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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.
The mass of an element is equal to the number of moles of that element. For example, hydrogen has a mass of one gram, which is equal to one mole of hydrogen, while, oxygen has a mass of sixteen grams, which is equal to one mole of oxygen. This is then used to determine the chemical formula of a substance. First, determine the masses of the atoms of the elements in the substance, and then convert it to moles. The ratio of the moles of each atom in the substance is the mole ratio, which is then used to determine the chemical formula.