Tag: atomic weight and molecular weight

Questions Related to atomic weight and molecular weight

What is the atomic mass of sodium?

chemistry the language of chemistry atomic weight and molecular weight masses of atoms and molecules chemical analysis and formulae

  1. $22\ g/mol$

  2. $23\ g/mol$

  3. $11\ g/mol$

  4. $20\ g/mol$

Show answer
Correct Option: B
Explanation:

A relative atomic mass is a measure of how heavy atoms are. It is the ratio of the average mass per atom of an element from a given sample to 1/12 the mass of a carbon-12 atom.

The relative atomic mass in 1 mole of isotopes of sodium atoms is 23 g/mol.

What is the relative atomic mass of cadmium?

chemistry the language of chemistry atomic weight and molecular weight masses of atoms and molecules chemical analysis and formulae

  1. 112.411 amu

  2. 20.00 amu

  3. 21.00 amu

  4. 20.43 amu

Show answer
Correct Option: A
Explanation:

The relative atomic mass is an average of the atomic masses of all the different isotopes in a sample, with each isotope's contribution to the average determined by how big a fraction of the sample it makes up.
The relative atomic mass of Cadmium is 112.411 amu.

Which of the following is/are correct?

chemistry the language of chemistry atomic weight and molecular weight masses of atoms and molecules chemical analysis and formulae

  1. One atomic mass unit is a mass unit equal to exactly one -twelfth (1/12th) the mass of one atom of carbon-12.

  2. One atomic mass unit is a mass unit equal to exactly one - sixteenth (1/16th) the mass of one atom of oxygen-16.

  3. The relative atomic mass of the atom of an element is defined as the average mass of the atom, as compared to 1/12h the mass of one carbon-12 atom.

  4. None of the above.

Show answer
Correct Option: A,B,C
Explanation:

The following are correct. One atomic mass unit is a mass unit equal to exactly one -twelfth (1/12th) the mass of one atom of carbon-12.
One atomic mass unit is a mass unit equal to exactly one - sixteenth (1/16th) the mass of one atom of oxygen-16.
The relative atomic mass of the atom of an element is defined as the average mass of the atom, as compared to 1/12h the mass of one carbon-12 atom.
For example, the mass of one carbon-12 atom is 12 amu. The mass of one magnesium-24 atom is 24 amu. The mass of one calcium-40 atom is 140 amu.

Oxygen occurs in nature as a mixture of isotopes $^16O$, $^17O$ and $^18O$ having atomic masses of 15.995 u, 16.999 u and 17.999 u and relative abundance of 99.763%, 0.037%, and 0.200% respectively. What is the average atomic mass of oxygen?

chemistry the language of chemistry atomic weight and molecular weight masses of atoms and molecules chemical analysis and formulae

  1. 15.999 u

  2. 16.999 u

  3. 17.999 u

  4. 18.999 u

Show answer
Correct Option: A
Explanation:
 Average atomic mass of an element existing in different isotopes is given by:
$M _{ avg }=\dfrac { \sum _{ i=1 }^{ n }{ { M } _{ i }{ A } _{ i } }  }{ \sum _{ i=1 }^{ n }{ A _{ i } }  } $
where $M _i=$atomic mass of an isotope with relative abundance of $A _i$
Given:$M _1=15.995 u,A _1=99.763,M _2=16.999 u, A _2=0.037,M _3= 17.999 u, A _3=0.200$
on subtitutiing we get:
${ M } _{ avg }=\dfrac { 15.995\times 99.763+16.999\times 0.037+17.999\times 0.200 }{ 99.763+0.037+0.200 } $
${ M } _{ avg }=15.999\ u$
option A is correct

For every ,one $^{37}Cl$ isotope there are three $^{35}Cl$ isotopes, in a sample of chlorine. What will be the average atomic mass of chlorine?

chemistry the language of chemistry atomic weight and molecular weight masses of atoms and molecules chemical analysis and formulae

  1. 35

  2. 37

  3. 35.5

  4. 35.6

Show answer
Correct Option: C
Explanation:
Average atomic mass of an element existing in different isotopes is given by:
$M _{ avg }=\dfrac { \sum _{ i=1 }^{ n }{ { M } _{ i }{ A } _{ i } }  }{ \sum _{ i=1 }^{ n }{ A _{ i } }  } $
where $M _i=$atomic mass of an isotope with relative abundance of $A _i$
Given:$M _1=37 u,A _1=1,M _2=35 u, A _2=3$
on subtitutiing we get:
${ M } _{ avg }=\dfrac { 37\times 1+35\times 3 }{ 1+3 } $
${ M } _{ avg }=35.5\ u$
option C is correct

One gm metal $M^{3+}$ was discharged by the passage of $1.81\times 10^{23}$ electrons. What is the atomic mass of metal?

chemistry the language of chemistry atomic weight and molecular weight masses of atoms and molecules chemical analysis and formulae

  1. $8g/mol$

  2. $9g/mol$

  3. $10g/mol$

  4. None of these

Show answer
Correct Option: C
Explanation:
Applying faraday's first law-
$ \dfrac{Q}{F} = \dfrac{Wt}{Mwt}\times V.f.$
$ \dfrac{ne}{F}= \dfrac{1}{Mwt}\times 3$
$  Mwt         = \dfrac{1\times F\times 3}{ne}$
$  Mwt         = 10\dfrac{gm}{mol}$