DefinitionDefinition◦Analytical method in which a standard solution is used to determine the concentration of an unknown solution.

standard solution

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Buret

stopcock

Erlenmeyer flask

Titrant◦The substance added to the analyte in a titration (a standard solution)

Analyte◦The substance being analyzed

Equivalence point◦The point in a titration at which the quantity of titrant is exactly sufficient for stoichiometric reaction with the analyte.

Titrant

Analyte

If the concentration of the titrant is known, then the unknown concentration of the analyte can be determined.

Quantitative analysis — used to determine the amounts or concentrations of substances present in a sample by using a combination of chemical reactions and stoichiometric calculations

The “perfect pink” for a titration with phenolphthalein

Indicator - changes color to indicate pH change

Volume base added

Example… phenolphthalein is colorless in acid and pink in basic solution

pH

Endpoint =7

pink

point at which exactly enough reactant has been added for the solution to be neutralized and no more

◦Point at which equal amounts of H3O+ and OH- have been added.

◦Determined by… indicator color change dramatic change in pH

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moles H3O+ = moles OH-

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25.5 mL of 1.3M KOH are required to neutralize 50.0 mL of HCl. Find the molarity of HCl.

Acid (H3O+)

M = ?V = 50.0 mL

Base (OH-)

M = 1.3MV = 25.5 mL MA = 0.66M HCl

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equivalence point

14.0

12.0

10.0

8.0

6.0

4.0

2.0

0.00.0 10.0 20.0 30.0 40.0

pH

Volume of 0.100Volume of 0.100 M M NaOH added NaOH added(mL)

Titration of an Acid With an Base

0.00 1.0010.00 1.3720.00 1.9522.00 2.1924.00 2.7025.00 7.0026.00 11.3028.00 11.7530.00 11.9640.00 12.3650.00 12.52

NaOH added (mL) pH

Titration Data

Solutionof NaOHSolutionof NaOH

Solutionof HCl H+

H+ H+

H+

Cl-

Cl-

Cl-

Cl-

Na+

Na+

Na+

Na+

OH-

OH-OH-

OH-

25 mL

phenolphthalein - colorless

phenolphthalein - pink

• ArrheniusArrhenius - In aqueous solution… - In aqueous solution…

HCl(aq) H+(aq)+ Cl-(aq)

AcidsAcids increase hydrogen ion concentration [H+]

H

HH H H

H

ClClO O

–+

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A Brønsted-Lowry acid is a proton donorA Brønsted-Lowry base is a proton acceptor

acidconjugate

basebase conjugate

acid

From the Latin word conjugare, meaning “to join together.”

Reactions between acids and bases always yield their conjugate bases and acids.

HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids.

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

The strength of an acid (or base) is determined by the amount of IONIZATION.

The strength of an acid (or base) is determined by the amount of IONIZATION.

Weak acids are much less than 100% ionized in water.

One of the best known is acetic acid = CH3CO2H

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

Strong Base: 100% dissociated in water.

NaOH (aq) ---> Na+ (aq) + OH- (aq)

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

Other common strong Other common strong bases include KOH and bases include KOH and Ca(OH)Ca(OH)22..

CaO (lime) + HCaO (lime) + H22O -->O -->

Ca(OH)Ca(OH)22 (slaked lime) (slaked lime)CaOCaO

Weak base: less than 100% ionized in water

One of the best known weak bases is

ammoniaNH3 (aq) + H2O (l) NH4

+ (aq) + OH- (aq)

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

The more polar the H-X bond and/or the weaker the H-X bond, the more acidic the compound.

Acidity increases from left to right across a row and from top to bottom down a group.

H2O can function as both an ACID and a

BASE.

Equilibrium constant for water = KEquilibrium constant for water = Kww

KKww = [H = [H33OO++] [OH] [OH--] = 1.00 x 10] = 1.00 x 10-14-14 at 25 at 25 ooCC

Timberlake, Chemistry 7th Edition, page 335

1.0 MHCl0

gastricjuice1.6

vinegar2.8

carbonated beverage3.0

orange3.5

apple juice3.8

tomato4.2

lemonjuice2.2 coffee

5.0

bread5.5

soil5.5

potato5.8

urine6.0

milk6.4

water (pure)7.0

drinking water7.2

blood7.4

detergents8.0 - 9.0

bile8.0

seawater8.5

milk of magnesia10.5

ammonia11.0

bleach12.0

1.0 MNaOH(lye)14.0

8 9 10 11 12 14133 4 5 621 70

acidic neutral basic[H+] = [OH-]