LL ee cc tt uu rr ee 11

Analytical chemistry. Analytical chemistry.

Chemical analysisChemical analysis.. Calculation of рН.Calculation of рН.

Associate profAssociate prof . L.V. Vronska. L.V. VronskaAssociate profAssociate prof . M.M. Mykhalkiv

OutlineOutline Object and task of analytical chemistry. Chemical analysis Object and task of analytical chemistry. Chemical analysis

and its varieties. The importance of analytical chemistry in and its varieties. The importance of analytical chemistry in PharmacyPharmacy. Methods of analysis, their classification.. Methods of analysis, their classification.

Main principles in the theory of strong electrolytes.Main principles in the theory of strong electrolytes. The Law of Mass Action in analytical chemistry. Main types of The Law of Mass Action in analytical chemistry. Main types of

chemical equilibrium, which are utilized in analytical chemical equilibrium, which are utilized in analytical chemistry.chemistry.

Bronsted-Lowry theory of acids and bases.Bronsted-Lowry theory of acids and bases.

1.1. Calculation of рН and рОН aqueous solutions of acid and Calculation of рН and рОН aqueous solutions of acid and base.base.

2.2. Calculation of рН solutions of ampholytes.Calculation of рН solutions of ampholytes.

3.3. Calculation of рН solutions of salts.Calculation of рН solutions of salts.

4.4. Calculation of рН of buffer solutions.Calculation of рН of buffer solutions.

5.5. Acid-base equilibrium in nonaqueous solvents.Acid-base equilibrium in nonaqueous solvents.

1. Object and task of analytical 1. Object and task of analytical chemistry. Chemical analysis and its chemistry. Chemical analysis and its

varieties. The importance of varieties. The importance of analytical chemistry in analytical chemistry in PharmacyPharmacy. .

Methods of analysis, their Methods of analysis, their classification.classification.

Analytical chemistryAnalytical chemistry – a sub-discipline of – a sub-discipline of

Chemistry about methods of the analysis or Chemistry about methods of the analysis or

methods of reception of the information about methods of reception of the information about

elementary objects.elementary objects.

Analytical chemistryAnalytical chemistry a sub-discipline of a sub-discipline of

Chemistry which develops theoretical basis and Chemistry which develops theoretical basis and

methods of the chemical analysis.methods of the chemical analysis.

ObjectObject of analytical chemistry is to define of analytical chemistry is to define

chemical compounds in substances.chemical compounds in substances.

Main divisions of Analytical Main divisions of Analytical Chemistry:Chemistry:

The qualitative analysis: fractional and The qualitative analysis: fractional and systematic methodssystematic methods

The quantitative analysis:The quantitative analysis:

1. chemical methods1. chemical methods

2. instrumental methods:2. instrumental methods:

- physical methods of analysisphysical methods of analysis

- physical-chemical methods of analysisphysical-chemical methods of analysis

Aliquots identical mixtures

Reagent F

Reagent W Reagent Q

Scheme of Fractional Analysis of Complex Mixtures

Component I Components J M

Mixture of components I, J, K, L, M groups

ComponentsI M

ComponentsI M

ComponentsI M

ComponentsI M

ComponentsI M

Component J Components I, K, L, M

Component L

Components I, J, K, M

Scheme of Systematic Path of Complex Scheme of Systematic Path of Complex Mixture AnalysisMixture Analysis

Mixture of substances of I, J, K, M group

Group IComponents I1, I2, I3 …

Mixture of substancesof groups J … M

Group JComponents J1, J2, J3

…

Mixture of substancesof groups K, M

Reagent A

Reagent B

Scheme of Analysis of Group Scheme of Analysis of Group JJComponents J1, J2, J3, J4, J5

Components J1, J2 Components J3, J4, J5

Component J3

Components J4, J5

Component J4 Component J5

Component J1 Component J2

Reagent Y

Reagent N

Reagent Z

Reagent T

The main goal of the qualitative analysis is The main goal of the qualitative analysis is

searching of elements, ions or chemical searching of elements, ions or chemical

compounds that are contained in the investigated compounds that are contained in the investigated

substance.substance.

The main goal of the quantitative analysis is to The main goal of the quantitative analysis is to

define the quantity of the mixture ratio or define the quantity of the mixture ratio or

percentage of elements (ions) in substance. percentage of elements (ions) in substance.

Reactions in analytical chemistryReactions in analytical chemistry

Specific Specific SelectiveSelective

Specific reactions give an analytical effect only with one individual substance.

NH4+ + OH - = NH3 + H2O.

Selective reactions give identical or similar analytical effects with small number of ions (2-5). HCl: Pb2+ + 2Cl- =PbCl2↓

Ag+ + Cl- =AgCl ↓Hg2

2+ + 2Cl- =Hg2Cl2 ↓

•The The group reagentgroup reagent is the reagent which will is the reagent which will meet the following requirements:meet the following requirements:

•It should It should precipitate cationsprecipitate cations virtually, virtually, quantitatively (concentration of cations in a quantitatively (concentration of cations in a solution should be less than 10solution should be less than 10-6-6 M); M);

•The precipitate should be easily dissolved in The precipitate should be easily dissolved in certain reagents;certain reagents;

•Excess reagent should not alter determination Excess reagent should not alter determination of those ions which remain in solution.of those ions which remain in solution.

Tasks of analytical chemistry:Tasks of analytical chemistry: Research methods of qualitative and quantitative Research methods of qualitative and quantitative

analysis of analysis of Nb, Ta, Zr, Ti, Hf, Mo, WNb, Ta, Zr, Ti, Hf, Mo, W, , rare-earth rare-earth andand other other elementelements in mixture, because s in mixture, because they are they are used in the modern techniquesused in the modern techniques..

Research methods Research methods for detection and definition of for detection and definition of

microquantities of elementsmicroquantities of elements, because often , because often physical and chemical properties of materials are physical and chemical properties of materials are predetermined by their presence.predetermined by their presence.

Detect and Define chemical elements and Detect and Define chemical elements and substances in the environment: soil, air, water, substances in the environment: soil, air, water, plantsplants

Investigate the complex influence of related Investigate the complex influence of related substances on a life of plants, animals and people.substances on a life of plants, animals and people.

The Importance of analytical chemistry in The Importance of analytical chemistry in PharmacyPharmacy..

Synthesis of drugs (synthetic or natural) is Synthesis of drugs (synthetic or natural) is necessarily supervised by methods of analytical necessarily supervised by methods of analytical chemistry. chemistry.

Definition of period of drugs validity is based on Definition of period of drugs validity is based on methods of analytical chemistry. methods of analytical chemistry.

Chemical analysis and its Chemical analysis and its varieties:varieties:

Elemental analysisElemental analysis Function analysisFunction analysis Molecular analysisMolecular analysis Phase analysisPhase analysis Diffraction analysisDiffraction analysis

Elemental analysisElemental analysis is qualitative and quantitative is qualitative and quantitative analysis of elements in compound clear substanceanalysis of elements in compound clear substance

Function analysisFunction analysis is the analysis which answer is the analysis which answer what functional groups are contained in what functional groups are contained in investigated substanceinvestigated substance

Methods of the Methods of the molecular analysismolecular analysis receive the receive the information about substances which consist information about substances which consist of molecules or formular parts.of molecules or formular parts.

Phase analysisPhase analysis – detection and definition of – detection and definition of different phases (solid, liquid, gas), which are different phases (solid, liquid, gas), which are contained in the investigated system.contained in the investigated system.

Diffraction analysisDiffraction analysis determines the crystal lattice determines the crystal lattice structure containing atoms, molecules and structure containing atoms, molecules and ions.ions.

Pharmaceutical analysis is determination of Pharmaceutical analysis is determination of drug quality (manufactured or pharmacy drug quality (manufactured or pharmacy

compounded)compounded)

Pharmaceutical analysis includes:Pharmaceutical analysis includes: analysis of drugsanalysis of drugs analysis of medicinal herbsanalysis of medicinal herbs process monitoring of drugsprocess monitoring of drugs toxicological analysistoxicological analysis judicial-chemical analysisjudicial-chemical analysis

IUPAC Classification of analytical methods in IUPAC Classification of analytical methods in accordance with mass and volume of analytic accordance with mass and volume of analytic

samplesampleMethod nameMethod name Mass of sample, gMass of sample, g Volume of sample, Volume of sample,

mlml

Gramm-methodGramm-method 1–101–10 10–10010–100

Cantigramm-methodCantigramm-method 0,05–0,50,05–0,5 1–101–10

Milligramm-methodMilligramm-method 1010-6-6–0,001–0,001 1010-4-4–0,1–0,1

Microgramm-methodMicrogramm-method 1010-9-9–10–10-6-6 1010-6-6–10–10-4-4

Nanogramm-methodNanogramm-method 1010-12-12–10–10-9-9 1010-10-10–10–10-7-7

Picogramm-methodPicogramm-method 1010-12-12 1010-10-10

The signal which bears the information on The signal which bears the information on elementary objects, is called as an elementary objects, is called as an analytical analytical signalsignal..

The analytical signal can be the carrier for both The analytical signal can be the carrier for both qualitative and quantitative information.qualitative and quantitative information.

Sensitivity of analytical reactionSensitivity of analytical reaction is the least is the least amount of substance, which can be detected with amount of substance, which can be detected with the reagent in one drop of solution.the reagent in one drop of solution.

The sensitivity express to next correlated values:The sensitivity express to next correlated values:

Limit of detection = Determined minimumLimit of detection = Determined minimum (m) (m) – the least amount of substance, which present in – the least amount of substance, which present in analysed solution and can be detected with the analysed solution and can be detected with the reagent. Calculatereagent. Calculatedd in in g. 1 g. 1 g = 0,000001 g.g = 0,000001 g.

Limit of concentration = Minimal concentrationLimit of concentration = Minimal concentration (C(Cminmin) – the least concentration of substance in the ) – the least concentration of substance in the

solution which still can be detected in small solution which still can be detected in small portion or volume of analysed solution.portion or volume of analysed solution.

Maximum of dilutionMaximum of dilution (W = 1/Cmin) – (W = 1/Cmin) – quantity (ml) of solution, containing 1 g of quantity (ml) of solution, containing 1 g of the analysed substance, which can be the analysed substance, which can be detected with a definite reaction (reagent).detected with a definite reaction (reagent).

Analytical reaction is considered more Analytical reaction is considered more sensitive under conditions when sensitive under conditions when determined minimumdetermined minimum and and minimal minimal concentrationconcentration of analyzed solution are low of analyzed solution are low and and maximum of dilutionmaximum of dilution is high. is high.

2. Main principles of theory of 2. Main principles of theory of strong electrolytes.strong electrolytes.

activityactivity (а)(а) – – effective concentrationeffective concentration of ions in of ions in solutionsolution, , when it reactswhen it reacts

.1lim0

C

a

C

To calculate activity coefficients use the To calculate activity coefficients use the followingfollowing::

1.1. Ionic strengthIonic strength of solution of solution

where where cci and i and zzi are the concentration and charge of i are the concentration and charge of the the iith ion.th ion.

2.2. Activity coefficients for ionic solutes, depend on Activity coefficients for ionic solutes, depend on the ionic strength of solution by using the the ionic strength of solution by using the extended Debye–Hückel theoryextended Debye–Hückel theory

22

1ii ZC

To calculate activity coefficients use To calculate activity coefficients use the Debye–Hückel equationthe Debye–Hückel equation

ifif 0,01 0,01

ifif 0,1 0,1

ifif 1,0 1,0

,512,0lg 2 ii Zf

,1

512,0lg

2

i

iZ

f

,1,01

512,0lg 2

2

ii

i ZZ

f

Experimentally is possible to find Experimentally is possible to find only the Mean activity coefficient: only the Mean activity coefficient:

for binary electrolyte AB for binary electrolyte AB

for electrolyte structure for electrolyte structure AAmmBBnn

,BA fff

,nB

mA

nmfff

Mean activity coefficient may be Mean activity coefficient may be calculated theoretically by using calculated theoretically by using

Debye–Hückel equationDebye–Hückel equation:: ifif 0,01 0,01

ifif 0,1 0,1

ifif 1,0.1,0.

,512,0lg BAZZf

,1

512,0lg

BAZZ

f

.1,01

512,0lg

BABA ZZ

ZZf

For simplification of calculations of For simplification of calculations of activity coefficients use these activity coefficients use these

assumptions:assumptions:

1. Activity coefficients of ions with identical 1. Activity coefficients of ions with identical charge irrespective of ion’s radius are charge irrespective of ion’s radius are approximately equal. approximately equal.

2. Activity coefficients of neutral parts in dilute 2. Activity coefficients of neutral parts in dilute solutions of electrolytes equals 1.solutions of electrolytes equals 1.

3. Very dilute solutions of electrolytes are possible 3. Very dilute solutions of electrolytes are possible to consider ideal. to consider ideal.

3. The Law of Mass Action in 3. The Law of Mass Action in Analytical Chemistry.Analytical Chemistry.

ConcentrationalConcentrational ( (realreal) ) constantconstant of chemicalof chemical equilibriumequilibrium

nA + mB nA + mB lC +pD lC +pD

p-p-functionfunction of constantof constant equilibriumequilibrium

pK = –lgK.pK = –lgK.

.][][

][][mn

plR

BA

DCK

ККТТ – – thermodynamicthermodynamic equilibriumequilibrium constantconstant (it (it depends on depends on temperature and pressuretemperature and pressure))

where f – activity coefficientwhere f – activity coefficient

We use KWe use KRR, when we have real conditions , when we have real conditions (influence of ionic strength, temperature and (influence of ionic strength, temperature and pressure)pressure)

;m

Bn

A

pD

lCR

mB

nA

pD

lCT

ff

ffK

aa

aaK

ККC C – – conditionalconditional equilibrium constantequilibrium constant

where C – where C – formality, formality, is a substance’s total is a substance’s total concentration in solution regardless of its specific concentration in solution regardless of its specific chemical form.chemical form.

where where - - parts per molparts per mol

,mB

nA

pB

lCC

CC

CCK

.b

Ba

A

dD

cC

bB

aA

dD

cCTC

ff

ffKK

ionion C

ion][

We use KWe use KCC, when we have the following , when we have the following real conditions (influence of ionic real conditions (influence of ionic strength, temperature and pressure, strength, temperature and pressure, competitive reactions)competitive reactions)

Mass balance equationMass balance equation, , which is simply a which is simply a statement of the conservation of matter. In a statement of the conservation of matter. In a solution of a monoprotic weak acid (base), for solution of a monoprotic weak acid (base), for example, the combined concentrations of the example, the combined concentrations of the conjugate weak acid (base), HA, and the conjugate weak acid (base), HA, and the conjugate weak base (acid), Aconjugate weak base (acid), A––, must equal the , must equal the weak acid’s (base’s) initial concentration, weak acid’s (base’s) initial concentration, CCHAHA..

HH22S S H H++ + HS + HS--

HSHS-- H H++ + S + S2-2-

CCSS = [S = [S2–2–] + [HS] + [HS––] + [H] + [H22S].S].

A charge balance equationA charge balance equation is a statement of solution is a statement of solution electroneutrality.electroneutrality.

Total positive charge from cations = total negative charge Total positive charge from cations = total negative charge from anionsfrom anions

Mathematically, the charge balance expression is expressed Mathematically, the charge balance expression is expressed asas

where [Mwhere [Mzz++]]ii and [Aand [Az–z–]]jj are, respectively, the concentrations are, respectively, the concentrations

of the of the iith cation and the th cation and the jjth anion, and (th anion, and (zz+)+)i i and (and (zz–)–)j j are are the charges of the the charges of the iith cation and the th cation and the jjth anion.th anion.

The charge balance equation for an aqueous solution of Ca(NO3)2 is

2 [Ca2+] + [H3O+] = [OH–] + [NO3–]

Main types of chemical reactions which are Main types of chemical reactions which are used in analytical chemistryused in analytical chemistry::

Acid-base reactionAcid-base reaction ((the reaction of an acid with a the reaction of an acid with a

basebase))

CHCH33COOHCOOH((aqaq)) + NH + NH3(3(aqaq)) CH CH33COOCOO––((aqaq)) + NH + NH44

++((aqaq))

A precipitation reactionA precipitation reaction occurs when two or more occurs when two or more

soluble species combine to form an insoluble productsoluble species combine to form an insoluble product..

PbPb2+2+((aqaq)) + 2Cl + 2Cl––

((aqaq)) PbCl PbCl22((ss))

reaction between the metal ion and the reaction between the metal ion and the ligand ligand is is

typical of a typical of a complexation reactioncomplexation reaction..

CdCd2+2+((aqaq)) + 4(:NH + 4(:NH33))((aqaq)) Cd(:NH Cd(:NH33))44

2+2+((aqaq))

redox reactionredox reaction - - an electron-transfer reaction.an electron-transfer reaction.

2Fe2Fe3+3+((aqaq)) + H + H22CC22OO4(4(aqaq)) + 2H + 2H22OO(l)(l) 2Fe 2Fe2+2+

((aqaq)) + 2CO + 2CO2(2(gg))

+ 2H+ 2H33OO++((aqaq))

4. Bronsted-Lowry theory of acids 4. Bronsted-Lowry theory of acids and bases.and bases.

A substance, that dissolves in water to give an A substance, that dissolves in water to give an

electrically conducting solution is called an electrically conducting solution is called an

electrolyteelectrolyte. .

A substance, that dissolves in water to give A substance, that dissolves in water to give

nonconducting or very poorly conducting nonconducting or very poorly conducting

solution is called a solution is called a nonelectrolytenonelectrolyte..

According to According to Svante ArrheniusSvante Arrhenius concept: concept:

AcidAcid is any substance that, when dissolved in water, is any substance that, when dissolved in water, increase the concentration of hydrogen ion Hincrease the concentration of hydrogen ion H++..

BaseBase is any substance that, when dissolved in water, is any substance that, when dissolved in water, increase the concentration of hydroxide ion OHincrease the concentration of hydroxide ion OH––..

NaOH NaOH Na Na++ + OH + OH––

HCl HCl H H++ + Cl + Cl––

A useful definition of acids and bases was indepen-A useful definition of acids and bases was indepen-dently introduced by Johannes Brønsted (1879–1947) dently introduced by Johannes Brønsted (1879–1947)

and Thomas Lowry (1874–1936) in 1923.and Thomas Lowry (1874–1936) in 1923.

acidsacids are proton donorsare proton donors

basesbases are proton acceptorsare proton acceptors

Acid Acid Base + Н Base + Н++

Constant reaction of a dissociationConstant reaction of a dissociation solventsolvent hashas equationequation

AutoprotolysisAutoprotolysis constantconstant of solvent is product of solvent is product of activity lyonium and lyateof activity lyonium and lyate

.2

2

HSolv

SolvSolvHHSolv

T

a

aaK

,2

SolvSolvHTHSolv aaK

Neutrality of solution determines activity of Neutrality of solution determines activity of lyonium and lyate іons:lyonium and lyate іons:

Condition of neutralityCondition of neutrality

pSolvpHaaSolvSolvH

,2

THSolvpKpH 2/1

рН рН of some solventsof some solvents

SolventSolvent Limits Limits рНрН

HH22SOSO44 0 – 3,60 – 3,6

HCOOHHCOOH 0 – 6,700 – 6,70

HH22OO 0-140-14

CHCH33COOHCOOH 0 – 14,40 – 14,4

CHCH33OHOH 0 – 17,30 – 17,3

acetoneacetone 0 – 21,10 – 21,1

SolventSolvent Limits Limits рНрН

CC22HH55OHOH 0 – 19,000 – 19,00

CHCH33– C – C N N 0 – 19,000 – 19,00

lliiquid ammoniaquid ammonia 0 – 22,00 – 22,0

FMAFMA 0 – 17,00 – 17,0

DMFADMFA 0 – 18,00 – 18,0

TheThe Brønsted-Lowry concept of acids and bases Brønsted-Lowry concept of acids and bases has greater scope than the Arrhenius concept:has greater scope than the Arrhenius concept: the general description of acid-base reactionthe general description of acid-base reaction possibility a quantitative estimation strength of possibility a quantitative estimation strength of

acid and baseacid and base

НА + ННА + Н22О О Н Н33ОО++ + А + А––

B + HB + H22O O BH BH++ + OH + OH––

HA

AOHTa a

aaK

3

B

OHBHTb a

aaK

SolventsSolvents::

progenic progenic (A species that can serve as a proton (A species that can serve as a proton donor)donor)

protophilic protophilic (A species that can serve as a (A species that can serve as a proton acceptor)proton acceptor)

amphiprotic amphiprotic (A species that can serve as both a (A species that can serve as both a proton donor and a proton acceptor)proton donor and a proton acceptor)

aproticaprotic (A species that can’t serve a proton)(A species that can’t serve a proton)

proton acceptor’s properties increase proton acceptor’s properties increase HH22SOSO44; CCl; CCl33COOH; CHCOOH; CH33COOH; HCOOH; H22O; CO; C22HH55OH; NHOH; NH33; C; C55HH55NN

proton donor’s properties increase proton donor’s properties increase

5. Calculation of рН and рОН aqueous 5. Calculation of рН and рОН aqueous solutions of acid and base.solutions of acid and base.

Calculation of рН and Calculation of рН and рОН of strong acid’s рОН of strong acid’s and base’s solutions.and base’s solutions.

pH + pOH=14pH + pOH=14 For dilute solutions of For dilute solutions of

strong acid and base strong acid and base (if C(if C111010-4-4 M):M):

HACpH lg

BCpOH lg

2

4][

2WHAHA KCC

H

.2

4][

2WBB KCC

OH

Calculation of рН and рОН of weak Calculation of рН and рОН of weak acid’s and base’s solutions.acid’s and base’s solutions.

2

4][

2HAHAHAHA CKKK

H

.2

4][

2BBBB CKKK

OH

If weak acid has dissociation degree () 0,03 – 0,05 than рН calculates:

HAHA

HAHA

CpKpH

CKH

lg2

1

2

1

][

BB CKOH ][

BB CpKpH lg2

1

2

114

For dilute solutions (if C110-4 M) of weak acid (base) with К 10–6 :

WHAHA KCKH ][

WBB KCKOH ][

][][][ 21 21HAKHAKH HAHA

][][][

21 21BKBK

KH

BB

W

pH of mixture two acid (base)medium strength calculates

.][2211 HAHAHAHA CKCKH

2211

][BBBB

WCKCK

KH

If weak acids (bases) has dissociation degree () 5 % than рН calculates:

66. . Calculation of рН solutions of Calculation of рН solutions of ampholytes.ampholytes.

][

)][(][

2

2

HAK

KHAKKH

AH

WHAAH

HAAH KKH

2][

77. . Calculation of рН solutions of Calculation of рН solutions of saltssalts..

Salt solutions can be neutral, acidic, or basic, depending on the acid–base properties of the constituent cations and anions

Salts formed by reaction of a strong acid with a strong base are neutral and pH=7

Strong acidStrong acid + + Strong baseStrong base →→Neutral solutionNeutral solution

Strong AcidStrong Acid + + Weak baseWeak base →→ Acidic solutionAcidic solution

Weak acidWeak acid + + Strong baseStrong base →→ Basic solutionBasic solution

Some 0.10 M aqueous salt solutions (left to right): NaCl, NH4Cl, AlCl3, NaCN, and (NH4)2CO3.A few drops of universal indicator have been added to each solution. The color of the indicator shows that the NaCl solution is neutral, the NH4Cl and AlCl3 solutions are acidic, and the NaCN and (NH4)2CO3 solutions are basic.

salts formed by reaction of a weak acid with a strong base are basic and pH calculate

CsaltK

KOH

HA

W ][

saltB CKOH ][

Salts formed by reaction of a strong acid with a weak base are acidic and pH calculate

salta CKH ][

saltB

W CK

KH ][

B

HAWK

KKH

][

Salts formed by reaction of a weak acid with a weak base are nearly neutral and pH calculate

8. Calculation of рН of buffer solutions.8. Calculation of рН of buffer solutions.

Solutions which contain a weak acid and its conjugate base, are called buffer solutionsbuffer solutions because they resist drastic changes in pH.

If a small amount of OH- is added to a buffer solution, the pH increases, but not by much because the acid component of the buffer solution neutralizes the added OH-.

If a small amount of H3O+ is added to a buffer solution, the pH decreases, but again not by much because the base component of the buffer solution neutralizes the added H3O+.

Buffer Solutions activity

Buffer: weak acid and its salt (CHBuffer: weak acid and its salt (CH33COOH + COOH + CHCH33COONa)COONa)

The added strong acid::

CHCH33COOCOO-- + H + H++ CH CH33COOHCOOH

The added strong base::

CHCH33COOH + OHCOOH + OH-- CH CH33COOCOO-- + H + H22OO

Buffer: weak base and its salt Buffer: weak base and its salt (NH(NH33+NH+NH44Cl)Cl)

The added strong acidThe added strong acid::

NHNH33 + H + H++ NH NH44++

The added strong baseThe added strong base::

NHNH44++ + OH + OH–– NH NH33HH22OO

The color of each solution is due to the presence of a few drops of methyl red, an acid–base indicator that is red at pH less than about 5.4 and yellow at pH greater than about 5.4. (a) 1.00 L of HCl (b) the solution from part (a) turns yellow (pH > 5.42) after addition of only a few drops of 0.10 M NaOH; (c) 1.00 L of a 0.10 M acetic acid–0.10 M sodium acetate buffer solution (pH = 4.74) (d) the solution from part (c) is still red (pH < 5.42) after addition of 100 mL of 0.10 M NaOH.

Prepackaged buffer solutions of known pH, and solid ingredients for preparing buffer solutions of

known pH.

a pH meter

To calculate pH of buffer use equation To calculate pH of buffer use equation (Henderson–Hasselbalch equation)(Henderson–Hasselbalch equation)

salt

acida С

СpKpH lg

salt

baseb С

СpKpH lg14

Buffer CapacityBuffer capacity as a measure of the amount of acid or base that

the solution can absorb without a significant change in pH.

Buffer capacity is also a measure of how little the pH changes

with the addition of a given amount of acid or base.

To calculate Buffer capacityTo calculate Buffer capacity

use equationuse equation

BA

BACC

CCП

3,2

Buffer capacity depends on:

how many moles of weak acid and conjugate

base are present.

For equal volumes of solution, the more

concentrated the solution, the greater the buffer

capacity.

For solutions having the same concentration, the

greater the volume, the greater the buffer

capacity.

Useful buffer mixturesUseful buffer mixturesComponentsComponents рНрН pH rangepH range

HCOOH + HCOONaHCOOH + HCOONa 3,83,8 2,8 – 4,82,8 – 4,8

CC66HH55COOH + COOH +

CC66HH55COONaCOONa4,24,2 3,2 – 5,23,2 – 5,2

CHCH33COOH + COOH +

CHCH33COONaCOONa

4,84,8 3,8 – 5,83,8 – 5,8

NaHNaH22POPO

44 + Na + Na22HPOHPO

44 6,66,6 5,6 – 7,65,6 – 7,6

NHNH44OH + NHOH + NH

33 9,29,2 8,2 – 10,28,2 – 10,2

9. Acid-base equilibrium in nonaqueous solvents.

Solvent classification for inductivitySolvent classification for inductivity Polar SolventsPolar Solvents: : 30 (dissociating power is well) - 30 (dissociating power is well) -

HH22O (O (=78,5), =78,5), FMAFMA ( (=109,5), N-=109,5), N-MFMAMFMA ( (=182,4), =182,4), DDММFFА (А (=36,7), =36,7),

ДМСО (ДМСО (=48,9)=48,9)

low-polarity Solvents :low-polarity Solvents : =10 =10 30 (dissociating 30 (dissociating power is low) - power is low) - CC22HH55OH (OH (=24,3), C=24,3), C33HH77OH (OH (=20,1), C=20,1), C44HH99OH OH

((=17,1), acetone (=17,1), acetone (=20,7)=20,7) Non-Polar Solvents:Non-Polar Solvents: 10 (don’t have dissociating 10 (don’t have dissociating

power) - power) - CC44HH44ClCl22 ( (=10,4), acetic acid (=10,4), acetic acid (=6,2), =6,2), CHClCHCl33 ( (=4,7), =4,7),

benzene (benzene (=2,3), CCl=2,3), CCl44 ( (=2,2).=2,2).

Solvent classification for acid-base propertiesSolvent classification for acid-base properties::

progenic (H2SO4, HCOOH)

protic: protophilic (liquid ammonia, pyridine)

amphiprotic (H2O, C2H5OH)

aprotic (benzene, chloroform, etc.)

Solvent classification for iSolvent classification for ionising onising propertiesproperties

Ionizing solvent - An electron-pair donor (H2O, pyridine, DMFA)

Non-ionizing solvent doesn’t have An electron-pair (CC44HH44ClCl22, , CHClCHCl33, benzene, CCl, benzene, CCl44)

For calculations of solution’s pH in For calculations of solution’s pH in nonaqueous solvent must knownonaqueous solvent must know::

Value of AutoprotolysisValue of Autoprotolysis constant of solventconstant of solvent

Value of Acid (Base)Value of Acid (Base) constant in this solventconstant in this solvent

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