Chapter 4: Types of Chemical Reactions and Solution Stoichiometry

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1 Chapter 4: Types of Chemical Reactions and Solution Stoichiometry Collision A bag of mostly water - Star Trek - Rareness No mobility Solution is the solution.

larger amount Solution Solvent Solute Soft drink (l) H 2 O Sugar, CO 2 Air (g) N 2 O 2, Ar, CH 4 Soft Solder

2 Water, the Common Solvent A bag of mostly water - Star Trek - Solution : a homogenous mixture of 2 or more substances Solute : the substance(s) present in the smaller amount(s) Solvent : the substance present in the larger amount Solution Solvent Solute Soft drink (l) H 2 O Sugar, CO 2 Air (g) N 2 O 2, Ar, CH 4 Soft Solder (s) Pb Sn Aqueous Solution Plenty of water -> Plenty of chemical reactions -> Plenty of diversified matters Why water?

Hydration : the process in which an ion is surrounded by water molecules arranged in a specific manner.

3 Water, the Common Solvent Why water? Because water can dissolve many chemical substances. The most Universal Solvent known. Polarity of water which allows it to interact ionic and nonionic substances. Hydration : the process in which an ion is surrounded by water molecules arranged in a specific manner. Dissolving NaCl And For Life Range of temperatures in which water is maintained in a liquid state (0 o C ~ 100 o C). Different density of the liquid and solid state, which allows ice to float on liquid water. Ethanol Like dissolves Like. * Universal solvent: A substance that has the ability to dissolve both bases and acids.

The Nature of Aqueous Solutions: Strong and Weak Electrolytes Electric conductivity of a solution Arrhenius' postulation : the extent to which a solution can conduct an electric current depend

4 The Nature of Aqueous Solutions: Strong and Weak Electrolytes Electric conductivity of a solution Arrhenius' postulation : the extent to which a solution can conduct an electric current depend directly on the number of ions presnet in the solution (as usual, the postulation was not accepted in the scientific society at the time of 1880s, but later (1890s) accepted) Solute Electrolyte : a substance that, when dissolved in water, results in a solution that can conduct electricity. Strong electrolyte solution Weak electrolyte solution Nonelectrolyte solution Nonelectrolyte : a substance that, when dissolved, results in a solution that does not conduct electricity.

H 2 O HCl H + (aq) + Cl - (aq) H 2 O HNO 3 H + (aq) + NO 3- (aq) H 2 O H 2 SO 4 H + (aq) + HSO 4- (aq) Strong bases - react

5 The Nature of Aqueous Solutions: Strong and Weak Electrolytes Strong electrolytes - 100% dissociation occurs to produce cations and anions when they are dissolved in a solvent Ionic compunds (Sugar) Strong acids - dissociate completely to produce H + in solution H 2 O HCl H + (aq) + Cl - (aq) H 2 O HNO 3 H + (aq) + NO 3- (aq) H 2 O H 2 SO 4 H + (aq) + HSO 4- (aq) Strong bases - react completely with water to give OH - ions. H 2 O NaOH Na + (aq) + OH - (aq) H 2 O NaCl(s) Na + (aq) + Cl - (aq) H 2 O KOH K + (aq) + OH - (aq)

The Nature of Aqueous Solutions: Strong and Weak Electrolytes Weak bases - react only slightly with water to give OH - ions (Sugar) NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH - (aq) Weak electrolytes -

6 The Nature of Aqueous Solutions: Strong and Weak Electrolytes Weak bases - react only slightly with water to give OH - ions (Sugar) NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH - (aq) Weak electrolytes - not 100% dissociation occurs when they are dissolved in a solvent Weak acids - dissociate to a slight extent to give H + in solution Nonelectrolytes - no dissociation occurs when they are dissolved in a solvent CH 3 COOH(aq) H + (aq) + CH 3 COO - (aq) H 2 O C 12 H 22 O 11 C 12 H 22 O 11 (aq) completely dissolve but no dissociation nondissovable substances - not solutes

7 The Composition of Solutions Dissolving helps chemical reactions Dissolving process separating bulk material to each molecule or ion Now a molecule or an ion can have chance to meet other molecules or ions to initiate chemical reactions in aqueous solution (liquid phase). Stoichiometric calculation in solution - must know (1) the nature of the reaction (which chemicals are involved) (2) the amount of the chemicals (solution composition) Expressions of a solution composition Molarity (M), Mass(weight) percent,mole fraction ( ), Molality (m), Normality (N) Molarity (M) (concentration of solution) = moles of solute per volume of solution in liters: A Molarity (M) moles of solute (mol) liter of solution (L)

The Composition of Solutions Ex) Molarity of a solution prepared by dissolving 1.56 g of gaseous HCl in enough water to make 26.8 ml of solution. (HCl => 36.46 g/mol) Molarity 1mol 1.56g HCl 36.46g 4.

8 The Composition of Solutions Ex) Molarity of a solution prepared by dissolving 1.56 g of gaseous HCl in enough water to make 26.8 ml of solution. (HCl => g/mol) Molarity 1mol 1.56g HCl 36.46g mol HCl mol HCl mol HCl mL L 1.60M HCl Ex) Concentration and number of moles of Cl - ions in 1.75 L of 1.0 mm ZnCl 2? ZnCl 2 (aq) Zn 2+ (aq) + 2Cl - (aq) => Molarity of Cl - = 2.0 mm Molarity (M) moles of solute (mol) moles of volume of solution (L) solute (mol) molarity (M) volume of solution (L) mM Cl 1.75L 3.5mmol Cl mol Cl - Ex) Typical blood serum is about 0.14 M NaCl. What volume of blood contains 1.0 mg NaCl? (NaCl => g/mol) 1mol 1.0 mg NaCl g mol NaCl V 0.14M NaCl mol 4 NaCl L 0.12mL

9 The Composition of Solutions Standard solution - a solution whose concentration is accurately known. Preparation of a standard aqueous solution Common Terms of Solution Concentration Stock - routinely used solutions prepared in concentrated form. (stock solution) Concentrated - relatively large ratio of solute to solvent. (5.0 M NaCl) Dilute - relatively small ratio of solute to solvent. (0.01 M NaCl) pipet volumetric flask Steps for Dilution dilution with water does not alter the numbers of moles of solute present M 1V1 M2V2

10 The Composition of Solutions Ex) To make 1.50 L of an aqueous M K 2 Cr 2 O 7 solution, How much solid K 2 Cr 2 O 7 must be wieghed out? (K 2 Cr 2 O 7 => g/mol) 0.500mol K2Cr2O7 1.50L solution 0.750mol K2Cr 1L solutiom g 0.750mol K2Cr2O7 221g K2Cr2O7 1mol 2 O 7 g? 1.50 L Ex) What volume of the above K 2 Cr 2 O 7 solution must be used to prepare 1.50 L of 2.00 mm K 2 Cr 2 O 7 solution? M V M V V 1 stock 1 Mdilute V M stock dilute L 6.00mL M 1.50L 0.500M L? 1.50 L

11 Types of Chemical Reactions Precipitation reaction : a reaction which results in the formation of an insoluble products, or precipitate. K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq) BaCrO 4 (s) + 2KNO 3 (aq) Acid-Base reaction : a reaction between an acid and a base. NaOH(aq) + HCl(aq) NaCl(aq) + H 2 O(l) Oxidation-reduction reaction : intermolecular electron transfer reaction. CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) hydrated methane

12 Precipitation Reactions Precipitation reaction : a reaction which results in the formation of an insoluble products, or precipitate. Ba(NO 3 ) 2 (aq) K 2 CrO 4 (aq) Ba 2+ NO 3 - K + CrO 4 2- Possible combinations: Ba(NO 3 ) 2, K 2 CrO 4, BaCrO 4, KNO 3 BaCrO 4, K +, NO 3 - K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq) BaCrO 4 (s) + 2KNO 3 (aq)

13 Precipitation Reactions AgNO 3 (aq) + KCl(aq) K + Cl - Ag + NO 3 - What is the solid product? Possible combinations: AgNO 3, KCl, AgCl, KNO 3

14 Precipitation Reactions

Precipitation Reactions AgNO 3 (aq) + KCl(aq) Ex) KNO 3 (aq) + BaCl 2 (aq) K

3 ) 3 (aq) Fe(OH) 3 (s) + KNO 3 (aq) 3KOH(aq) + Fe(NO 3 ) 3 (aq) Fe(OH) 3

(aq) Pb(NO 3 ) (aq) K + Cl - Ag + NO 3 - What is the solid product?

15 Precipitation Reactions AgNO 3 (aq) + KCl(aq) Ex) KNO 3 (aq) + BaCl 2 (aq) K + (aq) + NO 3- (aq) + Ba 2+ (aq) + 2Cl - (aq) (no reaction) KOH(aq) + Fe(NO 3 ) 3 (aq) Fe(OH) 3 (s) + KNO 3 (aq) 3KOH(aq) + Fe(NO 3 ) 3 (aq) Fe(OH) 3 (s) + 3KNO 3 (aq) Na 2 SO 4 (aq) + Pb(NO 3 ) 2 (aq) Pb(SO 4 )(s) + 2NaNO 3 (aq) Pb(NO 3 ) (aq) K + Cl - Ag + NO 3 - What is the solid product? Possible combinations: AgNO 3, KCl, AgCl, KNO 3 AgNO 3 (aq) + KCl(aq) AgCl(s) + KNO 3 (aq)

Describing Reactions in Solution K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq) BaCrO 4 (s) + 2KNO 3 (aq) Formula equation (reactants and products as compounds) K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq) BaCrO 4 (s) +

16 Describing Reactions in Solution K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq) BaCrO 4 (s) + 2KNO 3 (aq) Formula equation (reactants and products as compounds) K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq) BaCrO 4 (s) + 2KNO 3 (aq) Complete ionic equation (all strong electrolytes shown as ions) Ba 2+ (aq) + 2NO 3- (aq) + 2K + (aq) + CrO 4 2- (aq) BaCrO 4 (s) + 2K + (aq) + 2NO 3- (aq) Net ionic equation (show only components that actually react) Ba 2+ (aq) + CrO 4 2- (aq) BaCrO 4 (s) Spectator ions K +, NO 3 - Formula equation : AgNO 3 (aq) + KCl(aq) AgCl(s) + KNO 3 (aq) Complete ionic equation : Ag + (aq) + NO 3- (aq) + K + (aq) + Cl - (aq) AgCl(s) + K + (aq) + NO 3- (aq) Net ionic equation : Ag + (aq) + Cl - (aq) AgCl(s) Spectator ions : K +, NO 3 -

17 Stoichiometry of Precipitation Reactions Ex) Calculate the mass of PbSO 4 formed when 1.25 L of M Pb(NO 3 ) 2 and 2.00 L of M Na 2 SO 4 are mixed. Na 2 SO 4 (aq) + Pb(NO 3 ) 2 (aq) Pb(SO 4 )(s) + 2NaNO 3 (aq) SO 4 2- (aq) + Pb 2+ (aq) PbSO 4 (s) L M Pb mol 2 Pb L M SO mol SO mol PbSO 4 (s) is formed g mol PbSO4 15.2g PbSO 4 1mol

18 Acid-Base Reactions Acid-Base reaction : a reaction between an acid and a base. NaOH(aq) + HCl(aq) NaCl(aq) + H 2 O(l) Acid Definitions Base Arrhenius H + producer OH - producer Defined only in aqueous solutions Brønsted-Lowry H + donor H + acceptor Defined in both aqueous and nonaqueous solutions Lewis e - pair acceptor e - pair donor Arrhenius NaOH(aq) + HCl(aq) Na + (aq) + Cl - (aq) + H 2 O(l) CH 3 COOH(aq) + KOH(aq) CH 3 COO - (aq) + K + (aq) + H 2 O(l) Net ionic equation H + (aq) + OH - (aq) H 2 O(l) OH - (aq) + K + (aq) CH 3 COO - (aq) + H + (aq) Strong acid, base Weak acid, base Neutralization Reaction

19 Acid-Base Reactions Ex) 28.0 ml of M HNO 3 and 53.0 ml of M KOH are mixed. 1) Number of moles of water formed? 2) Concentration of H + or OH - after the completion of the reaction? H + (aq) + OH - (aq) H 2 O(l) 28.0mL 0.250M H 7.00mmol 53.0mL 0.320M OH 17.0mmol H OH 10.0 mmol of OH - is left after the completion. 10.0mmol OH ( ) ml 0.123M OH 7.00 mmol of H 2 O is formed.

titration Analyte : substance being analyzed Equivalence point : enough titrant added to react exactly with the analyte (moles of H + = moles

20 Acid-Base Reactions Acid-Base Titrations Titration : quantitative/chemical analysis used for determining the concentration of a reactant. Acid-base titration : analysis used for determining the concentration of an acid or a base Titrant : solution of known concentration used in titration Analyte : substance being analyzed Equivalence point : enough titrant added to react exactly with the analyte (moles of H + = moles of OH - ) Endpoint : the indicator changes color so you can tell the equivalence point has been reached. (moles of H + moles of OH - ) Indicator

21 Acid-Base Reactions Acid-Base Titrations Ex) phenolphthalein ml NaOH solution Concentration of NaOH solution? Colorless Red g KHC 8 H 4 O 4 in any volume of H 2 O (KHC 8 H 4 O 4 => g/mol) HC 8 H 4 O 4- (aq) + OH - (aq) H 2 O(l) + C 8 H 4 O 4 2- (aq) H + (aq) + OH - (aq) H 2 O(l) g KHP 1mol g mol KHP mol H Concentrat ion of NaOH mol 41.20mL NaOH M NaOH

22 Oxidation-Reduction Reactions Oxidation-reduction reaction : intermolecular electron transfer reaction. CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) 2Mg(s) + O 2 (g) 2MgO(s) Na(s) Cl 2 (g) NaCl(s) How to know electron-transfer?

23 Oxidation-Reduction Reactions Oxidation state (Oxidation number) Formal charge : the net charge of an atom when a bond is considered as a completely covalent bond. H 0 A B halve the shared electrons formal charge = net charge of an atom Oxidation number : the net charge of an atom when a bond is considered as a completely ionic bond. H +1 H C H (for A > B ) H +1 an atom having bigger electronegativity ( A > B ) has the shared electrons A B 0 H 0 C 0 H 0 H oxidation number = net charge of an atom Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.

24 Oxidation-Reduction Reactions Oxidation state (Oxidation number)

25 Oxidation-Reduction Reactions Oxidation state (Oxidation number) Ex) Ox # of each atom? CO 2 O: -2, C: +4 SF 6 F: -1, S: +6 NO 3 - O: -2, N: +5 Fe 3 O 4 O: -2, Fe: +8/3

half-reaction O 2 + 4e - -> 2O 2- : reduction half-reaction 2Mg + O 2 -> 2Mg 2+ + 2O 2-2Mg 2+ + 2O 2- ->

26 Oxidation-Reduction Reactions The Characteristics of Oxidation-Reduction Reactions 2Mg (s) + O 2 (g) 2MgO (s) oxidation reduction Mg: reductant, O 2 : oxidant 2Mg -> 2Mg e - : oxidation half-reaction O 2 + 4e - -> 2O 2- : reduction half-reaction 2Mg + O 2 -> 2Mg O 2-2Mg O 2- -> 2MgO Oxidation and reduction reactions must occur simultaneously. Number of electron loss = Number of electron gain

27 Oxidation-Reduction Reactions The Characteristics of Oxidation-Reduction Reactions CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) oxidation reduction CH 4 : reductant, O 2 : oxidant CH 4 -> C H + + 8e - : oxidation half-reaction 2O 2 + 8e - -> 4O 2- : reduction half-reaction CH 4 + 2O 2 -> C O H + + 2O 2- CO 2 H 2 O

Oxidation-Reduction Reactions The Characteristics of Oxidation-Reduction Reactions Zn in CuSO 4 solution Cu in AgNO 3 solution Cu(s)+2AgNO 3 (aq)->cu(no 3 ) 2 (aq)+2ag(s) Cu(s)+2Ag + (aq) -> Cu 2+

28 Oxidation-Reduction Reactions The Characteristics of Oxidation-Reduction Reactions Zn in CuSO 4 solution Cu in AgNO 3 solution Cu(s)+2AgNO 3 (aq)->cu(no 3 ) 2 (aq)+2ag(s) Cu(s)+2Ag + (aq) -> Cu 2+ (aq)+2ag(s) oxidation reduction Cu -> Cu 2+ +2e - : ox. half-rxn 2Ag + +2e - -> Ag : re. half-rxn Zn(s)+CuSO 4 (aq)->znso 4 (aq)+ Cu(s) Zn(s)+Cu 2+ (aq) -> Zn 2+ (aq)+cu(s) Zn -> Zn 2+ +2e - : ox. half-rxn Cu 2+ +2e - -> Cu : re. half-rxn 2Ag+Cu 2+ ->Cu 2+ +2Ag + oxidation reduction Zn+Cu 2+ ->Zn 2+ +Cu

29 Balancing Oxidation-Reduction Equations The Half-Reaction Method for Balancing Oxidation-Reduction Reactions in Aqueous Solutions Ce 4+ (aq) + Sn 2+ (aq) Ce 3+ (aq) + Sn 4+ (aq) Is this equation correct? Two most fundametal priciples of chemical equations : Conservation of mass Conservation of charge Ce 4+ (aq) + e - Ce 3+ (aq) Sn 2+ (aq) Sn 4+ (aq) + 2e - (1) : reduction half-reaction (2) : oxidation half-reaction (1) x 2 + (2) : 2Ce 4+ (aq) + Sn 2+ (aq) 2Ce 3+ (aq) + Sn 4+ (aq) : balanced equation

30 Balancing Oxidation-Reduction Equations The Half-Reaction Method for Balancing Oxidation-Reduction Reactions in Aqueous Solutions In acidic solution 1. Write separate reduction, oxidation half-reactions. 2. For each half-reaction: Balance elements (except H, O) Balance O using H 2 O Balance H using H + Balance charge using electrons 3. If necessary, multiply one or both the half-reactions by an integer to equalize number of electrons transferred. 4. Add half-reactions. 5. Check that elements and charges are balanced. Ex) Balance the following equation for the redox rxn occuring in acid solution. 1. MnO 4- Mn 2+ Fe 2+ Fe MnO 4- Mn H 2 O MnO H + Mn H 2 O MnO H + + 5e - Mn H 2 O Fe 2+ Fe 3+ + e - 3. MnO H + + 5e - Mn H 2 O 5Fe 2+ 5Fe e - 4. MnO Fe H + Mn Fe H 2 O 5. Check charge and mass. MnO 4- (aq) + Fe 2+ (aq) Fe 3+ (aq) + Mn 2+ (aq) ox re

31 Balancing Oxidation-Reduction Equations The Half-Reaction Method for Balancing Oxidation-Reduction Reactions in Aqueous Solutions In basic solution 1. Write separate reduction, oxidation half-reactions. 2. For each half-reaction: Balance elements (except H, O) Balance O using H 2 O Balance H using H + Balance charge using electrons 3. Add OH - that equals H + ions (both sides!) 4. If necessary, multiply one or both the half-reactions by an integer to equalize number of electrons transferred. 5. Add half-reactions. 6. Check that elements and charges are balanced. Ex) Balance the following equation for the redox rxn occuring in basic solution. Ag(s) + CN - (aq) + O 2 (g) Ag(CN) 2- (aq) 0-1 (CN-) (CN-) 1. Ag + CN - Ag(CN) 2 - O 2 2. Ag + 2CN - Ag(CN) - 2 Ag + 2CN - Ag(CN) 2- + e - O 2 2H 2 O O 2 + 4H + 2H 2 O O 2 + 4H + + 4e - 2H 2 O 3. Ag + 2CN - Ag(CN) 2- + e - O 2 + 4H + + 4OH - + 4e - 2H 2 O + 4OH - O 2 + 4H 2 O + 4e - 2H 2 O + 4OH - O 2 + 2H 2 O + 4e - 4OH Ag + 8CN - 4Ag(CN) e - O 2 + 2H 2 O + 4e - 4OH Ag + 8CN - + O 2 + 2H 2 O 4Ag(CN) OH - 6. Check charge and mass. oxidation reduction

Chapter 4 - Types of Chemical Reactions and Solution Chemistry

Chapter 4 - Types of Chemical Reactions and Solution Chemistry 4.1 Water, the Common Solvent - the water molecule is bent with and H-O-H angles of approx. 105 º - O-H bonds are covalent - O is slightly