Tag: masses of atoms and molecules

Questions Related to masses of atoms and molecules

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 $=\dfrac{3.011\times 10^{24}}{6.022\times 10^{23}}=5\ gm\ mole$