Chemistry

Mole Concept and Stoichiometry

365 Questions

The mole concept is a core area of chemistry focusing on the quantitative relationships between reactants and products in chemical reactions. Questions cover molecular mass calculations, stoichiometric conversions, and determining the number of molecules. This topic is essential for most science entrance and competitive examinations.

molecular mass calculationsstoichiometric conversionsmole fraction problemsheavy water reactionsoxidation calculations

Mole Concept and Stoichiometry Questions

Multiple choice geography in the land of kerala introduction to metallurgy occurrence of metals study of kerala

Specific gravity of slag is always:

  1. much greater than the molten metal

  2. less than the molten metal

  3. same as molten metal

  4. more or less the metal depending on the metal
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In blast furnace, products are collected at bottom. So, molten metal should be at bottom and slag is at up. So slag should have low density compared to molten metal.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

What is the volume of $3.0\times {10}^{20}$ molecules of $HCl (g)$?

  1. $11.2L$
  2. $0.0224L$
  3. $0.0112L$
  4. $22.4L$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$1 \space Mole$ of gas at STP occupy $22.4 \space Litres$ of gas

As, $1 \space Mole = 6.02 \times 10^{23}$ molecules $\Rightarrow 22.4 Litres$ 
$3.0 \times 10^{20}$ molecules $\Rightarrow (X)$ 
$\Rightarrow X = \dfrac{22.4 \times 3 \times 10^{20}}{6.02 \times 10^{23}} = 0.0112\space L$

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

A sample of ammonia has a mass of $51.1g$. How many molecules are in this sample?

  1. $1.8\times {10}^{23}$ molecules
  2. $3.6\times {10}^{23}$ molecules
  3. $9.1\times {10}^{23}$ molecules
  4. $1.8\times {10}^{24}$ molecules
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
given mass of ammonia is 51.1g
in this number of moles =  $\dfrac{51.1}{17.031}$ = 18
Now in a mole, there are Na molecules, this is known $6.023\times 10^{23}$ 
since 1 mol = $6.023\times 10^{23}$ 

thus,

18 mol = $18\times 6.023\times 10^{23}$  = $1.8\times 10^{24}$
Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

The mass of a molecule of the compound $C {60}H _{122}$ is _________.

  1. $1.4\times 10^{-21}$ g
  2. $1.09\times 10^{-21}$ g
  3. $5.025\times 10^{23}$ g
  4. $16.023\times 10^{23}$ g
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Molecular mass of $C _{60}H _{122}=(60 \times 12+1 \times 122)=720+122=842$


Hence, one mole contains $6.022 \times 10^{23}$ molecules 


Therefore, 

Mass of one molecule $=\frac{842}{6.022 \times 10^{23}}$

$=1.4 \times 10^{-21}\;g$


The correct option is A.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

If you are given Avogadro's number of atoms of a gas $X$. If half of the atoms are converted into $X _{(g)}^+$ by energy $\Delta H$. The IE of $X$ is :

  1. $\dfrac{2\Delta H}{N _A}$
  2. $\dfrac{2N _A}{\Delta H}$
  3. $\dfrac{\Delta H}{2N _A}$
  4. $\dfrac{N _A}{\Delta H}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Given no. of atoms = Avogadro's no. of atoms = ${N} _{A} = 6.023 \times {10}^{23}$
Given that $\cfrac{{N} _{A}}{2}$ atoms are ionized, i.e.,
Ionization energy of $\cfrac{{N} _{A}}{2}$ atoms of gas X = $\Delta{H}$

$\therefore$ Ionization energy of 1 atom of gas X = $\cfrac{\Delta{H}}{\left( \cfrac{{N} _{A}}{2} \right)} = \cfrac{2. \Delta{H}}{{N} _{A}}$
Hence, Ionisation energy of gas X is $\cfrac{2. \Delta{H}}{{N} _{A}}$.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

The number of atoms in 67.2 L of ${ NH } _{ 3 }$(g) at STP is:

  1. 9 ${N } _{ A }$
  2. 12 ${N } _{ A }$
  3. 3 ${N } _{ A }$
  4. 4 ${N } _{ A }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
By Avogadro law,
 22.4 liter of any gas at STP$ = $1mole
                $ =6.022\times { 1 }0^{ 23 }$ molecules of gas
                $ =$NA (Avogadro number)

So, in 67.2 L of ${ NH } _{ 3 }=?$
    22.4 L of $ { NH } _{ 3 }=N _A$
     1 L of ${ NH } _{ 3 }=\cfrac { NA }{ 22.4 } $

67.2 L of $ { NH } _{ 3 }=\cfrac { 67.2 }{ 22.4 } \times NA$
                          $ =3N _A$ molecules

Now, each molecule contain 4 atoma
Number of atoms $= 4\times 3N _A = 12N _A$ atoms
Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

If  $N _ { A }$ is Avogadro's number, then calculate the number of electrons in  $4.2\ g$  of  $N ^ { 3- }$.

  1. $2.1 N _ { A }$
  2. $3 N _ { A }$
  3. $6 N _ { A }$
  4. $ N _ { A }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
$N^{3-}$ contains 10 electrons.

Number of moles $= \dfrac {4.2}{14} $
                                     
                                       $=0.3\ moles$

No of electrons in $0.3\ moles = 0.3\times N _A\times 10$

                                        $=3\ N _A$

Hence, option B is correct.
Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

Which of the following represents the Avogadro number?

  1. Number of molecule present in 1 L of gas at N.T.P

  2. Number of molecule present in 22.4 L of gas at N.T.P

  3. Number of molecule present in 22.4 of gas at 298K and 1 atm pressure

  4. Number of molecule present in one mole of gas at any temp and pressure
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Avogadro's number (6.022 x 10^23) represents the number of particles (atoms or molecules) in exactly one mole of a substance, regardless of the temperature or pressure.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

Statement 1: The number of gram molecules of oxygen in $6.02 \times 10^{24}\ CO$ molecules is 5.0.
Statement 2: The value of Avogadro number is $6.02 \times 10^{23}$

  1. Statement 1 is True, statement 2 is True, Statement 2 is a correct explanation of statement 1.

  2. Statement 1 is True, statement 2 is True, Statement 2 is not a correct explanation of statement 1.

  3. Statement 1 is True, Statement 2 is False.

  4. Statement 1 is False, Statement 2 is True.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$6.02\times 10^{24}$ molecules of $CO=6.02\times 10^{23}\times 10$ i.e.., 10 moles of CO.
10 moles of CO contains 10 gm atoms of oxygen i.e.  5 gm molecules of oxygen.
hence the correct answer is A the given assertion is correct and reason is the correct explanation to the assertion.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

14 g of nitrogen contains $3.01 \times 10^{23}$ nitrogen molecules.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

1 mole nitrogen contains $6.02\times10^{23}$ nitrogen molecules.

Thus 14 gram nitrogen will contain $14/28.Na=0.5Na=3.01\times10^{23}$ nitrogen molecules. ( Molecular weight of nitrogen is 28)

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

What is the mass of $6.022\times { 10 }^{ 23 }$ molecules of ${NH} _{3}$?

  1. $45.06g$
  2. $19.06\ g$
  3. $17.04g$
  4. $31.02g$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$1\space mole$ of $NH _3$ has $6.023 \times 10^{23}$ molecules of $NH _3$.

So, the mass of $6.023 \times 10^{23}$ molecules of $NH _3$. is the mass of $1\space mole$ of $NH _3$  i.e. molar mass of $NH _3.$ 
Molar mass $= 14.01 + 3(1.01) = 17.04 \space g$

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

How many molecules of water are present in a $0.25\ mole$ of $H _2O$?

  1. $6.0\times{10}^{22}$
  2. $4.5\times 10^{23}$
  3. $1.5\times{10}^{23}$
  4. $18\times 10^{23}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$1\space mole$ of a compound has $6.023\times 10^{23}$ molecules in it.

$\Rightarrow 1\space mole =$$6.023\times 10^{23}$ molecules
$ 0.25\space mole = x$ molecules
$\Rightarrow x = (\dfrac{6.023}{4}) \times 10^{23}$$= 1.5\times 10^{23}$ molecules of water.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

How many atoms of hydrogen are present in $7.8\ g$ of $Al{(OH)} _{3}$?

  1. $6.0\times {10}^{22}$
  2. $1.8\times {10}^{23}$
  3. $1.7\times {10}^{23}$
  4. $5.1\times {10}^{22}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Molar mass of $Al(OH) _3 = 27 + 3\times 16 + 3\times 1 = 78\space g$

So, no. of moles of $Al(OH) _3 = \dfrac{7.8}{78} = 0.1\space moles$
$1\space mole$ of $Al(OH) _3$ has $6.023 \times 10^{23}$ atoms.
So, $0.1\space moles$ has $6.023 \times 10^{22}$ atoms.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

$2K(s)+2{H} _{2}O(l)\rightarrow 2KOH(aq)+{H} _{2}(g)$
If $3.0$ moles of potassium react with excess water, what volume of hydrogen gas will be produced?

  1. $1.5L$
  2. $22.4L$
  3. $67.2L$
  4. $33.6L$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Given, $2K(s) + 2H _2O(l) \rightarrow 2KOH(aq) + H _2 (g)$

$2\space moles$ of Potassium on reaction gives $1 \space mole$ of Hydrogen [ 22.4 at STP]
$2\space moles$ of $K \rightarrow 22.4 \space Litres $ of $H _2$
$2\space moles$ of $K = \dfrac{3\times 22.4}{2} = 33.6 \space Litres$ of $H _2$
So, $33.6\space Litres$ of Hydrogen are produced.