Tag: molecular mass

Questions Related to molecular mass

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.