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ACIDS and bases

ACIDS and bases. Theories, definitions, neutralization, and pH/ pOH. Dissociation of Water. Hydroxide ion (OH-) – water that loses an H+ Hydronium ion (H 3 O+) – water that gains an H+ Pure water is neutral… for every OH- there is an H+/H 3 O+. Arrhenius Acids and Bases.

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ACIDS and bases

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  1. ACIDS and bases Theories, definitions, neutralization, and pH/pOH

  2. Dissociation of Water • Hydroxide ion (OH-) – water that loses an H+ • Hydronium ion (H3O+) – water that gains an H+ • Pure water is neutral… for every OH- there is an H+/H3O+

  3. Arrhenius Acids and Bases • Arrhenius acid – a compound that ionizes to produce H+ • Ex. HCl, H2CO3 • Note: Only H’s in very polar bonds will ionize • Arrhenius bases – compound that ionizes to produce OH- • Ex. NaOH

  4. ______- protic Acids • Monoprotic- acids that donate one H+ • HCl • Diprotic- donates 2 H+ • H2SO4 • Triprotic- donates 3 H+ • H3PO4

  5. Bronsted-Lowry Acids & Bases • Arrhenius doesn’t explain NH3— no hydroxide group! • Bronsted-Lowry Theory: • Acid – proton donor • Base – proton acceptor • Water = amphoteric – acts as both an acid & a base.

  6. Conjugate acid-base Pairs • Conjugate acid-base pair – two substances related by gain or loss of a proton • Conjugate acid –formed when a base gains a proton • Conjugate base –formed when an acid has lost a proton

  7. Practice • For each below, label the acid, base, conjugate acid and conjugate base. • NH3 + H2O  NH4+ + OH- • OH- + H3O+ H2O + H2O • HPO4-2 + H2O PO4-3 + H3O+

  8. Strong vs. Weak • STRONG acids ionize completely in water • High [H+] • more polar = easily ionized • Ex. HCl • WEAK acids do not ionize completely • low [H+] • Ex. Acetic Acid (HC2H3O2), organic acids • STRONGbases completely dissociate (ionize) • High [OH-] • Ex. NaOH • WEAKbases don’t completely dissociate • low [OH-] • sometimes not very soluble in water • Ex. NH3, covalently bonded bases

  9. STRONG ACIDS: • HNO3 nitric acid • HClhydrochloric acid • H2SO4 sulfuric acid • HClO4perchloric acid • HBrhydrobromicacid • HI hydroiodic acid • STRONG BASES: • RULE:hydroxides with alkali or alkaline earth metals (except Be) • Ex:NaOH, Ca(OH)2, KOH

  10. Neutralization • Neutralization Reactions: • Strong acid and strong base react in water to produce a salt and water – pH of ~7 • Ex. • HCl + NaOH • H2SO4 + KOH • These are a common way to prepare a pure salt. • How could you prepare low-sodium table salt (KCl)? • Balancing: • H+ and OH- react in a one to one ratio (H2O). BUT, not all compounds ionize just once. (ex: H2SO4 , Ca(OH)2 ) • Must use appropriate mole ratio.

  11. Neutralization Practice • How many moles of sodium hydroxide are required to neutralize 0.60 mol of nitric acid? • How many moles of potassium hydroxide are needed to neutralize 2.63 mol of phosphoric acid? • What is the molarity of phosphoric acid if 18.0 mL of the solution is neutralized by 35.5 mL of 0.15 M NaOH?

  12. Titrations • Titrations: • The molarity of an unknown acid/base can be determined by the carefully measured addition of a base/acid of known molarity. • Standard solution – the solution of known molarity • Equivalence point (S) – the point at which the two solutions are in chemically equivalent amounts (ie. They neutralize) • Indicator- Solution that changes color at a certain pH • End point – the point at which the indicator changes color • Which indicator used determines if the end point and equivalence point are the same.

  13. pH & pOH Calculations • Calculating pH: • pH = -(log [H+]) • ranges from 0-14. • 7 = neutral • pH < 7 = acid (high [H+]) • pH > 7 = base (low [H+]) • Calculating pOH • pOH = -(log [OH-]) • ranges from 0-14. • 7 = neutral • pOH < 7 = base (high [OH-]) • pOH > 7 = acid (low [OH-]) • pOH + pH = 14

  14. Practice • Determine the pH for the following solutions: • [H+] = 1 x 10-6M • [H+] = 0.0001 M • [OH-] = 3 x 10-2M • [OH-] = 4.3 x 10-11 M

  15. Calculating Molarity • Calculating Concentration(M) from pH: • [ ]=molarity/concentration • [H+] = 10-pH • [OH-] = 10-pOH • Practice: • Calculate the [H+] for the following solutions: • pH = 3.0 • pOH = 6.0 • pH = 7.4 • pOH = 1.34

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