General Chemistry/Measurement
Contents
Moles[edit]
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 something contains 6.02205 × 10^{23} particles. This rather large quantity is a constant called Avogadro's Number, which is abbreviated as N_{A}. It simply refers to the number of particles in one mole.
For example, one mole of helium gas contains 6.022×10^{23} atoms; 2 moles of oxygen gas contains 1.204×10^{24} molecules.
Moles and Mass[edit]
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 . 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 carbon12 is 12 g·mol^{−1}, so 1 mole of carbon12 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 Cl_{2} gas, so one mole of Cl_{2} gas weighs 70.90 g.
Measurement and Quantities[edit]
See the Units Appendix for tables of SI fundamental and derived units.
Commonly used units in Chemistry[edit]
Quantity[edit] 
Commonly used units and symbols[edit] 
Conversions (etc)[edit] 
amount of substance 
mole, mol 
1 mol = 6.022×10^{23} particles 
concentration (solutions) 
mole per litre, mol L^{1} 
(mol L^{1})(g mol^{1}) = g L^{1} 
electric charge 
coulomb, C 

electric current 
ampere, A 

electromotive force 
volt, V 

energy 
joule, J 
1000 J = 1 kJ 
density 
gram per litre, g L^{1} 

mass 
gram, g 
1 tonne = 1000 kg = 1×10^{6} g 
molar volume 
litre per mole, L mol^{1} 
22.41 L (S.T.P) 
pressure 
kilopascal, kPa 
1 atm = 101.324 kPa = 760.0 mmHg 
temperature 
kelvin, K 
T_{K} = T_{C} + 273.15 
time 
second, s 
1 h = 3600 s 
volume 
litre, L 
1 L = 1000 mL = 1 dm^{3} = 1000 cm^{3} 
Commonly used prefixes[edit]
Prefix[edit] 
Symbol[edit] 
Factor[edit] 
tera 
T 
10^{12} 
giga 
G 
10^{9} 
mega 
M 
10^{6} 
kilo 
k 
10^{3} 
milli 
m 
10^{−3} 
micro 
µ 
10^{−6} 
nano 
n 
10^{−9} 
pico 
p 
10^{−12} 