1. If 24 grams of carbon combine with 64 grams of oxygen to form carbon dioxide with no carbon or oxygen left over, how much carbon dioxide is formed?
Since the total mass of substances used up in the reaction must be equal to the amount of product formed, according to the conservation of mass law, there must be 64 g + 24 g = 88 g of carbon dioxide present after the reaction.
2. An iron nail rusts if exposed to oxygen in the air for a long time. If a 11.2-gram nail reacts to form 14.4 grams of iron(II) oxide (FeO), how much oxygen was used out of the air?
From the law of conservation of mass, we know that the amount of the two substances used in the reaction must add up to the amount of substance present after the reaction is complete. This means that the amount of oxygen used would be:
14.4 g - 11.2 g = 3.2 g.
3. What is the proper combining ratio (by mass) for carbon to oxygen in the reaction that forms carbon dioxide (CO2)?
From the data given in question 1, since 64 grams of oxygen reacts with 24 grams of carbon, the ratio must be 64 to 24, which is 2.7 parts oxygen to 1 part carbon.
We can also find this ratio from the atomic masses of these elements. According to the formula for carbon dioxide (CO2), it requires two atoms of oxygen (2 x 16 u) for each atom of carbon (12 u). The ratio is then 32 u to 12 u, or 2.7 parts oxygen to 1 part carbon, the same as we found using the actual combining masses of the substances in the reaction.
4. What would be the ratio of carbon to oxygen if carbon monoxide (CO) were formed instead of carbon dioxide, the usual product of this reaction?
In this case we must use the second method described above. Only one atom of oxygen combines with each atom of carbon, so the ratio must be 16 u to 12 u, or 1.3 parts oxygen to 1 part carbon.
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