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Acid/Base Reactions

Acid/Base Reactions. Acids. Brønsted -Lowry – proton donor Arrhenius – acids produce H + ions in water HCl  H + + Cl - HCl , HBr , HI, H 2 SO 4 , HC 2 H 3 O 2. Bases. Brønsted -Lowry – proton acceptor Arrhenius – bases produce OH - ions in water NaOH  Na + + OH -

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Acid/Base Reactions

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  1. Acid/Base Reactions

  2. Acids • Brønsted-Lowry – proton donor • Arrhenius – acids produce H+ ions in water • HCl H+ + Cl- • HCl, HBr, HI, H2SO4, HC2H3O2

  3. Bases • Brønsted-Lowry – proton acceptor • Arrhenius – bases produce OH- ions in water • NaOH Na+ + OH- • NaOH, KOH, LiOH, Ba(OH)2, Ca(OH)2

  4. Acid-Base Reactions • Net ionic equation for acid-base reactions • H+ + OH- H2O • Acid + base  H2O + salt

  5. Titrations • Procedure for determining the concentration of an unknown acid (or base) solution using a known concentration of a base (or acid) • Titrant – solution of known concentration • Analyte – solution of unknown concentration • Known volume • Indicator – substance added at the beginning of the titration that changes color at the equivalence point

  6. Titrations • Equivalence Point - Point at which exactly enough base solution has been added to the acid until the acid is neutralized • Concentration (M) and volume (V) of base are known, number of moles of acid can be calculated moles of acid neutralized • Acid concentration = liters of acid solution

  7. Example • What volume of 0.900 M HCl is required to completely neutralize 25.0 g of Ca(OH)2? • 1. Write and balance the equation • 2. Determine number of moles of Ca(OH)2 • 3. Determine the number of moles of HCl required to neutralize • 4. Determine the volume of acid that contains the required amount of moles of HCl

  8. More on Acids & Bases

  9. Acids/Bases • Acids - Donate H+ into solution • Acidic solutions have lots of H+ ions • Proton donors • Bases – Donate OH- into solutions • Basic solutions have lots of OH- ions • Proton acceptors • Water is a nonelectrolyte • Doesn’t exist as ions in solution • H+ + OH-  H2O

  10. Strength • Strong acids and bases completely dissociate into ions • Acids produce H+ (or H3O) • Bases produce OH- • Weak acids/bases cannot dissociate as easily • Weak acids only partially dissociates in water to give H+ and an anion • HF  H+ + F- • Weak bases – most are anions of weak acids • Don’t give OH-, react with water to form OH- • C2H3O2- (weak base) from HC2H3O2 (weak acids)

  11. Conjugates • Conjugate pairs – acid and base pair • One can accept a proton and the other can donate • NH3 + H2O NH4+ +OH- • NH3(base)  NH4+ (conjugate acid) • H2O(acid)  OH- (conjugate base) • Stronger acid/base, weaker the conjugate

  12. Sample • A student carries out an experiment to standardize (determine the concentration of) a NaOH solution. The student weighs out 1.3009 g of potassium hydrogen phthalate (KHP – KHC8H4O4). KHP has one acidic hydrogen. The student dissolves the KHP in distilled water, adds phenolphthalein, and titrates the resulting solution with the NaOH solution to the endpoint. The difference between the final and initial burette readings is 41.20 mL. Calculate the concentration of NaOH solution.

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