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Molecular mass - class-XII

Description: molecular mass
Number of Questions: 37
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Tags: basic concepts of chemistry chemistry gas laws and mole concept some basic concepts of chemistry atoms and molecules moles and equations atoms, molecules and chemical reactions mole concept and stoichiometry stoichiometry stoichiometric relationships quantitative chemistry chemical formula and mole concept
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The relative atomic mass of $ Ne$ is $20.$ Its relative molecular mass is:

chemistry basic concepts of chemistry molecular mass relative formula mass masses of atoms and molecules

  1. $10$

  2. $20$

  3. $30$

  4. $40$

Show answer
Correct Option: B
Explanation:

The relative atomic mass of  $Ne$ is $20.$ Its relative molecular mass is also $20$ as Neon is mono-atomic.

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

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

  1. $4g$ equivivalent oxygen

  2. $2g$ equivivalent oxygen

  3. $32g$ equivivalent oxygen

  4. $8g$ equivivalent oxygen

Show answer
Correct Option: A
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 .

How many grams of carbon dioxide is dissolved in 1 litre bottle of carbonated water if the manufacturer uses a pressure of 2.4 atmosphere in the bottling process at 25 degree Celsius?

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

  1. 1.52

  2. 4.2

  3. 3.1

  4. 3.52

Show answer
Correct Option: D

Common salt obtained from sea-water contains $ 8.775\%$ $NaCl$ by mass. The number of formula units of $NaCl$ present in 25 g of this salt is :

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

  1. $3.367 \times { 10 }^{ 23 }$ formula units

  2. $2.258 \times { 10 }^{ 22 }$ formula units

  3. $3.176 \times {10 }^{ 23 }$ formula units

  4. $4.73 \times {10 }^{ 25}$ formula units

Show answer
Correct Option: A

How many grams of phosphoric acid $(H _2PO _4)$ would be needed to neutralise $100$g of magnesium hydroxide $(Mg(OH) _2)$?

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

  1. $66.7$ g

  2. $252$

  3. $112.6$ g

  4. $168$ g

Show answer
Correct Option: C
Explanation:
Apply the formula
${\left( {\dfrac{W}{Equivalent\ wt.}} \right) _{{H _3}P{O _4}}} = \left( {\dfrac{W}{Equivalent\ wt.}} \right) _{Mg{\left( {OH} \right) _2}}$
Hence,
${\dfrac{W}{{98 \times 3}} = \dfrac{{100}}{{58 \times 2}}}$
$\therefore{W = 112.6{\text{ }}gram}$

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

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

  1. 16

  2. 8

  3. 32

  4. 4

Show answer
Correct Option: A
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.

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 $S _8$?

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

  1. $1280.0$

  2. $640.0$

  3. $960.0$

  4. $320.0$

Show answer
Correct Option: B
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 $SO _3$

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. 

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

  1. 1.096 ml

  2. 1.32 ml

  3. 5.48 ml

  4. None of these

Show answer
Correct Option: C

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 ${ SO } _{ 8 }$?

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

  1. $1280 g$

  2. $690 g$

  3. $640 g$

  4. $320 g$

Show answer
Correct Option: C
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.

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

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

  1. $2.45$

  2. $24.5$

  3. $0.25$

  4. $245$

Show answer
Correct Option: B
Explanation:
$Moles\quad of\quad { H } _{ 2 }{ SO } _{ 4 }=0.25\\ Molecular\quad mass(M)\quad of\quad { H } _{ 2 }{ SO } _{ 4 }=2+32+16\times 4\\ \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad =34+64\\ \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad =98\quad amu\\ no.\quad of\quad grams(w)\quad =\quad ?\\ we\quad have,\quad no.\quad of\quad moles\quad =\frac { w }{ M } \\ \qquad \qquad \qquad \qquad \qquad W=\quad no.\quad of\quad moles\times M\\ \qquad \qquad \qquad \qquad \qquad \quad \quad =0.25\times 98\\ \qquad \qquad \qquad \qquad \qquad \quad =24.5g\quad of\quad { H } _{ 2 }{ SO } _{ 4 }$

$4 g$ atom of $Ag$ contains: 

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

  1. $108 g$

  2. $4 g$

  3. $432g$

  4. none of these

Show answer
Correct Option: C
Explanation:

$1g$ atom of $Ag$ implies $1$ mole of it

Hence, $4g$ atom is $4$ moles of $Ag$
$1$ moles of $Ag= 108g$
$\therefore 4g$ atom of $Ag$ contains $4 \times 108=432g$

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

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

  1. $640$ grams

  2. $160$ grams

  3. $80$ grams

  4. $320$ grams

Show answer
Correct Option: D
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.

In the following charge,  $3Fe + 4{H _2}O \to F{e _2}{O _4}$ If the atomic weight of iron is $56$, then its equivalent weight will be

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

  1. 42

  2. 21

  3. 63

  4. 84

Show answer
Correct Option: D

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

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

  1. 75%

  2. 25%

  3. 60%

  4. 80%

Show answer
Correct Option: A
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 $Cu _2O$.

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

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

  1. $0.1N _{A}$

  2. $0.2N _{A}$

  3. $0.3N _{A}$

  4. $N _{A}$

Show answer
Correct Option: D
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 $D$

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 :

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

  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

Show answer
Correct Option: B
Explanation:

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

Which of the following statements are true?

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

  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.

Show answer
Correct Option: D
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.

The relative atomic mass of $N$ and relative molecular mass of $N _2$ are:

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

  1. $14, 28$

  2. $7, 14$

  3. $14, 14$

  4. $7, 28$

Show answer
Correct Option: A
Explanation:
Relative atomic mass is the ratio of the average mass of one atom of an element to one-twelfth of the mass of an atom of carbon-12.

The relative atomic mass of N is 14  and relative molecular mass of $N _2$ is 28.

Hence, option A is correct.

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.

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

  1. $16 gm$

  2. $32 gm$

  3. $160 gm$

  4. $80 gm$

Show answer
Correct Option: B
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 $= 16 gm$

The element chlorine consists of mixture of 75.53% $ _{17}$Cl$^{35}$ and 24.47% $ _{17}$Cl$^{37}$ having a mass of 34.97 amu and 36.95 amu, respectively. The atomic weight of chloride is:

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

  1. 35.25

  2. 35.45

  3. 36.25

  4. 36.45

Show answer
Correct Option: B
Explanation:

Given - $ _{17} Cl^{35} - 75.53$% and mass of $Cl$ 34.97 amu
$ _{17} C^{37} - 24.47$% and mass of $Cl$ 36.95 amu
$\therefore $ Atomic weight of chlorine
$= \displaystyle \frac{(75.53 \times 34.97)+(24.47 \times 36.95)}{100} = \frac{3545.45}{100}$
$=35.45$

The formula of oxide of a metal is $MO$ and equivalent weight of metal is $20$. The atomic weight of metal is

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

  1. $40$

  2. $20$

  3. $30$

  4. $10$

Show answer
Correct Option: A
Explanation:

Valency of $M$ in $MO=2$
Equivalent wt. of $M = 20$
Atomic wt. of $\text{M = Equivalent wt. Valency}$
$\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;=20\times2=40$

Two flasks A and B of equal volumes are kept under similar conditions of temperature and pressure. If flask A holds 16.2 g of gas X while flask B holds 1.012 g of hydrogen, calculate the relative molecular mass of gas X:

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

  1. 20 g

  2. 32 g

  3. 28 g

  4. 44 g

Show answer
Correct Option: B
Explanation:

A mole is equal to the relative molecular mass of a gas. As given, the number of moles of gas X and hydrogen are same in the two flasks.
Therefore no. of moles in 2g of hydrogen gas = 1
No. of moles in 1.01g of hydrogen gas = 1/2
Now the weight of gas X that contains 1/2 moles = 16.2g
Weight of gas X that contains 1mole = $\frac{16.2}{1/2}$ = 32g

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

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

  1. $16$

  2. $32$

  3. $64$

  4. $48$

Show answer
Correct Option: B
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 $32 \ g$

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?

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

  1. 24

  2. 39

  3. 40

  4. 30

Show answer
Correct Option: C
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.

What was the need for using relative atomic mass or relative molecular mass?

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

  1. To round off every atomic mass as a multiple of 2

  2. To create new terminologies

  3. As the mass of atoms or molecules were small

  4. None of the above

Show answer
Correct Option: C
Explanation:

Relative atomic mass or relative molecular mass was used as the mass of the atoms or molecules were very small. Therefore there was a need to be taken relative to some other elements.

How many gram-equivalents of NaOH are required to neutralise 25 cm$^3$ of a decinormal HCl solution ?

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

  1. 0.00125

  2. 0.0025

  3. 0.0050

  4. 0.025

Show answer
Correct Option: B
Explanation:
For acid-base reactions,
$\underset{(HCl)}{g-equivalent of acid}\, =\, \underset{(NaOH)}{g-equivalent of base}$
$\therefore$ g-equivalent of acid = $(25\,\times\, 10^{-3})dm^3\, \times\, \displaystyle \frac{1}{10}$
$=\, 25\, \times\, 10^{-4}$
$=\, 0.0025$

The atomic mass of sodium is 23. The gram-atomic mass of sodium is _______.

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

  1. 23 g

  2. 46 g

  3. 42 g

  4. 11.5 g

Show answer
Correct Option: A
Explanation:

Gram atomic mass is the mass, in grams, of one mole of atoms in a monoatomic chemical element. It is numerically equal to the relative atomic mass in grams. The atomic mass of an element expressed in grams is called gram atomic mass.

$\therefore$  gram atomic mass of sodium $=23gm$

How many gram atoms are present in $256 g$ of ${ O } _{ 2 }$?

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

  1. $16$ gram atoms

  2. $32$ gram atoms

  3. $14$ gram atoms

  4. $36$ gram atoms

Show answer
Correct Option: A
Explanation:

Given that, 
Mass of $O _2$ = 256 g


We know that, 
Number of moles = $[{Mass/Molar mass}]$

So, 
Moles of $O _2$ = $\dfrac {256}{32} =8$ 


Number of gram atoms = Number of moles$*$Numer of atoms 

                                        = $8 \times 2=16$ gram atoms 

Thus, option A is the correct answer.

An ornamental ring contains 275 carats of diamond. How many grams diamond does it have?

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

  1. $275 \times 200 \times 10^{4}\, g$

  2. $275 \times 200 \times 10^{-3}\, g$

  3. $275 \times 200 \times 10^{3}\, g$

  4. $275 \times 200 \times 10^{-4}\, g$

Show answer
Correct Option: B
Explanation:

One carat is equal to 200 milligrams, or 0.2 grams.

so the 275 carats having weight $275 \times 200 \times 10^{-3}$ gm
answer B is correct

 How many grams of $NaCl$ represent 1 mole?

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

  1. $58.5$

  2. $108 g$

  3. $85.7 g$

  4. $74.6 g$

Show answer
Correct Option: A
Explanation:

 Molecular weight of $NaCl$ is $58.5$ grams,

 $=> 1$ mole represent $58.5$ grams of $NaCl.$
Hence.
option $A$ is correct answer.

The charge to mass ratio of $\alpha - particle$ is approximately ____  of the charge to mass ratio of a proton is:

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

  1. half

  2. twice

  3. 4 times

  4. 6 times

Show answer
Correct Option: B
Explanation:
Alpha particle is a helium nucleus containing two protons and two neutrons so its charge is $twice$ the proton’s charge while the mass is about 4 times greater.
Let the charge of the proton be $+e$, then the charge of the alpha particle will be $+2e$. Similarly mass of the proton be m, then the mass of the alpha particle will be $4m$.
Specific charge = charge/mass of the substance.
For proton, specific charge =$\dfrac { e }{ m } $
For alpha particle, specific charge = $\dfrac { 2e }{ 4m } $
Therefore the ratio is = $\dfrac { e }{ m } $ x $\dfrac { 4m }{ 2e }  = 2:1$
Hence, the charge to mass ratio of an alpha particle is approximate twice the charge to mass ratio of a proton.  
So, the correct option is $B$

How many grams of phosphoric acid would be needed to neutralize $100$ gm of magnesium hydroxide? (Molecular weight of $H _3PO _4=98$ and $Mg(OH) _2=58.3 gm$)

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

  1. 66.7 gm

  2. 252 gm

  3. 112 gm

  4. 168 gm

Show answer
Correct Option: C

The weight of $1$ litre of a glass at STP is $2$ grams, its molecular weight is:

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

  1. $44.4$

  2. $44.8$

  3. $44.1$

  4. $55.8$

Show answer
Correct Option: B
Explanation:

$At\quad STP,\quad volume\quad of\quad 1\quad mole\quad gas\quad =\quad 22.4\quad L\ Mass\quad of\quad 1L\quad gas\quad =\quad 2g\ Mass\quad of\quad 22.4L\quad gas\quad =\quad 2\times 22.4\quad =\quad 44.8\ So,\quad molecular\quad weight\quad of\quad gas\quad =\quad 44.8\ So,\quad correct\quad answer\quad is\quad option\quad B.$

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

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

  1. $10$ gm moles

  2. $5$ gm moles

  3. $1$ gm mole

  4. $0.5$ gm mole

Show answer
Correct Option: B
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 $=\dfrac{3.011\times 10^{24}}{6.022\times 10^{23}}=5\ gm\ mole$

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

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

  1. (a) 249 (b) 249

  2. (a) 124.5 (b) 124.5

  3. (a) 249 (b) 124.5

  4. (a) 124.5 (b) 249

Show answer
Correct Option: B
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 $=\dfrac { 249 }{ 2 } =124.5$

10 ml of 0.1 M solution sodium hydroxide is completely neutralised by 25 ml of 3 gram of dibasic acid in one solution the molecular weight of acid is:

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

  1. 225 g

  2. 250 g

  3. 300 g

  4. 150 g

Show answer
Correct Option: D
Explanation:
Given,
Concentration of $NaOH=0.1 N$
Volume$=10\,mL$
Mass of Dibasic acid$=3g$
Volume$=25\,mL$
Using,
$n _{1}M _{1}V _{1}=n _{2}M _{2}V _{2}$
$n _{2}=2$
$\Rightarrow 1\times 0.1\times 10=2\times25\times\cfrac{3}{M}$
$\Rightarrow M=\cfrac{2\times 25\times 3}{10\times 0.1}$
$\Rightarrow M=150\,g$

M g of a substance when vaporised occupy a volume of 5.6 litre at NTP. The molecular mass of the substance will be: 

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

  1. $M$

  2. $2M$

  3. $3M$

  4. $4M$

Show answer
Correct Option: D
Explanation:
Given,
$Mg$ of substance occupy volume$=5.6\,litre $ at NTP.
At NTP,
1 mol occupy 22.4 litre of volume.
5.6 litre$=Mg$
22.4 litres$=4\,Mg$ of substance.
So, Molecular mass of gas$=4\,Mg/mol$
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