3.90 g of a mixture of Al and Al2O3, when reacted with a solution of NaOH produced 840 mL of gas at NTP. Find % of Al2O3 in mixture (as nearest integer).
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Solution
The reactions that are involved are: 2Al(s)+2NaOH+6H2O→2Na++2[Al(OH)4]−+3H2(g) 2 moles 3 moles gas Al2O3+2NaOH+3H2O→2Na++2[Al(OH)4]− So, mass of Al in sample =2×27×8403×22400=0.675 g So, % of Al=0.675×1003.9=17.3 and % of Al2O3 in mixture =83