Oc 1. elemental B.Pharm Organic Chemistry by amit z chaudhari

ELEMENTS

Amit Z Chaudhari

Quantitative analysis of elements

3Organic Chemistry_ AZC_2016_ Elemental

Estimation of C and H[sum12]

Principle:- Organic substance is burnt in excess of oxygen gas. C and H are

oxidized to CO2 and water.

CxHy + O2 xCO2 + y/2 H2O

Figure:

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Apparatus :- Oxygen supply: it oxidizes and flows the generated water and CO2

toward adsorbent assembly.- Furnace: heating purpose- Combustion Tube:

- is a hard round glass tube.- Substance, CuO gauze and copper oxide (CuO) are placed

in it as in figure.- CuO gauze (placed at front) prevents the backward diffusion of

the products.- Substance is place in porcelain boat.- CuO layer and CuO gauze(placed in toward the end) prevents any

vapours of substance leaving the tube unoxidized.


Organic Chemistry_ AZC_2016_ Elemental

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Absorption apparatus :- A U-tube packed with Conc. H2SO4 to absorb water.- A set of bulbs containing conc. KOH, to absorb CO2.- A Guard-tube filled with anhydrous CaCl2, to prevent entry of atm

moisture. Procedure:- Combustion tube heated in furnace to remove moisture and CO2

already present.- Note down the weigh U-tube and bulbs filled by absorbents- Then assamble all parts.- Heat- Pass O2 - After combustion of all sub. Pass strong flow of O2 to remove all

CO2 and water and finally detaches all assembly.



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Calculation:

- % of C = 12y/44 * 100/w where,

y = increase wt of potash bulb (wt of CO2)w = wt of substance

- % of H = 2x/18 * 100/w where,

x = increase wt of U-tube (wt of H2O)w = wt of substance





Estimation of N[win14, win12, sum14, sum15]

- Two methods and



Dumas method[win 14, win13]

Principle:- Nitrogenous compound when heated with copper oxide in atm of

CO2 yield free nitrogen.

- CxHyNz + CuO xCO2 + y/2H2O + z/2 N2



Dumas methodFigure:



Dumas method

Apparatus:- CO2 generator: generated by chemical methods (magnesite

(MgCO3) or a Kipp’s apparatus containing marble and dil. HCl.)- Gas is passed to combustion tube.- Combustion Tube: Substance, CuO gauze and coarse copper

oxide (CuO) and copper spirals are placed in it as in figure.- CuO gauze (placed at front) prevents the backward diffusion of

the products of combustion.- Substance is mixed with excess fine CuO.- Coarse CuO layer generates N2 gas by oxidizing the sample.- Reduced copper spiral (placed in toward the end) reduces any

oxides of N formed during combustion, to N2.



Dumas method

Apparatus:- Schiff’s Nitrometer: N2 is estimated by passing into this apparatus

where CO2 and other gas byproducts are absorbed by caustic potash soln and the N2 collects in the upper part of the graduated tube.



Dumas method

Procedure:- The assembly is fitted up as shown in fig. - Keep the tap of nitrometer is left open.- CO2 is passed to replace air. When the air babble rising through

the potash soln disappear, it shows that only CO2 is coming and all air is removed from assembly.

- After leveling the potash layer in graduated tube, the tap of nitrometer is closed.

- Heat the combustion tube. - Formed N2 is collected automatically in nitrometer.- When the combustion is complete, a strong current of CO2 is

passed to sweep the last traces of N2 from it.- The volume of N2 collected is noted.



Dumas method

Calculation:



Kjeldahl’s Method[win15, win11] [sum13]

Principle:- Nitrogenous compound when heated with H2SO4, ammonium

sulphate is formed.- Ammonium sulphate is than treated with excess alkali and the

librated ammonia gas absorbed in excess of standard acid.- Back titration of acid gives the amount of ammonia (and hence of

N).



Kjeldahl’s MethodFigure:



Kjeldahl’s MethodApparatus:- Kjeldahl flask- Kjeldahl trap: serves to retain any alkali comes up on vigorous

boiling.- Water condenserProcedure:- Take substance , conc. H2SO4 in Kjeldahl flask- Add little amt of K2SO4 (raises the b.p.) and CuSO4 (as catalyst).- Flask is loosely Stoppard and heated.- After completion of heating, cool it and transferred in to round

bottomed flask.- Add NaOH solution.



Kjeldahl’s Method- Assemble the apparatus as in fig.- Upon heating of RBF, the liberated ammonia distilled into conical

flask containing acid soln.- When no more NH3 comes from reaction. conical flask is

displaced and excess of acid is back titrated.



Kjeldahl’s MethodCalculation:



Estimation of X

Carious method[win12]

Principle:- When substance containing X is heated with fuming nitric acid in

presence of silver nitrate, reaction will form silver halide from which amount of X is calculated.

Figure:



Carious methodApparatus:- Carious tube: a hard glass bomb tube- Narrow weighing tube: for organic compound- Iron jacket present in furnaceProcedure:- An accurately weighed amount of org. compound is taken in a

narrow weighing tube.- Carious tube is loaded with fuming nitric acid, small amt of

AgNO3 crystals and tube containing org. compound as shown in figure.

- Upper end of carious tube is sealed.- It is enclosed in iron tube and strongly heated in a furnace. - Org. compound ionized and the halide combines with silver

nitrate to give a ppt of silver halide.



Carious method- After 6 hr, the tube is cooled and then broken.- Ppt of silver halide are washed, dried and weighed.

Calculation:

End of topic

Reference:Organic Chemistry – Bahl &

BahlOrganic Chemistry – P.L.

Sony

IMP Q. For 1st MID Sem Exam

(1)quantitative estimation of nitrogen (5)(2)Dumas method (5)(3) kjeldahl’s method (5)

Oc 1. elemental B.Pharm Organic Chemistry by amit z chaudhari

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