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Acids and Bases

This resource provides an overview of the properties of acids and bases, including their reactions with metals, electrolytic properties, and definitions according to Arrhenius and Bronsted-Lowry. It also covers the concepts of conjugate acids and bases, amphoteric substances, and pH calculations.

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Acids and Bases

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  1. Acids and Bases Ch. 15 p. 530

  2. 5.1 What are the properties of acids? p. 530 Acids react with metals to produce hydrogen gas. Word Equation: Metal + acid  hydrogen gas e.g. rxn of Mg with hydrochloric acid

  3. Properties of acids p. 531 Acids are electrolytes A substance that dissolves in water to conduct electricity.

  4. Arrhenius Acid “When an acid dissolves in water….. it produces an hydronium ion H3O+”

  5. Review: Lewis Structures Challenge: Draw the Lewis structure of the hydronium ion H3O+ See p. 203 for a reminder of how to draw the Lewis structure of a polyatomic ion.

  6. Strong acids/Weak acids Strong acid = hydrochloric acid HCl (stomach acid) dissociates completely (100%) Weak acid = acetic acid CH3COOH (vinegar) dissociates partially (equilibrium) pHETsim: acid-base solutions

  7. Arrhenius definition of bases Base = Basic = Alkali = Alkaline “When a base dissolves in water….. it produces an hydroxide ion OH-”

  8. Review: Lewis Structures Challenge: Draw the Lewis structure of the hydroxide ion OH- See p. 203 for a reminder of how to draw the Lewis structure of a polyatomic ion.

  9. Strong bases andweak bases Examples: Strong base = sodium hydroxide NaOH (drain cleaner) Weak base = ammonia NH3 (glass cleaner)

  10. Bronsted-Lowry definition Acids are hydrogen-ion-donating substances, and……. bases are hydrogen-ion-accepting substances.

  11. Bronsted-Lowry definition ‘Proton’ = ‘hydrogen ion’ 11. Acids are proton donors e.g. hydrogen chloride (HCl)

  12. Bronsted-Lowry definition 12. Bases are proton acceptors e.g. water, in: e.g. ammonia in: ammonia + water 

  13. Polyprotic acids Can donate more than one proton e.g. sulfuric acid (diprotic)

  14. Polyprotic acids Can donate more than one proton e.g. phosphoric acid (triprotic)

  15. Amphoteric substances 14. An amphoteric substance can act as an acid or a base. e.g. compare the action of water in: ammonia + water  vs.

  16. Water is amphoteric water can act as an acid by donating a proton to a base Ammonia + water 

  17. Water is amphoteric water can act as a base by accepting a proton from an acid Hydrochloric acid + water 

  18. Conjugate acids and bases Conjugate acids and bases are the PRODUCTS of acid/base reactions. Acid + base  conjugate base + conjugate acid See Table 3 p.537

  19. Standards CH5. Acids, bases, and salts are three classes of compounds that form ions in water solutions. As a basis for understanding this concept: CH5. a. Students know the observable properties of acids, bases, and salt solutions. CH5. b. Students know acids are hydrogen-ion-donating and bases are hydrogen-ion-accepting substances. CH5. c. Students know strong acids and bases fully dissociate and weak acids and bases partially dissociate. CH5. d. Students know how to use the pH scale to characterize acid and base solutions.

  20. Logarithms* Log Base 10 Log base 10, also known as the common logarithm or decadic logarithm, is the logarithm to the base 10. The common logarithm of x is the power to which the number 10 must be raised to obtain the value x. For example, the common logarithm of 10 is 1, the common logarithm of 100 is 2 and the common logarithm of 1000 is 3. It is often used in various engineering fields, logarithm tables and handheld calculators.

  21. Logarithms Resources Khan Academy: Logarithm Basics https://www.mathsisfun.com/algebra/logarithms.html http://mathinsight.org/logarithm_basics

  22. 15.2 Indicators Litmus paper • Red litmus paper turns blue in a base • Blue litmus paper turns red in an acid pH paper and Universal Indicator solution • See color chart on fig 12 p. 546 Phenolphthalein • Clear solution turns pink in base

  23. KWL: pH definition avalueusedtoexpresstheacidityorbasicityofasolutionapHof7isneutralapHoflessthansevenisacidandapHofgreaterthansevenisbasic A value used to express the acidity or basicity of a solution. A pH of 7 is neutral, a pH of less than seven is acid, and a pH of greater than seven is basic. p.542

  24. 15.2 Self Ionization of Water [H3O+] = [OH−] = 1.00 × 10−7 M

  25. Do you have a scientific calculator?

  26. 15.2 Equilibrium constant [H3O+][OH−] = Kw= (1.00 × 10−7)(1.00 × 10−7) = 1.00 × 10−14

  27. KWL: pH • pH stands for ‘power of Hydrogen’ • pH tells us how much hydronium ion is dissolved in solution • pH = -log10[H3O+] • A change in one pH unit corresponds to 10 times change in conc of hydronium ion • e.g pH 2 has 10X more hydronium than pH 3 • e.g pH 2 has 100X more hydronium than pH 4 • Read Calculating pH from [H3O+] p. 543

  28. 15.2 Calcualating pH pH is not a linear scale, it is a logarithmic scale (The Richter scale is another example of a logarithmic scale) What is the pH of a 0.000 10 M solution of HNO3, a strong acid? pH = - log[H3O+] See Skills Toolkit p. 543 Teacher notes: pH table vs [H3O+] table

  29. Practice What is the pH of a solution with a hydronium concentration of 0.000001 M? (a calculator is not necessary to answer this question) ANS: pH = 6

  30. 15.2 Calculating [H3O+] from pH* Sample Problem C What is the concentration of the hydronium ion in a sample of rain that has a pH of 5.05? The pH equation may be rearranged to calculate the hydronium ion concentration from the pH. [H3O+] = 10−pH

  31. pH calcs Calculating pH from [H3O+] p. 544 Practice #1,2 #3,4 (use pH + pOH = 14) Calculating [H3O+] from pH # 1-4

  32. 15.3 Notes: Neutralization Read sec 15.3 p. 548-555 thereactionofanacidwithabasetoformasaltandwater The reaction of an acid with a base to form a salt and water. p.548 Gizmo: Titration

  33. Acid-base reactions Acid + Base  ‘Salt’ + Water Example: HCl + NaOH  NaCl + H2O Overall: H+(aq) + OH−(aq)  H2O(l)

  34. Indicators are organic dyes that change color in response to acid/base. Indicator molecules absorb slightly different wavelengths of light depending on if they are in acidic or basic solution. pH Indicators p. 546

  35. titration amethodtodeterminetheconcentrationofasubstanceinasolutionbyaddingasolutionofknownvolume andconcentrationuntilthereactioniscompletedwhichisusuallyindicatedbyacolorchange A method to determine the concentration of a substance in a solution by adding a solution of known volume and concentration until the reaction is completed, which is usually indicated by a color change. (p. 550)

  36. Venn diagram:acid/base/neutral • Hydronium ion • Hydroxide ion • pH less than 7 • pH equals 7 • pH greater than 7 • Proton donor • Proton acceptor • Electrolyte • non-electrolyte • Litmus paper turns red • Litmus paper turns blue • Phenolphthalein is clear • Phenolphthalein turns pink • reaction with metal

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