One thousand kilograms of a 32 wt sodium carbonate (Na2CO3) solution in water ar
ID: 959669 • Letter: O
Question
One thousand kilograms of a 32 wt sodium carbonate (Na2CO3) solution in water are cooled slowly to 20 OC. The crystals formed are the decahydrate, Na2Co3.10H20. The solubility ofthe decahydrate at 20 oC is 21.5 parts of Na2co3 (calculated as the anhydrous salt per 100 parts of water. Na 23, C 12 O 16, H 1 Use simple atomic weights Calculate: (a) The mass fractions of anhydrous Na2Co3 and water in the decahydrate crystals (Na2CO3.10H20) (b) The mass (kg) of the decahydrate crystals produced. Use the following nomenclature: s-kg of saturated solution at 20 oc, and D kg of decahydrate crystals at 20 oC. (c) The percentage of the original anhydrous Na2CO3 recovered in the crystals. (d) Complete the following table. Decahydrate Saturated Feed Stream Decahydrate Saturated Solution Solution Crystals Na2CO3 (kg) H20 (kg) Total (kg)Explanation / Answer
Basis : 1000 kg of Sodium Carbonate solution
Sodium Carbonate in the feed = 32%, hence sodium Carbonate in the feed= 1000*32/100= 320 kgs
Amount of water in the feed= 1000-320 = 680 kgs
Solubility at 20 deg.c= 21.5 parts/ 100 parts of water
Weight percent of Na2CO3 in the anhydrous sample= 100*21.5/121.5=17.69%
Let x= amount of decahydrate crystals formed
% of Na2CO3 in the crystals= 100*x*106/(106+180)=37.06x
Writing material balance of Na2CO3
Na2CO3 in the feed = Na2CO3 inthe crystals+ Na2CO3 inthe solution
320= 0.3706x+(1000-x)*0.1769
143.1= 0.1937x
Therefore x= 143.1/0.1937 =738 dehydrate crystals
Water in the decahydrate= 738*(1-0.3706)
Na2CO3 in the crystals= 0.3706*738=273.5 kgs
Na2CO3 originally present = 320
% crystalization= 100*273.5/320=85.46%
Kgs
Feed
Decahydrate
Saturated solution
Decahydrate+satruated solution
Na2CO3
320
273.5
46.5
46.5+273.5=320
Water
680
464.5
215.5
680
Total
1000
738
262
1000
Kgs
Feed
Decahydrate
Saturated solution
Decahydrate+satruated solution
Na2CO3
320
273.5
46.5
46.5+273.5=320
Water
680
464.5
215.5
680
Total
1000
738
262
1000
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