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

2. 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 orusing the left and right arrow keys on the keyboard KNOCKHARDY PUBLISHING ACIDS, BASES AND SALTS

3. BRØNSTED-LOWRY THEORY ACIDproton donorHCl ——> H + (aq) + Cl¯(aq) BASEproton acceptor NH 3 (aq) + H + (aq) ——> NH 4 + (aq) ACIDS AND BASES

4. BRØNSTED-LOWRY THEORY ACIDproton donorHCl ——> H + (aq) + Cl¯(aq) BASEproton acceptor NH 3 (aq) + H + (aq) ——> NH 4 + (aq) Conjugate systems Acids are related to bases ACID PROTON + CONJUGATE BASE Bases are related to acids BASE + PROTON CONJUGATE ACID ACIDS AND BASES

5. BRØNSTED-LOWRY THEORY ACIDproton donorHCl ——> H + (aq) + Cl¯(aq) BASEproton acceptor NH 3 (aq) + H + (aq) ——> NH 4 + (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 CH 3 COO¯ + H 2 O CH 3 COOH + OH¯ base acid acid base ACIDS AND BASES

6. STRONG ACIDS completely dissociate (split up) into ions in aqueous solution e.g. HCl ——> H + (aq) + Cl¯(aq) MONOPROTIC1 replaceable H HNO 3 ——> H + (aq) + NO 3 ¯(aq) H 2 SO 4 ——> 2H + (aq) + SO 4 2- (aq) DIPROTIC 2 replaceable H’s STRONG ACIDS AND BASES

7. STRONG ACIDS completely dissociate (split up) into ions in aqueous solution e.g. HCl ——> H + (aq) + Cl¯(aq) MONOPROTIC1 replaceable H HNO 3 ——> H + (aq) + NO 3 ¯(aq) H 2 SO 4 ——> 2H + (aq) + SO 4 2- (aq) DIPROTIC 2 replaceable H’s STRONG BASES completely dissociate into ions in aqueous solution e.g. NaOH(aq) ——> Na + (aq) + OH¯(aq) STRONG ACIDS AND BASES

8. Weak acids partially dissociate into ions in aqueous solution e.g. ethanoic acid CH 3 COOH(aq) CH 3 COO¯(aq) + H + (aq) When a weak acid dissolves in water an equilibrium is set upHA(aq) + H 2 O(l) A¯(aq) + H 3 O + (aq) The water stabilises the ions To make calculations easier the dissociation can be written... HA(aq) A¯(aq) + H + (aq) WEAK ACIDS

9. Weak acids partially dissociate into ions in aqueous solution e.g. ethanoic acid CH 3 COOH(aq) CH 3 COO¯(aq) + H + (aq) When a weak acid dissolves in water an equilibrium is set upHA(aq) + H 2 O(l) A¯(aq) + H 3 O + (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 ACIDS

10. 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 NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH¯ (aq) as in the case of acids it is more simply written NH 3 (aq) + H + (aq) NH 4 + (aq) WEAK BASES

11. 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 NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH¯ (aq) as in the case of acids it is more simply written NH 3 (aq) + H + (aq) NH 4 + (aq) The weaker the basethe less it dissociates the more the equilibrium lies to the left The relative strengths of bases can be expressed as K b or pK b values. WEAK BASES

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

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

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

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

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

17. Metalsmagnesium + dil. hydrochloric acid ——> magnesium chloride + hydrogen Mg(s) + 2HCl(aq)——> MgCl 2 (aq) + H 2 (g) REACTIONS OF HYDROCHLORIC ACID 1. 1.WRITE OUT THE BALANCED EQUATION FOR THE REACTION

18. Metalsmagnesium + dil. hydrochloric acid ——> magnesium chloride + hydrogen Mg(s) + 2HCl(aq)——> MgCl 2 (aq) + H 2 (g) Mg(s) + 2H + (aq) + 2Cl¯(aq) ——> Mg 2+ (aq) + 2Cl¯(aq) + H 2 (g) REACTIONS OF HYDROCHLORIC ACID 1. 1.WRITE OUT THE BALANCED EQUATION FOR THE REACTION 2. 2.DILUTE ACIDS AND SALTS CONTAIN IONS; WATER, HYDROGEN & CARBON DIOXIDE DON’T

19. Metalsmagnesium + dil. hydrochloric acid ——> magnesium chloride + hydrogen Mg(s) + 2HCl(aq)——> MgCl 2 (aq) + H 2 (g) Mg(s) + 2H + (aq) + 2Cl¯(aq) ——> Mg 2+ (aq) + 2Cl¯(aq) + H 2 (g) cancel ions Mg(s) + 2H + (aq) ——> Mg 2+ (aq) + H 2 (g) REACTIONS OF HYDROCHLORIC ACID 1. 1.WRITE OUT THE BALANCED EQUATION FOR THE REACTION 2. 2.DILUTE ACIDS AND SALTS CONTAIN IONS; WATER, HYDROGEN & CARBON DIOXIDE DON’T 3. 3.CANCEL OUT THE IONS WHICH APPEAR ON BOTH SIDES OF THE EQUATION

20. Metalsmagnesium + dil. hydrochloric acid ——> magnesium chloride + hydrogen Mg(s) + 2HCl(aq)——> MgCl 2 (aq) + H 2 (g) Mg(s) + 2H + (aq) + 2Cl¯(aq) ——> Mg 2+ (aq) + 2Cl¯(aq) + H 2 (g) cancel ions Mg(s) + 2H + (aq) ——> Mg 2+ (aq) + H 2 (g) Basic Oxidescopper(II) oxide + dil. hydrochloric acid ——> copper(II) chloride + water CuO(s) + 2HCl(aq) ——> CuCl 2 (aq) + H 2 O(l) Cu 2+ O 2- (s) + 2H + (aq) + 2Cl¯(aq) ——> Cu 2+ (aq) + 2Cl¯(aq) + H 2 O(l) cancel ions O 2- + 2H + (aq) ——> H 2 O(l) REACTIONS OF HYDROCHLORIC ACID

21. Alkalissodium hydroxide + dil. hydrochloric acid ——> sodium chloride + water NaOH(aq) + HCl(aq) ——> NaCl(aq) + H 2 O(l) Na + (aq) + OH¯(aq) + H + (aq) + Cl¯(aq) ——> Na + (aq) + Cl¯(aq) + H 2 O(l) cancel ions H + (aq) + OH¯(aq) ——> H 2 O(l) REACTIONS OF HYDROCHLORIC ACID

22. Alkalissodium hydroxide + dil. hydrochloric acid ——> sodium chloride + water NaOH(aq) + HCl(aq) ——> NaCl(aq) + H 2 O(l) Na + (aq) + OH¯(aq) + H + (aq) + Cl¯(aq) ——> Na + (aq) + Cl¯(aq) + H 2 O(l) cancel ions H + (aq) + OH¯(aq) ——> H 2 O(l) Carbonates calcium carbonate + hydrochloric acid ——> calcium chloride + carbon dioxide + water CaCO 3 (s) + 2HCl(aq) ——> CaCl 2 (aq) + CO 2 (g) + H 2 O(l) Ca 2+ CO 3 2- (s) + 2H + (aq) + 2Cl¯(aq) ——> Ca 2+ (aq) + 2Cl¯(aq) + CO 2 (g) + H 2 O(l) cancel ions CO 3 2- + 2H + (aq) ——> CO 2 (g) + H 2 O(l) REACTIONS OF HYDROCHLORIC ACID

23. Alkalissodium hydroxide + dil. hydrochloric acid ——> sodium chloride + water NaOH(aq) + HCl(aq) ——> NaCl(aq) + H 2 O(l) Na + (aq) + OH¯(aq) + H + (aq) + Cl¯(aq) ——> Na + (aq) + Cl¯(aq) + H 2 O(l) cancel ions H + (aq) + OH¯(aq) ——> H 2 O(l) Carbonates calcium carbonate + hydrochloric acid ——> calcium chloride + carbon dioxide + water CaCO 3 (s) + 2HCl(aq) ——> CaCl 2 (aq) + CO 2 (g) + H 2 O(l) Ca 2+ CO 3 2- (s) + 2H + (aq) + 2Cl¯(aq) ——> Ca 2+ (aq) + 2Cl¯(aq) + CO 2 (g) + H 2 O(l) cancel ions CO 3 2- + 2H + (aq) ——> CO 2 (g) + H 2 O(l) Hydrogen carbonates H + (aq) + HCO 3 ¯ ——> CO 2 (g) + H 2 O(l) REACTIONS OF HYDROCHLORIC ACID

24. SUMMARY METALS react to givea salt + hydrogen METAL OXIDES react to givea salt + water METAL HYDROXIDES react to givea salt + water CARBONATES react to give a salt + water + carbon dioxide HYDROGENCARBONATES react to give a salt + water + carbon dioxide AMMONIA reacts to givean ammonium salt REACTIONS OF HYDROCHLORIC ACID

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