Chem II - Wed, 9/14/16

Transcription

1 Chem II - Wed, 9/14/16 Do Now Drop off any study guides you want color coded Pull out stoich HW Homework See board Agenda Stoich Ch 4 Labish thing

2 Chapter 4 Chemical Reactions & Solution Stoich

3 Water Possesses the ability to dissolve many substances Draw the Lewis Dot Diagram now! 3

4 Polarity Water is a polar molecule Polar molecule: unequal distribution of charge, created by a difference in electronegativities

5 Ionic Solid Dissolving in Water

6 Hydration Process by which positive ends of H 2 O molecules are attached to negatively charged ions and vice versa Causes salt to split when dissolved in water When ionic salts dissolve in water, they break into individual cations and anions H 2 O ( l ) s aq aq NH NO NH NO

7 Concept of Solubility Solubility of ionic substances in water varies depending on: The attraction among ions The attraction of ions for water molecules Polar and ionic substances > nonpolar substances

8 Parts of a Solution Solute: Substance being dissolved Solvent: The dissolving medium Example - Water Copyright Cengage Learning. All rights reserved 8

9 Types of Solutes Strong electrolytes: complete dissociation, high electrical conductivity Example NaCl, strong acid, strong base Weak electrolytes: partial dissociation, moderate electrical conductivity Example - Acetic acid, weak acid, weak base Nonelectrolytes: no dissociation, no electrical conductivity Example - Sugar 9

10 Electrical Conductivity

11 Svante Arrhenius Postulated that the extent to which a solution can conduct an electric current directly depends on the number of ions present

12 Soluble Salts Salts such as NaCl contain an array of cations and anions Disintegrate and undergo hydration when the salt dissolves

13 Nature of Acids Acids: Substance that produces H + ions when it is dissolved in water Caused by the polarity of water, pulls of H+ HO 2 HCl H aq + Cl aq HO 2 HNO H + NO aq aq 3 3 HO 2 H SO H + HSO aq aq 2 4 4

14 Nature of Acids (Continued) If every molecule ionizes/dissociates-> Strong acids: Examples - HCl, HNO 3, and H 2 SO 4 If only some molecules ionizes/dissociates -> weak acids: Examples HC 2 H 3 O 2 Typically illustrated using a double arrow to indicate the reaction can happen in either direction aq l aq aq HC H O + H O H O + C H O

15 Bases Soluble ionic compounds that contain the OH (hydroxide) ion When dissolved in water, cations and OH ions separate and move independently Strong and weak exist based on same criteria as acids Example Dissolving potassium hydroxide in water s aq aq KOH K + OH

16 Nonelectrolytes Substances that dissolve in water but do not produce any ions Leads to absence of electrical conductivity Examples Ethanol (C 2 H 5 OH) Table sugar (sucrose, C 12 H 22 O 11 )

17 Chemical Reactions of Solutions Occur when two solutions are mixed To perform stoichiometric calculations, one must know: The nature of the reaction Depends on the exact forms taken by the chemicals when dissolved The amounts of chemicals present in the solutions Expressed as concentrations Copyright Cengage Learning. All rights reserved 17

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19 Chem II - Fri, 9/16/16 Do Now PT and calculator for quiz Homework See board Agenda Stoich Ch 4 Labish thing

20 Molarity (M) Commonly used expression for concentration moles of solute M = molarity = liters of solution Copyright Cengage Learning. All rights reserved 20

21 Interactive Example Concentration of Ions II Calculate the number of moles of Cl ions in 1.75 L of M ZnCl 2 Copyright Cengage Learning. All rights reserved 21

22 Interactive Example Solution Where are we going? To find the moles of Cl ion in the solution What do we know? M ZnCl L What information is needed to find moles of Cl? Balanced equation for dissolving ZnCl 2 Copyright Cengage Learning. All rights reserved 22

23 Interactive Example Solution (Continued 1) How do we get there? What is the balanced equation for dissolving the ions? 2 HO 2 2+ s aq aq ZnCl Zn + 2Cl What is the molarity of Cl ion in the solution? M = M Cl Copyright Cengage Learning. All rights reserved 23

24 Interactive Example Solution (Continued 2) How many moles of Cl? L solution M Cl 1.75 L solution 3 = mol Cl mol Cl L solution Copyright Cengage Learning. All rights reserved 24

25 Standard Solution Solution whose concentration is accurately known Process of preparation Place a weighed amount of the solute into a volumetric flask, and add a small amount of water Dissolve the solid by swirling the flask Add more water until the level of the solution reaches the mark etched on the flask Mix the solution by inverting the flask several times

26 Prepare a standard solution

27 Dilution Process of adding water to a concentrated (stock) solution to achieve the molarity desired for a particular solution Since only water is added to accomplish dilution: Moles of solute after dilution = moles of solute before dilution Copyright Cengage Learning. All rights reserved 27

28 Dilution - Alternate Method Central idea behind performing calculations associated with dilution is to ascertain that the moles of solute are not changed by the dilution M1V 1 = M2V2 M 1 and V 1 - Molarity and volume of original solution M 2 and V 2 - Molarity and volume of the diluted solution

29 Interactive Example Concentration and Volume What volume of 16 M sulfuric acid must be used to prepare 1.5 L of a 0.10-M H 2 SO 4 solution?

30 Interactive Example Solution Where are we going? To find the volume of H 2 SO 4 required to prepare the solution What do we know? 1.5 L of 0.10 M H 2 SO 4 is required We have 16 M H 2 SO 4

31 Interactive Example Solution (Continued 1) What information do we need to find the volume of H 2 SO 4? Moles of H 2 SO 4 in the required solution How do we get there? What are the moles of H 2 SO 4 required? M V = mol 0.10 mol H2SO4 1.5 L solution L solution 0.15 mol H2SO4

32 Interactive Example Solution (Continued 2) What volume of 16 M H 2 SO 4 contains 0.15 mole of H 2 SO 4? V Solving for V gives: 16 mol H2SO mol H 2 SO 4 L solution V 0.15 mol H2SO4 16 mol H2SO4 L solution L or 9.4 ml solution

33 Interactive Example Solution (Continued 3) Conclusion To make 1.5 L of 0.10 M H 2 SO 4 using 16 M H 2 SO 4, we must take 9.4 ml of the concentrated acid and dilute it with water to 1.5 L The correct way to do this is to add the 9.4 ml of acid to about 1 L of distilled water and then dilute to 1.5 L by adding more water

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35 Types of Solution Reactions Precipitation reactions Acid base reactions Oxidation reduction reactions Copyright Cengage Learning. All rights reserved 35

36 Precipitation Reaction Precipitate insoluble solid that is formed in precipitation reaction DEMO! Copyright Cengage Learning. All rights reserved 36

37 The Reaction of Aqueous Potassium Chromate and Barium Nitrate

38 Simple Rules for the Solubility of Salts in Water

39 But who wants that Here s a song!!!!!!! SONG

40 Types of Equations Used to Represent Reactions in Solution POGIL Copyright Cengage Learning. All rights reserved 40

41 Interactive Example Determining the Mass of Product Formed II When aqueous solutions of Na 2 SO 4 and Pb(NO 3 ) 2 are mixed, PbSO 4 precipitates 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

42 Interactive Example Solution Where are we going? To find the mass of solid PbSO 4 formed What do we know? 1.25 L of M Pb(NO 3 ) 2 and 2.00 L of M Na 2 SO 4 Chemical reaction Pb aq + SO aq PbSO s What information do we need? The limiting reactant 4 4

43 Interactive Example Solution (Continued 1) How do we get there? What are the ions present in the combined solution? Na + SO 4 2 Pb 2+ NO 3 Reaction - Since NaNO 3 is soluble and PbSO 4 is insoluble, solid PbSO 4 will form What is the balanced net ionic equation for the reaction? aq aq s Pb + SO PbSO

44 Interactive Example Solution (Continued 2) What are the moles of reactants present in the solution? 1.25 L mol Pb L 2 2 = mol Pb 2.00 L mol SO 4 L 2 2 = mol SO 4

45 Interactive Example Solution (Continued 3) Which reactant is limiting? Since Pb 2+ and SO 4 2 react in a 1:1 ratio, the amount of SO 4 2 will be limiting ( mol SO 4 2 is less than mole of Pb 2+ ) What number of moles of PbSO 4 will be formed? Since SO 4 2 is limiting, only mole of solid PbSO 4 will be formed

46 Interactive Example Solution (Continued 4) What mass of PbSO 4 will be formed? g PbSO mol PbSO4 = 15.2 g PbSO4 1 mol PbSO 4

47 Definitions - Acid, Base, and Neutralization Reaction Brønsted Lowry definitions for acids and bases Acid: Proton donor Base: Proton acceptor Neutralization reaction: General name given to acid base reactions An acid is neutralized when enough base reacts exactly with it in a solution Copyright Cengage Learning. All rights reserved 47

48 Problem-Solving Strategy - Performing Calculations for Acid Base Reactions 1. List the species present in the combined solution before any reaction occurs Decide what reaction will occur 2. Write the balanced net ionic equation for the reaction 3. Calculate moles of reactants For reactions in solution, use the volumes of the original solutions and their molarities Copyright Cengage Learning. All rights reserved 48

49 Problem-Solving Strategy - Performing Calculations for Acid Base Reactions (Continued) 4. Determine the limiting reactant where appropriate 5. Calculate the moles of the required reactant or product 6. Convert to grams or volume (of solution), as required Copyright Cengage Learning. All rights reserved 49

50 Interactive Example Neutralization Reactions II In a certain experiment, 28.0 ml of M HNO 3 and 53.0 ml of M KOH are mixed What is the concentration of H + or OH ions in excess after the reaction goes to completion?

51 Interactive Example Solution Where are we going? To find the concentration of H + or OH in excess after the reaction is complete What do we know? 28.0 ml of M HNO ml of M KOH Chemical reaction aq aq l + H + OH H2O

52 Interactive Example Solution (Continued 1) How do we get there? What are the ions present in the combined solution? H + NO 3 K + OH What is the balanced net ionic equation for the reaction? aq aq l + H + OH H2O

53 Interactive Example Solution (Continued 2) What are the moles of reactant present in the solution? 28.0 ml HNO L mol H 1000 ml L HNO mol H 53.0 ml KOH 1 L 1000 ml mol OH L KOH mol OH

54 Interactive Example Solution (Continued 3) Which reactant is limiting? Since H + and OH ions react in a 1:1 ratio, the limiting reactant is H + What amount of OH will react? mole of OH is required to neutralize the H + ions present To determine the excess of OH ions, consider the following difference: Original amount amount consumed = amount in excess

55 Interactive Example Solution (Continued 4) Excess OH is: mol OH mol OH = mol OH The volume of the combined solution is the sum of the individual volumes Original volume of HNO 3 + original volume of KOH = total volume ml ml = 81.0 ml = L

56 Interactive Example Solution (Continued 5) What is the molarity of the OH ions in excess? 2 mol OH mol OH 2 L solution L Reality check M OH This calculated molarity is less than the initial molarity, as it should be

57 Volumetric Analysis Technique used for ascertaining the amount of a certain substance by doing a titration Titration: Delivery of a titrant into an analyte Titrant - Solution of known concentration Analyte - Solution containing the substance being analyzed Copyright Cengage Learning. All rights reserved 57

58 Acid Base Titrations Equivalence (stoichiometric) point: Marks the point in titration where enough titrant has been added to react exactly with the analyte Indicator: Substance added at the beginning of the titration Changes color at the equivalence point Endpoint: Point where the indicator actually changes color Copyright Cengage Learning. All rights reserved 58

59 Requirements for a Successful Titration Exact reaction between titrant and analyte must be known and must be rapid Equivalence point must be accurately marked Volume of titrant that is needed to reach the equivalence point must be accurately known

60 Indicator Used in Acid Base Titrations Phenolphthalein Colorless in an acidic solution Pink in a basic solution When an acid is titrated with a base, the indicator remains colorless until after the acid is consumed and the first drop of excess base is added

61 Figure Titration of an Acid with a Base

62 Interactive Example Neutralization Titration A student carries out an experiment to standardize (determine the exact concentration of) a sodium hydroxide solution To do this, the student weighs out a g sample of potassium hydrogen phthalate (KHC 8 H 4 O 4, often abbreviated KHP) KHP (molar mass g/mol) has one acidic hydrogen

63 Interactive Example Neutralization Titration (Continued) The student dissolves the KHP in distilled water, adds phenolphthalein as an indicator, and titrates the resulting solution with the sodium hydroxide solution to the phenolphthalein endpoint The difference between the final and initial buret readings indicates that ml of the sodium hydroxide solution is required to react exactly with the g KHP Calculate the concentration of the sodium hydroxide solution

64 Interactive Example Solution Where are we going? To find the concentration of NaOH solution What do we know? g KHC 8 H 4 O 4 (KHP), molar mass ( g/mol) ml NaOH solution to neutralize KHP The chemical reaction 2 HC H O aq + OH aq H O l + C H O aq

65 Interactive Example Solution (Continued 1) How do we get there? What are the ions present in the combined solution? K + HC 8 H 4 O 4 Na + OH What is the balanced net ionic equation for the reaction? 2 aq aq l aq HC H O + OH H O + C H O

66 Interactive Example Solution (Continued 2) What are the moles of KHP? 1 mol KHC8H 4O g KHC8H 4O g KHC H O mol KHC8H 4O4 Which reactant is limiting? This problem requires the addition of just enough OH ions to react exactly with the KHP present We do not need to be concerned with limiting reactant here

67 Interactive Example Solution (Continued 3) What moles of OH are required? mole of OH is required to neutralize the KHP present What is the molarity of the NaOH solution? 3 mol NaOH mol NaOH Molarity of NaOH L solution L = M

68 Oxidation Reduction (Redox) Reactions Involve the transfer of one or more electrons Example Formation of sodium chloride from elemental sodium and chlorine s g s 2Na + Cl 2NaCl 2 Copyright Cengage Learning. All rights reserved 68

69 Oxidation States (Oxidation Numbers) For atoms in covalent compounds, the oxidation state refers to imaginary charges that atoms would have if: Shared electrons were equally divided between identical atoms bonded to each other In different atoms, the shared electrons were all assigned to the atom in each bond that has greater electron affinity

70 Oxidation States (Oxidation Numbers) (Continued) In ionic compounds that contain monatomic ions, the oxidation states of the ions are equal to the ion charges For electrically neutral compounds, the sum of oxidation states must be zero

71 Table Rules for Assigning Oxidation States Copyright Cengage Learning. All rights reserved 71

72 Interactive Example Assigning Oxidation States Assign oxidation states to all atoms in the following: a. CO 2 b. NO 3

73 Exercise Assign oxidation states for all atoms in each of the following compounds: a. KMnO 4 K = +1; O = 2; Mn = +7 b. Na 4 Fe(OH) 6 c. (NH 4 ) 2 HPO 4 d. C 6 H 12 O 6 Na = +1; Fe = +2; O = 2; H = +1 H = +1; O = 2; N = 3; P = +5 C = 0; H = +1; O = 2

74 Terminologies Oxidation: Increase in oxidation state Characterized by electron loss Reduction: Decrease in oxidation state Characterized by electron gain Reducing agent: Electron donor Oxidizing agent: Electron acceptor

75 Figure Summary of an Oxidation Reduction Process

76 Interactive Example Oxidation Reduction Reactions Metallurgy, the process of producing a metal from its ore, always involves oxidation reduction reactions In the metallurgy of galena (PbS), the principal leadcontaining ore, the first step is the conversion of lead sulfide to its oxide (a process called roasting): s g s g 2PbS + 3O 2PbO + 2SO 2 2

77 Interactive Example Oxidation Reduction Reactions (Continued) The oxide is then treated with carbon monoxide to produce the free metal: s g s g PbO + CO Pb + CO 2 For each reaction, identify the atoms that are oxidized and reduced, and specify the oxidizing and reducing agents

78 Interactive Example Solution For the first reaction, we can assign the following oxidation states: s g s g 2PbS + 3O 2PbO + 2SO (each O) The oxidation state for the sulfur atom increases from 2 to +4 Thus, sulfur is oxidized

79 Interactive Example Solution (Continued 1) The oxidation state for each oxygen atom decreases from 0 to 2 Oxygen is reduced The oxidizing agent is O 2, and the reducing agent is PbS For the second reaction we have s g s g PbO + CO Pb + CO (each O)

80 Interactive Example Solution (Continued 2) Lead is reduced (its oxidation state decreases from +2 to 0), and carbon is oxidized (its oxidation state increases from +2 to +4) PbO is the oxidizing agent, and CO is the reducing agent

81 Problem-Solving Strategy - Balancing Oxidation Reduction Reactions by Oxidation States Write the unbalanced equation Determine the oxidation states of all atoms in the reactants and products Show electrons gained and lost using tie lines Add appropriate states Balance the rest of the equation by inspection Use coefficients to equalize the electrons gained and lost Copyright Cengage Learning. All rights reserved 81

82 Activity Series of Elements

83 Activity Series of Elements (Continued 1)

84 Activity Series of Elements (Continued 2)

85 Example Balancing Oxidation Reduction Reactions Balance the reaction between solid lead(ii) oxide and ammonia gas to produce nitrogen gas, liquid water, and solid lead

86 Example Solution What is the unbalanced equation? PbO s + NH g N g + H O l + Pb s What are the oxidation states for each atom? PbO + NH N + H O + Pb

87 Example Solution (Continued 1) How are electrons gained and lost? 3 e lost (each atom) PbO + NH N + H O + Pb e gained The oxidation states of all other atoms are unchanged

88 Example Solution (Continued 2) What coefficients are needed to equalize the electrons gained and lost? 3 e lost (each atom) multiply by 2 PbO + NH N + H O + Pb e gained multiply by 3

89 Example Solution (Continued 3) What coefficients are needed to balance the remaining elements? Balance O 3PbO + 2 NH N + H O + 3Pb PbO + 2NH N + 3 H O + 3Pb 3 2 2

90 Example Solution (Continued 4) All the elements are now balanced The balanced equation with states is: s g g l s 3PbO + 2NH N + 3H O + 3Pb 3 2 2