Useful Molecular and Chemical Equations
Formula Weight & Molecular Weight
Formula weight (FW) and molecular weight (MW) are calculated by summing the atomic weights (AW measured in atomic mass units, amu) of the individual atoms.
Avogadro’s Number & mole
1 mole of atoms / molecules has a mass equal to the atomic / molecular weight in grams.
e.g. 1 mole (1mol) NaCl is the number of molecules in 58.44g of NaCl. (1mol NaCl = 58.44g)
Avogadro’s number is the number of atoms / molecules in 1 mole of any substance, which is equal to 6.02214x1023.
Molarity – Molar Concentration
Molarity is the number of moles of solute per litre of solution.
e.g. 6 molar (6M) HCl is equal to 6 moles (6mol) of HCl per litre (L). (6M HCl = 6mol/L)
Based on the previous two equations:
Primers are dissolved in sterile distilled water (sdH2O) to a concentration of 500pmol. Use one of the following to determine what volume of sdH2O to use:
Weight / mole Percentage
The percentage weight of an element in a compound is calculated using the atomic weight and formula weight.
Percentage weight of Cl in HCl:
Similarly, mole percentage is a ratio.
Percentage mole of Cl in HCl:
Density and Specific Gravity
Density is the mass of a substance per volume.
Specific gravity is a unitless ratio, so for all purposes; SG ≡ D. Cubic centimetres are equivalent to millilitres; cc ≡ mL.
D2 = Density of H2O @ 4°C = 1.00g/cc
Molarity, Specific Gravity and Percentage Composition
Calculating Molarity from specific gravity and percentage composition:
Percentage composition means xg of pure compound per 100g of solution, i.e. 37g/100ml = 37%. To calculate the molarity, the mass of pure compound is needed; however the solution’s specific gravity needs to be taken into account, and the volume; which we’ll take to be 1L.
Where 1L = 1000cc For HCl: