Question

The difference between the total number of hydrogen
atoms in 78 g of ethyne and 168 g of baking soda
is
(1) 2NA
(2) 3NA
(3) 6NA
(4) 4NA​

Answer 1

Answer:

(4) 4NA​

Explanation:

Number of atoms = Mass/Avogadro’s constant × No. of atoms in a molecule

Where Avogadro’s constant, is NA = 6.022 × 10²³ mol⁻¹

Finding the hydrogen atoms in 78 gms of ethyne  

Molecular weight of ethyne, C₂H₂ = 26 g/mol

26 g of C₂H₂contains (2NA) atoms of hydrogen  

Thus, the total no. of Hydrogen atoms in 78 g Ethyne  

= [2NA/26] × 78 = 6NA -- 1

Finding the hydrogen atoms in 168 gms of baking soda  

Molecular weight of baking soda, NaHCO₃ = 84 g/mol

84 g of NaHCO₃ contains (1NA) atoms of hydrogen  

Thus, the total no. of Hydrogen atoms in 168 g NaHCO₃  

= [1NA/84] × 168 = 2NA -- 2

Therefore, from 1 and 2

Difference = [6NA] – [2 NA]

= 4 NA