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Acids & Bases

Acids & Bases. Chemistry 6.0. Naming Acids Review :. A. Binary – H +one anion Prefix “hydro”+ anion name +“ic”acid Ex) HCl hydrochloric acid Ex) H 3 P hydrophosphoric acid B. Tertiary – H + polyatomic anion no Prefix “hydro”

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Acids & Bases

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  1. Acids & Bases Chemistry 6.0

  2. Naming Acids Review: A. Binary – H +one anion Prefix “hydro”+ anion name +“ic”acid Ex) HCl hydrochloric acid Ex) H3Phydrophosphoric acid B. Tertiary –H + polyatomic anion no Prefix “hydro” (oxo) end “ate” = “ic” acid end “ite” = “ous” acid Ex) H2SO4sulfuric acid Ex) H2SO3 sulfurous acid

  3. Properties of Acids and Bases:

  4. Indicators: Turn 1 color in an acid and another color in a base. • Litmus Paper: Blue and Red An aciD turns blue litmus paper reD A Base turns red litmus paper Blue. • Phenolphthalein: colorless in an acid and pink in a base • pH paper: range of colors from acidic to basic • pH meter: measures the concentration of H+ in solution

  5. Reactions • Neutralization: A reaction between an acidand base. When an acid and base neutralize, water and a salt (ionic solid) form. Acid+ Base → Salt+ Water Ex) HCl + NaOH → NaCl + HOH

  6. Reactions • Acids and Metals • HA + M  H2 + MA • A = anion • M = metal • 2HCl + Mg  H2 + MgCl2 • Acids and Carbonates • HA + MCO3 MA + CO2 + H2O • HCl + Li2CO3 2LiCl + CO2 + H2O

  7. Arrhenius Definition (1884): A. An acid dissociates in water to produce more hydrogen ions, H+. HCl  H+1 + Cl-1 B. A base dissociates in water to produce more hydroxide ions, OH-. NaOH  Na+1 + OH-1 C. Problems with Definition: • Restricts acids and bases to watersolutions. • Oversimplifies what happens when acids dissolve in water. • Does not include certain compounds that have characteristic properties of acids & bases. Ex) NH3 (ammonia) doesn’t fit

  8. Bronsted-Lowry Definition (1923): A. An acid is a substance that can donate hydrogen ions. Ex) HCl → H+ + Cl- • Hydrogen ion is the equivalent of a proton. • Acids are often called proton donors. • Monoprotic (HCl), diprotic (H2SO4) , triprotic (H3PO4) B. A base is a substance that can accept hydrogen ions. Ex) NH3 + H+→ NH4+ • Bases are often called proton acceptors. C. Advantages of Bronsted-Lowry Definition •Acids and bases are defined independently of how they behave in water. •Focuses solely on hydrogen ions.

  9. Hydronium Ion: Hydronium Ion – H3O+ This is a complex ion that forms in water. H+1 + H2O  H3O+1 To more accurately portray the Bronsted-Lowry, the hydronium ion is used instead of the hydrogen ion.

  10. STRONG Acid/Base versus WEAK Acid/Base Strength refers to the % of molecules that form IONS. A strong acid or base will completely ionize (>95% as ions). This is represented by a single ()arrow. HNO3 + H2O  H3O+ + NO3- A weak acid or base will partially ionize (<5% as ions). This is represented by a double (↔) arrow. HOCl + H2O ↔ H3O+ + ClO-

  11. HF < HCl < HBr < HIincreasing strength 7 Strong Acids HNO3 H2SO4 HClO3 HClO4 HCl HBr HI 8 Strong Bases LiOH NaOH KOH RbOH CsOH Ca(OH)2 Sr(OH)2 Ba(OH)2

  12. Strength vs. Concentration • Strength refers to the percent of molecules that form ions • Concentration refers to the amount of solute dissolved in a solvent. Usually expressed in molarity. • See “Acids: Concentration vs. Strength”

  13. Conjugate Acid-Base Pairs: A pair of compounds that differ by only one hydrogen ion • Acid donates a proton to become a conjugate base. • Base accepts proton to become a conjugate acid. • A strong acid will have a weak conjugate base. • A strong base will have a weakconjugate acid.

  14. Acid (A), Base (B), Conjugate Acid (CA), Conjugate Base (CB) NH3 + H2O ↔ NH4+ + OH- HCl + H2O ↔ Cl- + H3O+ • Base and Conjugate Acid are a Conjugate Pair. • Acid and Conjugate Base are a Conjugate Pair. B A CA CB A B CB CA

  15. AciDonates & Bases accept • H2O + H2O ↔ H3O+ + OH− B A CA CB • H2SO4 + OH− ↔ HSO4− + H2O A B CB CA • HSO4− + H2O ↔ SO4−2 + H3O+ A B CB CA • OH− + H3O+ ↔ H2O + H2O B A CA CB

  16. Ionization of Acids & Bases • H2SO4 2 H+ + SO4-2 • Sulfuric acid • H3PO3  • Phosphorous acid • Ca(OH)2 • Calcium hydroxide 3 H+ + PO3-3 Ca+2 + 2 OH-1

  17. The Self-ionization of Water & pH 1. Water is amphoteric, it acts as both an acid and a base in the same reaction. Ex) H2O(l) + H2O(l) ↔ H3O+(aq) + OH-(aq) Keq = equilibrium constant = [H3O+] [OH-] Because reactants and products are at equilibrium, liquid water is not included in the equilibrium expression @ 25C, [H3O+] = 1 x 10-7M and [OH-] = 1 x 10-7M Kw = ion product constant or equilibrium constant for water Kw = [H3O+] [OH-] = 1 x 10-14M2 1.0 x 10-14 M2= [1.0 x 10-7 M] [1.0x10-7 M] 1.0 x 10-14 = [H3O+] [OH-]

  18. Acids: [H3O+] > 1 x 10-7 M Bases: [OH-] > 1 x 10-7 M Using Kw in calculations: If the concentration of H3O+ in the blood is 4.0 x 10-8M, what is the concentration of OH­ ions in the blood? Is blood acidic, basic or neutral? Kw = [H3O+] [OH-] 1.0 x 10-14M2 = [4.0 x 10-8M] [OH-] 2.5 x 10-7 M = [OH-] slightly basic

  19. The pH scale (1909): the power of Hydrogen • Measure of H3O+ in solution. • pH = -log[H3O+] • Range of pH: 0-14 pH < 7: acid pH > 7: base pH = 7: neutral • pOH = -log[OH-] • pH + pOH = 14

  20. pH = -log [H3O+] • [H3O+] [OH-] = 1.0 x 10-14 • pH + pOH = 14 pH 1 7 14 H+ OH-

  21. 14 H+ OH- 1

  22. Significant Digits Rule • The number of digits AFTER THE DECIMAL POINT in your answer should be equal to the number of significant digits in your original number • Ex -log[8.7x10-4M] • Calc Answer = 3.0604807474 • Sig Fig pH = 3.06

  23. Acid-Base Titration 1. An acid-base titration is a carefully controlled neutralization reaction or redox which can determine concentration of an unknown solution. 2. To determine the concentration of an unknown substance, a standard solution is needed. This solution has a knownconcentration. 3. Titration curve: graph that shows how pH changes during a titration.

  24. An indicator, usually phenolphthalein, is used in a titration. • Colorless in an acid, pink in a base. 5. The point at which enough standard solution is added to neutralize the unknown solution is called the equivalence point.

  25. 6. The point at which the indicator changes color is called the endpoint. 7. Therefore: [H+] = [OH-] at the equivalence point

  26. Ex) A volume of 50.0 mL of 0.150M sodium hydroxide neutralizes 30.0mL of a sulfuric acid solution. What is the concentration of the sulfuric acid solution? H2SO4 + NaOH  Na2SO4 + HOH Note: Mole ratio between acid an base in not 1:1 2 2 Mb = 0.125M

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