1 / 22

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.

nhu
Télécharger la présentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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.

More Related