor NH3 (aq) + H+(aq) ——> NH4+(aq)

  10. ACIDS AND BASES BRØNSTED-LOWRY THEORY ACIDproton donor HCl ——> H+(aq) + Cl¯(aq) BASEproton acceptor NH3 (aq) + H+(aq) ——> NH4+(aq) Conjugatesystems Acids are related to bases ACID PROTON + BASE Bases are related to acids BASE + PROTON ACID

  11. ACIDS AND BASES BRØNSTED-LOWRY THEORY ACIDproton donor HCl ——> H+(aq) + Cl¯(aq) BASEproton acceptor NH3 (aq) + H+(aq) ——> NH4+(aq) Conjugatesystems Acids 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

  12. ACIDS AND BASES LEWIS THEORY – this is A2 ACIDlone pair acceptor BF3 H+ AlCl3 BASElone pair donor NH3 H2O LONE PAIR ACCEPTOR LONE PAIR DONOR LONE PAIR DONOR LONE PAIR ACCEPTOR

  13. STRONG ACIDS AND BASES STRONG ACIDScompletely 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

  14. STRONG ACIDS AND BASES STRONG ACIDScompletely 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 BASES completely dissociate into ions in aqueous solution e.g. NaOH ——> Na+(aq) + OH¯(aq)

  15. WEAK 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 in water 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)

  16. WEAK 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 in water 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.

  17. WEAK 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)

  18. WEAK 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 dissociates the more the equilibrium lies to the left

  19. Hydrogen ion concentration [H+(aq)] Introduction hydrogen ion concentration determines the acidity of a solution hydroxide ion concentration determines the alkalinity for strong acids and bases the concentration of ions is very much larger than their weaker counterparts which only partially dissociate. Strong / Weak concentrated / dilute –depends on ionisation – depends on the number of particles in a set volume

  20. [H+] 100 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-13 10-14 OH¯ 10-14 10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 10-0 pH 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 STRONGLY ACIDIC WEAKLY ACIDIC WEAKLY ALKALINE STRONGLY ALKALINE NEUTRAL Hydrogen ion concentration [H+(aq)] pH hydrogen ion concentration can be converted to pH pH = - log10 [H+(aq)] to convert pH into hydrogen ion concentration [H+(aq)] = antilog (-pH) in both the above, [ ] represents the concentration in mol dm-3 The calculation is A2 but the understanding is AS ! www.johnkyrk.com/pH.html

  21. 1.1.10 Acids and Bases Tasks – page 22-23 Key definitions an acid . . a base . . an alkali . . . Examiners tips are . . Worksheet Questions : 1, 2 Rainbow fizz ?

  22. REACTIONS OF HYDROCHLORIC ACID Is a typical acid in dilute aqueous solution HCl ——> H+(aq) + Cl¯(aq) 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.

  23. REACTIONS OF HYDROCHLORIC ACID Is a typical acid in dilute aqueous solution HCl ——> H+(aq) + Cl¯(aq) 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.

  24. REACTIONS OF HYDROCHLORIC ACID Is a typical acid in dilute aqueous solution HCl ——> H+(aq) + Cl¯(aq) 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.

  25. REACTIONS OF HYDROCHLORIC ACID Is a typical acid in dilute aqueous solution HCl ——> H+(aq) + Cl¯(aq) HYDROGEN CHLORIDE HYDROCHLORIC ACID colourless gas Appearance colourless soln. covalent molecule Bonding aqueous ions HCl(g) Formula HCl(aq) poor Conductivity good no reaction Dry blue litmusgoes red

  26. REACTIONS OF HYDROCHLORIC ACID Is a typical acid in dilute aqueous solution HCl ——> H+(aq) + Cl¯(aq) Appearance Bonding and formula Conductivity Dry litmus hydrogen chloride colourless gas covalent molecule HCl(g) poor no reaction hydrochloric acid colourless soln. aqueous ions HCl(aq) good goes red

  27. Practical Activities • Reactive Metals and Acids • Magnesium : Mg • Hydrochloric Acid : HCl : 1.0 M • Put 5 cm3 of HCl in a boiling tube • drop in the Mg strip • Seal with hand • Wait for 1 to 2 minutes – until the pressure builds up • Attempt to ignite the trapped gas • Record your observations • The metal reactants – dissolves into the acid • The metal disappears ? • Acid in excess? • A clear colourless solution forms • A soluble compound is form – no precipitate / solid formed • Effervescence occurs – a gas is produced • It’s colourless, its flammable gas - squeaky pop inference – H2 • magnesium + hydrochloric acid →

  28. REACTIONS OF HYDROCHLORIC ACID Metalsmagnesium + hydrochloric acid ——> magnesium chloride + hydrogen Mg(s) + 2HCl(aq) ——> MgCl2(aq) + H2(g) • WRITE OUT THE BALANCED EQUATION FOR THE REACTION

  29. REACTIONS OF HYDROCHLORIC ACID Metalsmagnesium + hydrochloric acid ——> magnesium chloride + hydrogen Mg(s) + 2HCl(aq) ——> MgCl2(aq) + H2(g) Mg(s) + 2H+(aq) + 2Cl¯(aq) ——> Mg2+(aq) + 2Cl¯(aq) + H2(g) • WRITE OUT THE BALANCED EQUATION FOR THE REACTION • DILUTE ACIDS AND SALTS CONTAIN IONS; WATER, HYDROGEN & CARBON DIOXIDE DON’T

  30. REACTIONS OF HYDROCHLORIC ACID Metalsmagnesium + dil. hydrochloric acid ——> magnesium chloride + hydrogen Mg(s) + 2HCl(aq) ——> MgCl2(aq) + H2(g) Mg(s) + 2H+(aq) + 2Cl¯(aq) ——> Mg2+(aq) + 2Cl¯(aq) + H2(g) cancel ionsMg(s) + 2H+(aq) ——> Mg2+(aq) + H2(g) • WRITE OUT THE BALANCED EQUATION FOR THE REACTION • DILUTE ACIDS AND SALTS CONTAIN IONS; WATER, HYDROGEN & CARBON DIOXIDE DON’T • CANCEL OUT THE IONS WHICH APPEAR ON BOTH SIDES OF THE EQUATION

  31. Practical Activities • Bases and Acids • Insoluble Metal Oxide : Copper Oxide • Hydrochloric Acid : HCl : 1.0 M • Put ½ a spatula of CuO in a boiling tube • Add 5-10 cm3 HCl ( that’s about a 1/3 of a Boiling tube ) • Mix by gentle agitation • Wait for the reaction – warm gently if required • Record your observations • The metal oxide (black/grey power solid) reactants slowly • It dissolves into the acid/reacts with the acid • A clear ? Green/blue ? solution forms • A soluble compound is form – no precipitate / solid left is ? • No Effervescence occurs – no gas is produced • Acid in excess ? • copper(II) oxide + hydrochloric acid →

  32. REACTIONS OF HYDROCHLORIC ACID Basic Oxides Insoluble oxides copper(II) oxide + 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)

  33. Practical Activities • Metal Hydroxides and Acids • soluble Metal hydroxide : sodium hydroxide : NaOH • Hydrochloric Acid : HCl : 1.0 M • Put 25cm3NaOH in insulated beaker add 2-3 drops of indicator • Record initial temperature and colour of the indicator • Add 1.0 HCl 2 cm3 at a time – record the temperature • Add a maximum of 40 cm3 1.0 HCl • Record any observations- results table • Plot – SKETCH your results – on graph paper • Volume v ∆T ( or just T ) – add indicator colour changes • Does the max temperature correlate with the indicator change ? • At what volume did the maximum ∆T occur • sodium hydroxide + hydrochloric acid →

  34. REACTIONS OF HYDROCHLORIC ACID Alkalis sodium hydroxide + 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)

  35. REACTIONS OF HYDROCHLORIC ACID Alkalis sodium hydroxide + 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)

  36. Practical Activities • Alkalis and Acids • Sparing soluble Metal Hydroxide : Magnesium Hydroxide • Hydrochloric Acid : HCl : 1.0 M • Put one a spatula of MgO / Mg(OH)2 in beaker/conical flask • Add about 25 cm3 of water and 2-3 drops of Universal Indicator • Add HCl slowly : that’s 2-3 cm3 at a time • Mix by gentle agitation • Stop when you have added about 30 cm3 • Record your observations • The metal oxide/hydroxide (white power solid) does not readily dissolve • Alkalis solution formed • Acid reacts with alkali neutralizing it but on standing reverts back to alkali. • A soluble compound is form – no precipitate / solid left ? • No Effervescence occurs – no gas is produced • Acid in excess ?

  37. REACTIONS OF HYDROCHLORIC ACID Alkalis magnesium hydroxide – add water . . Check pH magnesium hydroxide + hydrochloric acid ——> magnesium chloride + water Mg(OH)2(s) + 2 HCl(aq) ——> MgCl2 (aq) + 2 H2O(l) Mg2+(aq) + 2 OH¯(aq) +2H+(aq) + 2 Cl¯(aq) ——> Mg2+(aq) + 2 Cl¯(aq) + 2 H2O(l) cancel ions 2H+(aq) + 2 OH¯(aq) ——> 2 H2O(l)

  38. Practical Activities • Carbonates and Acids • Insoluble Metal carbonates : calcium carbonate: CaCO3 • Hydrochloric Acid : HCl : 1.0 M • Add 5 cm3HCl ( that’s less than a 1/3 of a Boiling tube ) • Add universal indicator • Put 4 - 5 lumps CaCO3 in a boiling tube • Mix by gentle agitation • Wait for the reaction to go to completion • Test the gas with a lighted splint • Record your observations • The solid CaCO3 reactants slowly • Effervescence occurs – a gas is produced . . Not flammable • Called CO2 – test ? • Universal indicator changes colour RED to PINK ? To . . . GREEN • It dissolves into the acid/reacts with the acid • A clear ? solution forms ? • A soluble compound is form – no precipitate / solid left is ? • Acid in excess ?

  39. REACTIONS OF HYDROCHLORIC ACID Carbonates– add water . . . Check pH 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 ionsCO32- + 2H+(aq) ——> CO2(g) + H2O(l) Test for Carbon Dioxide Calcium hydroxide + carbon dioxide ——> Calcium carbonate + water Ca(OH) 2 + CO2(g) ——> CaCO3(s) + H2O(l) Ca2+(aq) + 2 OH¯(aq) + CO2(g) ——> Ca2+ (s)+ + CO32-(s) + H2O(l) 2 OH¯(aq) + CO2(g) ——> CO32-(s) + H2O(l)

  40. Practical Activities • Bubbling CO2 into water/lime water • Straws • Boiling tubes • Phenolphthalein indicator / universal indicator • Limewater • Tap water • Put 5 cm3 of water in a boiling tube • 2 drop of universal indicator • Record your observations • Put 5 cm3 of lime water in a boiling tube • 2 drop of phenolphthalein indicator • Record your observations • Why does the precipitate disappear ?

  41. REACTIONS OF HYDROCHLORIC ACID Carbonates– add water . . . Check pH 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 ionsCO32- + 2H+(aq) ——> CO2(g) + H2O(l) Hydrogen carbonates – add water . . . Check pH Sodium hydrogen carbonate + hydrochloric acid ——> sodium chloride + carbon dioxide + water NaHCO3(aq) + HCl(aq) ——> NaCl(aq) + CO2(g) + H2O(l) Na+ (aq) + HCO3¯(aq) + H+(aq) + Cl¯(aq) ——> Na+(aq) + Cl¯(aq) + CO2(g) + H2O(l) HCO3¯ (aq) + H+(aq)——> CO2(g) + H2O(l)

  42. REACTIONS OF HYDROCHLORIC ACID What happens if you keep bubbling CO2 into water ? carbon dioxide + water——> carbonic acid CO2(g) + H2O(l) ——> H2CO3(aq) 2 H2CO3 (aq) + CaCO3 (s) ——> Ca ( HCO3)2(aq) + CO2(g) + H2O(l) Ca2+CO32-(s) + 2H+(aq) + CO32- (aq) ——> HCO3¯ (aq) + CO2(g) + H2O(l)

  43. Practical Activities • ammonia and hydrochloric acid • conc. NH3/conc. HCl • 2 gas jars. Universal indicator Paper • 2 -3 drops in separate gas jars – check pH • Invert one jar over the other. • Record observations NH3 HCl

  44. REACTIONS OF HYDROCHLORIC ACID ammonia+ hydrochloric acid ——> ammonium chloride NH3(g) + HCl(g) ——> NH4Cl(s) NH3 (g) + HCl(g) ——> NH4+(s) + Cl¯(s)

  45. REACTIONS OF HYDROCHLORIC ACID Ammonium hydroxide Ammonium hydroxide + hydrochloric acid ——> ammonium chloride + water NH4OH(aq) + HCl(aq) ——> NH4Cl (aq) + H2O(l) NH4+ (aq) + OH¯(aq) + H+(aq) + Cl¯(aq) ——> NH4+ (aq) + Cl¯(aq) + H2O(l) cancel ions OH¯(aq) +H+(aq)——> H2O(l)

  46. REACTIONS OF HYDROCHLORIC ACID Metals magnesium + hydrochloric acid ——> magnesium chloride + hydrogen Basic Oxides copper(II) oxide + hydrochloric acid ——> copper(II) chloride + water Alkalis sodium hydroxide + hydrochloric acid ——> sodium chloride + water Carbonates calcium carbonate + hydrochloric acid ——> calcium chloride + carbon dioxide + water Hydrogen carbonates Sodium hydrogen carbonate + hydrochloric acid ——> sodium chloride + carbon dioxide + water ammonia ammonia+ hydrochloric acid ——> ammonium salts

  47. REACTIONS OF HYDROCHLORIC ACID SUMMARY METALS react to give a salt + hydrogen METALOXIDES react to give a salt + water METALHYDROXIDES 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

  48. Tasks . . . Page 24 - 25 Key definitions a salt . . an anion . . a cation . . . Examiners tips are . . Worksheet – word equations . . to symbol equations Questions : 1, 2

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