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Titration

Titration. Acid–Base Titration. The concentration of an acid especially a weak one or a weak base in water is difficult to measure directly. But we can calculate the conc from the results of titration. A titration is a carefully controlled neutralization reaction.

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Titration

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  1. Titration

  2. Acid–Base Titration • The concentration of an acid especially a weak one or a weak base in water is difficult to measure directly. • But we can calculate the conc from the results of titration. • A titration is a carefully controlled neutralization reaction. • Titration is a lab technique for measuring the conc of an unknown acid or base

  3. Acid–Base Titration • The average titration involves three components • An acid or base of unknown concentration • You need a standard soln • A standard is a solution of known conc • Should be opposite of the unknown • An indicator

  4. Acid–Base Titration • The purpose of the indicator is used to indicate when the acid and base ions are equal • Let’s the person performing the titration know when neutralization has occurred • Phenolphthalein is a very common indicator chosen • It undergoes a color change at a pH of about 7.6 • clear in acid • Light pink in neutral • Dark pink in base

  5. Acid–Base Titration • In titration, the stand-ard is slowly added to the unknown soln • As the 2 solns mix, the acid in one neutralizes the base in the other • Eventually, enough standard soln is added to neutralize all of the acid or base in the unknown soln. • Indicator changes color

  6. Procedure for Titration • The point at which this occurs is called the equivalence point. • We can calculate the conc from the results of titration • @ the equivalence point the [H30+] = [OH-] • The point at which the indicator changes color is called the end point of the titration. • If the indicator is chosen correctly the end point should be very close to the equivalence point.

  7. Procedure for Titration • Therefore, at approximately the end point of a titration the total mols of H+ donated by the acid is equal to the total mols of H+ accepted by the base. • We call these molar equivalences (stoichiometric equivalences) • Calculate moles of standard soln • Calculate moles of unknown (stoichiometry) • Claculateconc of unknown *Remember: (conc)(vol in L) = moles

  8. Sample Problem Solutions of NaOH are used to unclog drains. A 43.0 ml volume of NaOH was titrated with 32.0 ml of .100M HCl. What is the molar concentration of the NaOH solution?

  9. Sample Problem 200 ml of a 0.1 M solution of sodium hydroxide was needed to neutralize 125 ml of a sulfuric acid solution. What conc was the sulfuric acid soln?

  10. Titration Practice: • Calculate the conc of a nitric acid solution if a 20 ml sample of the acid required an average vol of 55 ml of a 0.047 M soln of Ba(OH)2 to reach the endpoint of the titration. • 15 ml of 12 M Hydrochloric acid is diluted to 250 ml. A 10.0 ml aliquot is measured and titrated with an unknown conc of Potassium hydroxide (vol of 20ml). What is the conc of the hydrochloric acid? What is the conc of the Potassium hydroxide solution?

  11. Titration Curves: • We can also track the titration using a pH meter or indicator paper to record the pHs as we add excess acid or base. • If we graph the results, we get a characteristic curve called a titration curve • Graphing pH vs. volume of titrant • Using a titration curve we can determine the equivalence point by analyzing the vertical of the titration curve.

  12. Strong Acid/Base Titration: pKa=pH

  13. Weak Acid w/Strong Base: Buffer Region

  14. Polyprotic acid titration:

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