General Chemistry/Measurement

Moles
The mole is a unit used to measure the number of particles in a substance (where particles can be atoms, molecules, electrons, ions etc.). One mole of substance contains 6.02205 &times; 1023 particles. This rather large quantity is a constant called Avogadro's Number, which is abbreviated as NA. It simply refers to the number of particles in one mole.

$$N_A = 6.02214 \times 10^{23}\hbox{ mol}^{-1}$$

For example, one mole of helium gas contains 6.022&times;1023 atoms; 2 moles of oxygen gas contains 1.204&times;1024 molecules.

Moles and Mass
It would be useful to be able to convert between the number of moles and the mass of a substance. The molar mass is the mass of one mole of a substance, measured in grams per mole or $$\hbox{g}\cdot\hbox{mol}^{-1}$$. Not by coincidence, the molar mass is the same as the atomic weight of a substance (this is how the concept of moles was originally defined).

For example, the molar mass (and atomic weight) of carbon-12 is 12 g&middot;mol−1, so 1 mole of carbon-12 weighs 12 grams. Similarly, chlorine has a molar mass of 35.45 g·mol−1, so one mole of chlorine atoms weighs 35.45 g. There are two chlorine atoms in one molecule of Cl2 gas, so one mole of Cl2 gas weighs 70.90 g.

Measurement and Quantities
See the Units Appendix for tables of SI fundamental and derived units.

Commonly used units in Chemistry
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Quantity

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Commonly used units and symbols

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Conversions (etc)
amount of substance mole, mol 1 mol = 6.022&times;1023 particles concentration (solutions) mole per litre, mol L-1 gram per litre, g L-1 (mol L-1)(g mol-1) = g L-1 (g L-1)/(g mol-1) = mol L-1 electric charge coulomb, C electric current ampere, A electromotive force volt, V energy joule, J kilojoule, kJ 1000 J = 1 kJ density gram per litre, g L-1 mass gram, g kilogram, kg ton 1 tonne = 1000 kg = 1&times;106 g molar volume litre per mole, L mol-1 22.41 L (S.T.P) 22.47 L (25 °C, 101.325 kPa) pressure kilopascal, kPa atmosphere, atm millimetre of mercury, mmHg 1 atm = 101.324 kPa = 760.0 mmHg temperature kelvin, K degree celsius, &deg;C TK = TC + 273.15 time second, s hour, h 1 h = 3600 s volume litre, L millilitre, mL cubic centimetre, cm3 cubic decimetre, dm3 1 L = 1000 mL = 1 dm3 = 1000 cm3
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Commonly used prefixes
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Prefix

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Symbol

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Factor
tera T 1012 giga G 109 mega M 106 kilo k 103 milli m 10−3 micro &micro; 10−6 nano n 10−9 pico p 10−12
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