CHEMISTRY - ZUMDAHL 2E CH.6 - TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY

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Barnard Edgar Cain
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2 CONCEPT: MOLARITY Molarity (M) can serve as the connection between the interconversion of to and vice versa. For example, a 5.8 M NaCl solution really means per. ( Molarity = MolesSolute ) (LitersSolution) A typical mixture consists of a smaller amount of one substance, the, dissolved in a larger amount of another substance, the. Together they form a. Page 2

3 PRACTICE: MOLARITY EXAMPLE 1: 2.64 grams of an unknown compound was dissolved in water to yield 150 ml of solution. The concentration of the solution was M. What was the molecular weight of the substance? ( M = MolesSolute ) (Liters Solution) EXAMPLE 2: A solution is prepared by dissolving mol calcium nitrate, Ca(NO3)2, in enough water to make ml of stock solution. If 20.0 ml of this solution is then mix with an additional 90 ml of deionized water, calculate the concentration of the calcium nitrate solution. PRACTICE 1: What is the molarity of calcium ions of a 650 ml solution containing 42.7 g of calcium phosphate? PRACTICE 2: A solution with a final volume of ml was prepared by dissolving ml of benzene (C6H6, density = g ) in dichloromethane. Calculate the molarity of benzene in the solution. ml Page 3

4 CONCEPT: MOLARITY & CHEMICAL REACTIONS Whenever we are provided given information in a reaction we use to find any unknown information. In aqueous reactions, this given information is typically in units of or. Entities means, or. Entities of Unknown Volume of Given Moles of Given Moles of Unknown Volume of Unknown Grams of Unknown Use this chart when given a chemical equation with the known quantity in either or of a compound or element and asked to find the unknown quantity of another compound or element. EXAMPLE: How many grams of sodium metal are needed to react with ml of M NaOH? 2 Na (s) + 2 H2O (l) H2 (g) + 2 NaOH (aq) Page 4

5 PRACTICE: MOLARITY & CHEMICAL REACTIONS PRACTICE 1: How many milliliters of M HCl are needed to react with 16.2 g of magnesium metal? ( M = MolesSolute ) (Liters Solution) 2 HCl (aq) + Mg (s) MgCl2 + H2 (g) PRACTICE 2: What is the molarity of a hydrobromic acid solution if it takes ml of HBr to completely neutralize ml of M Ca(OH)2? 2 HBr (aq) + Ca(OH)2 (aq) CaBr2 (aq) + 2 H2O (l) PRACTICE 3 (CHALLENGE): Iron (III) can be oxidized by an acidic K2Cr2O7 solution according to the net ionic equation: Cr2O Fe H + 2 Cr Fe H2O If it takes 30.0 ml of M K2Cr2O7 to titrate a 25 ml Fe 2+ solution, what is the molar concentration of Fe 2+? Page 5

6 CONCEPT: AQUEOUS SOLUTIONS The of a compound represents the maximum amount of solute that dissolves in a solvent. SOLUBILITY RULES SOLUBLE IONIC COMPOUNDS 1. Group 1A ions (Li +, Na +, K +, etc.) and ammonium ion (NH4 + ) are soluble. 2. (Nitrates) NO3 -, (acetates) CH3COO - or C2H3O2 -, and most perchlorates (ClO4 - ) are soluble. INSOLUBLE IONIC COMPOUNDS 1. (Hydroxides) OH - and (Sulfides) S 2-, are insoluble except when with Group 1A ions (Li +, Na +, K +, etc.), ammonium ion (NH4 + ) and Ca 2+, Sr 2+, Ba (Carbonates) CO3 2- and (Phosphates) PO4 3- are insoluble except when with Group 1A ions (Li +, Na +, K +, etc.), ammonium ion (NH4 + ). 3. Cl -, Br -, and I - are soluble, except when paired with Ag +, Pb 2+, Cu + and Hg (Sulfates) SO4 2- are soluble, except those of Ca 2+, Sr 2+, Ba 2+, Ag +, and Pb 2+. When we classify a compound as soluble it means that the compound is, it is also known as a(n) because it conducts electricity. NaNO3 (s) H 2 O Na + (aq) + NO3 (aq) When we classify a compound as insoluble it means that the compound is a, it is also known as a(n) because it doesn t conduct electricity. CH3OH (l) BaSO4 (s) H 2 O H 2 O CH3OH (aq) BaSO4 (aq) Page 6

7 CONCEPT: WRITING CHEMICAL REACTIONS EXAMPLE: Predict whether a reaction occurs, and write the balanced molecular equation. a. LiOH (aq) + MgSO4 (aq) EXAMPLE: Predict whether a reaction occurs, and write the balanced molecular equation, the total and net ionic equations. Molecular: Na 2 CO 3 (aq) + HBr (aq) Total Ionic: Net Ionic: Page 7

8 PRACTICE: Predict whether a reaction occurs, and write the balanced total and net ionic equations. Molecular: Ag 2 SO 4 (aq) + KCl (aq) Total Ionic: Net Ionic: PRACTICE: Predict whether a reaction occurs, and write the balanced total and net ionic equations. Molecular: MgBr 2 (aq) + NaC 2 H 3 O 2 (aq) Total Ionic: Net Ionic: Page 8

9 CONCEPT: ELECTROLYTES Whenever we add a solute into a solvent three outcomes are possible: the solute will dissolve ( STRONG electrolytes). the solute will dissolve ( WEAK electrolytes). the solute will dissolve ( NON electrolytes). Classification of Solutes in Aqueous Solution STRONG ELECTROLYTES WEAK ELECTROLYTES NONELECTROLYTES 1. STRONG ACIDS: HCl,, HI, HNO3,,,. 2. STRONG BASES: Group 1A Metal with OH -, H -, O 2- or NH2-1. WEAK ACIDS: HF,,,,. 2. WEAK BASES: Be(OH)2, Mg(OH)2,,. 1. MOLECULAR COMPOUNDS: C6H12O6 (glucose) C12H22O11 (sucrose) Groups 2A Metal, Calcium or Lower, with OH -, H -, O 2- or NH2-3) SOLUBLE IONIC COMPOUNDS: Page 9

10 PRACTICE: ELECTROLYTES EXAMPLE: Each of the following reactions depicts a solute dissolving in water. Classify each solute as a strong electrolyte, a weak electrolyte or a non-electrolyte. a. PbSO4 (s) PbSO4 (aq) b. HC2H3O2 (aq) H + (aq) + C2H3O2 (aq) c. CaS (s) Ca 2+ (aq) + S 2- (aq) d. Hg (l) Hg (aq) PRACTICE: Classify each of the following solutes as either a strong electrolyte, a weak electrolyte or a non-electrolyte. a. Perbromic acid, HBrO4 b. Lithium chloride, LiCl c. Formic Acid, HCO2H d. Methylamine, CH3NH2 e. Zinc bromide, ZnBr2 f. Propanol, C3H8OH Page 10

11 CONCEPT: OXIDATION-REDUCTION REACTIONS Chemists use some important terminology to describe the movement of electrons. In reactions we have the movement of electrons from one reactant to another. L E O Agent G E R Agent Rules for Assigning an Oxidation Number (O.N.) A. General Rules 1. For an atom in its elemental form (Na, O2, S8, etc.): O.N. = 0 2. For an ion the O.N. equals the charge: Na +, Ca 2+, NO3 B. Specific Rules 1. Group 1A: O.N. = Group 2A: O.N. = For hydrogen: O.N. = +1 with nonmetals O.N. = -1 with metals and boron 4. For Fluorine: O.N. = For oxygen: O.N. = -1 in peroxides (X2O2, X = Group 1(A) element) O.N. = 1 in superoxides (XO2, X = Group 1(A) element) 2 O.N. = - 2 in all other compounds 6. Group 7A O.N. = -1 (except when connected to O) Page 11

12 CONCEPT: OXIDATION-REDUCTION REACTIONS (PRACTICE) EXAMPLE: In the following reaction identify the oxidizing agent and the reducing agent: a. 2 C6H6 (l) + 15 O2 (g) 12 CO2 (g) + 6 H2O (g) PRACTICE: What is the oxidation number of each underlined element? a. P4 b. BO3 3- c. AsO4 2- d. HSO4 PRACTICE: In the following reaction identify the oxidizing agent and the reducing agent: a. Cr2O Fe H + 2 Cr Fe H2O Page 12

13 } } CONCEPT: BASIC REDOX CONCEPTS OXIDATION-REDUCTION (REDOX) reactions deal with the transfer of electrons from one reactant to another. Lose Electrons Oxidation } Element becomes more positive Li (s) + Cl 2 (g) Li + (aq) + 2 Cl aq) Oxidation Gain } Element Number Electrons becomes Increases more negative Reduction } } Oxidation Number Decreases Reducing Agent (Reductant) Oxidizing Agent (Oxidant) Li (s) Li + (aq) + e Cl 2 (g) + 2 e 2 Cl (aq) Electrical Charge The units for electrical charge are measured in (C). ( C) ( mol 1 ) = C 1 mole e charge mole e Charge of 1 electron Faraday Constant q = n F Faraday Constant Electrical Current The units for electrical current are in (A). I = q t Current Charge Time Electrical Voltage The relationship between work and voltage can be expressed as: w = E q Work Voltage Charge The relationship between Gibbs Free Energy and electric potential can be expressed as: ΔG = n F E Gibbs Free Energy mole e Faraday Constant Voltage Ohm's Law The units for resistance are in (Ω). I = E R Current Voltage Resistance Power Power represents work done per unit of time. The units for power are in (W). P = E I Power Voltage Current Page 13

14 CONCEPT: SINGLE REPLACEMENT REACTIONS In a single replacement or displacement reaction one element displaces another element from a compound. More reactive or active metals displace less reactive metals or hydrogen from compounds. Metals Lithium (Li) > Potassium (K) > Barium (Ba) > Strontium (Sr) > Calcium (Ca) > Sodium (Na) Activity Metals in this category can displace hydrogen from liquid water, steam and acids: Metals Magnesium (Mg) > Aluminum (Al) > Zinc (Zn 2+ ) > Chromium (Cr 2+, Cr 3+ ) > Iron (Fe 2+, Fe 3+ ) Activity Metals in this category can displace hydrogen from steam and acids: Activity Increases Metals Cadmium (Cd 2+ ) > Cobalt (Co 2+, Co 3+ ) > Nickel (Ni 2+ ) > Tin (Sn 2+, Sn 4+ ) > Lead (Pb 2+, Pb 4+ ) Activity Metals in this category can displace hydrogen from acids: Hydrogen and Metals Hydrogen (H) > Antimony (Sb 3+ ) > Arsenic (As 3+, As 5+ ) > Bismuth (Bi 3+ ) > Copper (Cu +, Cu 2+ ) > Mercury (Hg2 2+, Hg 2+ ) > Silver (Ag + ) > Palladium (Pd 3+ ) > Platinum (Pt 2+, Pt 3+ ) > Gold (Au +, Au 3+ ) Page 14

15 PRACTICE: SINGLE REPLACEMENT REACTIONS EXAMPLE 1: Based on your understanding of activities determine if a reaction occurs and if so provide the products formed. Ba (s) + H2O (g) EXAMPLE 2: Based on your understanding of activities determine if a reaction occurs and if so provide the products formed. Zn (s) + NiCl2 (aq) EXAMPLE 3: If the activity of halogens is stated as: Fluorine > Chlorine > Bromine > Iodine, determine if a reaction occurs and if so provide the products formed. Cl2 (g) + AlBr3 (aq) Page 15

16 CONCEPT: BALANCING REDOX REACTIONS Now that you have refreshed your memory in terms of redox reactions you now have to master balancing them. Generally, you will need to balance a redox reaction in an acidic or basic solution. Balancing A Redox Reaction in Acidic Reactions: STEP 1: Write the equation into 2 half-reactions. STEP 2: Balance elements that are not oxygen or hydrogen. STEP 3: Balance Oxygens by adding H2O. STEP 4: Balance Hydrogens by adding H +. STEP 5: Balance overall charge by adding electrons (e ) to the more side. STEP 6: Combine the half-reactions and cross out reaction intermediates. Balancing A Redox Reaction in Basic Reactions: Follow Steps 1-6 from above. STEP 7: Balance H + by adding OH ions to both sides of the chemical reaction. Page 16

17 CONCEPT: BALANCING REDOX REACTIONS Now that you have refreshed your memory in terms of redox reactions you now have to master balancing them. Generally, you will need to balance a redox reaction in an acidic or basic solution. Balancing A Redox Reaction in Acidic Reactions: STEP 1: Write the equation into 2 half-reactions. STEP 2: Balance elements that are not oxygen or hydrogen. STEP 3: Balance Oxygens by adding H2O. STEP 4: Balance Hydrogens by adding H +. STEP 5: Balance overall charge by adding electrons (e ) to the more side and make sure both half reactions have the same number of electrons. STEP 6: Combine the half-reactions and cross out reaction intermediates. Balancing A Redox Reaction in Basic Reactions: Follow Steps 1-6 from above. STEP 7: Balance H + by adding OH ions to both sides of the chemical reaction. Page 17

18 PRACTICE: BALANCING ACIDIC REDOX REACTIONS EXAMPLE: Balance the following reaction in an acidic solution. NO2 + MnO4 NO3 + Mn 2+ PRACTICE: Balance the following reaction in an acidic solution. Cl2(g) + S2O3 2- (aq) Cl - (aq) + SO4 2- (aq) Page 18

19 PRACTICE: BALANCING BASIC REDOX REACTIONS EXAMPLE: Balance the following reaction in a basic solution. Mo3O9 3- (aq) + Br (aq) Mo (aq) + BrO4 2- (aq) PRACTICE: Balance the following reaction in a basic solution. XeO2 (aq) H2Xe (aq) + XeO4 Page 19

20 16. How many milligrams of NaCN are required to prepare 712 ml of M NaCN? Page 20

21 17. What volume (in µl) of M HBr contains moles of HBr? Page 21

22 18. How many moles of Ca 2+ ions are in L of a M solution of Ca3(PO4)2? Page 22

23 19. How many chloride ions are present in 65.5 ml of M AlCl3 solution? a) chloride ions b) chloride ions c) chloride ions d) chloride ions e) chloride ions Page 23

24 22. To what final volume would 100 ml of 5.0 M KCl have to be diluted in order to make a solution that is 0.54 M KCl? Page 24

25 23. If 880 ml of water is added to ml of a M HBrO4 solution what is the resulting molarity? Page 25

26 26. Consider the following balanced redox equation: H2O + 2 MnO4 + 3 SO3 2-2 MnO2 + 3 SO OH How many grams of MnO2 (MW: g/mol) are produced when 32.0 ml of M MnO4 - (MW: g/mol) reacts with excess water and sulfite? Page 26

27 27. Iron (III) can be oxidized by an acidic K2Cr2O7 solution according to the net ionic equation: Cr2O Fe H + 2 Cr Fe H2O If it takes 35.0 ml of M FeCl2 to titrate 50 ml of a solution containing Cr2O7 2-, what is the molar concentration of Cr2O7 2-? Page 27

28 28. Vinegar is a solution of acetic acid, CH3COOH, dissolved in water. A 5.54 g sample of vinegar was neutralized by ml of M NaOH. What is the percent by weight of acetic acid in the vinegar? Page 28

29 29. What is the molar mass of a g sample of a monoprotic acid if it requires 50.0 ml of M Ca(OH)2 to completely neutralize it? Page 29

30 30. Give the complete ionic equation for the reaction (if any) that occurs when aqueous solutions of sodium sulfide and copper (II) nitrate are mixed. a) Na+ (aq) + SO4 2- (aq) + Cu+(aq) + NO3 - (aq) CuS(s) + Na+(aq) + NO3 - (aq) b) Na+ (aq) + S-(aq) + Cu+(aq) + NO3 - (aq) CuS(s) + NaNO3(aq) c) 2 Na+(aq) + S2-(aq) + Cu2+(aq) + 2 NO3 - (aq) Cu2+(aq) + S2-(aq) + 2 NaNO3(s) d) 2 Na+(aq) + S2-(aq) + Cu2+(aq) + 2 NO3 - (aq) CuS(s) + 2 Na+(aq) + 2 NO3 - (aq) e) No reaction occurs. Page 30

31 31. Give the net ionic equation for the reaction (if any) that occurs when aqueous solutions of H2SO4 and KOH are mixed. a) H+(aq) + OH-(aq) H2O(l) b) 2 K+(aq) + SO4 2- (aq) K2SO4(s) c) H+(aq) + OH-(aq) + 2 K+(aq) + SO4 2- (aq) H2O(l) + K2SO4(s) d) H2 2+ (aq) + OH-(aq) H2(OH)2(l) e) No reaction occurs. Page 31

32 32. Give the net ionic equation for the reaction (if any) that occurs when aqueous solutions of Na2CO3 and HCl are mixed. a) 2 H+(aq) + CO3 2- (aq) H2CO3(s) b) 2 Na+(aq) + CO3 2- (aq) + 2 H+(aq) + 2 Cl-(aq) H2CO3(s) + 2 NaCl(aq) c) 2 H+(aq) + CO3 2- (aq) H2O(l) + CO2(g) d) 2 Na+(aq) + CO3 2- (aq) + 2 H+(aq) + 2 Cl-(aq) H2CO3(s) + 2 Na+(aq) + 2 Cl-(aq) e) No reaction occurs. Page 32

CHEMISTRY - CLUTCH CH.4 - CHEMICAL QUANTITIES & AQUEOUS REACTIONS

CHEMISTRY - CLUTCH CH.4 - CHEMICAL QUANTITIES & AQUEOUS REACTIONS !! www.clutchprep.com CONCEPT: MOLARITY Molarity (M) can serve as the connection between the interconversion of to and vice versa. For example, a 5.8 M NaCl solution really means per. ( Molarity = MolesSolute