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Chapter 10 Acids and Bases

Chapter 10 Acids and Bases. (10.1) Acid-Base Strength. Strong Acid (SA). an acid that dissociates completely into ions in water Ex.)all molecules of HCl (aq) dissociate into H + and Cl - ions the H + ions that are formed bond with H 2 O to form H 3 O +

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Chapter 10 Acids and Bases

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  1. Chapter 10Acids and Bases (10.1) Acid-Base Strength

  2. Strong Acid (SA) • an acid that dissociates completely into ions in water • Ex.)all molecules of HCl(aq) dissociate into H+ and Cl- ions • the H+ ions that are formed bond with H2O to form H3O+ HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)

  3. Strong Acid (SA) other SA’s are….. HBr HI HNO3 H2SO4 HClO4

  4. Concentration • the conc. of H3O+(aq) ions, [H3O+], in a dilute solution of a SA is equal to the conc. of the acid, [acid] [H3O+] = [strong acid] • Ex.) In a sample of 1.0 mol/L HCl(aq) [H3O+] = 1.0 mol/L Recall: C = n V square bracket Molar Concentration

  5. Dissociation (Strong Acid) Text p 381 Figure 10.6 100% of hydrogen chloride molecules dissociate

  6. Dissociation (Weak Acid) Text p 382 Figure 10.7 1% of acetic acid molecules dissociate. In solution there are mostly acetic acid molecules and only some ions.

  7. Weak Acid (WA) • an acid that dissociates very slightlyinto ions in water • Ex.) not all molecules of CH3COOH(aq) break apart, some remain intact • only about 1% of acetic acid molecules dissociate • In a sample of 1.0 mol/L CH3COOH (aq) , [H3O+] <<< 1.0 mol/L • That is, [H3O+] < [weak acid]

  8. Strong Base (SB) • a base that dissociates completely into ions in water • Ex.) all molecules of NaOH(aq) dissociate into Na+ and OH- ions • other SB’s are… KOH Ca(OH)2 Ba(OH)2

  9. Concentration • the conc. of OH1-(aq) ions, [OH1-], in a dilute solution of a SB is equal to the conc. of the base, [base] [OH1-] = [strong base] • Ex.) In a sample of 1.0 mol/L NaOH(aq) [OH1-] = 1.0 mol/L

  10. Weak Base (WB) • most bases are weak • WB dissociates very slightly into ions in water • Ex.) ammonia [OH1-] < [weak base]

  11. Acid Dissociation • few acids contain only a single H+ ion • monoproticacid: produces one H+ ion  • Ex.) HF(aq) + H2O(l) H3O+(aq) + F-(aq) (simplified) HF(aq)  H+(aq) + F-(aq)

  12. Acid Dissociation • many acids contain 2 or more H+ ions • diprotic acid: produces two H+ ions • Ex.) H2SO4 (aq) H+(aq) + HSO4-(aq) HSO4-(aq) H+(aq) + SO42-(aq) H2SO4(aq) 2H+(aq) + SO42-(aq)

  13. Acid Dissociation • triprotic acid: produces three H+ ions • Ex.) H3PO4 (aq) H+(aq) + H2PO4-(aq) H2PO4-(aq) H+(aq) + HPO42-(aq) HPO42-(aq) H+(aq) + PO43-(aq) H3PO4(aq) 3 H+(aq) + PO43-(aq)

  14. Measuring Strength – pH Scale • In pure water, [H3O+] = [OH-] = 1.0 x 10-7 mol/L • In acidic sol’n, [H3O+] > [OH-] • In basic sol’n, [H3O+] < [OH-]

  15. Measuring Strength – pH Scale • In any aqueous sol’n the product can be calculated, [H3O+] x [OH-] = 1.0 x 10-14 • The values of [H3O+] range from 10 mol/L to 10-15 mol/L

  16. pH Scale • We use system of logarithms to handle the range of exponents for [H3O+] • Ex.) log (1x102) = 2 log (1x10-6)= - 6 • simply, use the exponent when the value is written as 1 x base 10 or • use your calculator

  17. pH Scale pH = -log[H3O+(aq)] • Ex.) [H3O+(aq)] = 1.0 x10-4 pH = -log[1.0 x10-4] = +4

  18. pH Scale Calculate, • pH if [H3O+(aq)] = 3.8 x10-3 mol/L (ans: 2.42) 2) [H3O+(aq)] if pH = 3.85 (ans: 1.4 x 10-4 mol/L) 3) pH of 0.082 mol/L HCl(aq) (ans: 1.09) [H3O+(aq)] = 10-pH

  19. pOH Scale pOH = -log[OH-(aq)] • Ex.) [OH-(aq)] = 1.0 x10-6 pH = -log[1.0 x10-6] = +6 pOH + pH = 14

  20. Homework

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