l e c t u r e 1
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L e c t u r e 1. Analytical chemistry. Chemical analysis . Calculation of рН. Associate prof . L.V. Vronska Associate prof . M.M. Mykhalkiv. Outline. - PowerPoint PPT PresentationTRANSCRIPT
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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