Can anyone tell me how to do calculations based on the Law of Multiple Proportions. I also do not know the significance of the ratio acquired at the end of the calculations.

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ncchemist | eNotes Employee

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The law of multiple proportions states that for a given chemical compound made up of multiple elements, the elements will combine with fixed ratios of whole numbers.  This is denoted in a compound's chemical formula, where the elements are listed and the subscripts denote the ratios of the elements to each other.  We can use this in chemical calculations.  For example, if we are asked to find out how much oxygen is required to combine with 100 grams of carbon to make carbon dioxide, we only have to look at the chemical formula for carbon dioxide to get our answer.  The formula for carbon dioxide is CO2, so we know that for every atom of carbon we need two atoms of oxygen.  Since comparing moles is mathematically easier than comparing individual numbers of atoms, we know that 100 g of carbon is 100/12=8.33 moles of carbon.  Since the ratio is 2:1, we need 8.33*2=16.66 moles of oxygen.  This equates to 16.66*16=266 grams of oxygen.

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