08 Molecular Weight

Posted by Unknown on |


Molecular Weight is the number which shows how many times a molecule of a substance is heavier than 1/12th part of an atom of C12 isotope. In other words molecular weight is the sum of atomic weight of all atoms present in a molecule of a substance.
eg. Mol. wt. of CaCO3 =1×40 + 1×12 + 3×16 = 100 


Gram Molecular Weight 
When molecular weight of a substance is expressed in gram, then it is called gram molecular weight. One gram molecular weight equals to one mole and its contains 6.023×1023 molecules.
For Eg.
Molecular Weight of CaCO3 = 100
100gm of CaCO3 = 1 gram molecular weight of CaCO3
                            =  1 Mole of CaCO3
                            = 6.023×1023 molecules of CaCO3





Q. Calculate the number of moles and number of molecules present in 80gm of CaCO3.
Solution:
Molecular Weight of CaCO3 = 100
100gm of CaCO3 = 1 Mole of CaCO3





Q. Calculate the number of atoms of Ca, C and O present in 150gm of CaCO3.
Solution:
Molecular weight of CaCO3 = 100
Weight of  CaCO3 = 150gram
Number of Moles = ?
Number of Molecules = ?
Number of atoms of Ca, C and O = ?




Number of molecules = Number of moles × 6.023×1023
                                 = 1.5×6.023×1023
                                 = 9.0345×1023
1 molecule of  CaCO3 contains 1 atom of Ca.
9.0345×1023 molecule of CaCO3 contains 9.0345×1023 atoms of Ca.
1 molecule of CaCO3 contains 1 atom of C.
9.0345×1023 molecule of CaCO3 contains 9.0345×1023 atoms of C.
1 molecule of CaCO3 contains 3 atoms of Oxyen.
 9.0345×1023 molecule of CaCO3 contains 3×9.0345×1023 atoms of C.
                                                                 = 2.7103×1023 atoms of C.

Q. Calculate the number of moles and number of atoms of oxygen present in 80gm of oxygen.
Solution:
Molecular Weight of Oxygen = 32
Weight of Oxygen = 80gm
 



Number of molecules = 2.5 × 6.023×1023
                                 = 1.5058×1024

One molecule of oxygen contains 2 atoms of oxyegn.
1.5058×1024 molecules of oxygen contains 2×1.5058×1024
                                                                  = 3.01×1024 atoms of oxygen











Enter your email address to subscribe news feed:

Contact Me

Rijan KC
Kalika Muncipality-5, Padampur
Chitwan, Nepal
Cell: +977 9845080226, 9855080226
E-mail: mail@rijankc.com.np
Facebook: /kc.rijan

Recently Uploaded Matter

Sponsor