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Chapter 7 Reactions in Aqueous Solutions Chemistry 101.

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Presentation on theme: "Chapter 7 Reactions in Aqueous Solutions Chemistry 101."— Presentation transcript:

1 Chapter 7 Reactions in Aqueous Solutions Chemistry 101

2 Reactions in Aqueous Solutions Ionic compounds (Salt) Aqueous solution: solvent is water

3 Reactions in Aqueous Solutions In our body reactions occur in the aqueous solution. Chemical reactions that occur in water.

4 Water in our body 1.About 60% of our body. 2.Most of the reactions occur in aqueous solution. 3.Participates in many biochemical reactions. 4.Transports reactants and products from one place in our body to another. 5. Eliminates the waste materials from cells and our body (urine).

5 Why does a chemical reaction occur? 1.Formation of a solid 2.Formation of water 3.Transfer of electrons 4.Formation of a gas Several driving forces:

6 Why does a chemical reaction occur? Several driving forces: 1.Formation of a solid 2.Formation of water 3.Transfer of electrons 4.Formation of a gas

7 Formation of a solid Precipitation reactions Precipitate KI + Pb(NO 3 ) 2  ?

8 Ionic Compounds When an ionic compound dissolves in water, ions are produced. Each ion is surrounded by water molecules. Ions Hydrated by H 2 O Hydration

9 Ionic Compounds 1.Soluble solid: it completely dissolves in water (ions are formed). 2.Slightly soluble solid: it partially dissolves in water. 3.Insoluble solid: it does not dissociate in water (almost). Note: the terms insoluble and slightly soluble mean such a miniscule amount dissolves that you can’t see any decrease in the amount of solid present.

10 Solubility Rules Memorize these RULES! Soluble Insoluble Preceding rules trump following rules.

11 Another way of showing the same rules. Solubility Rules

12 +- electrolyte Na + Cl - bulb Electrolytes Electrolyte: conducts an electric current. Ionization ( Dissociation) NaCl → Na + + Cl - strong electrolytes: molecules dissociate completely into ions (NaCl). weak electrolytes: molecules dissociate partially into ions (CH 3 COOH). nonelectrolytes: molecules do not dissociate into ions (DI water).

13 Formation of a solid Precipitation reactions Precipitate KI + Pb(NO 3 ) 2  ?

14 Aqueous Solution (ionic compounds) KI (s) K + (aq) + I - (aq) Dissociation (Ionization) aqueous solution: solvent is water H2OH2O KI Pb(NO 3 ) 2 K+K+ Pb(NO 3 ) 2 (s) Pb 2+ (aq) + 2NO 3 - (aq) H2OH2O I-I- Pb 2+ NO 3 -

15 Aqueous Solution (ionic compounds) KIKI Pb(NO 3 ) 2 K+K+ I-I- Pb 2+ NO 3 - sometimes the ions react with each other. Positive ions will interact with negative ions. 2KI (aq) + Pb(NO 3 ) 2 (aq)  PbI 2 (s) + 2KNO 3 (aq) Sometimes they stick together to form a solid (precipitate).

16 2K + (aq) + Pb 2+ (aq) + 2 I - (aq) + 2NO 3 - (aq)  Pb I 2 (s) + 2K + (aq) + 2NO 3 - (aq) Complete Ionic equation: Molecular equation: 2As 3+ (aq) + 3s 2- (aq)  As 2 S 3 (s) total charge on left side = total charge on right side balanced equation 2K I (aq) + Pb(NO 3 ) 2 (aq)  Pb I 2 (s) + 2KNO 3 (aq) 2K + (aq) + Pb 2+ (aq) + 2 I - (aq) + 2NO 3 - (aq)  Pb I 2 (s) + 2K + (aq) + 2NO 3 - (aq) Pb 2+ (aq) + 2 I - (aq)  Pb I 2 (s) Net ionic equation: Spectator ions

17 Pb(NO 3 ) 2 (aq) + Na 2 SO 4 (aq)  ? Pb(NO 3 ) 2 (aq) + Na 2 SO 4 (aq)  PbSO 4 (s) + NaNO 3 (aq) Example Pb(NO 3 ) 2 (aq) + Na 2 SO 4 (aq)  PbSO 4 (s) + 2 NaNO 3 (aq) Balance it: Pb 2+ (aq) + 2 NO 3 - (aq) + 2 Na + (aq) + SO 4 2- (aq)  PbSO 4 (s) + 2 Na + (aq) + 2 NO 3 - (aq) Complete ionic equation

18 Pb 2+ (aq) + 2 NO 3 - (aq) + 2 Na + (aq) + SO 4 2- (aq)  PbSO 4 (s) + 2 Na + (aq) + 2 NO 3 - (aq) The ions that do not react are called spectator ions. Example Net ionic equation:Pb 2+ (aq) + SO 4 2- (aq)  PbSO 4 (s)

19 1.Molecular equation 3 KOH(aq) + Fe(NO 3 ) 3 (aq)  ? 2.Balancing 3.Complete ionic equation 4.Net ionic equation Practice

20 Why does a chemical reaction occur? 1.Formation of a solid 2.Formation of water 3.Transfer of electrons 4.Formation of a gas Several driving forces:

21 Acids and Bases Acids: sour Bases: bitter or salty

22 Acids and Bases NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH - (aq) Acid: produces H 3 O + (H + ) in water. Base: produces OH - in water. Arrhenius definition: CH 3 COOH(aq) + H 2 O(l) CH 3 COO - (aq) + H 3 O + (aq) H 3 O + (Hydronium ion):H + (aq) + H 2 O(l) H 3 O + (aq) NaOH(s) Na + (aq) + OH - (aq) H2OH2O

23 Acids and Bases Weak acid and base: it is partially ionized in aqueous solution. CH 3 COOH(aq) + H 2 O(l)CH 3 COO - (aq) + H 3 O + (aq) NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH - (aq) produces less H + and OH - Strong acid and base: it is completely ionized in aqueous solution. HCl(aq) + H 2 O(l) Cl - (aq) + H 3 O + (aq) NaOH(aq) + H 2 O(l) Na + (aq) + OH - (aq) produces more H + and OH -

24 Acid-Base Reactions Neutralization NaOH(aq) + HCl(aq) NaCl(aq) + H 2 O(l) Na + (aq) + OH - (aq) + H + (aq) + C l - (aq) +  Na + (aq) + Cl - (aq) + H 2 O(l) H + (aq) + OH - (aq) H 2 O(l) The only chemical change is the formation of water. Strong acid + Strong base → Salt + H 2 O

25 Why does a chemical reaction occur? 1.Formation of a solid 2.Formation of water 3.Transfer of electrons 4.Formation of a gas Several driving forces:

26 Na → Na + + e - Cl + e - → Cl - Oxidation and Reduction reactions (redox) 2Na(s) + Cl 2 (g) 2NaCl(s) e-e-

27 Oxidation and Reduction reactions (redox) oxidation: it is the loss of electrons. reduction: it is the gain of electrons. Remember – LEO says GER. Loss of Electrons is Oxidation Gain of Electrons is Reduction. Na → Na + + e - Cl + e - → Cl -

28 Metal + Nonmetal : Transfer of electrons Oxidation and Reduction reactions (redox) Oxidation and reduction always occur together. (The lost e - must go somewhere!)

29 Oxidation and Reduction reactions (redox) Zn(s)  Zn 2+ (aq) + 2e - Zn is oxidized (reducing agent) Cu 2+ (aq) + 2e -  Cu(s)Cu 2+ is reduced (oxidizing agent) oxidation: it is the loss of electrons. reduction: it is the gain of electrons. Zn(s) + Cu 2+ (aq)  Zn 2+ (aq) + Cu(s) redox reaction

30 Oxidation and Reduction reactions (redox) oxidation: is the gain of oxygen / loss of hydrogen. reduction: is the loss of oxygen / gain of hydrogen. CH 4 (s) + 2O 2 (g)  CO 2 (g) + 2H 2 O(g) redox reaction C gains O and loses H is oxidized (reducing agent) O gains H Is reduced (oxidizing agent) single replacement reaction and combustion reactions  redox reactions double replacement reactions  non redox

31 Oxidation and Reduction reactions (redox) 2 Al(s) + Fe 2 O 3 (s)  2 Fe(s) + Al 2 O 3 (s) Called the Thermite reaction. Let’s just say it’s vigorous! Example 2: is oxidized is reduced

32 Oxidation and Reduction reactions (redox) Example 3: Cu(s) + 2 Ag + (aq)  2 Ag(s) + Cu 2+ (aq) is oxidized is reduced

33 Zn(s) + 2 HCl(aq)  H 2 (g) + ZnCl 2 (aq) Note: this reaction also shows the fourth driving force of a reaction, namely, the formation of a gas. Example 4: Oxidation and Reduction reactions (redox) is oxidizedis reduced Zn(s) + 2 H + (aq)  H 2 (g) + Zn 2+ (aq)

34 2 Mg(s) + O 2 (g)  2 MgO(s) Oxidation and Reduction reactions (redox) Practice:

35 Classification of chemical reactions Chemical reactions Precipitation Reactions Oxidation-Reduction Reactions Acid-Base Reactions Combustions Reactions Synthesis (combination) Reactions (Reactants are elements.) Decomposition (Analysis) Reactions (Products are elements.)


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