[spirochete]

Here's a problem and my answer.  Would anybody mind checking it?  Thanks in advance.

3 Compounds have the following mass ratios of Oxygen:Nitrogen

1.143 g oxygen:1 g Nitrogen
2.286 g oxygen: 1 g Nitrogen
2.857 g oxygen: 1 g Nitrogen

Show that these compounds obey the law of multiple proportions.  To do this I compared the three compounds to each other.  My answer is:

1.143 g O:2.286 g N = 0.5:1 = 1:2
1.143:2.857 = 0.4:1 = 2:5
2.286:2.857 = 0.8:1 = 4:5

This whole process seems so sketchy and I was hoping somebody could check this.

[Borek]

Shouldn't you compare masses of oxygen between them? (Or nitrogen, but it should be ratio of masses of the same element, not list of ratios of both elements in all compounds).

[spirochete]

Sorry there was a typo there.  The last part should read:

1.143 g O:2.286 g O = 0.5:1 = 1:2
1.143:2.857 = 0.4:1 = 2:5
2.286:2.857 = 0.8:1 = 4:5

[Borek]

Looks OK to me. Three compounds are NO, NO₂ and N₂O₅, so oxygen ratios are correct.

[spirochete]

One thing that still confuses me:  How do you use those 3 ratios to determine the formulas for the compounds?  Without having any knowledge of the mole, that is.

[Borek]

One thing that still confuses me:  How do you use those 3 ratios to determine the formulas for the compounds?

You don't. Law of the multiple proportions was one of the first things that were discovered about the way elements react - nobody knew at the time what it really means. It was just an observation that was later explained using atoms and valencies.