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

1 ml ${ O } _{ 2 }$ will be equal to :

  1. $4g$ equivivalent oxygen
  2. $2g$ equivivalent oxygen
  3. $32g$ equivivalent oxygen
  4. $8g$ equivivalent oxygen
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Weight of $1$ mole of $O _2=32g$

$1g$ equivalent is the weight of substance which displaces $8g$ of $O _2$
$\therefore 32g$ of $O _2=\cfrac {32}{8}=4g$ equivalents of oxygen .

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

What is the mass in grams of $6.022\times 10^{23}$ atoms of oxygen?

  1. 16

  2. 8

  3. 32

  4. 4
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The mass in grams of $6.022\times 10^{23}$ atoms of oxygen is 16 grams. Because $6.022\times 10^{23}$ is avagadro number. Avagadro number of particles are equals to the weight of its molecular weight. So atomic weight of $6.022\times 10^{23}$ atoms of oxygen is  16 which is the atomic weight of oxygen.
Hence option B is correct.
Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

Sulphur trioxide is prepared by the following two reactions:
$S _8(s)+8O _2(g)\rightarrow 8SO _2(g)$
$2SO _2(g)+O _2(g)\rightarrow 2SO _3(g)$
How many grams of $SO _3$ are produced from $1$ mole of $S _8$?

  1. $1280.0$
  2. $640.0$
  3. $960.0$
  4. $320.0$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

${S _8} _{(s)}+{8O _2} _{(g)} \longrightarrow {8SO _2} _{(g)}$

${2SO _2} _{(g)}+{O _2} _{(g)}\longrightarrow {2SO _3} _{(g)}$
By stoichiometry, $1$ mole of ${S _8} _{(s)}$ produces $8$ mole ${SO _2} _{(g)}$
Also, $2$ mole of ${SO _2} _{(g)}$ produces $2$ mole ${SO _3} _{(g)}$
Therefore, $8$ mole ${SO _2} _{(g)}$ produces $8$ moles ${SO _3} _{(g)}$
i.e. $1$ mole ${S _8} _{(s)}$ produces $8$ moles ${SO _3} _{(g)}$
                                         i.e. $8 \times 80g$ of $SO _3$
                                         i.e $640g$ of $SO _3$

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

Calculate the total volume of $0.1$ molar $KMn{O _4}$ solution that is needed to oxidized 100 mg of each furious oxalate and furious sulphate in a mixture in acidic medium. 

  1. 1.096 ml

  2. 1.32 ml

  3. 5.48 ml

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Calculate the milliequivalents of ferrous oxalate and ferrous sulphate. Since KMnO4 acts as an oxidizing agent in acidic medium, use the n-factor to determine the volume of 0.1 M solution required to neutralize the total equivalents.

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

Consider the following reaction sequence:


${ S } _{ 8 }(s)+{ 80 } _{ 2 }(g)\rightarrow { 8SO } _{ 2 }(g)$

${ 2SO } _{ 8 }(g)+{ O } _{ 2 }(g)\rightarrow { 2SO } _{ 3}(g)$

How many grams of ${ SO } _{ 3 }$ are produced from $1$ mole ${ SO } _{ 8 }$?

  1. $1280 g$
  2. $690 g$
  3. $640 g$
  4. $320 g$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
${{S} _{8}} _{\left( s \right)} + 8 {{O} _{2}} _{\left( g \right)} \longrightarrow 8 {S{O} _{2}} _{\left( g \right)}$

As we have $1$ mole of ${S} _{8}$

According to reaction, one mole of $S{O} _{2}$ produces 8 mles of $S{O} _{2}$

Further,

$2 {S{O} _{8}} _{\left( g \right)} + {{O} _{2}} _{\left( g \right)} \longrightarrow 2 {S{O} _{3}} _{\left( g \right)}$

As per the reaction,

No. of moles of $S{O} _{3}$ produced by $2$ moles of $S{O} _{2} = 2 \text{ moles}$

$\therefore$ No. of moles of $S{O} _{3}$ produced by $8$ moles of $S{O} _{2} = 8 \text{ moles}$

As we know that,

$\text{Wt. of compound} = \text{no. of moles} \times \text{molar mass}$

$\therefore$ Weight of $S{O} _{3}$ in 8 moles $= 8 \times 80 = 640 g \; \left[ \because \text{Molar mass of } S{O} _{3} = 80 g \right]$

Hence, $640$ grams of $S{O} _{3}$ are produced by $1$ mole of ${S} _{8}$.

The correct option is C.
Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

How many grams of $H _{2}SO _{4}$ are present in $0.25\ g$ mole of $H _{2}SO _{4}$?

  1. $2.45$
  2. $24.5$
  3. $0.25$
  4. $245$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
$Moles\quad of\quad { H } _{ 2 }{ SO } _{ 4 }=0.25\\ Molecular\quad mass(M)\quad of\quad { H } _{ 2 }{ SO } _{ 4 }=2+32+16\times 4\\ \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad =34+64\\ \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad =98\quad amu\\ no.\quad of\quad grams(w)\quad =\quad ?\\ we\quad have,\quad no.\quad of\quad moles\quad =\frac { w }{ M } \\ \qquad \qquad \qquad \qquad \qquad W=\quad no.\quad of\quad moles\times M\\ \qquad \qquad \qquad \qquad \qquad \quad \quad =0.25\times 98\\ \qquad \qquad \qquad \qquad \qquad \quad =24.5g\quad of\quad { H } _{ 2 }{ SO } _{ 4 }$
Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

What weight of $SO _2$ can be made by burning sulphur in $5.0$ moles of oxygen?

  1. $640$ grams
  2. $160$ grams
  3. $80$ grams
  4. $320$ grams
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$S+O _2\rightarrow SO _2$


$1$ mole of $O _2$ gives $1$ mole of $SO _2$


Thus $5$ mole of $O _2$ will give 5 mole of $SO _2$

Thus amount of $SO _2$ in 5 mole $SO _2$ is 

$m=5mole\times 64 g/mole\\m=320g$

Thus $5$ mole of $O _2$ will obtain $320g$ of $SO _2$


Hence, the correct option is D.

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

A sample of impure cuprite, $Cu _2O$, contains 66.6% copper. What is the percentage of pure $Cu _2 O$ in the sample: 

  1. 75%

  2. 25%

  3. 60%

  4. 80%
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Number of moles of $Cu$ in $66.6g= \cfrac {66.6 g}{63.5}=1.05$ moles

We have $1$ mole of oxygen per $2$ mole of $Cu$

So, moles of oxygen is $0.525$.
Weight of oxygen present= $0.525 mol\times 16g/mol= 8.4g$

So, we have $(66.6+8.4)g=75g$

Our sample is $75$% pure $Cu _2O$.

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

The number of electrons in 1.8 ml of $H _{2}O$ will be:

  1. $0.1N _{A}$
  2. $0.2N _{A}$
  3. $0.3N _{A}$
  4. $N _{A}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
There is a total of 10 electrons in $ H _{2}O$ molecule.

moles of $H _{2}O(n)=\dfrac{mass\, of\, substance}{molar\, mass}$

Therefore, 1.8 ml of $H _{2}O$ means 0.1 mole
of $H _{2}O$

Number of atoms = $n\times $ Avogrdro Number

Number of atom = $0.1\times 6.022\times 10^{23}$

$= 0.6022\times 10^{23}$

Number of electron of $H _{2}O$ = $0.6022\times 10^{23}\times 10$

$= 6.022\times 10^{23}$ = Avogard's number

So, the correct option is $D$
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 $32 \ g$