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2014-09-07T12:44:02+03:00
Nr moli = masa Na2S/masa molara Na2S 
masa molara = 23*2+32=78 g/mol
nr moli = 15.6/78 = 0,2 moli Na2S
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2014-09-07T12:45:09+03:00
N=m/masa molara 
masa molara laNa2S=23X2+32=78 g
n=15.6/78=0.2 moli
2 3 2