Question

42. If atomic mass unit "u" were defined to be 20%
by weight of an atom of C-12 isotope, what
would be the atomic weight of nitrogen? Atomic
weight of nitrogen on conventional scale is 14.
a)5.83
b) 33.6
c) 7
d) 70
​

Answer 1

Answer:

The atomic mass on the relative scale is C – 12 and all the masses of the elements are determined relative to C – 12. Hence, the correct answer is option B. Note: The standard unit of the mass of an atom is the atomic mass unit, which is equal to 112ththe mass of an atom C-12.

Explanation:

Answer 2

The atomic weight of nitrogen would be 5.83 and option ( a) is correct.

Explanation:

Given:

Atomic mass unit "u" were defined to be 20% by weight of an atom of C-12 isotope.

Atomic weight of nitrogen on conventional scale is 14.

To Find:

The atomic weight of nitrogen.

Concept Used:

An atom is consist of two regions. The center of the atom containing protons and neutrons are called the nucleus is in one region and the other region which is called  the outer region contain electrons in orbit around the nucleus. Protons and neutrons have  the same mass (approx.) as the atomic mass unit(amu).

Solution:

1 atomic mass unit (amu) =  1.67×10−24gms

Atomic mass is  equal to  the number of protons or electrons of the atom. Because many elements have isotopes and  they use average atomic mass.

In the periodic table, the mass of carbon is  12.011 amu, which is the average mass of the carbon atom.

The atomic mass on the relative scale is C – 12 and all the masses of the elements are  calculated  relative to C – 12.

$Relative\ atomic\ mass =\frac{mass of an atom}{\frac{1}{12} \ of\ C-12}$

Now consider $\frac{1}{5} th$  of the mass of an atom C-12, then

$Relative\ atomic\ mass =\frac{mass of an atom}{\frac{1}{5} \ of\ C-12}$

Weight of N on conventional scale = 14 based on $\frac{1}{12} th$ a standard scale,

As per  the given scale the atomic mass unit ‘u’ was defined to be $\frac{1}{5} th$ of the mass of an atom C-12 $=14\times\frac{12}{5} =5.834u$.

Thus,the atomic weight of nitrogen would be 5.83 and option ( a) is correct.

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Answer 3

The atomic weight of nitrogen would be 5.83 and option ( a) is correct.

Explanation:

Given:

Atomic mass unit "u" were defined to be 20% by weight of an atom of C-12 isotope.

Atomic weight of nitrogen on conventional scale is 14.

To Find:

The atomic weight of nitrogen.

Concept Used:

An atom is consist of two regions. The center of the atom containing protons and neutrons are called the nucleus is in one region and the other region which is called  the outer region contain electrons in orbit around the nucleus. Protons and neutrons have  the same mass (approx.) as the atomic mass unit(amu).

Solution:

1 atomic mass unit (amu) =  1.67×10−24gms

Atomic mass is  equal to  the number of protons or electrons of the atom. Because many elements have isotopes and  they use average atomic mass.

In the periodic table, the mass of carbon is  12.011 amu, which is the average mass of the carbon atom.

The atomic mass on the relative scale is C – 12 and all the masses of the elements are  calculated  relative to C – 12.

$Relative\ atomic\ mass =\frac{mass of an atom}{\frac{1}{12} \ of\ C-12}$

Now consider $\frac{1}{5} th$  of the mass of an atom C-12, then

$Relative\ atomic\ mass =\frac{mass of an atom}{\frac{1}{5} \ of\ C-12}$

Weight of N on conventional scale = 14 based on $\frac{1}{12} th$ a standard scale,

As per  the given scale the atomic mass unit ‘u’ was defined to be $\frac{1}{5} th$ of the mass of an atom C-12 $=14\times\frac{12}{5} =5.83u$.

Thus,the atomic weight of nitrogen would be 5.83 and option ( a) is correct.

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