Tag: chemistry

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

What weight of sodium contains the same number of atoms as those in $8$ grams of oxygen?

  1. $10.5 g$
  2. $13.5 g$
  3. $11.5 g$
  4. $14.2 g$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Atomic weights of sodium and oxygen are 23 g/mol and 16 g/mol respectively.

8 g oxygen $ \displaystyle = \dfrac {8 \ g}{16 \ g/mol}= 0.5 \ $ moles of oxygen atoms.

Number of moles of sodium $ \displaystyle =$ number of moles of oxygen atoms $ \displaystyle = $ 0.5.

Weight of sodium $ \displaystyle = 0.5 \ mol \times 23 \ g/mol = 11.5 \ g$.

Note: Since sodium and oxygen samples have same number of atoms, they will have same number of moles.
Multiple choice chemistry the language of chemistry atomic weight and molecular weight masses of atoms and molecules chemical analysis and formulae

What is the atomic mass of sodium?

  1. $22\ g/mol$
  2. $23\ g/mol$
  3. $11\ g/mol$
  4. $20\ g/mol$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

What is the relative atomic mass of cadmium?

  1. 112.411 amu

  2. 20.00 amu

  3. 21.00 amu

  4. 20.43 amu
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

Which of the following is/are correct?

  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.
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
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.

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

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?

  1. 15.999 u

  2. 16.999 u

  3. 17.999 u

  4. 18.999 u
Reveal answer Fill a bubble to check yourself
A Correct answer
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
Multiple choice chemistry the language of chemistry atomic weight and molecular weight masses of atoms and molecules chemical analysis and formulae

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?

  1. 35

  2. 37

  3. 35.5

  4. 35.6
Reveal answer Fill a bubble to check yourself
C Correct answer
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
Multiple choice chemistry the language of chemistry atomic weight and molecular weight masses of atoms and molecules chemical analysis and formulae

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

  1. $8g/mol$
  2. $9g/mol$
  3. $10g/mol$

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
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}$
Multiple choice chemistry natural resources- air, water and land environment and pollution environment pollution for a pollution free nature

Which will not cause any atmospheric pollution?

  1. Hydrogen

  2. Sulphur dioxide

  3. Carbon dioxide

  4. Carbon monoxide
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Causes of Air pollution:
1. Burning of Fossil Fuels:
Sulfur dioxide emitted from the combustion of fossil fuels like coal, petroleum and other factory combustibles is one the major cause of air pollution. Carbon Monooxide caused by improper or incomplete combustion and generally emitted from vehicles is another major pollutant along with Nitrogen Oxides, that is produced from both natural and man made processes.
2. Agricultural activities: Ammonia is a very common by product from agriculture related activities and is one of the most hazardous gases in the atmosphere. Use of insecticides, pesticides and fertilizers in agricultural activities has grown quite a lot. They emit harmful chemicals into the air and can also cause water pollution.
3. Exhaust from factories and industries: Manufacturing industries release large amount of carbon monoxide, hydrocarbons, organic compounds, and chemicals into the air thereby depleting the quality of air. Manufacturing industries can be found at every corner of the earth and there is no area that has not been affected by it. Petroleum refineries also release hydrocarbons and various other chemicals that pollute the air and also cause land pollution.
4. Mining operations: Mining is a process wherein minerals below the earth are extracted using large equipments. During the process dust and chemicals are released in the air causing massive air pollution.
5. Indoor air pollution: Household cleaning products, painting supplies emit toxic chemicals in the air and cause air pollution.