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 quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

In an ionic compound, mole ratio of cation to anion is $1:2$. If atomic masses of metal and non-metal respectively are 138 and 19, then correct statement is :

  1. molecular mass of compound is 176

  2. formula mass of compound is 176

  3. formula mass of compound is 157

  4. molecular mass of compound is 157
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

1 mole of ionic compound contains 1 mole of cations and 2 moles of anions.
The formula mass of the compound is $138+2(19)=176 \ g/mol$.

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

Which of the following statements are true?

  1. $1$ mole $H$ atoms $=6.02\times 10^{23}H$ atoms.
  2. $6.02\times 10^{23}H$ atoms have a mass of $1.008$ g.
  3. The formula mass of $O _2=32.00$ amu.

  4. All of the above are true.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

(A) $ 1 $ mole of any substance contains Avogadro's number of atoms or molecules. Thus, $1$ mole of H atoms corresponds to $=6.02\times 10^{23}H$ atoms.
Hence, the option A is true.
(B) $6.02\times 10^{23}H$ atoms have mass equal to molar mass of H. it is equal to $1.008$ g.
 Hence, the option B is true.
(C) The formula mass of $O _2=32.00 amu$. Thus, $1$ oxygen molecule weighs $32$ amu and $1$ mole of oxygen molecules weighs $32$ g.
Hence, the option C is true.
As we know, 1 mole is the collection of $6.02\times 10^{23}$ entities. Here entities may represent atoms, ions, molecules.
And mass of one mole of H is $1.008$ g so $6.02\times 10^{23}H$ atoms have a mass of $1.008$ g.
The formula mass of $O _2= 2(8p+8n) = 2\times16 = 32.0$ amu.

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

Find the relative molecular mass of methyl alcohol $(CH _3OH)$, if $160 gm$ of the alcohol on vaporization has a volume of $112$ litres at STP.

  1. $16 gm$
  2. $32 gm$
  3. $160 gm$
  4. $80 gm$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

As we know, one mole of a gaseous substance occupies $22.4$ litres volume.


Mole $= \dfrac{w}{M}$


$\dfrac{160}{M} = \dfrac{112}{22.4}$

$M = 32 gm$

Also, molar mass $=2\times vapour  density$
Therefore, vapour density $= 16 gm$

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The amount in parts by weight of sulphur present in one sulphuric acid molecule:

  1. $16$
  2. $32$
  3. $64$
  4. $48$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
$H _2SO _4$ is sulphuric acid. 
Molecular mass of $H _2SO _4= 2+32 + (4 \times 16)=38 \ g$
Weight of sulphur in it $= 32 \ g$
So, amount in parts by weight of sulphur in one sulphuric acid molecule is $32 \ g$
Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The molecular mass of a salt of oxy acid of chlorine of a divalent metal which contains more number of oxygen atoms than its corresponding '-ic' acid is $239\ g/mole$.
What is the atomic mass of the metal?

  1. 24

  2. 39

  3. 40

  4. 30
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The formula of the salt with molecular weight 239 is $Ca(ClO _{4}) _{2}$ and thus the divalent metal is calcium with atomic weight 40.

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The number of gram-molecules of oxygen in $6.022\times 10^{24}$ molecules of $CO$ is:

  1. $10$ gm moles
  2. $5$ gm moles
  3. $1$ gm mole
  4. $0.5$ gm mole
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Number of oxygen atoms = Number of $CO$ molecules$=6.022\times 10^{24}$

Number of oxygen molecule $=\dfrac12\times$  Number of oxygen atoms $=3.011\times 10^{24}$
Number of g-molecule of $O _2$ molecules $=\dfrac{3.011\times 10^{24}}{6.022\times 10^{23}}=5\ gm\ mole$

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The molar mass of $CuSO _4.5H _2O$ is 249. Its equivalent mass in the reaction (a) and (b) would be:
(a) Reaction $CuSO _4 + KI \rightarrow$ product
(b) Electrolysis of $CuSO _4$ solution

  1. (a) 249 (b) 249

  2. (a) 124.5 (b) 124.5

  3. (a) 249 (b) 124.5

  4. (a) 124.5 (b) 249
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In water, ${ CuSO } _{ 4 }\cdot 5{ H } _{ 2 }O$ dissociates into ${ Cu }^{ 2+ }$ & ${ SO } _{ 4 }^{ 2- }$. The ions are doubly charged. Hence half as much is needed to react with a compound that dissociates into singly charged species.

(a) Reaction of ${ CuSO } _{ 4 }+KI\longrightarrow $ products.
     Eq. wt of ${ CuSO } _{ 4 }=249/2=124.5$
(b) Electrolysis of ${ CuSO } _{ 4 }$
     At Cathode ${ \underset { +2 }{ Cu }  }^{ 2+ }+{ 2e }^{ - }\longrightarrow \underset { 0 }{ Cu } $
$\therefore$   Charge in oxidation state $=2=n-$factor
$\therefore$   Eq. wt $=\dfrac { 249 }{ 2 } =124.5$

Multiple choice chemistry ionic equilibrium introduction to ionic equilibria in solution ionic equilibrium in solution ionisation of weak acids and weak bases

The value of observed and calculate molecular weights of silver nitrate are $92.64$ and $170$ respectively. 


The degree of dissociation of silver nitrate will be :

  1. $60\%$
  2. $83.5\%$
  3. $85.3\%$
  4. $41.6\%$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The degree of dissociation alpha is calculated by (normal molar mass - observed molar mass) / (observed molar mass * (n-1)). For AgNO3, n=2. (170-92.64) / (92.64 * 1) = 77.36 / 92.64 = 0.835, which is 83.5%.

Multiple choice chemistry materials we use soap and detergents soap soap and detergent

Washing powders contain detergents in the range of (by mass):

  1. $10-15\%$
  2. $15-30\%$
  3. $50-60\%$
  4. $40-50\%$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Modern synthetic detergents are alkyl or aryl sulphonates produced from petroleum (or coal) and sulphuric acid. They can be defined as the sodium or potassium salt of a long chain alkyl benzene sulphonic acid or the sodium or potassium salt of a long chain alkyl hydrogen sulphate, that has cleansing properties in water.
They are used in washing powders in a proportion of about $15-30\%$.

Multiple choice zoology respiratory system do plants breathe? plant respiration respiration-plants

General formula for aerobic respiration is

  1. 6CO$ _2$ + 6H$ _2$O $\rightarrow$ C$ _6$H$ _{12}$O$ _6$ + 6O$ _2$
  2. C$ _6$H$ _{12}$O$ _6$ + 6O$ _2$ $\rightarrow$ 6CO$ _2$ + 6H$ _2$O + 686 kcal
  3. C$ _6$H$ _{12}$O$ _6$ $\rightarrow$ 2C$ _2$H$ _5$OH + 2CO$ _2$ + 2ATP
  4. C$ _6$H$ _{12}$O$ _6$ $\rightarrow$ 2C$ _3$H$ _6$O$ _3$+2 ATP
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Aerobic respiration requires oxygen and it takes place in mitochondria and produces carbon dioxide, water and 686 kilo calories of energy.

So the correct option is '

C$ _6$H$ _12$O$ _6$ + 6O$ _2$ → 6CO$ _2$ + 6H$ _2$O + 686 kcal.'

Multiple choice chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

Suppose the chemists hed selected $10^{20}$ as the number of particles in a mole. The molar mass of oxygen gas would be (Use Avogadro number $=6.0\times 10^{23}$)

  1. $5.33\times 10^{-3}g$
  2. $5.35\times 10^{-23}g$
  3. $5.33\times 10^{-43}g$
  4. $32\times 10^{3}g$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Molar mass of oxygen we know is $32$g.

$\therefore 1$ molecule oxygen weighs $\cfrac { 32 }{ 6\times { 10 }^{ 23 } } $g
$\Rightarrow { 10 }^{ 20 }$ molecules would weigh $\cfrac { 32 }{ 6\times { 10 }^{ 23 } } \times { 10 }^{ 20 }$
$\therefore 1 $mole would weigh $=5.33\times { 10 }^{ -3 }$g.

Multiple choice chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

The number of electrons present in $100ml$ of $0.1N$ ${H} _{2}{SO} _{4}$ is:

  1. $6.85\times {10}^{22}$
  2. $7.50\times {10}^{23}$
  3. $1.5\times {10}^{23}$
  4. $1.8\times {10}^{22}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Normality=$n\times Molarity$

$\therefore 0.1=2\times \cfrac { moles\quad  of\quad  H _2SO _4}{ 0.1 }$
$\therefore Moles\quad  of\quad  H _2SO _4=0.005\quad moles$

$1$ molecule of $H _2SO _4$ contains $50$ electrons.

No. of molecules in $0.005$ moles=$0.005\times6.022\times {10}^{ 23 }$
=$0.03011\times {10}^{ 23 }$ molecules

$\therefore$ No. of electrons in $0.005$ moles=$0.03011\times {10}^{ 23 }\times 50$
=$1.5\times {10}^{ 23 }$ electrons