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Lecture three Volumetric Analysis

Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

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Page 1: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

Lecture three Volumetric Analysis

Page 2: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 3: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

: Types of Titrimetric Methods

Complexometric titrations

A standard solution: is a reagent of exactly known concentration that is used in a titrimetric analysis

Titration: is a process in which a standard reagent is added to a solution of an analyte until the reaction between the analyte and reagent is judged to be complete.

Page 4: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

Back-titration : is a process in which the excess of a standard solution used to consume an analyte is determined by titration with a second standard solution. Back-titrations are often required when the rate of reaction between the analyte and reagent is slow or when the standard solution lacks stability.

Page 5: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

End point: is the point in a titration when a physical change occurs that is associated with the condition of chemical equivalence. In volumetric methods, the titration error Et is given by Et = Vep - Veq where (Vep) is the actual volume of reagent required to reach the end point and (Veq) is the theoretical volume to reach the equivalence point.

Indicators: are organic materials (almost weak acid or weak base) are often added to the analyte solution to produce an observable physical change (the end point) at or near the equivalence point.

Page 6: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 7: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 8: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

Ph.ph Indicator for acid – base titration

Page 9: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 10: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

A secondary standard: is a compound whose purity has been established by chemical analysis and that serves as the reference material for a titrimetric method of analysis.

A primary standard: is an ultrapure compound that serves as the reference material for a titrimetric method of analysis.

Page 11: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 12: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 13: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

Titer or Chemical Factor:

A + T _______ Product Titer of A = Molarity of T(mmole / ml) x mole ratio(mmole A / mmole T) x M.WT (A)

Page 14: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 15: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 16: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 17: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 18: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 19: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 20: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 21: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 22: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 23: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 24: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 25: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 26: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 27: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 28: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

Example: Generate the hypothetical titration curve and calculate the pH for the titration 0.1M from HCl with 25ml (0.1M) Ammonia?

a) Before addition HCl (V=0 ml)

Kb = 1.75 x 10 -5

Page 29: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

b) Before the equivalent point ( V = 10ml from HCl)

After addition 10ml from HCl , ammonium chloride NH4Cl will formed and excess from ammonia. Which is buffer solution and in this case we can calculate pOH and then pH as.

= [NH4Cl] salt

= Residual of Ammonia

Page 30: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

c) At the equivalent point: Which is mean addition equal volume (25m) from HCl to 25ml(0.1M) Ammonia to form salt of weak base only NH4Cl and we can calculate the pH to the salt of weak base as.

d) Post equivalent point: This case mean addition from HCl, like addition 26ml. We can calculate the pH from the excess of HCl as.

Page 31: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 32: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

Weak acid versus Weak base: In this type of titration the change in the pH at the equivalent point is very small, no suitable simple indicator is used to determine the eq.point.

NH4OH + HOAC ↔ NH4OAC + H2O Example: Titration 0.1M NH4OH with 50ml(0.1M) CH3COOH. a) Before the addition of NH4OH.

b) After addition 10ml NH4OH. Buffer solution from HOAC/ OAC- will formed.

Page 33: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

c) At the equivalent point, addition 50ml from NH4OH, and Ammonium acetate will formed, salt of both weak acid and weak base.

Page 34: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

d) Post equivalent point , after addition 60ml from ammonia. That is mean another buffer solution will form that produce all HOAC were convert to Ammonium acetate , and the excess of ammonia.

Page 35: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

1

1-

2-

3-

Ka2= Ka1=

Page 36: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

4-

(A) Point (B) point

(C) point= first eq.point (D) point

(E) point= second eq.point

Page 37: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

(A) point: before any addition(at 0.0ml volume from HCl) In this case we have only sodium carbonate and the pH is determined from the hydrolysis of Bronsted base as:

1 a

pOH= 2.34 pH = 14 – pOH = 11.7

(B) point: After addition 25ml HCl: In this case a part from carbonate is converted to and buffer region is established.

= (50-25) x0.1 / VT(75ml)= 2.5mmole / 75ml

Page 38: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

= 25 x0.1 / Vt(75ml) = 2.5mmole/75ml = 4.69 x10-11 pH= 10.32 (C) point: first eq.point( addition 50ml HCl): In this case all were converted to and we calculate the pH for mono-protanted salt from Ka1 and Ka2 as. = (50-50) x0.1/ Vt(100ml) = 0.0mmole/100ml = 50x0.1 / Vt(100ml) = 5mmole / 100ml

pH= 8.3

(D) point: After first eq.point (addition 75ml HCl):

Page 39: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

= 50x0.1 /Vt(125ml) = 5mmole / 125ml will formed = (50 – 25 ) x0.1 M / 125ml = 2.5mmole / 125ml residual concentration = 25 x0.1 / Vt(125ml) = 2.5 mmole / 125ml will formed from

a

pH = 6.37

(E) point: second eq.point( addition 100ml HCl): At the second equivalence point (E) the pH is determined by the extent of

dissociation of carbonic acid, the principal species present, and [H+] is calculated from Equation.

Ka1=

Page 40: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

= 50 x 0.1 / Vt(150ml)= 0.0333

1.177 pH= 3.92

Important notes: 1-

2-

3- 4-

5-

Page 41: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

1-

For example of diprotic acids are H2A, H3PO4, And

2-

3-

4- Two indicators must be used to detect the equivalent points in the titration od diprotic acid H2A with sodium hydroxide NaOH.

Page 42: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

5-

1 eq.point

2 eq.point

Page 43: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

Example:

Page 44: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

Solution

(Addition 0.0ml from NaOH)

Page 45: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

(After addition 50ml from NaOH), in this case the solution contains both HA- and H2A which is buffer solution: [HA-] = 50 x0.1 / Vt(150ml)= 0.033Molar [H2A] = (100 – 50) x0.1 / Vt(150ml) = 0.033M [HA-] = [ H2A] pH = pKa1 + log HA- / H2A pH = pKa1= 2.82

In this case all H2A was converted to HA-, which is mono-protic salt and we can calculate the pH from the above law or .

(After addition 100ml from NaOH)

Page 46: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

After addition 150ml from NaOH), in this case 100ml from NaOH will convert all H2A to HA-, and the other 50ml will convert an equal amount from HA- to A-2. Which is buffer solution contains A-2 / HA- and we can calculate the pH as: [HA-] formed = 100ml x 0.1 / Vt( 250ml) = 0.04M [HA-] remaining or residual = (100 – 50) x0.1 / Vt(250ml) = 0.02M [A-2] formed = 50 x0.1 / Vt(250ml) = 0.02M [HA-] = [A-2] pH = pKa2 + log [A-2] / [HA-] = 5.70

Page 47: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

After addition : 0.0ml , 5ml, 24.9ml, 25ml(first eq.point), 25.01ml , 25.5ml , 49.9ml and 50ml(second eq.point) from NaOH.

Page 48: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 49: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

So when: 1-

2- If and [HA-] / Ka1 ≤ 1

Page 50: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

3- If and [HA-] /

Ka2× [HA- ] ≤ Kw Kw is not negligible Ka1 >> 1 1 is negligible

Page 51: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 52: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations
Page 53: Lecture three Volumetric Analysiscopharmacy.nahrainuniv.edu.iq/.../02/...2010-Volumetric-Analysis.pdf · Volumetric Analysis . Types of : Titrimetric Methods. Complexometric titrations

Volumetric apparatus