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Chapter 4: CHEMICAL REACTIONS

Chapter 4: CHEMICAL REACTIONS. Vanessa Prasad- Permaul Valencia Community College CHM 1045. IONS IN AQUEOUS SOLUTION. IONIC THEORY OF SOLUTIONS AND SOLUBILITY RULES CERTAIN SUBSTANCES PRODUCE FREELY MOVING IONS WHEN THEY DISSOLVE IN WATER

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Chapter 4: CHEMICAL REACTIONS

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  1. Chapter 4: CHEMICAL REACTIONS Vanessa Prasad-Permaul Valencia Community College CHM 1045

  2. IONS IN AQUEOUS SOLUTION • IONIC THEORY OF SOLUTIONS AND SOLUBILITY RULES • CERTAIN SUBSTANCES PRODUCE FREELY MOVING IONS WHEN THEY DISSOLVE IN WATER • THOSE IONS CONDUCT AN ELECTRICAL CURRENT IN AQUEOUS SOLUTION

  3. IONS IN AQUEOUS SOLUTION • ELECTROLYTE: A SUBSTANCE THAT DISSOLVES IN WATER TO GIVE AN ELECTRICALLY CONDUCTING SOLUTION In general, ionic solutions are electrolytes NaCl(aq) Na+(aq) + Cl-(aq) some electrolytes are molecular substances HCl (aq) H+(aq) + Cl-(aq) • NONELECTROLYTE: A SUBSTANCE THAT DISSOLVES IN WATER TO GIVE A NONCONDUCTING OR VERY POORLY CONDUCTING SOLUTION H2O H2O

  4. IONS IN AQUEOUS SOLUTION • STRONG ELECTROLYTE: AN ELECTROLYTETHAT EXISTS IN SOLUTION ALMOST ENTIRELY AS IONS • MOSTLY IONIC SUBSTANCES • NaCl(aq) Na+(aq) + Cl-(aq) • WEAK ELECTROLYTE: AN ELECTROLYTE THAT DISSOLVES IN WATER TO GIVE A RELATIVELY SMALL PERCENTAGE OF IONS • GENERALLY MOLECULAR SUBSTANCES H2O

  5. IONS IN AQUEOUS SOLUTION WEAK ELECTROLYTES: NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) NH4+(aq) + OH-(aq) NH3(aq) + H2O(l) NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

  6. IONS IN AQUEOUS SOLUTION SOLUBILITY RULES FOR IONIC COMPOUNDS

  7. IONS IN AQUEOUS SOLUTION EXERCISE 4.1 Determine whether the following compounds are soluble or insoluble in water: • NaBr • Ba(OH)2 • CaCO3 • Hg(NO3)2 • AgCl

  8. IONS IN AQUEOUS SOLUTION • a. According to the chart, all compounds that contain sodium, Na+ are soluble, so NaBr is soluble in water. • b. According to Table 4.1, most compounds that contain hydroxides, OH, are insoluble in water. However, Ba(OH)2 is listed as one of the exceptions to this rule, so it is soluble in water. • According to the chart, most compounds that contain • carbonate, CO32−, are insoluble. CaCO3 is not one of the • exceptions, so it is insoluble in water. • Mercuric nitrate or Hg(NO3)2 is soluble because all forms of nitrates are soluble. • AgCl is insoluble. According to the chart, all Cl- • containing compounds are soluble except Ag, Hg & Pb

  9. IONS IN AQUEOUS SOLUTION MOLECULAR & IONIC EQUATIONS Molecular equation: a chemical equation in which all compounds are written as molecules (even if ions): Ca(OH)2(aq) + Na2CO3(aq) CaCO3(s) + 2NaOH(aq) Complete Ionic Equations: a chemical equation in which strong electrolytes are written as separate ions: Ca2+(aq) + 2OH-(aq) + 2Na+(aq) + CO32-(aq) CaCO3(s) + 2Na+(aq) + 2OH-(aq)

  10. IONS IN AQUEOUS SOLUTION Spectator Ion: an ion that does not take part in an ionic equation: Ca2+(aq) + 2OH-(aq) + 2Na+(aq) + CO32-(aq) CaCO3(s) + 2Na+(aq) + 2OH-(aq) Net Ionic Equation: an ionic equation from which the spectator ions have been cancelled: Ca2+(aq) + CO32-(aq) CaCO3(s)

  11. IONS IN AQUEOUS SOLUTION EXERCISE 4.2 Write the complete net ionic equation for each of the following: 2HNO3(aq) + Mg(OH)2(s)  2H2O(l) + MgNO3(aq) *nitric acid is a strong electrolyte PbNO3(aq) + Na2SO4(aq)  PbSO4(s) + 2NaNO3(aq) 2HClO4(aq) + Ca(OH)2(aq) Ca(ClO4)2(aq) + 2H2O(l) *perchloric acid is a strong electrolyte HC2H3O2(aq) + NaOH(aq) NaC2H3O2(aq) + H2O(l)  

  12. IONS IN AQUEOUS SOLUTION The resulting complete ionic equation is: 2H+(aq) + 2NO3−(aq) + Mg(OH)2(s)  2H2O(l) + Mg2+(aq) + 2NO3−(aq) The corresponding net ionic equation is: 2H+(aq) + Mg(OH)2(s)  2H2O(l) + Mg2+(aq) The resulting complete ionic equation is: Pb2+(aq) + 2NO3−(aq) + 2Na+(aq) + SO42−(aq)  PbSO4(s) + 2Na+(aq) + 2NO3−(aq) The corresponding net ionic equation is: Pb2+(aq) + SO42−(aq)  PbSO4(s)

  13. TYPES OF CHEMICAL REACTIONS • PRECIPITATION REACTIONS: Two ionic solutions mix and a solid ionic substance (precipitate) forms. • ACID-BASE REACTIONS: an acidic substance reacts with as basic substance. This reaction involves the transfer of a proton between reactants. • Neutralization • Acid-Base with Gas Formation • OXIDATION-REDUCTION REACTIONS: a reaction in which there is a transfer of electrons between the reactants.

  14. TYPES OF CHEMICAL REACTIONS: PRECIPITATION REACTIONS • PRECIPITATION REACTIONS: Two ionic solutions mix and a solid ionic substance (precipitate) forms. • Molecular Equation: • MgCl2(aq) + 2AgNO3(aq) 2AgCl(s) + Mg(NO3)2(aq) • Complete Ionic Equation: • Mg2+(aq)+ 2Cl-(aq) + 2Ag+(aq) + 2NO3- (aq) • 2AgCl(s) + Mg2+(aq) + 2NO3-(aq) • Net Ionic Equation: 2Cl-(aq) + 2Ag+(aq) 2AgCl(s)

  15. TYPES OF CHEMICAL REACTIONS: PRECIPITATION REACTIONS EXERCISE 4.3 • For each of the following, decide whether a precipitation reaction occurs. If it does, write the balanced molecular equation and then the net ionic equation. If no precipitation reaction occurs, write NPR. • Aqueous solution of sodium chloride and iron(II) nitrate are mixed • Aqueous solution of aluminum sulfate and sodium hydroxide are mixed • You mix an aqueous solution of sodium iodide and lead (II) acetate. If a reaction occurs, write the balanced molecular equation, the complete ionic equation and the net ionic equation.

  16. TYPES OF CHEMICAL REACTIONS: PRECIPITATION REACTIONS The formulas of the compounds are NaI which is soluble and Pb(C2H3O2)2 is also soluble. Exchanging anions, you get sodium acetate, NaC2H3O2 which is soluble, and lead(II) iodide, PbI2 which is insoluble and will form a precipitate. The balanced molecular equation is: Pb(C2H3O2)2(aq) + 2NaI(aq)  PbI2(s) + 2NaC2H3O2(aq) To get the net ionic equation, first get the complete ionic equation: Pb2+(aq) + 2C2H3O2-(aq) + 2Na+(aq) + 2I-(aq)  PbI2(s) + 2Na+(aq) + C2H3O2-(aq) The final result is: Pb2+(aq) + 2I−(aq)  PbI2(s)

  17. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS COMMON ACIDS AND BASES

  18. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS Acid–Base Neutralization:A process in which an acid reacts with a base to yield water plus an ionic compound called a salt. The driving force of this reaction is the formation of the stable water molecule. HCl(aq) + NaOH(aq)NaCl(aq) + H2O(l)

  19. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS • Arrhenius Acid:A substance which dissociates in water to form hydrogen ions (H+). • HNO3(aq) H+(aq) + NO3-(aq) • Arrhenius Base: A substance that dissociates in (or reacts with) water to form hydroxide ions (OH–). • NaOH(s) Na+(aq) + OH-(aq) • Limitations: Has to be an aqueous solution and doesn’t account for the basicity of substances like NH3. • NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) H2O H2O

  20. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS • Brønsted Acid:Can donate protons (H+) to another substance. • Brønsted Base:Can accept protons (H+) from another substance. (NH3)

  21. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS H+ NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) base acid HNO3(aq) H+(aq) + NO3-(aq) HNO3(aq) + H2O(l) H3O+(aq) + NO3-(aq) HNO3(aq) + H2O(l) H3O+(aq) + NO3-(aq) H2O H+ acid base

  22. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS • Strong acid: strong electrolyte - almost completely dissociates in water: • HCl, H2SO4, HNO3, HClO4, HI • HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq) • Weak acid: weak electrolyte - does not dissociate well in water: • HF, HCN, CH3CO2H • HF(aq) + H2O(l) H3O(aq) + CN-(aq)

  23. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS • Strong base: strong electrolyte - almost completely dissociates in water: • Metal hydroxides • NaOH(s) Na+(aq) + OH-(aq) • Weak base:does not dissociate well in water: • NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) H2O

  24. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS STRONG ACIDS AND BASES Other Weak bases – trimethyl ammonia N(CH3)3, C5H5N pyridine, ammonium hydroxide NH4OH, H2O water

  25. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS • EXERCISE 4.4 • Label each of the following as a strong or weak acid or base: • H3PO4 • HClO • HClO4 • Sr(OH)2

  26. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS • H3PO4 is not listed as a strong acid in the table so it is a weak acid. • Hypochlorous acid, HClO, is not one of the strong acids listed in the table, so we assume that HClO is a weak acid. • As noted in the table, HClO4 is a strong acid. • d. As noted in the table, Sr(OH)2 is a strong base.

  27. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS NEUTRALIZATION REACTIONS:A reaction of an acid and a base that results in an ionic compound (salt)and possibly water: 2HCl(aq) + Ca(OH)2(aq) CaCl2(aq) + 2H2O(l) HCN(aq) + KOH(aq) KCN(aq) + H2O(l) acid acid base salt base salt

  28. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS • EXERCISE 4.5 • Write the molecular equation and the complete ionic equation and the net ionic equation for the neutralization of nitrous acid by sodium hydroxide, both in aqueous solution. • Write the molecular equation and the complete ionic equation and the net ionic equation for the neutralization of hydrocyanic acid by lithium hydroxide (both in aqueous solution).

  29. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS HCN(aq) + LiOH(aq)LiCN(aq) + H2O(l) Note that LiOH (a strong base) and LiCN (a soluble ionic substance) are strong electrolytes; HCN is a weak electrolyte (it is not one of the strong acids in the table HCN(aq) + Li+(aq) + OH-(aq) Li+(aq) + CN-(aq) + H2O(l) After eliminating the spectator ions (Li+ and CN−), the net ionic equation is: HCN(aq) + OH−(aq)  H2O(l) + CN−(aq)

  30. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS EXERCISE 4.6 Write the molecular equation, the complete ionic equation and the net ionic equation for the successive neutralization of each of the acidic hydrogens of sulfuric acid with potassium hydroxide

  31. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS The first step in the neutralization is described by the following molecular equation: H2SO4(aq) + KOH(aq) KHSO4(aq) + H2O(l) The corresponding net ionic equation is: H+(aq) + OH−(aq)  H2O(l) The reaction of the acid salt KHSO4 is given by the following molecular equation: KHSO4(aq) + KOH(aq)  K2SO4(aq) + H2O(l) The corresponding net ionic equation is: HSO4−(aq) + OH−(aq)  H2O(l) + SO42−(aq)

  32. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS Acid-Base Reactions with Gas Formations Na2CO3(aq) + 2HCl(aq) 2NaCl(aq) + H2O(l) + CO2(g) carbonate acid salt gas Na2CO3(aq) + 2HCl(aq) 2NaCl(aq) + H2CO3(aq) CO32-(aq) + 2H+(aq) H2O(l) + CO2(g)

  33. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS • EXERCISE 4.7 • Write the molecular equation and the net ionic • equation for the reaction of zinc sulfide with • hydrochloric acid. • Write the molecular equation and the net ionic • equation for the reaction of calcium carbonate • with nitric acid.

  34. TYPES OF CHEMICAL REACTIONS: ACID-BASE REACTIONS First, write the molecular equation for the exchange reaction, noting that the products of the reaction would be soluble Ca(NO3)2 and H2CO3. The carbonic acid decomposes to water and carbon dioxide gas. The molecular equation for the process is: CaCO3(s) + 2HNO3(aq) Ca(NO3)2(aq) + H2O(l) + CO2(g) The corresponding net ionic equation is CaCO3(s) + 2H+(aq) Ca2+(aq) + H2O(l) + CO2(g)

  35. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS Oxidation-Reduction Reactions: reactions involving a transfer of electrons from one species to another (or in which atoms change oxidation states). Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s) Net ionic equation: Fe(s) + Cu2+(aq) Fe2+(aq) + Cu(s) Iron loses electrons = oxidized Copper gains electrons = reduced

  36. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS Oxidation Number: the actual charge of the atom if it exists as a monatomic ion (or a hypothetical charge assigned to the atom in the substance by simple rules). 2Ca(s) + O2(g) 2CaO(s) 0 0 +2 -2 2Ca(s) + O2(g) 2CaO(s) *The concept of oxidation numbers (states) was developed as a simple way of keeping track of electrons in a reactions

  37. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS Rules for Assigning Oxidation Numbers • Free elements are assigned an oxidation state of zero. • The sum of the oxidation states of all that atoms in a species must be • equal to the net charge on the species. • 3. The alkali metals (Li, Na, K, Rb, and Cs) in compounds are always assigned an oxidation state of +1. • 4. Fluorine in compounds is always assigned an oxidation state of -1. • The alkaline earth metals (Be, Mg, Ca, Sr, Ba, and Ra) and also Zn and • Cd in compounds are always assigned an oxidation state of +2. • 6. Hydrogen in compounds is assigned an oxidation state of +1. • 7. Oxygen in compounds is assigned an oxidation state of -2. • 8. Halogen in compounds is assigned an oxidation state of -1.

  38. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS • EXERCISE 4.8 • Use the oxidation number rules to obtain the oxidation number of the chlorine atom in each of the following: • HClO4 • ClO3- • Obtain the oxidation numbers of the atoms in • each of the following: • Potassium dichromate • Permanganate ion

  39. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS A) For potassium dichromate, K2Cr2O7: 2 x (oxidation number of K) + 2 x (oxidation number of Cr) + 7 x (oxidation number of O) = 0 For oxygen, the oxidation number is −2 (rule 3), and for potassium ion, the oxidation number is +1 (rule 2) [2 x (+1)] + 2 x (oxidation number of Cr) + [7 x (−2)] = 0 Therefore, 2 x oxidation number of Cr = − [2 x (+1)] − [7 x (−2)] = +12 or, oxidation number of Cr = +6. B) For the permanganate ion, MnO4−: (Oxidation number of Mn) + 4 x (oxidation number of O) = −1 For oxygen, the oxidation number is −2 (rule 3). (oxidation number of Mn) + [4 x (−2)] = −1 Therefore, Oxidation number of Mn = −1 − [4 x (−2)] = +7

  40. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS • Redox reactionsare those involving the oxidation and reduction of species. • Oxidation and reduction mustoccur together. They cannot exist alone. • Fe2+ + Cu0 Fe0 + Cu2+ • Half-reaction: one of two parts of an oxidation-reduction reaction. One part involves a loss of electron, the other a gain of electrons: • Reduced: Iron gained 2 electrons Fe2+ + 2 e  Fe0 • Oxidized: Copper lost 2 electrons Cu0 Cu2+ + 2e

  41. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS reduction • Fe2+ + Cu0 Fe0 + Cu2+ • Fe2+ gains electrons, is reduced, and we call it an oxidizing agent • Oxidizing agent is a species that can gain electrons and this facilitates in the oxidation of another species. (electron deficient) • Cu0 loses electrons, is oxidized, and we call it a reducing agent • Reducing agent is a species that can lose electrons and this facilitates in the reduction of another species. (electron rich) oxidizing agent reducing agent oxidation

  42. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS • Some Common Oxidation-Reduction Reactions: • Combination Reaction • Decomposition Reaction • Displacement Reaction • Combustion Reaction

  43. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS • Combination Reaction: two substances combine to form a third substance: • 2Na(s) + Cl2(g) 2NaCl(s) • 2Sb(s) + 3Cl2(g) 2SbCl3(s)

  44. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS • 2. Decomposition Reaction: a single compound reacts to give two or more substances. • 2HgO(s) 2Hg(l) + O2(g) • 2KClO3(s) 2KCl(s) + 3O2(g) MnO2

  45. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS • 3. Displacement Reaction (Single Replacement Reaction): an element reacts with a compound displacing another element from that compound • Cu(s) + 2 AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s) • Zn(s) + 2H+ZnCl2(aq) + H2(g)

  46. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS • 4. Combustion Reaction: a substance reacts with oxygen, usually with a rapid release of heat to produce a flame. • 2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g) • 4Fe(s) + 3O2(g)2Fe2O3(s)

  47. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS • Half-Reaction Method:Allows you to focus on the transfer of electrons. This is important when considering batteries and other aspects of electrochemistry. • The key to this method is to realize that the overall reaction can be broken into two parts, or half-reactions. (oxidation half and reduction half)

  48. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS • Balance for an acidic solution: • MnO4–(aq) + Br–(aq) Mn2+(aq) + Br2(aq) • 1. Determine oxidation and reduction half-reactions: • Oxidation half-reaction: Br–(aq)  Br20(aq) • Reduction half-reaction: MnO4–(aq)  Mn2+(aq) • 2. Balance for atoms other than H and O: • Oxidation: 2 Br–(aq)  Br2(aq) • Reduction: MnO4–(aq)  Mn2+(aq)

  49. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS • 3. Balance for oxygen by adding H2O to the side with less oxygen • Oxidation: 2 Br–(aq)  Br2(aq) • Reduction: MnO4–(aq)  Mn2+(aq) + 4 H2O(l) • 4. Balance for hydrogen by adding H+ to the side with less hydrogens • Oxidation: 2 Br–(aq)  Br2(aq) • Reduction: MnO4–(aq) + 8 H+(aq)  Mn2+(aq) + 4 H2O(l)

  50. TYPES OF CHEMICAL REACTIONS: REDOX REACTIONS • 5. Balance for charge by adding electrons (e–): • Oxidation: 2 Br–(aq)  Br2(aq) + 2 e– • Reduction: MnO4–(aq) + 8 H+(aq) + 5 e– Mn2+(aq) + 4 H2O(l) • 6. Balance for numbers of electrons by multiplying: • Oxidation: 5[2 Br–(aq)  Br2(aq) + 2 e–] • Reduction: 2[MnO4–(aq) + 8 H+(aq) + 5 e– Mn2+(aq) + 4 H2O(l)]

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