there is 6.10g of Cobalt (II) Nitrate, Co(NO3)2, what is the molar mass?

Question

there is 6.10g of Cobalt (II) Nitrate, Co(NO3)2, what is the molar mass?

 

Answer 1

Molar mass is generally expressed as grams per mole. This is the same thing as formula weight for a compound.

 

It is a constant for any given element or compound, no matter how much you have.  The molar mass (formula weight) of Co(NO₃)₂ is the sum of the atomic masses from the periodic table:

1 Co atom = 58.9332

2 N atoms = 2 x 14.0067

6 O atoms = 6 x 15.9994

Total formula weight is 182.943 g per mol.  This means that if you have 1 mol of it, then it will weigh 182.943 g. 

NOTE: If you don't have 1 mol of it, then it won't weigh that much!  ;)

 

If you have 6.10 grams of it, or if you have 1.0 grams of it, or if you have a ton of it - it doesn't matter!  The formula weight or molar mass is still 182.943 g/mol.

 

If you have 6.10 g of it, you can find the MOLES of this substance using the formula weight or molar mass.

6.10 g of Co(NO₃)₂  x (1 mol / 182.943 g) = 0.0333 mol of Co(NO₃)₂ 

 

But that's not the molar mass, it's just the quantity expressed in moles (instead of grams).

Answer 2

Molar mass is equivalent to moles per gram. If we look at it this way we can just say: 

 

We have 6.10g of Co(NO₃)₂ and there is 1mole /177g (from the periodic table) of Cobalt II nitrate. Thus, we get 0.0344 moles/gram for this compound. 

 

Hope this helps!