Chemistry

Mole Concept and Stoichiometry

354 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 chemistry further aspects of equilibria dissociation constants ionisation of weak acids and weak bases ionization constants of weak acids and weak bases

The value of observed and calculated molecular weight of silver nitrate are $92.64$ and 170 respectively. The degree of dissociation of silver nitrate is :

  1. $60\%$
  2. $83.5\%$
  3. $46.7\%$
  4. $60.23\%$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The van't Hoff factor i = (Calculated MW) / (Observed MW) = 170 / 92.64 = 1.835. For AgNO3, i = 1 + alpha(n-1). Since n=2, i = 1 + alpha. Thus, alpha = 0.835 or 83.5%.

Multiple choice group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

Iodide of MilIon's base is :

  1. $HIO _3$
  2. $K _2Hgl _4$
  3. $NH _2HgO.HgI $
  4. $Hg(NH _2)I$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Iodide of MilIon's base is $\displaystyle NH _2HgO.HgI$
It is formed when Nessler's reagent (alkaline solution of $\displaystyle K _2[HgI _4]$) reacts with $NH _3$. 

Iodide of MilIon's base is a reddish brown ppt.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation applications of floatation principle of floatation and its applications when do objects float on water?

A beaker containing water weighs $100$ g. It is placed on the pan of a balance and a piece of metal  weighing 70 g and having a volume of $10c{m^3}$ is placed inside the water in beaker. The weight of the beaker and the metal would be:

  1. $170g$
  2. $160$g
  3. $100$g
  4. $30g$
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice chemistry energy rocks and minerals petroleum and natural gas fossil fuels

What is the octane number of triptane?

  1. 45

  2. 25

  3. 100

  4. 125
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Octane number is the percentage by volume of iso-octane present in a mixture of iso-octane and heptane which has the same knocking performance as the sample fuel. For eg - octane number of triptane is 125. Hence, the answer is D.

Multiple choice chemistry energy rocks and minerals petroleum and natural gas fossil fuels

The RON/MON values of $n$-heptane is:

  1. $0$
  2. $100$
  3. $1000$
  4. $50$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Octane number can be determined by RON, MON and AKI. The most common method used for the measurement is RON. RON is determined by running the fuel in a test engine and comparing the results with those for mixtures of iso- octane and $n$- heptane. The RON/MON value for $n$- heptane is 0.

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

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.