Acids and Bases. Properties of Acids. Properties of Bases

Transcription

1 Chemistry 2A/2B Term 3 Notes B 1 Coghlan Chemistry 2A/2B Term 3 Notes B Properties of Acids Acids and Bases 1. Neutralise. 2. Turns litmus red. 3. Conducts when in with water form an (acids ). 4. React with most A + H taste. 6. React with CO 3 2- & HCO 3 - A salt + + H 2 O. 7. Corrosive. 8. React with hydroxides A salt + H 2 O. 9. React with oxides A salt + H 2 O. Note: (1) If spilt on skin, flush with copious cold. (2) When diluting concentrated acid always to NOT water to acid due to nature of the ionisation process. Properties of Bases 1. Neutralise. 2. Turns litmus blue. 3. Conducts electricity when in solution with water form an (metallic hydroxides ). 4. React with some metals ( metals; Al, Cr, Zn) A complex salt + H taste. 6. Dissolve amphoteric metal. 7. React with non-metal A + H 2 O. Note: If spilt on skin, flush immediately with copious cold water. Common acids Common bases

2 Chemistry 2A/2B Term 3 Notes B 2 Coghlan Arrhenius Theory Acids A substance that produces (aq) in solution with water. A strong acid is one that is essentially fully in solution. HCl(l) H + (aq) + Cl - (aq) 100% HCl (, ) H 2 SO 4 HNO 3 perchloric chloric A acid is one that is only partially ionised in. CH 3 COOH(l) I H + (aq) + CH 3 COO - (aq) 1% HF H 2 CO 3 The attraction between the H 2 O and the H + is greater than that for other ions so H 3 O + is formed. the ion Non-metal oxides are acidic Bases A substance that produces OH - (aq) in with water. A strong base is one that is fully in solution. NaOH(s) Na + (aq) + OH - (aq) 100% Because sodium hydroxide is an substance, it already has ions in the solid form. The in water merely the ionic ions are not created, they can now simply separate into solution.

3 Chemistry 2A/2B Term 3 Notes B 3 Coghlan NaOH Ca(OH) 2 Ba(OH) 2 A base is one that is only partially dissociated in. NH 3 (aq) + H 2 O(l) I NH 4 + (aq) + OH - (aq) 1% CH 3 COOK MgF 2 Na 3 PO 4 Metallic oxides are basic Brønsted-Lowry Theory Acids and Bases An acid is a proton. A is a proton. A acid can only 1 proton. HCl, HNO 3, CH 3 COOH A polyprotic acid can donate than proton. H 2 SO 4, H 2 CO 3 HCl(g) + NH 3 (g) NH 4 Cl(s) Bases Accept Acids Donate ph Scale Acid Neutral Base ph = -log 10 [H + ]

4 Chemistry 2A/2B Term 3 Notes B 4 Coghlan Ex/ ph = 2.0 [H + ] = ph = [H + ] = Strong acids Weak acids Strong bases Weak bases Reactions of Acids and Bases 1. Acid + Base ( ) Acid + Base Salt + H 2 O 2. Acid + Metal Oxide (Neutralisation) Since oxides are ; Acid + Base Salt + H 2 O

5 Chemistry 2A/2B Term 3 Notes B 5 Coghlan 3. Acid + Metal Only for the following metals; Acid + Metal Salt + H 2 4. Acid + Carbonate Acid + Carbonate Salt + H 2 O + CO 2 5. Acid + Hydrogencarbonate ( ) Acid + Hydrogencarbonate Salt + H 2 O + CO 2 6. Acid + Sulfite For concentrated acids only. Acid + Sulfite Salt + H 2 O + SO 2 Concentrated Sulfuric acid + sodium sulfite 7. Acid + Sulfide Group I & II and Fe, Ni, Co, Zn, Mn sulfides only

6 Chemistry 2A/2B Term 3 Notes B 6 Coghlan Acid + Sulfide Salt + H 2 S Iron(II) sulfide + Hydrochloric acid Amphoteric Behaviour Certain metals,, and, react with acids to produce a salt + H 2. These metals,, and, also react with to produce a salt + H 2. Al(OH) 3, Cr(OH) 3 and Zn(OH) 2 also react with both and and are also termed. With acids With bases Note; [Al(OH) 4 ] - [Cr(OH) 4 ] - [Zn(OH) 4 ] 2- ion ion ion Al 2 O 3, Cr 2 O 3 and ZnO also react with both and and are also termed. EC Set 26, 27

7 Chemistry 2A/2B Term 3 Notes B 7 Coghlan Oxidation - Reduction 1. Oxidation is the process whereby substances oxygen. is the process whereby substances lose. 2Hg(l) + O 2 (g) 2HgO(s) 2Mg(s) + O 2 (g) 2MgO(s) CuO(l) + H 2 (g) Cu(s) + H 2 O(g) Fe 2 O 3 (l) + 3CO(g) 2Fe(s) + 3CO 2 (g) 2. Oxidation is the process whereby substances lose. is the process whereby substances hydrogen. 2H 2 S(g) + O 2 (g) 2S(s) + H 2 O(g) H 2 S loses H 2 - oxidation O 2 gains H 2 reduction The two processes of oxidation and are dependent. 3. Best Definition Oxidation is the process that involves the of electrons. Reduction is the process that involves the of electrons. The burning of magnesium in oxygen. Mg Mg e - Oxidation O 2 + 4e - 2O 2- Reduction 2Mg(s) + O 2 (g) 2MgO(s) Redox Zinc metal added to copper nitrate solution. Zn Zn e - Oxidation Cu e - Cu Reduction Zn(s) + Cu 2+ (aq) Zn 2+ (aq) + Cu(s) Redox

8 Chemistry 2A/2B Term 3 Notes B 8 Coghlan Zn(s) has been it is the agent. Cu 2+ (aq) has been it is the agent. The species that is is the agent. The species that is reduced is the agent. Oxidation Numbers The use of oxidation numbers allows you to use a technique to determine whether or not a particular reaction is redox. Rules for assigning oxidation numbers. 1. The oxidation number of all elements is. 2. The oxidation number of everything else is its. 3. The oxidation number of H is +1 except in metal. Exercise: Assign individual oxidation numbers to the following. H 2 O NaOH CaSO 4 H 3 PO 4 NH 3 Na 2 S 2 O 7 KMnO 4 Fe(NO 3 ) 3 Co 2+ OH - C 2 O 4 2- NH 4 + An in oxidation number indicates that oxidation has taken place. An in oxidation number indicates that has taken place. Mg(s) + 2H + (aq) Mg 2+ (aq) + H 2 (g) Is it a redox reaction? is oxidised it is the agent. is reduced it is the agent. MnO 4 - (aq) + 8H + (aq) + 5Fe 2+ (aq) Mn 2+ (aq) + 4H2O(l) + 5Fe 3+ (aq) Is it a redox reaction? is oxidised it is the agent.

9 Chemistry 2A/2B Term 3 Notes B 9 Coghlan is reduced it is the agent. NaHCO 3 (s) + H + (aq) Na + (aq) + H 2 O(l) + CO 2 (g) Is it a redox reaction? Half-Equations Can be used to balance redox reactions. Cu(s) + I 2 (g) CuI 2 (s) Metal lose electrons when they and so tend to be. Cu Cu e - Oxidation half-equation I 2 + 2e - 2I - Reduction half-equation Exercise: Write half-equations and balance the following reactions. Fe 2+ (aq) + Mg (s) Fe(s) + Mg 2+ (aq) 2H + (aq) + Al (s) H 2 (g) + Al 3+ (aq) Cr 2 O 7 2- (aq) + H + (aq) + Fe(s) Redox Displacement Reactions A redox displacement reaction occurs when an element, A, donates its electron/s to an ion, B 2+, in solution and then B 2+ solution becomes an element, B. A(s) + B 2+ (aq) A 2+ (aq) + B(s) fluorine gas is bubbled into a solution of sodium bromide

10 Chemistry 2A/2B Term 3 Notes B 10 Coghlan chlorine gas is bubbled into a solution of sodium bromide copper in a silver nitrate solution zinc in a magnesium sulfate solution e.html Predicting a displacement reaction - activity series (Standard Reduction Potentials) chlorine gas is bubbled into a solution of sodium fluoride metals with dilute acid EC Set 28, 29, 30