mg to or from millimoles

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mg to or from millimoles

Postby Guest » Sun Apr 10, 2005 1:06 pm

Where can I find the resources to convert anything between mg and millimoles; for example sodium chloride?
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Postby Guest » Sun Apr 10, 2005 5:54 pm

You need to know the chemical formula of the material, and you need a periodic table to look up the atomic mass of each element, and add them up to determine the molecular weight.

A mole of a substance is an amount in which the weight in grams of the substance is equal to its molecular weight, and therefore the number of molecules is equal to Avogadro's number.

There may be slight confusion over atoms and molecules, since a mole of either could be defined. You can define a mole of NaCl, but if you dissolve it in water, it will dissociate and you'll have 1 mol of sodium ions and 1 mol of chlorine ions.

For your specific example, atomic mass of sodium is 22.99 amu, chlorine 35.45amu. so 1 mol NaCl = 58.44 g.

The numbers are non-integer for two reasons:
*Many elements have two or more isotopes with different atomic masses. The number in the periodic table is an average based on the ratio that occurs in nature. Atomic masses for each isotope are also available.
*The binding energy in the nucleus makes the total mass slightly different than expected from number of neutron and protons (very small)
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