Chapter 4 Titration and oxidation numbers Part VI

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.

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

Requirements There are 3 requirements for a successful titration. 1. T he exact reaction between titrant and analyte must be known (and rapid). 2. T he equivalence point must be accurately marked. 3. T he volume of the titrant used to reach equivalence point must be known accurately.

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

Example: Standardization A g sample of KHP potassium hydrogen phtalate (KHC 8 H 4 O 4 ) with molar mass of g/mol is weighed out. It has one acidic hydrogen. A g sample of KHP potassium hydrogen phtalate (KHC 8 H 4 O 4 ) with molar mass of g/mol is weighed out. It has one acidic hydrogen. It is dissolved in water and phenolpthalein, an indicator is added. 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 mL. The student titrates the unknown NaOH to the pink endpoint. The difference in the buret reading is mL. Calculate the concentration of NaOH. Calculate the concentration of NaOH.

Answer: Reaction: Reaction: OH - (aq)+ HC 8 H 4 O 4 - (aq)  H 2 O (l)+ C 8 H 4 O 4 2- (aq) Ratio is 1: g KHP x 1mol/204.22g= mol KHP mol KHP = mol NaOH M NaOH = mol NaOH/ liters M NaOH

A tough one: You have a mixture of carbon tetrachloride, (CCl 4 ) and benzoic acid (HC 7 H 5 O 2 ) a weak acid with one acidic hydrogen. A sample of this mixture weighing g was mixed with water and the resulting solution required mL of M NaOH for neutralization. What was the mass percent of benzoic acid in this solution? You have a mixture of carbon tetrachloride, (CCl 4 ) and benzoic acid (HC 7 H 5 O 2 ) a weak acid with one acidic hydrogen. A sample of this mixture weighing g was mixed with water and the resulting solution required mL of M NaOH for neutralization. What was the mass percent of benzoic acid in this solution?

Answer: You have both CCl 4 and HC 7 H 5 O 2 in solution but only the acid will react with NaOH, and in a 1:1 ratio. You have both CCl 4 and HC 7 H 5 O 2 in solution but only the acid will react with NaOH, and in a 1:1 ratio. HC 7 H 5 O 2 (aq) + OH - (aq)  H 2 O(l) +C 7 H 5 O 2 - (aq) How many moles of NaOH used? How many moles of NaOH used? 10.59ml x (1L/1000mL) x ( mol/1 L)= mol OH- = mol HC 7 H 5 O mol HC 7 H 5 O 2 x g/1 mol = g HC 7 H 5 O 2

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

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

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

Oxidation states or Oxidation numbers cont. 4. Oxygen is usually -2 in its compounds. The exceptions are peroxides O 2 -2 O=-1 5. Hydrogen is +1 in its compounds 6. Also Important: the sum of oxidation numbers in a neutral compound = zero. The sum of oxidation numbers in an ion equal its charge.

Try CO 2 CO 2 SF 6 SF 6 NO 3 - NO 3 - C=+4, O=-2 C=+4, O=-2 S=+6, F=-1 S=+6, F=-1 N=+5, O=-2 N=+5, O=-2