Chapter 4Chapter 4

Titration and oxidation Titration and oxidation numbersnumbers

Part VIPart VI

TitrationTitration Acid base reactions Acid base reactions

are often called are often called neutralization neutralization reactions.reactions.

One type of One type of neutralization reaction neutralization reaction is a titration.is a titration.

Titration: using a Titration: using a measured volume of a measured volume of a solution of known solution of known concentration to find concentration to find the concentration of the concentration of an unknown solution.an unknown solution.

VocabularyVocabulary Titration is a type of Titration is a type of volumetric analysisvolumetric 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 The equivalence point is marked with a

color change by an color change by an indicatorindicator. (. (as close as as close as possible)possible)

This color changed is called the This color changed is called the endpointendpoint..

RequirementsRequirements There are 3 requirements for a There are 3 requirements for a

successful titration.successful titration.1.1. The exact reaction between titrant The exact reaction between titrant

and analyte must be known (and and analyte must be known (and rapid).rapid).

2.2. The equivalence point must be The equivalence point must be accurately marked.accurately marked.

3.3. The volume of the titrant used to The volume of the titrant used to reach equivalence point must be reach equivalence point must be known accurately.known accurately.

TitrationTitration

Not all titrations Not all titrations are acid-base are acid-base neutralization neutralization reactions. reactions.

The next lab is a The next lab is a neutralization neutralization titration known as titration known as Standardization of Standardization of a Solution.a Solution.

Example: StandardizationExample: Standardization A 1.3009 g sample of KHP potassium A 1.3009 g sample of KHP potassium

hydrogen phtalate (KHChydrogen phtalate (KHC88HH44OO44) with ) with molar mass of 204.22 g/mol is weighed molar mass of 204.22 g/mol is weighed out. It has one acidic hydrogen.out. It has one acidic hydrogen.

It is dissolved in water and It is dissolved in water and phenolpthalein, an indicator is added.phenolpthalein, an indicator is added.

The student titrates the unknown NaOH The student titrates the unknown NaOH to the pink endpoint. The difference in to the pink endpoint. The difference in the buret reading is 41.20 mL. the buret reading is 41.20 mL.

Calculate the concentration of NaOH.Calculate the concentration of NaOH.

Answer:Answer: Reaction: Reaction:

OHOH-- (aq)+ HC (aq)+ HC88HH44OO44-- (aq) (aq) H H22O (l)+ CO (l)+ C88HH44OO44

2-2-

(aq)(aq)

Ratio is 1:1Ratio is 1:1

1.3009g KHP x 1mol/204.22g=0.0063701 1.3009g KHP x 1mol/204.22g=0.0063701 mol KHPmol KHP

0.0063701 mol KHP = 0.006371 mol NaOH0.0063701 mol KHP = 0.006371 mol NaOH

M NaOH = 0.0063701 mol NaOH/0.04120 M NaOH = 0.0063701 mol NaOH/0.04120 litersliters

0.1546 M NaOH0.1546 M NaOH

A tough one:A tough one: You have a mixture of carbon You have a mixture of carbon

tetrachloride, (CCltetrachloride, (CCl44) and benzoic acid ) and benzoic acid (HC(HC77HH55OO22) a weak acid with one ) a weak acid with one acidic hydrogen. A sample of this acidic hydrogen. A sample of this mixture weighing 0.3518 g was mixture weighing 0.3518 g was mixed with water and the resulting mixed with water and the resulting solution required 10.59 mL of 0.1546 solution required 10.59 mL of 0.1546 M NaOH for neutralization. What M NaOH for neutralization. What was the mass percent of benzoic was the mass percent of benzoic acid in this solution?acid in this solution?

Answer:Answer: You have both CClYou have both CCl44 and HC and HC77HH55OO22 in solution in solution

but only the acid will react with NaOH, and but only the acid will react with NaOH, and in a 1:1 ratio.in a 1:1 ratio.

HCHC77HH55OO22(aq) + OH(aq) + OH--(aq) (aq) H H22O(l) +CO(l) +C77HH55OO22-- (aq) (aq)

How many moles of NaOH used?How many moles of NaOH used?

10.59ml x (1L/1000mL) x (0.1546 mol/1 L)=10.59ml x (1L/1000mL) x (0.1546 mol/1 L)=

0.001637 mol OH- = 0.001637 mol HC0.001637 mol OH- = 0.001637 mol HC77HH55OO22- -

0.001637 mol HC0.001637 mol HC77HH55OO22 x 122.12g/1 mol x 122.12g/1 mol

= 0.1999 g HC= 0.1999 g HC77HH55OO22

Is that the answer?Is that the answer?

% mass% mass (0.1999 g of acid/ 0.3518 total (0.1999 g of acid/ 0.3518 total

mass)*100mass)*100 =56.82%=56.82% Reread the question!!Reread the question!!

Oxidation RulesOxidation Rules

In many reactions In many reactions there is an exchange there is an exchange of electrons.of electrons.

This transfer is called This transfer is called an oxidation-an oxidation-reduction reaction of reduction reaction of redox for short.redox for short.

LEO says GRELEO says GRE

Oxidation states or Oxidation Oxidation states or Oxidation numbersnumbers

A method for tracking electrons:A method for tracking electrons:

6 simple rules6 simple rules

1.1. An atom in an element is zero An atom in an element is zero Na(s) ONa(s) O22(g)(g)

2.2. A monatonic ion is the same as A monatonic ion is the same as its charge. H+ =+1, O2- = -2its charge. H+ =+1, O2- = -2

3.3. Fluorine is -1 in its compoundsFluorine is -1 in its compounds

Oxidation states or Oxidation Oxidation states or Oxidation numbers cont.numbers cont.

4.4. Oxygen is usually -2 in its compounds.Oxygen is usually -2 in its compounds.

The exceptions are peroxides OThe exceptions are peroxides O22-2 -2 O=-1O=-1

5.5. Hydrogen is +1 in its compoundsHydrogen is +1 in its compounds

6.6. Also Important: the sum of oxidation Also Important: the sum of oxidation numbers in a neutral compound = numbers in a neutral compound = zero. The sum of oxidation numbers zero. The sum of oxidation numbers in an ion equal its charge.in an ion equal its charge.

TryTry

COCO22

SFSF66

NONO33--

C=+4, O=-2C=+4, O=-2 S=+6, F=-1S=+6, F=-1 N=+5 , O=-2N=+5 , O=-2