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Showing posts with label SOME BASIC CONCEPT OF CHEMISTRY. Show all posts
Showing posts with label SOME BASIC CONCEPT OF CHEMISTRY. Show all posts

## Tuesday, August 29, 2023

### Average molar weight (Molecular weight): or Mean Molecular Mass

We know that for gas:

Pressure fraction = Mole fraction= Volume fraction

Pressure % = Mole % = Volume %

Consider mixture of two different gases (A) and (B) and their moles nA

and nB

Illustrated Examples:

### N2O4 on decomposition gives its monomer NO2 and they are found to be in equilibrium at 300 K. if the VD of such a mixture is 41.4 the calculate % composition by (1) Moles of NO2 and N2O4 (2) By mass O2

Answer Key: (1) 20% and 80% (2) 11.1%

### A mixture of blue and green balls contains 25% by number blue balls. Mass of each blue balls is 40 gm and mass of each green balls is 20 gm calculate (1) Average mass of ball (2) % by mass

Answer Key: (1) 25 gm (2) 40 %

### Air contains 20% of O2 and 80 % N2 by moles find the average molecular mass weight and % by mass of oxygen and nitrogen.

Answer Key:  Mav = 23.8 amu ,  %  by mass of Oxygen =  22.3 %  and % by mass of Nitrogen is 77.7 %

### Calculate the average atomic mass of silicon if relative abundance is 92.23 ,isotope Si^28, 4.77 % isotope = Si^29 and 3% isotope = Si^39 .

Answer Key: The average atomic mass of silicon is 28.1 amu

### Silver contains two isotopes Ag 107 and Ag109 and average atomic weight of silver is 108.5 find percentage abundant of isotopes of silver.

Answer Key: Ag (107) 25% and Ag (109) 75%

SOLUTION:

### Calculate the molar mass of naturally occurring argon. Using the date given in the following table to ..

SOLUTION: Molar mass of Ar

= 35.96755 × 0.071 + 37.96272 × 0.163 + 39.96924 × 0.766

= 39.352 g mol−1

### Average Atomic Mass/weight or Relative Atomic Mass:

Elements are found in different isotopic forms (atoms of same elements having different atomic mass), so the atomic mass of any element is the average of all the isotopic mass within a given sample.

(A) If an elements exists in two isotopes having atomic masses ‘M1’ and ‘M2 in the ratio   X: Y, then

or

(B) If an elements exists in two isotopes having atomic masses ‘M1’ and ‘M2  and their abundant  percentage (%)  are  X % and Y % then

Since the atomic mass is a ratio, it has no units and is expressed in amu.

Illustrative Examples: