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ACIDS, BASES AND SALTS A guide for A level students

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

  2. KNOCKHARDY PUBLISHING ACIDS, BASES AND SALTS INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... www.knockhardy.org.uk/sci.htm Navigation is achieved by... either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard

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

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

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

  6. 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

  7. 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 BASEScompletely dissociate into ions in aqueous solution e.g. NaOH(aq) ——> Na+(aq) + OH¯(aq)

  8. 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)

  9. 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.

  10. 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)

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

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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. 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

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

  18. 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) • WRITE OUT THE BALANCED EQUATION FOR THE REACTION • DILUTE ACIDS AND SALTS CONTAIN IONS; WATER, HYDROGEN & CARBON DIOXIDE DON’T

  19. 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

  20. 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) Basic Oxidescopper(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)

  21. REACTIONS OF HYDROCHLORIC ACID Alkalissodium 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)

  22. REACTIONS OF HYDROCHLORIC ACID Alkalissodium 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) Carbonatescalcium 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)

  23. REACTIONS OF HYDROCHLORIC ACID Alkalissodium 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) Carbonatescalcium 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 carbonatesH+(aq) + HCO3¯ ——> CO2(g) + H2O(l)

  24. 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

  25. ACIDS, BASES AND SALTS THE END © 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING