MOLE-MASS conversion | conversion factors method|

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Points to Recall

  • Mole is a basic physical quantity for measuring quantity of a substance in chemistry. There is no physical balance or device to measure moles of a substance directly . Firstly we take mass( grams) by physical balance then we convert this mass into moles.

  • Molar Mass is calculated simply by  multiplying relative masses - which are obtained from periodic table- to Molar mass constant -which is 1g/mol.

Like
Relative atomic of potassium (K) = 39.01 a.m.u
Molar Mass of K =39.01 x 1g/mol= 39.01g/mol

Conversion Factor | Definition|

"Conversion factor is a ratio - this ratio is always equal to 1 - used to covert one unit into other unit. Units are inter-converted simply by multiplying or dividing the suitable conversion factor".

For Mole-Mass conversions the prior information to make conversions factors is:

1 mol.= Molar Mass(g)
So, the two conversion factor will be
(i) mol/g 
(ii) g/ mol
Note: select the conversion factor in such a way that same units cut each other. 

Practice problem 1:

How many moles in 31g of phosphorus (P4)?

Select suitable conversion factor between two, as in problem mass(g) is given hence select that conversion factor in which mass is lying below in ratio. So conversion factor (i) mol/ g is suitable.

Solution:

mole-mass-conversion-factor-problems

Practice problem 2:

calculate the mass(in grams) of 75 moles of H2?

Select suitable conversion factor between two, as in problem mass(g) is given hence select that conversion factor in which mass is lying below in ratio. So conversion factor (ii) g/ mol is suitable.
Solution:
mole-mass-conversion-factor-problems








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