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1) That looks right. 2) Step 1: Moles=Mass/Mr, so it's 144/72= 2mol. Step 2: Stoichiometry means the ratio of oxygen to pentane is 1:8 so moles of oxygen is moles of pentane times 8. 2*8=16mol of oxygen. Step 3: 16= 9.6*10^24. 3) The ratio of oxygen to carbon in CO2 is 1:2. so it's 192/3 = 64.
any member of a group of compounds with structures that have two silicate tetrahedrons (a central silicon atom surrounded by four oxygen atoms at the corners of a tetrahedron) linked together. Because one oxygen atom is shared by two tetrahedrons, the chemical formula contains Si 2O 7, as in melilite or hemimorphite.