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Reactions in Aqueous Solutions Chapter 7 Chapter 7.

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

1 Reactions in Aqueous Solutions Chapter 7 Chapter 7

2 Aqueous Solutions Water is the dissolving medium, or solvent.

3 Driving Forces for Chemical Reactions 1. Formation of a precipitate (solid). 2. Formation of molecular substance (water). 3. Formation of a gas. 4. Transfer of electrons (Redox).

4 Types of Solution Reactions -Precipitation reactions AgNO 3 (aq) + NaCl(aq) AgCl(s) + NaNO 3 (aq) -Acid-base reactions NaOH(aq) + HCl(aq) NaCl(aq) + H 2 O(l)

5 Electrolytes Strong - conduct current efficiently - many ions in solution. NaCl, KNO 3, HNO 3, NaOH NaCl, KNO 3, HNO 3, NaOH Weak - conduct only a small current - few ions in solution, HC 2 H 3 O 2, aq. NH 3, tap H 2 O Non - no current flows - no ions in solution. pure H 2 O, sugar solution, glycerol

6 In what two ways can a solid ionic compound be made to conduct electricity? Dissolve it in water. Melt or fuse it. Ions must be free to move (mobile) in order to conduct electricity!

7 Dissociation ionic compounds metal + nonmetal (Type I & II) metal + polyatomic anion Ammonium compounds Acids When ionic compounds dissolve in water the anions and cations are separated from each other; this is called dissociation We know that ionic compounds dissociate when they dissolve in water because the solution conducts electricity

8 Dissociation potassium chloride dissociates in water into potassium cations and chloride anions KCl(aq) = K + (aq) + Cl - (aq) copper(II) sulfate dissociates in water into copper(II) cations and sulfate anions CuSO 4 (aq) = Cu +2 (aq) + SO 4 2- (aq) K+K+ Cl - K Cl Cu +2 SO 4 2- Cu SO 4

9 Dissociation potassium sulfate dissociates in water into potassium cations and sulfate anions K 2 SO 4 (aq) = 2 K + (aq) + SO 4 2- (aq) K+K+ SO 4 2- K+K+ KK SO 4

10 Ionic Compounds in Solution In aqueous solution, soluble ionic compounds exist in the form of ions. K 2 CrO 4(aq) + Ba(NO 3 ) 2(aq) ----> BaCrO 4(s) + 2KNO 3(aq)

11 Figure 7.1: The precipitation reaction that occurs when yellow potassium chormate, K 2 CrO 4 (aq), is mixed with a colorless barium nitrate solution, Ba(NO 3 ) 2 (aq)

12 Solubility 1. A soluble solid readily dissolves in water-- designated with (aq). 2. A slightly soluble solid only dissolves to a tiny extent in water--designated with (s). 3. An insoluble solid does not dissolve to any appreciable extent in water--designated with (s).

13 Simple Rules for Solubility 1.Most nitrate (NO 3 ), acetate (C 2 H 3 O 2 -), & chlorate (ClO 3 - ) salts are soluble. 2.Most alkali (group 1A) salts and NH 4 + are soluble. 3.Most Cl, Br, and I salts are soluble (NOT Ag +, Pb 2+, Hg 2 2+ ) 4.Most sulfate salts are soluble (NOT BaSO 4, PbSO 4, HgSO 4, CaSO 4 ) 5.Most OH salts are only slightly soluble (NaOH, KOH are soluble, Ba(OH) 2, Ca(OH) 2 are marginally soluble) 6.Most S 2, CO 3 2, CrO 4 2, PO 4 3 salts are only slightly soluble.

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15 Precipitation Reactions In all precipitation reactions, the ions of one substance are exchanged with the ions of another substance when their aqueous solutions are mixed At least one of the products formed is insoluble in water KI(aq) + AgNO 3 (aq) KNO 3 (aq) + AgI s KI(aq) + AgNO 3 (aq) KNO 3 (aq) + AgI s K+K+ I-I- Ag + NO 3 - K+K+ Ag I

16 Describing Reactions in Solution 1.Molecular equation (reactants and products as compounds) AgNO 3 (aq) + NaCl(aq) AgCl(s) + NaNO 3 (aq) 2.Complete ionic equation (all strong electrolytes shown as ions) Ag + (aq) + NO 3 (aq) + Na + (aq) + Cl (aq) Ag + (aq) + NO 3 (aq) + Na + (aq) + Cl (aq) AgCl(s) + Na + (aq) + NO 3 (aq)

17 Describing Reactions in Solution (continued) 3.Net ionic equation (show only components that actually react) Ag + (aq) + Cl (aq) AgCl(s) Na + and NO 3 are spectator ions.

18 Solutions of: AgNO 3 Na 2 SO 4

19 If AgNO 3 is mixed with Na 2 SO 4 what ions are most abundant in the solution? AgNO 3 Na 2 SO 4 With what ions is the solution saturated?

20 2AgNO 3(aq) + Na 2 SO 4(aq) 2 NaNO 3 (aq) + Ag 2 SO 4(s) Silver Sulfate Precipitate 2Ag + (aq) + 2 NO 3 - (aq) + 2Na + (aq) + SO 4 2- (aq) 2Na + (aq) + 2 NO 3 - (aq) + Ag 2 SO 4(s) 2Ag + (aq) + SO 4 2- (aq) Ag 2 SO 4(s) Molecular Equation Overall Ionic Equation Net Ionic Equation

21 Acids The nature of acids was discovered by Svante Arrhenius. Acids are characterized by: a sour taste (lemons -- citric acid).a sour taste (lemons -- citric acid). producing H + ions (protons) in aqueous solution.producing H + ions (protons) in aqueous solution. turn blue litmus red.turn blue litmus red.

22 Acids Strong acids -dissociate completely (nearly 100 %) to produce H + in solution HCl, H 2 SO 4, HNO 3, HBr, HI, & HClO 4 Weak acids - dissociate to a slight extent (approximately 1 %) to give H + in solution HC 2 H 3 O 2, HCOOH, HNO 2, & H 2 SO 3

23 Figure 7.5: When gaseous HCl is dissolved in water, each molecule dissociates to produce H + and Cl - ions

24 Bases Bases are characterized by: bitter taste (soap).bitter taste (soap). feel slippery.feel slippery. produce hydroxide (OH - ) ions in aqueous solution.produce hydroxide (OH - ) ions in aqueous solution. turn red litmus blue.turn red litmus blue. A basic solution is said to be alkaline since they often contain one of the alkali metals --Na, K, Li, etc.

25 Bases Strong bases - react completely with water to give OH ions. sodium hydroxide Weak bases - react only slightly with water to give OH ions. ammonia

26 Acid-Base Reactions Acid + Base ----> Salt + water Molecular Equation HCl (aq) + NaOH (aq) ----> NaCl (aq) + HOH (l) Complete Ionic Equation H + (aq) + Cl - (aq) + Na + (aq) + OH - (aq) -----> Na + (aq) + Cl - (aq) + HOH (l) Net Ionic Equation H + (aq) + OH - (aq) -----> HOH (l)

27 Acid-Base Neutralization The net ionic equation for the neutralization of any strong acid and base will always be: H + (aq) + OH - (aq) -----> HOH (l)

28 Salts Salts are ionic compounds consisting of: a. metal & nonmetal -- KCl b. metal & polyatomic ion -- CuSO 4 c. polyatomic ion & nonmetal -- NH 4 Cl d. two polyatomic ions -- (NH 4 ) 2 SO 4

29 Oxidation-Reduction Reactions (Redox Reactions) Redox reaction -- involves the transfer of electrons loss and gain of electrons must be exactly equal.loss and gain of electrons must be exactly equal. loss and gain of electrons must be simultaneous.loss and gain of electrons must be simultaneous.

30 Oxidation loss of electronsloss of electrons metal atoms -- Na, Ca, & Kmetal atoms -- Na, Ca, & K Na o ---> Na 1+ + 1e -Na o ---> Na 1+ + 1e - Ca o ---> Ca 2+ + 2e -Ca o ---> Ca 2+ + 2e - nonmetal ions -- Cl -, S 2-, & O 2-nonmetal ions -- Cl -, S 2-, & O 2- Cl 1- ---> Cl o + 1e-Cl 1- ---> Cl o + 1e- S 2- ---> S o + 2 e-S 2- ---> S o + 2 e-

31 Reduction gain of electrons.gain of electrons. nonmetal atoms.nonmetal atoms. O o + 2e - ---> O 2-O o + 2e - ---> O 2- F o + 1e - ---> F 1-F o + 1e - ---> F 1- metal ions.metal ions. K 1+ + 1e - ---> K oK 1+ + 1e - ---> K o Ba 2+ + 2e - ---> Ba oBa 2+ + 2e - ---> Ba o

32 Figure 7.7: When powdered aluminum and iodine (shown in the foreground) are mixed (and a little water added), they react vigorously

33 Oxidation & Reduction Half- Reactions Always add electrons (negative) to the more positive side of the equation.Always add electrons (negative) to the more positive side of the equation. The charge on both sides of an equation must be equal.The charge on both sides of an equation must be equal. Oxidation -- Na o ----> Na 1+ + 1 e-Oxidation -- Na o ----> Na 1+ + 1 e- Reduction -- Cl 2 + 2 e - ----> 2 Cl -Reduction -- Cl 2 + 2 e - ----> 2 Cl -

34 OIL RIG Oxidation Is Loss. Reduction Is Gain.

35 Redox Reactions Metal-nonmetal reactions are always redox reactions.Metal-nonmetal reactions are always redox reactions. Any reaction that has a free element (such as O 2 ) as a reactant or product are redox.Any reaction that has a free element (such as O 2 ) as a reactant or product are redox. All single replacement reactions are redox.All single replacement reactions are redox. All combustion reactions are redox.All combustion reactions are redox.

36 Synthesis I (Composition) A + X ----> AX ALWAYS REDOX Element + Element -----> Binary Compound Fe (s) + S (s) ----> FeS (s) 4 Al (s) + 3 O 2(g) ----> 2 Al 2 O 3(s)

37 Synthesis II (Composition) A + X ----> AX NOT REDOX Compound + Compound ----> Compound (3 or more elements) Ammonia + Acid ----> Ammonium Salt NH 3(g) + HCl (g) ----> NH 4 Cl (s) 2 NH 3(aq) + H 2 SO 4(aq) ----> (NH 4 ) 2 SO 4(aq)

38 Synthesis II (Composition) Continued Water + An Oxide Rule # 1 --Water + Metal Oxide ----> Metal Hydroxide (Base) HOH (l) + CaO (s) ----> Ca(OH) 2(s) HOH (l) + Na 2 O (s) ----> 2 NaOH (aq) Rule # 2 --Water + Nonmetal Oxide ----> Acid HOH (l) + SO 3(g) ----> H 2 SO 4(aq) HOH (l) + N 2 O 5(g) ----> 2 HNO 3(aq)

39 Single Replacement I A + BX ----> AX + B ALWAYS REDOX Element + Compound ----> Different Element + Different Compound Metal Reactivities: K > Na > Ca > Mg > Al > Zn > Cr > Fe > Cd > Co > Ni > Sn > Pb > H > Sb > Cu > Hg > Ag > Pt > Au

40 Single Replacement I (Continued) A is a metal. A is more reactive than B A + BX ----> AX + B Cu (s) + 2 AgNO 3(aq) ---->Cu(NO 3 ) 2(aq) + 2 Ag (s) Zn (s) + 2 HCl (aq) ----> ZnCl 2(aq) + H 2(g) Rule # 3 -- Active Metal + Water ----> Metal Hydroxide + Hydrogen Ca (s) + 2 HOH (l) ----> Ca(OH) 2(s) + H 2(g)

41 Single Replacement I (Continued) A is a metal. A is less reactive than B A + BX ----> No Reaction (NR) Cu (s) + HCl (aq) ----> NR

42 Single Replacement II Y + BX ----> BY + X ALWAYS REDOX Element + Compound ----> Different Element + Different Compound Nonmetal Reactivities: F > O > Cl > Br > I

43 Single Replacement II (Continued) Y is a nonmetal. Y is more reactive than X Y + BX ----> BY + X Cl 2(g) + 2 KBr (aq) ----> 2 KCl (aq) + Br 2(aq) Y is less reactive than X Y + BX ----> No Reaction Cl 2(g) + KF (aq) ----> NR

44 Single Replacement (Continued) Remember!! Metals replace metals. Mg (s) + 2 Ag(NO 3 ) 2(aq) ----> 2 Ag (s) + Mg(NO 3 ) 2(aq) Nonmetals replace nonmetals. Cl 2(g) + 2 KBr (aq) ----> Br 2(aq) + 2 KCl (aq)

45 Figure 7.6: The thermite reaction gives off so much heat that the iron formed is molten

46 Decomposition I AX ----> A + X ALWAYS REDOX AX is a binary compound. Binary Compound ----> Element + Element elect 2 NaCl (l) ----> 2 Na (l) + Cl 2(g) elect 2 HOH (l) ----> 2 H 2(g) + O 2(g)

47 Decomposition II AX -----> A + X MAY OR MAY NOT BE REDOX AX is a ternary compound. Rule # 4 -- Metal Chlorates ----> Metal Chlorides + Oxygen 2 KClO 3(s) ----> 2 KCl (s) + 3 O 2(g) REDOX

48 Decomposition II (Continued) Rule # 5 -- Metal Carbonates ----> Metal Oxides + Carbon Dioxide CuCO 3(s) ----> CuO (s) + CO 2(g) NOT REDOX

49 Decomposition II (Continued) Rule # 6 -- Metal Hydroxides ----> Metal Oxides + Water Ca(OH) 2(s) ----> CaO (s) + HOH (g) NOT REDOX

50 Decomposition II (Continued) Rule # 7 -- Acid ----> Nonmetal Oxide + Water H 2 SO 4(aq) ----> SO 3(g) + HOH (g) NOT REDOX

51 Double Displacement (Double Replacement) AX + BY ----> AY + BX NEVER REDOX Compound + Compound ----> 2 New Compounds Acid-Base & Precipitation Reactions (Chapter 7) H 2 SO 4(aq) + 2 NaOH (aq) ----> Na 2 SO 4(aq) + 2 HOH (l) NaCl (aq) + AgNO 3(aq) ----> NaNO 3(aq) + AgCl (s)

52 Combustion AX + O 2 ALWAYS REDOX AX is a hydrocarbon. C x H y + O 2(g) ----> CO 2(g) + HOH (g) CH 4(g) + 2 O 2(g) ----> CO 2(g) + 2 HOH (g) 2 C 6 H 6(l) + 15 O 2(g) ----> 12 CO 2(g) + 6 HOH (g)


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