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Chapter 4

Chapter 4. Titration and oxidation numbers Part V. Titration. Acid base reactions are often called neutralization reactions. One type of neutralization reaction is a titration.

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Chapter 4

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  1. Chapter 4 Titration and oxidation numbers Part V

  2. Titration • Acid base reactions are often called neutralization reactions. • One type of neutralization reaction is a titration. • Titration: using a measured volume of a solution of known concentration to find the concentration of an unknown solution.

  3. Vocabulary • Titration is a type of volumetric analysis. • Titrant: aka standard solution. • Analyte: solution being analyzed. • Equivalence point: where [H+] = [OH-] • The equivalence point is marked with a color change by an indicator. (as close as possible) • This color changed is called the endpoint.

  4. Requirements • There are 3 requirements for a successful titration. • The exact reaction between titrant and analyte must be known (and rapid). • The equivalence point must be accurately marked. • The volume of the titrant used to reach equivalence point must be known accurately.

  5. Titration • Not all titrations are acid-base neutralization reactions. • The next lab is a neutralization titration known as Standardization of a Solution.

  6. Example: Standardization • A 1.3009 g sample of KHP potassium hydrogen phtalate (KHC8H4O4) with molar mass of 204.22 g/mol is weighed out. It has one acidic hydrogen. • It is dissolved in water and phenolpthalein, an indicator is added. • The student titrates the unknown NaOH to the pink endpoint. The difference in the buret reading is 41.20 mL. • Calculate the concentration of NaOH.

  7. Answer: • Reaction: OH- (aq)+ HC8H4O4- (aq) H2O (l)+ C8H4O42-(aq) Ratio is 1:1 1.3009g KHP x 1mol/204.22g=0.0063701 mol KHP 0.0063701 mol KHP = 0.006371 mol NaOH M NaOH = 0.0063701 mol NaOH/0.04120 liters 0.1546 M NaOH

  8. A tough one: • You have a mixture of carbon tetrachloride, (CCl4) and benzoic acid (HC7H5O2) a weak acid with one acidic hydrogen. A sample of this mixture weighing 0.3518 g was mixed with water and the resulting solution required 10.59 mL of 0.1546 M NaOH for neutralization. What was the mass percent of benzoic acid in this solution?

  9. Answer: • You have both CCl4 and HC7H5O2 in solution but only the acid will react with NaOH, and in a 1:1 ratio. HC7H5O2(aq) + OH-(aq)  H2O(l) +C7H5O2- (aq) • How many moles of NaOH used? 10.59ml x (1L/1000mL) x (0.1546 mol/1 L)= 0.001637 mol OH- = 0.001637 mol HC7H5O2- 0.001637 mol HC7H5O2 x 122.12g/1 mol = 0.1999 g HC7H5O2

  10. Is that the answer? • % mass • (0.1999 g of acid/ 0.3518 total mass)*100 • =56.82% • Reread the question!!

  11. Oxidation Rules • In many reactions there is an exchange of electrons. • This transfer is called an oxidation-reduction reaction or redox for short. • LEO says GER

  12. Oxidation states or Oxidation numbers • A method for tracking electrons: 6 simple rules • An atom in an element is zero Na(s) O2(g) • A monatomic ion is the same as its charge. H+ =+1, O2- = -2 • Fluorine is -1 in its compounds

  13. Oxidation states or Oxidation numbers cont. • Oxygen is usually -2 in its compounds. The exceptions are peroxides O2-2 O=-1 • Hydrogen is +1 in its compounds • Also Important: the sum of oxidation numbers in a neutral compound = zero. The sum of oxidation numbers in an ion equal its charge.

  14. Try • CO2 • SF6 • NO3- • C=+4, O=-2 • S=+6, F=-1 • N=+5 , O=-2

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