# Do chemists in the United States use lb-mol/oz-mol?

A mole is the number of atoms needed to equal the substance’s molecular weight. So 1.01lb of hydrogen is one lb-mol.

In all of my chemistry classes we have used gram moles without any indication that there ever could be anything different. But every now and then in my engineering classes they give us lb-mol.

So my question is: if the coroner on CSI says something about milli-mols, should I be thinking 10^-3 lb-mol, or 10^-3 g-mol.

We use metric just like you.

You should be thinking moles. A mole is the amount of a substance that has 6.02*10[sup]23[/sup] particles (typically molecules) in it. This is true in any measurement system.

The relationship with molecular weights is that the weight of one mole of particles, in grams, is equal to the weight of a single particle, in atomic mass units. So 1 mole of hydrogen molecules weighs 2 grams, and a single hydrogen molecule weighs 2 AMU. In other words, the number of particles in a mole (Avagadro’s number) is the conversion factor from AMU to grams.

As i learned it, a mole is defined as the number of atoms in 12 grams of carbon-12. It may be that he has expected that Americans would define 1 mole as the number of atoms in 12 ounces of carbon-12. This is not the first time I have heard of a mole refered to as a g-mole.

we use slugs

Christopher is correct, Chronos. A mole has never been defined as equal to Avogadro’s number (6.022 x 10[sup]23[/sup]) of particles.

Even today, the SI system defines a mole as:

The SI definition for a mole is that of a “g-mol.” A lb-mol would be defined as the amount of substance of a system which contains as many elementary entities as there are atoms in 12 pounds of carbon 12.

The only time that I have see the abominable units of lb-mol and oz-mol are in environmental chemistry textbooks written by old-timer environmental/sanitary engineers. Thankfully, its use appears to be dying out.

That’s basically what I was wondering. Now I’m wondering where the other half of all my hydrogens went :smack: .

Wikipedia (and my non-linkable texts) supports the idea that people do use [imperial]-mols. I expected that since everything else in the US is in imperial units that mols would be [imperial]-mols.

Robby: it’s good to hear that I won’t have to use them.

Your definition is equivalent to Chronos’s, though, as Avogadro’s number is equivalent to “the number of carbon-12 atoms in 12 grams of carbon-12.”

Not quite equivalent since the kilogram is losing weight

A good rule of thumb is that any industry in the US that has a practical need for SI prefixes uses metric (with the glaring exception of the stubbornly conservative construction industry).

So chemistry, yes; transportation; no (1000 m/km is nice, but irrelevant for travel, so miles remain).