2. Indicators: Turn 1 color in an acid and another color in a base. A. Litmus Paper: An aciD turns blue litmus paper reD A Base turns red litmus paper Blue. B. Phenolphthalein: colorless in an acid/pink in a base C. pH paper: range of colors from acid to basic D. pH meter: measures the concentration of H+ in solution
3. Neutralization: A reaction between an acid and base. When an acid and base neutralize, salts form. Acid+ Base → Salt+ Water Ex) HCl + NaOH → NaCl + HOH
4. Arrhenius Definition: A. An acid dissociates in water to produce hydrogen ions, H+. B. A base dissociates in water to produce hydroxide ions, OH-. 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
5. Bronsted-Lowry Definition: A. An acid is a substance that can donate hydrogen ions. Ex) HCl → H+ + Cl- B. A base is a substance that can accept hydrogen ions. Ex) NH3 + H+→ NH4+ C. Advantages of Bronsted-Lowry Definition •Acids and bases are defined independently of how they behave in water. •Focuses solely on hydrogen ions. D. Hydrogen ion is the equivalent of a proton. Therefore, acids are often called proton donors and bases are called proton acceptors.
6. Hydronium Ion: A. Hydronium Ion – H3O+ This is a complex that forms in water. B. To more accurately portray the Bronsted-Lowry, the hydronium ion is used instead of the hydrogen ion. C. Amphoteric: A substance that can act as either an acid or a base. Ex.) Water - can gain or lose a H+
7. Conjugate Acid-Base Pairs: A pair of compounds that differ by only one hydrogen ion A. When an acid loses a hydrogen ion, it becomes its conjugate base. B. When an base gains a hydrogen ion, it becomes its conjugate acid.
Acid (A), Base (B), Conjugate Acid (CA), Conjugate Base (CB) NH3 + H2O ↔ NH4+ + OH- HCl + H2O ↔ Cl- + H3O+ • A strong acid will have a weak conjugate base. • A strong base will have a weakconjugate acid. CA CB B A CB A CA B
STRONG Acid/Base C. A strong acid or base will completely dissociate(break apart)in water. This is represented by a single ()arrow. HNO3 H+ + NO3- NaOH Na+ + OH-
WEAK Acid/Base D. A weak acid or base will partially dissociatein water. This is represented by a double (↔) arrow. CH3COOH ↔ H+ + CH3COO- NH4OH ↔ NH4+ + OH-
8. 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
15-2 The Self-ionization of Water and 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) 2. In pure water at 25C, both hydronium ions and hydroxide ions are found at concentrations of 1 x 10-7M. Because they are at equilibrium and you do not include liquid water in the equilibrium expression, Keq or Kw (water) can be expressed as follows: A. Formula for Kw = [H3O+] [OH-]
A. Formula for Kw = [H3O+] [OH-] 1.0 x 10-14 M = [1.0 x 10-7 M] [1.0x10-7 M] 1.0 x 10-14M = [H3O+] [OH-] B. 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 10-14M = [4.0 x 10-8M] [OH-] 4.0 x 10-8M 4.0 x 10-8M 2.5 x 10-7 M = [OH-] slightly basic
3. The pH scale: • Used to determine if something is an acid or a base. A way to express H3O+ concentration based on logarithms. pH changes by a factor of 10. Ex) 10,000 = 104 therefore log 10,000 = 4 0.001 = 10-3 therefore log 0.001 = -3 B. pH 1-6.9: acid pH 7.1-14: base pH of 7.0: neutral
pH = -log [H3O+] • [H3O+] [OH-] = 1.0 x 10-14M • pH + pOH = 14 OH- H+
pH 14 13 12 11 10 9 8 7 6 5 4 3 2 1 H+ OH- EQUAL
H. 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[8.7 x 10-4 M] • Calc Answer = 3.0604807474 • Sig Fig pH = 3.06
Example #1: [H3O+] = 7.3 x 10-5MWhat is the pH value? Is it an acid, base or neutral? Which equation should you use? Kw = [H3O+] [OH-] OR pH = -log [H3O+] pH = -log [7.3 x 10-5M] pH = 4.14 ACID
Example #2: [OH-] = 5.0 x 10-2MWhat is the pH value? Is it an acid, base or neutral? Which equation should you use? Kw = [H3O+] [OH-] OR pH = -log [H3O+] Kw = [H3O+] [OH-] 1 x 10-14M = [H3O+] [5.0 x 10-2M] 2.0 x 10-13M = [H3O+] pH = -log [2.0 x 10-13M] pH = 12.70 basic
Ionization of Acids & Bases • H2SO4 2 H+ + SO4-2 • Sulfuric acid donates 2 H+ ions per mole • This is called a “diprotic” acid • H3PO3 • Phosphorous acid donates 3 H+ ions per mole. This is called a “triprotic acid” • Ca(OH)2 • Calcium hydroxide dissociates into 2 OH- ions per mole 3 H+ + PO3-3 Ca+2 + 2 OH-1
15-3 Acid-Base Titration 1. An acid-base titration is a carefully controlled neutralization reaction which can determine the 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 pHchanges during a titration.
4. An indicator, usually phenolphthalein, is used in a titration. 5. The point at which enough standard solution is added to neutralize the unknown solution is called the equivalence point. 6. The point at which the indicator changes color is called the endpoint.
7. Therefore: [H+] = [OH-] at the equivalence point (which is usually the endpoint) Volume (acid) Conc.(acid) = Volume (base) Conc.(base) VaMa = VbMb (L) x Moles = (L) x Moles Liter Liter moles of H+ = moles of OH-
VaMa = VbMb Ex #1) Solutions of sodium hydroxide are used to unclog drains. A 43.0 mL volume of sodium hydroxide was titrated with 32.0 mL of 0.100 M HCl. What is the molarity of the sodium hydroxide solution? HCl (a) = NaOH (b) (32.0 mL)(0.100 M HCl) = (Mb)(43.0 mL) 43.0 mL43.0 mL 0.0744 M = Mb
H2SO4 + 2NaOH Na2SO4 + 2H-OH Note: sulfuric acid has 2 H+ per mole of acid Therefore you need to multiply the acid side by a factor of 2 VaMa x 2 = VbMb (25.0 mL) (0.120 M) x 2 = (40.0 mL) x Mb Mb = 0.150 M Ex #2) A volume of 25.0 mL of 0.120 M sulfuric acid neutralizes 40.0 mL of a sodium hydroxide solution. What is the concentration of the sodium hydroxide solution?
Ex #3) 24.9 mL of 2.88 M calcium hydroxide completely neutralizes 38.9 mL of a hydrobromic acid solution. What is the molarity of the hyrdobromic acid? Ca(OH)2 + 2HBr CaBr2 + 2HOH Note: there are 2 hydroxide ions per mole of base Therefore you need to multiply the base side by a factor of 2 VaMa = VbMb x 2 (38.9 mL) x Ma = (24.9 mL) (2.88 M) x 2 Ma = 3.69 M