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Announcements

Announcements. REMINDER: NO LAB THIS WEEK EXAM CLARIFICATION/FRIDAY DEADLINE SET CLICKER TO CHANNEL 41. Bases. Strong bases are hydroxide salts For now, only important weak base is NH 3 Ionization of weak acid produces a weak base.

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Announcements

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  1. Announcements REMINDER: NO LAB THIS WEEK EXAM CLARIFICATION/FRIDAY DEADLINE SET CLICKER TO CHANNEL 41

  2. Bases • Strong bases are hydroxide salts • For now, only important weak base is NH3 • Ionization of weak acid produces a weak base

  3. If the oxalate anion (C2O4-) reacts in an acid-base reaction, which of the following can’t it make? • H2C2O4 • HC2O4- • 2CO2 0

  4. Acid Base Reactions

  5. Acid Base Reactions • Strong Acid + Strong Base HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) acidbase“salt”water • What do we get if we mix: HBr (aq) + LiOH (aq) 

  6. Acid Base Reactions • Diprotic acids or bases H2SO4(aq) + NaOH(aq)  H2SO4(aq) + Ba(OH)2(aq)  HCl(aq) + Ba(OH)2(aq) 

  7. Acid Base Reactions • Strong Acid + Weak Base HCl(aq) + NH3(aq)  • What do we get if we mix: HNO3(aq) + NH3(aq) 

  8. Acid Base Reactions • Weak Acid + Strong Base (like strong acid+strong base) HCN(aq) + NaOH(aq)  NaCN(aq) + H2O(l) acidbase“salt”water • What do we get if we mix: HCOOH (aq) + KOH (aq)  formic acid

  9. Net Ionic Equations • Write a balanced chemical equation  Molecular equation • Write out all the ions Total ionic equation • Cancel out anything that appears on both sides  Net ionic equation

  10. Net Ionic Equations HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) What really happens: H+(aq) + OH-(aq)  H2O(l) Sodium ion and chloride ion are “spectator ions”

  11. Reactions Involving a Weak Base • Molecular equation: HCl(aq) + NH3(aq)  NH4Cl(aq) • Total ionic equation: H+(aq) + Cl-(aq) + NH3(aq)  NH4++Cl-(aq) • Net ionic equation: H+(aq) + NH3(aq)  NH4+ (aq) • What is the net ionic equation for: HNO3(aq) + NH3(aq)  NH4NO3(aq)

  12. CH3CO2H(aq) + NaOH(aq)  • CH3CO2H2+(aq) + NaO(aq) • CH3CO2-(aq) + H2O(l) + Na+(aq) • CH4(g) + CO2(g) + H2O(l) 20

  13. HCN(aq) + NH3(aq)  • NH4+(aq) + CN-(aq) • H2CN+(aq) + NH2-(aq) • C2N2(s) + 3 H2(g) 20

  14. The pH Scale • Quantitative measure of solution acidity • Remember solution concentration: • [NaCl]=0.25M means 0.25 moles of NaCl are in 1L of solution

  15. The pH Scale • In pure water, some molecules ionize to form H3O+ and OH- H2O + H2O  OH– + H3O+ • In acidic and basic solutions, these concentrations are not equal acidic: [H3O+] > [OH–] basic: [OH–] > [H3O+] neutral: [H3O+] = [OH–]

  16. The pH Scale • pH scale= measure of [H3O+] pH < 7.0 = acidic pH > 7.0 = basic pH = 7.0 = neutral • Measure of H3O+concentration (moles per liter) in a solution • As acidity increases, pH decreases

  17. The pH Scale • The pH scale is logarithmic 100 102 log(102) = 2 10 101 log(101) = 1 1 100 log(100) = 0 0.1 10–1 log(10–1) = –1 0.01 10–2 log(10–2) = –2 • pH = –log [H3O+] • pH if [H3O+] = 10–5? 10–9? Acidic or basic? • pH if [H3O+] = 0.000057 M?

  18. Finding [H3O+] from pH • [H3O+] = 10-pH or [H3O+] = log-1 (-pH) • Finding the inverse log (or log -1)of a number on your calculator: Enter the number, press the inverse (inv) or shift button, the press the log button (it might be labeled 10x) • What is [H3O+] if pH = 8.6?

  19. pH: Quantitative Measure of Acidity • Acidity is related to concentration of H+ (or H3O+) • pH = -log[H3O+] • [H3O+]=10-pH=log-1(-pH)

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