Anachem-Lab-M7 Activity 2-LAB PDF

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DETERMINATION OF SULFUR AS BARIUM SULFATEEXPERIMENTAL DATAA. CONSTANT WT. OF CRUCIBLE & COVER1 ST weighing 25 g 2 nd weighing 25 g 3 rd weighing 25 gConstant wt. of crucible & cover 25 g (average of 3 weighings)B. Weight of Na 2 SO 4 Sample 0C. Total Vol. of Precipitant (BaCl 2 ) used 6 mLD....

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DETERMINATION OF SULFUR AS BARIUM SULFATE EXPERIMENTAL DATA A. CONSTANT WT. OF CRUCIBLE & COVER 1ST weighing 25.4048 g 2nd weighing 25.4050 g 3rd weighing 25.4052 g Constant wt. of crucible & cover

25.4050 g

B. Weight of Na2SO4 Sample

0.4000g

C. Total Vol. of Precipitant (BaCl2) used

6.2 mL

(average of 3 weighings)

D. CONSTANT WT. OF CRUCIBLE & COVER WITH PRECIPITATE 1ST weighing 26.0250 g 2nd weighing 26.0255 g 3rd weighing 26.0258 g Constant wt. of crucible & cover with precipitate E. Weight of Precipitate (BaSO4)

26.0254 g (average of 3 weighings)

0.6204 (ave. D – ave. A)

F. Determination of % S % S (Experimental Value) 21.31 % % S (Theoretical Value ) 22.58 % % Error 5.624 % Reaction Involved between Na2SO4

&

BaCl2

Double displacement reaction occur and the reaction is as follows: Na2SO4 (aq) + Na2SO4 → BaSO4 (s) + 2 NaCl (aq) CALCULATIONS: MM of S___ % S = wt. of BaSO4 x MM of BaSO4 x 100 Wt. of sample

%S =

1 mol (32.07 g/mol S) 0.6204 g x 1 mol (233.4 g/mol BaSO4 ) 0.4000 g

x 100

= 21.31 % (Experimental Value) % Error = (% S Theoretical Value - %S Experimental Value) %Theoretical Value

x 100

% Error = (22.58 % - 21.31%) x 100 22.58% = 5.624 %

QUESTIONS: 1. What are the conditions for the precipitation of sulphur from the sample solution? Sulfur is determined by precipitating the hot acidic sample solution with BaCl 2 solution. The precipitate that will form is BaSO4. The precipitate can be collected through a process of filtration and it can be gravimetrically analysed by drying, igniting to ash, and weighing to determine the quantity of sulphate in the given sample solution. The precipitate is filtered with ashless filter paper and rinsed with hot water, distilled water, then ignited after the paper has been gently charred and the carbon has been wiped off. To prevent the precipitate from being reduced to sulphide, oxidizing conditions must be present during the charring, burning, and igniting processes.

2. Of what use is the acid in the isolation of the sought-for constituent? The presence of acid promotes the formation of bigger crystals of BaSO4. Also, atmospheric CO2 can dissolve in the solution and create carbonate ions, which are then precipitated by barium ions, although this is highly inhibited at low pH.

3. Why is digestion not necessary in this determination? Digestion is not necessary in the determination of Sulfur as Barium Sulfate because during the beginning of the experiment, both the precipitating agent and the sample solution were already heated....