All you need to know to perform a strong acid-base neutralization Acid & Base Titrations All you need to know to perform a strong acid-base neutralization 1

Strong Acid-Base Neutralization When equal moles of acid and base are present, neutralization occurs where a salt and water are formed HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) 2

Sample Problems H2CO3 + Sr(OH)2 HClO4 + NaOH HBr + Ba(OH)2 NaHCO3 + H2SO4 3

Titrations When you have a solution with an unknown concentration, you can find it by reacting it completely with a solution of known concentration This process is known as titrating To perform a titration, an instrument called a buret can be used to precisely measure amounts of solution, drop by drop 4

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Titration Termonology Equivalence point - the point at which the known and unknown concentration solutions are present in chemically equivalent amounts moles of acid = moles of base At pH = 7 [H3O+] = [OH-] Indicator - a weak acid or base that is added to the solution with the unknown concentration before a titration so that it will change color or “indicate” when in a certain pH range (pg. 660 in your text will show various indicators and their color ranges) 6

Phenolpthalein is clear at pH<8, End point - the point during a titration where an indicator changes color The 2 most common indicators we will use in our chemistry class will be: Phenolphthalein - turns very pale pink at a pH of 8-10 Bromothymol blue - turns pale green at a pH of 6.2-7.6 Phenolpthalein is clear at pH<8, pale pink at pH 8-10 and magenta at pH >10 Bromothymol blue 7

Practice Titration for an unknown acid Record the initial volume of acid in the buret. Add 5.0 mL of acid to a clean, dry Erlenmeyer flask. Record the final volume of acid in the buret. VF – VI = VA used in the titration equation Add 2-3 drops of indicator (phenolphthalein) to the flask - the color of the solution should be clear. Record the concentration (MB) of the base used to neutralize the acid. 8

Record the initial volume of the base in the buret. Add base to the acid in the Erlenmeyer flask slowly while continuously agitating, until a pH of 7 is reached. This will be noted by a pH probe and/or the end point of the indicator (for phenolphthalein, a pale pink color is desired). Record the final volume of the base in the buret. VF – VI = VB used in the titration equation Clean up. Pour solution down the drain with lots of water. Clean flask and put away materials to proper storage location.

Titration Equation MAVA = MBVB MA = molarity (mol/L) of acid VA = volume in mL of acid MB = molarity (mol/L) of base VB = volume in mL of base molesA = molesB [H3O+] = [OH-] 11. After calculating the molarity of the unknown acid experimentally, get the theoretical molarity from teacher and calculate % error 10

Practice titration for an unknown base Record the initial volume of base in the buret. Add 5.0 mL of base to a clean, dry Erlenmeyer flask. Record the final volume of base in the buret. VF – VI = VB used in the titration equation Add 2-3 drops of indicator (phenolphthalein) to the flask - the color of the solution should be magenta. Record the concentration (MA) of the acid used to neutralize the base. 11

Record the initial volume of the acid in the buret. Add acid to the acid in the Erlenmeyer flask slowly while continuously agitating, until a pH of 7 is reached. This will be noted by a pH probe and/or the end point of the indicator (for phenolphthalein, a pale pink color is desired). Record the final volume of the acid in the buret. VF – VI = VB used in the titration equation Clean up. Pour solution down the drain with lots of water. Clean flask and put away materials to proper storage location.