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Chapter 4: TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY

Chapter 4: TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY. Aqueous Solutions. Water is the dissolving medium, or solvent. Some Properties of Water Water is “ bent ” or V-shaped . The O-H bonds are covalent . Water is a polar molecule.

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Chapter 4: TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY

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  1. Chapter 4: TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY

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

  3. Some Properties of Water Water is “bent” or V-shaped. The O-H bonds are covalent. Water is a polar molecule. Hydration occurs when salts dissolve in water.

  4. Figure 4.1: (Left) The water molecule is polar. (Right) A space-filling model of the water molecule.

  5. Figure 4.2: Polar water molecules interact with the positive and negative ions of a salt assisting in the dissolving process.

  6. Figure 4.3: (a) The ethanol molecule contains a polar O—H bond similar to those in the water molecule. (b) The polar water molecule interacts strongly with the polar O—H bond in ethanol. This is a case of "like dissolving like."

  7. A Solute dissolves in water (or other “solvent”); changes phase(if different from the solvent); is present in lesser amount (if the same phase as the solvent). A Solvent retains its phase(if different from the solute); is present in greater amount (if the same phase as the solute).

  8. Figure 4.4: Electrical conductivity of aqueous solutions.

  9. Electrolytes Strong Electrolytes - conduct current efficiently NaCl, HNO3 WeakElectrolytes - conduct only a small current vinegar, tap water Nonelectrolytes - no current flows pure water, sugar solution ※ Svante Arrhenius postulated: the extend to which a solution can conduct an electric current depends on the number of ions present.

  10. Strong electrolytes: Substances that are completely ionized when they are dissolved in water . soluble salts, (2) strong acids, (3) strong bases.

  11. Figure 4.5: When solid NaCl dissolves, the Na+ and Cl- ions are randomly dispersed in the water.

  12. Arrhenius discoveries the nature of acids Figure 4.6: HCl(aq) is completely ionized.

  13. ※ Arrhenius proposed that an acid is a substance that produces H+. HCl H+(aq) + OH-(aq) HNO3H+(aq) + NO3-(aq) H2SO4H+(aq) + HSO4-(aq)

  14. Strong bases - react completely with water to give OH- ions. Figure 4.7: An aqueous solution of sodium hydroxide.

  15. Figure 4.8: Acetic acid (HC2H3O2) exists in water mostly as undissociated molecules. Only a small percentage of the molecules are ionized. Weak electrolytes:

  16. Weak bases - react only slightly with water to give OH- ions. Figure 4.9: The reaction of NH3 in water.

  17. Molarity Molarity (M) = moles of solute per volume of solution in liters:

  18. Common Terms of Solution Concentration Standard solution- concentration is exactly known. Stock solutions- routinely used solutions prepared in concentrated form. Concentrated solution-relatively large ratio of solute to solvent. (5.0 M NaCl) Diluted solution - relatively small ratio of solute to solvent. (0.01 M NaCl)

  19. Figure 4.10: Steps involved in the preparation of a standard aqueous solution.

  20. Figure 4.11: (a) A measuring pipet is graduated and can be used to measure various volumes of liquid accurately. (b) a volumetric (transfer) pipet is designed to measure one volume accurately.

  21. Figure 4.12: Dilution Procedure (a) A measuring pipet is used to transfer 28.7mL of 17.4 M acetic acid solution to a volumetric flask. (b) Water is added to the flask to the calibration mark. (c) The resulting solution is 1.00 M acetic acid.

  22. Eelectrophoresis

  23. 資料處理 系統 毛細管 毛細管 I.D. 25-100 mm 偵測器 注入端 偵檢端 白金電極 電解質緩衝溶液 電解質緩衝溶液 高電壓(KV) 毛細管電泳(Capillary Electrophoresis-CE)儀器結構簡圖

  24. m = er e0x / h

  25. + + n - - EOF + n Net - 毛細管電泳的向量圖

  26. CE-in-a-Chip Photograph of the micro-device with attached transfer capillary

  27. m-TAS (micro-TAS) concept: Miniture -Total Chemical Analysis system.

  28. Precipitation reactions AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq) Acid-base reactions NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l) Oxidation-reduction reactions Fe2O3(s) + Al(s)  Fe(l) + Al2O3(s) Types of Solution Reactions

  29. Figure 4.13: When yellow aqueous potassium chromate is added to a colorless barium nitrate solution, yellow barium chromate precipitates.

  30. Figure 4.14: Reactant Solutions: (a) Ba(NO3)2(aq) and (b) K2CrO4(aq)

  31. Figure 4.15a,b: The reaction of K2CrO4 and Ba(NO3)2(aq).

  32. Figure 4.15c: The reaction of K2CrO4 and Ba(NO3)2(aq). (cont'd)

  33. Figure 4.16: Precipitation of silver chloride by mixing solutions of silver nitrate and potassium chloride. The K+ and NO3- ions remain in solution.

  34. Figure 4.17: The reaction of KCl(aq) with AgNO3 to form AgCl(s).

  35. 1. Most nitrate (NO3) salts are soluble. 2. Most alkali (group 1A) salts and NH4+are soluble. 3. Most Cl, Br, and I salts are soluble(NOT Ag+, Pb2+, Hg22+) 4. Most sulfate salts are soluble(NOT BaSO4, PbSO4, HgSO4, CaSO4) 5. Most OH salts are only slightly soluble(NaOH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble) 6. Most S2, CO32, CrO42, PO43 salts are only slightly soluble. Table 4.1 Simple Rules for Solubility of Salts in Water

  36. 1. Molecular equation(reactants and products as compounds) AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq) 2. Complete ionic equation(all strong electrolytes shown as ions) Ag+(aq) + NO3(aq) + Na+(aq) + Cl(aq)  AgCl(s) + Na+(aq) + NO3(aq) 3. Net ionic equation(show only components that actually react) Ag+(aq) + Cl(aq)  AgCl(s) Na+ and NO3 are spectator ions. Describing Reactions in Solution

  37. Stoichiometry Steps for reactions in solution.

  38. Performing calculations for acid-base reactions.

  39. Titrant - solution of known concentration used in titration Analyte - substance being analyzed Equivalence point - enough titrant added to react exactly with the analyte (Stoichiometric point) Endpoint - the indicator changes color so you can tell the equivalence point has been reached. Indicator- a color substance with its color change to mark the endpoint of titration. Key Titration Terms

  40. Figure 4.18: The titration of an acid with a base.

  41. Figure 4.19: The reaction of solid sodium and gaseous chlorine to form solid sodium chloride.

  42. Sum of oxidation states = 0 in compounds Sum of oxidation states = charge of the ion

  43. Figure 4.20: A summary of an oxidation-reduction process, in which M is oxidized and X is reduced.

  44. 1. Write separate reduction, oxidation reactions. 2. For each half-reaction: Balance elements (except H, O) Balance O using H2O Balance H using H+ Balance charge using electrons 3. If necessary, multiply by integer to equalize electron count. 4. Add half-reactions. 5. Check that elements and charges are balanced. Balancing by Half-Reaction Method

  45. Cr2O72-(aq) + SO3-(aq) Cr3+(aq) + SO42-(aq) How can we balance this equation? Balancing Oxidation-Reduction Reactions

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