Law of Definite Proportions Example 1

by Jules Bruno
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So in this example, questions as to unknown compounds are examined. Compound A contains 2 g of hydrogen and 32 g of oxygen. Compound B contains 15 g hydrogen and 120 g off oxygen. New compounds A and B represent the same compound. All right, so they're having us examined two different samples. Remember, if we're following the law of definite proportions, if they represent the same compound, then they should give us the same mass ratio. So we'd say here that for them to be the same mass ratio A of compound A must equal the mass ratio off compound beat. All right, so remember we place the larger mass on top, and here we have 32 g of oxygen versus 2 g of hydrogen compound A. So that would be 32 g. Oh, divided by 2 g h. So when we do that, that's gonna give us 16 as our mass ratio. And then for Compound B, we put the larger mass again on top. So 120 g oxygen divided by g hydrogen. When we divide those two, that gives me a mass ratio of eight. Now, again these values were really saying that I have 16 g off oxygen toe, 1 g of hydrogen, and this is really saying that I have 8 g of oxygen per 1 g of hydrogen. Now we see that their mass ratios are definitely not the same. And since their mass ratios are not equal to one another, they cannot represent the same compound. So here we would say no. Compounds A and B do not represent the same compound because their mass ratios are not equal to one another. So remember, this is how we utilize the law different proportions to determine if different samples represent the same compound.