Mass Ratios and Mutiple Proportions

[Soaring Crane]

Main Question or Discussion Point

The "Law of Multiple proportions" states that if two elements combine in different ways to form different substances, the mass ratios are small, whole number multiples of each other. Suppose that you have 66g of carbon combined with oxygen in carbon dioxide (CO2), how many grams of oxygen would you expect to be involved?

Well, I looked at the atomic mass ratios of oxygen to carbon, or 32.00 to 12.01. By dividing this I get 8/3, so I multiply (8/3)*66 g for 176 g of O? Is this correct?

Oh, exactly how would I express this in significant figures (or the proper form)? 1.8*10^2 g (if this is correct)?

Thanks.

 

[bomba923]

"66 grams" implies two significant figures. The ratio of carbon to oxygen in pure carbon dioxide is 1 atom carbon : 2 atoms oxygen . So,

$$\left( {\frac{{66g\;{\text{C}}}}{1}} \right)\left( {\frac{{1{\text{ mole C}}}}{{12g\;{\text{C}}}}} \right)\left( {\frac{{{\text{2}}\;{\text{moles O}}}}{{1{\text{ mole C}}}}} \right)\left( {\frac{{{\text{16}}g\;{\text{O}}}}{{1{\text{ mole O}}}}} \right) = 176g\;{\text{O}} \Rightarrow \boxed{{\text{180g}}\;{\text{O}}}$$

Just 180 g is fine I think