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Department of Chemistry CHEM1010 General Chemistry ***********************************************

Department of Chemistry CHEM1010 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel: 931-6325 Email: hzhang@tntech.edu. CHEM1010/General Chemistry _________________________________________ Chapter 7. (L27)-Acids and Bases.

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Department of Chemistry CHEM1010 General Chemistry ***********************************************

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  1. Department of Chemistry CHEM1010 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel: 931-6325 Email: hzhang@tntech.edu

  2. CHEM1010/General Chemistry_________________________________________Chapter 7. (L27)-Acids and Bases • Today’s Outline ..Review: How to write acid and base molecules in molecular formula ..Review: Common acids and bases; strong acids and strong bases; weak acids and weak bases ..Review: Acidic and basic anhydrides ..Acidity ..pH scale to measure acidity

  3. Chapter 7. (L27)-Acids and Bases • How to write acid and base molecules in molecular formula ..Acids: We commonly put H or proton on the left and the anion on the right (for inorganic acids). Example: HCl, H2SO4, HNO3 ..Bases: We commonly put OH on the right and the cation on the left (for inorganic bases). Example: NaOH, Ca(OH)2

  4. Chapter 7. (L27)-Acids and Bases • Common acids ..Common acids (see Table 7.1 for more details): NameMolecular FormulaStrength hydrochloric acid HCl strong sulfuric acid H2SO4 strong nitric acid HNO3 strong phosphoric acid H3PO4moderate hydrogen sulfate HSO4- moderate carbonic acid H2CO3 weak acetic acid CH3COOH weak lactic acid CH3CHOHCOOH weak boric acid H3BO3 very weak hydrocyanic acid HCN very weak

  5. Chapter 7. (L27)-Acids and Bases • Common bases ..Common acids (see Table 7.2 for more details): NameMolecular FormulaStrength sodium hydroxide NaOH strong potassium hydroxide KOH strong lithium hydroxide LiOH strong calcium hydroxide Ca(OH)2 strong* magnesium hydroxide Mg(OH)2 strong* ammonia NH3 weak *very low solubility although classified as a strong base

  6. Chapter 7. (L27)-Acids and Bases • Acidic and basic anhydrides, nonmetal oxides: Acidic anhydrides Nonmetal oxides can react with water to form acids. These nonmetal oxides are called acidic anhydrides. Example: SO3 + H2O = H2SO4 SO2 + H2O = H2SO3 CO2 + H2O = H2CO3 General form: nonmetal oxide + H2O  acid anhydride means without water.

  7. Chapter 7. (L27)-Acids and Bases • Acidic and basic anhydrides, metal oxides: Basic anhydrides Metal oxides can react with water to form bases. These metal oxides are called basic anhydrides. Example: CaO + H2O = Ca(OH)2 BaO + H2O = Ba(OH)2 Li2O + H2O = 2LiOH General form: metal oxide + H2O  base

  8. Chapter 7. (L27)-Acids and Bases • Acidity of acids Question: How to know how much acid is present in a water solution? In other words, how to know how much protons, H+, are present (acid is a molecule that can dissociate to give H+ in a water solution) So, we need a quantity or parameter to tell us about the acidity of a solution.

  9. Chapter 7. (L27)-Acids and Bases • Acidity of acids One way to express acidity can be concentration of H+: Molarity Example: [H+] = 1 M or mole/L [H+] = 0.001 M or mole/L [H+] = 0.0001 M or mole/L [H+] = 0.0000001 M or mole/L

  10. Chapter 7. (L27)-Acids and Bases • Acidity of acids However, in natural environments and biological bodies, the acidity is commonly quite small. Example: Lake, river water [H+] = from 0.0000001M to 0.00000001M Clean rain water [H+] = from 0.00001M to 0.001M Blood [H+] = ~0.0000001M

  11. Chapter 7. (L27)-Acids and Bases • Acidity of acids In science, we like to use small numbers and values to express quantities Example: We use mole to represent 6.022×1023 molecules Question, can we have some way to express those very small values of acidity?

  12. Chapter 7. (L27)-Acids and Bases • Acidity of acids: pH scale In chemistry, we use pH scale to express very small values of acidity. Definition of pH: pH = -log[H+] where the unit of [H+] is M or mole/L pH value has no unit common pH range: 1-14 pH scale was first proposed in 1909 by a Danish biochemist, S.P. L. Sorensen.

  13. Chapter 7. (L27)-Acids and Bases • Acidity of acids: pH scale Express acidity in pH scale Examples: Lake water: [H+] = from 0.0000001M to 0.00000001M pH = -log(0.0000001) = -log (10-7) = -(-7) = 7 pH = -log(0.00000001) = -log (10-8) = -(-8) = 8 Clean rain water: [H+] = from 0.00001M to 0.000001M pH = -log(0.00001) = -log (10-5) = -(-5) = 5 pH = -log(0.001) = -log (10-6) = -(-6) = 6 Blood: [H+] = ~0.0000001M pH = -log(0.0000001) = -log (10-7) = -(-7) = 7

  14. Chapter 7. (L27)-Acids and Bases • Acidity of acids: pH scale Express acidity in pH scale: A special feature Because the definition of pH scale, the higher the concentration of H+, the lower the values of pH; So, the direction pH and concentration of H+ change is just opposite Example: [H+] = 0.00001M < 0.001M but, correspondingly, pH = 5 > 3

  15. Chapter 7. (L27)-Acids and Bases • Acidity of acids: pH scale Convert H+ concentration to pH scale: Example: [H+] = 0.0000001M pH = -log(0.0000001) = -log (10-7) = -(-7) = 7 General equation: pH = -log (10-x) = -log(-x) = x

  16. Chapter 7. (L27)-Acids and Bases • Acidity of acids: pH scale Convert pH scale to H+ concentration: Example: pH = 7 [H+] = 10-7 M General equation: pH = x = -log (10-x) [H+] = 10-x M

  17. Chapter 7. (L27)-Acids and Bases • Acidity of acids: pH scale Use pH scale to define acidic solution and basic solution: Acidic solutions: pH < 7 Basic solutions: pH > 7 This definition is based on the pH of pure water, which is 7 (6.9975) at 25 ºC. So, -if an aqueous solution has the acidity higher than pure water, then its pH is lower than water’s pH, or 7 -if an aqueous solution has the acidity lower than pure water, then its pH is higher than 7

  18. Chapter 7. (L27)-Acids and Bases • pH values of some common solutions SolutionpH value Lemon juice 2.1 Vinegar (4%) 2.5 Soda pop 2.0-4.0 Rainwater (thunderstorm) 3.5-4.2 Milk 6.3-6.6 Saliva 6.2-7.4 Urine 5.5-7.0 Pure water at 25 ºC 7.0 Blood 7.4 Fresh egg white 7.6-8.0 Washing soda 12.0

  19. Chapter 7. (L27)-Acids and Bases Quiz Time Which of the following is the definition of pH scale? (a) pH = log [H+]; (b) pH = [H+]; (c) pH = -[H+]; (d) pH = -log[H+].

  20. Chapter 7. (L27)-Acids and Bases Quiz Time If a solution has a pH of 4, then its concentration of H+ is (a) [H+] = 0.4 M; (b) [H+] = 4 M; (c) [H+] = 0.0001 M = 10-3 M; (d) [H+] = 0.0001 M = 10-4 M .

  21. Chapter 7. (L27)-Acids and Bases Quiz Time If a solution has a concentration of H+ being 0.00001 M, then its pH is (a) pH = 1; (b) pH = 0.00001 M; (c) pH = -5; (d) pH = 5.

  22. Chapter 7. (L27)-Acids and Bases Quiz Time If a solution has a concentration of H+ being 10-6, then its pH is (a) pH = 10; (b) pH = 0.6; (c) pH = -6; (d) pH = 6.

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