sulphur & phosphorous : Estimation

source : schools.agla sem.com

## Estimation of Sulphur By Carius Method-

In this method known amount of organic compd is heated with f HNO3 in a carius tube then sulphur is oxidised into H2SO4. This is precipitated as BaSO4 by adding BaCl2 Solution. Ppts. of BaSO4 are filtered, washed, dried & weighed, By knowing the wt. of organic compd & BaSO4, we can calculate % of S.

H2SO4 +BaCl2  —–> BaSO4  + 2HCl

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Calculation

Wt. of org. compd = w gm.

Wt. of BaSO4 = y gm

Mol. wt. of BaSO4 = 137+32+16×4=233

233 gm BaSO4 contains  S = 32 gm

x gm BaSO4 contains  S    =(32 y) /233

w gm of o.c. gives S          = (32 x y) /233

100 gm  of o.c. gives S  =      (32 x   y  x 100 ) / ( 233 w)

% of  S= (32 x   wt.of BaSO4 x 100 ) / ( 233  x wt. of o.c.)

Q —Quantitative analysis of 0.1254 gm. of an org. compd  gave 0.1292 gm BaSO4 in carius method . calculate % of S ?.

Solution :  weight of BaSO4 =0.1292 gm.

wt. of o.c. =0.1254 gm

Percentage  of  S= (32 x   wt.of BaSO4 x 100 ) / ( 233  x wt. of o.c.)

% of  S= (32 x  0.1292 x 100 ) / ( 233  x 0.1254)

## % of S= 14.15 %

Q — 0.32 gm of an org. compd when heated with conc. HNO3 & BaCl2 gave 0.932 gm. of BaSO4. Calculate  % of S ?

Solution:    wt. of o.c. 0.32 gm.

percentage of  S= (32 x   wt.of BaSO4 x 100 ) / ( 233  x wt. of o.c.)

= (32 x  0.932  x 100 ) / ( 233  x  0.32 )

## % of S = 40%

% of Phosphorous

Mg2P2O7 = Magnesium  pyrro Phosphate

% of P = 0.c + f HNO3 —-> Phosphorous is oxidised to H3PO4 ——> in presence of ammonical MgCl2 , ppts of magnesium ammonium phosphate (MgNH4PO4) ____> MgNH4PO4 on red hot gives Mg2P2 O7

% of P = (62 x wt. of Mg2P2O7 x 100 ) /( 222 x wt. of o.c.)