Prior to 1961, the atomic mass unit (amu) was defined as 1/16 the...

Question

Prior to 1961, the atomic mass unit (amu) was defined as 1/16 the mass of the atomic weight of oxygen; that is, the atomic weight of oxygen was defined as exactly 16. What was the mass of a 12C atom prior to 1961 if the atomic weight of oxygen on today’s scale is 15.9994?

Accepted Answer

Hi everyone. This problem reads. Initially, the atomic mass unit was defined as 1/16 of the atomic mass of oxygen. Atomic mass of oxygen equals 16 atomic mass units, determine the mass of a nitrogen 14. Ad using the old definition, if the current atomic mass of oxygen is 15.994 atomic mass units. The current atomic mass of nitrogen 14 is 14.3 atomic mass units. Okay, so our goal with this problem is to determine the mass of a nitrogen 14 atom. Using the old definition. So we have two definitions here. The old definition and the current definition. So let's go ahead and define these and write them out based off of what's told to us in the problem. So the old definition tells us that the atomic mass of oxygen is equal to atomic mass units and the atomic mass of nitrogen 14 is equal to X. Okay, so we don't know what it is. Okay, so that's what we need to solve for. On the other hand, our current definition is the following. Okay, so the current definition, the atomic mass Of oxygen is equal to 15.994 atomic mass units. And the atomic mass of nitrogen 14 is equal to 14.3 atomic mass units. So, our goal here Is to determine the mass of nitrogen 14 using the old definition, which is we defined here as X. So the way that we'll be able to do this is by setting the old definition equal to the current definition and then solving for X. So let's go ahead and do that. So we're going to set the current definition equal to the old definition. So our current definition, we're going to take the atomic mass of nitrogen over the atomic mass of oxygen. So we have 14.003 atomic mass units over 15.994 atomic mass units. This is the current definition equal to the old definition. So we're going to do the atomic mass of nitrogen over the massive oxygen. Alright, so we get X over 16 Atomic mass units. Okay, so our goal here, like we said, is to solve for X. So we're gonna go ahead and cross multiply and divide and once we do that and we isolate X. We get X is equal to 14.008 atomic mass units. And this is going to be our final answer. Alright, So this is the mass of nitrogen 14 of a nitrogen 14 atom. Using the old definition. Okay, so that is it for this problem. I hope this was helpful

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