Question
Tue November 22, 2011 By:
 

can you please give me the formulae on finding the number of moles and mass?

Expert Reply
Wed November 23, 2011
Number of moles can be calculated using the following formula:
1. 1 mole of a pure substance has a mass in grams equal to its molecular mass (MM) [also known as molecular weight (MW) or formula mass (FM) or formula weight (FW)].
This is often referred to as the molar mass.

 Carbon weighs 12.01 g/mole

Hydrogen weighs 1.008 g/mole
Oxygen weighs 16.00 g/mole

2. number of moles = weight in grams/ mass
 
TO find molar mass:

1 mole of a pure substance has a mass in grams equal to its molecular mass (MM). 
    eg, 1 mole of Helium (a monatomic gas with the formula He) has a mass equal to its relative atomic mass, 4.003g 
    eg, 1 mole of hydrogen gas (a diatomic gas with the formula H2) has a mass equal to 2 x 1.008 = 2.016g 
    eg, 1 mole of ammonia gas (NH3) has a mass equal to 14.01 + (3 x 1.008) = 17.034g 
    eg, 1 mole of water (H2O) has a mass equal to (2 x 1.008) + 16.00 = 18.016g

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