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Acids and Bases

Acids and Bases. Ionization of Water. Only happens to a small amount of water molecules H 2 O separates into H + and OH - Not the whole story H+ never occurs on its own In reality, another H 2 O molecule picks it up and becomes H 3 O + (hydronium ion). Acids and Bases.

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Acids and Bases

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  1. Acids and Bases

  2. Ionization of Water • Only happens to a small amount of water molecules • H2O separates into H+ and OH- • Not the whole story • H+ never occurs on its own • In reality, another H2O molecule picks it up and becomes H3O+ (hydronium ion)

  3. Acids and Bases

  4. Classifying Acids and Bases • Arrhenius • Acid- substance that dissociates into H+ and an anion • For Example: HCl and H2SO4 • Base- substance that dissociates into cation and OH- • For example: NaOH and Mg(OH)2 • Does not explain bases without an OH ion

  5. Classifying Acids and Bases (cont) • Brønsted-Lowry • Acid - Proton (H+) donor • For example: HCl and H2SO4 • Base - Proton (H+) acceptor • For example: NH3 and OH-

  6. Conjugate Acid and Bases • Occur on the other side of acid base equations. • Lets look again at • NH3 is a base. It will accept a proton (H+) • H2O is an acid. It will donate a proton (H+) • NH4+ is NH3’s conjugate acid. It can donate a proton (H+) to become NH3 again • OH- is water’s conjugate base. It can accept a proton (H+) to become H2O again

  7. Amphiprotic • Amphiprotic – • Substances that can act like an acid or a base • Water is an amphiprotic substance. • H2O can accept a proton to become H3O+ • H2O can donate a proton to become OH-

  8. Strength of Acids and Bases • Depends on how much they dissociate in water • Strong • Considered to dissociate completely in water • Weak • Only partially dissociate in water • Reaction is reversible () • Conjugate pairs • Strength is inversely proportional • For example: Strong acids have weak conjugate bases

  9. Acids • Strong acids • HI • HBr • HCl • HNO3 • H2SO4 • HClO4 • HClO3 • All have 100% of the molecules break apart. There is no reverse reaction. • Weak acids • All others

  10. Polyprotic Acids • Have multiple H’s • H2SO4 • H2SO4 gives up 1 H+ to form HSO4- • This happens to 100% of the molecules since H2SO4 is strong • HSO4- gives up another H+ to form SO4-2 • This only happens to some HSO4- because it is weak • Solution will contain • A lot of water molecules • H3O+ molecules (mostly from the first H+ but some from the second and from ionization of water) • HSO4- • a little bit of SO4-2 • A little bit of OH- (from the ionization of water)

  11. Acid Names • Binary acids (H with an element) • Prefix hydro- • Root of element name • Suffix –ic • Add acid • For example: HCl is hydrochloric acid • Acids with Oxygen (H with a polyatomic) • Root name of polyatomic (with polyatomic prefix if applicable) • Some polyatomic roots are modified slightly to be easier to say • Suffix • -ic with polyatomics ending in –ate • -ous with polyatomics ending in -ite • Add acid • For example: H2SO4 is sulfuric acid

  12. Bases • Strong bases • Group 1 metals with OH- • Ca, Sr, and Ba with OH- • These three are not very soluble in water, but the amount that does dissolve ionizes completely. • Weak bases • All others

  13. Ionization of Water • 2H2O(l)  H3O+(aq) + OH-(aq) • This equilibrium “lies to the left” • In other words, there is far more water molecules than hydronium and hydroxide ions in a sample • Kw = [H3O+] [OH-] • Kw = 1.0 x 10-14 • In pure water and neutral solutions, [H3O+] and [OH-] are 1.0 x 10-7 M • In acidic solutions, [H3O+] is greater than [OH-] • In basic solutions [OH-] is greater than [H3O+]

  14. pH • pH • Stands for potential of Hydrogen (really hydronium) • Logarithmic scale • pH = -log [H+] or [H+] = 10-pH • Values between 0-14 with each number representing a 10-fold increase from the previous number • pH  7 is acidic • pH = 7 is neutral • pH  7 is basic

  15. pOH • pOH = -log [OH-] or [OH-] = 10-pOH • Opposite scale • pOH  7 is basic • pOH = 7 is neutral • pOH  7 is acidic

  16. Indicators • Compounds that change color in the presence of different levels of pH

  17. Soil pH 5.0-5.5 Soil pH 6.0-6.5

  18. Neutralization (Acid-Base Reaction) • Special type of double displacement reaction • Acid + Base  Water + Salt

  19. Titration • Process of neutralizing an acid (or base) with an unknown concentration with a base (or acid) of a known concentration • Moles of H3O+ must equal moles of OH- for neutralization to occur • Often indicators are used to determine the end of the reaction • VaMa = VbMb • Va = volume in L of acid • Ma = molarity of acid • Vb = volume in L of base • Mb = molarity of base

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