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The difference between mass and weight is pretty straightforward so then how can we WEIGH a substance then ask how many Daltons (atomic MASS units) are in that substance without a conversion in there for gravity? Or vice versa. For example:

Question: How many moles of potassium are in 156.4 grams?

Answer: Atomic mass of potassium, K = 39.1 Amount of potassium is 156.4g, sample = 156.4/39.1 = 4.00mol. There are 4 moles of potassium in 156.4 grams of potassium.

Nowhere is there any sort of conversion for earth's gravity even though we are weighing out a substance that is obviously high enough to deserve one. I am assuming the amu of all elements is the same in the universe.

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  • $\begingroup$ To get this question re-opened, as a minimum, use the terms 'mass' and 'weight' according to their standard scientific meaning (rather than their common meaning). $\endgroup$ – Qmechanic Sep 25 '14 at 12:41
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Your figure of 156.4 grams is a mass, not a weight. If you used a set of masses and a pan balance, then you are comparing it with known masses in a nearly uniform gravitational field. Since gravity is the same on both, it does not need to be known.

If you used a digital balance, then that device already converted from the forces it detected to a mass. It probably uses a fixed value for earth's gravity to do that.

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