Tag: relative formula mass

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

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:

  1. 20 g

  2. 32 g

  3. 28 g

  4. 44 g
Reveal answer Fill a bubble to check yourself
B Correct answer
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

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

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

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

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

  1. 0.00125

  2. 0.0025

  3. 0.0050

  4. 0.025
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
For acid-base reactions,
$\underset{(HCl)}{g-equivalent of acid}\, =\, \underset{(NaOH)}{g-equivalent of base}$
$\therefore$ g-equivalent of acid = $(25\,\times\, 10^{-3})dm^3\, \times\, \displaystyle \frac{1}{10}$
$=\, 25\, \times\, 10^{-4}$
$=\, 0.0025$
Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

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

  1. 23 g

  2. 46 g

  3. 42 g

  4. 11.5 g
Reveal answer Fill a bubble to check yourself
A Correct answer
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 $=23gm$

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

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

  1. $16$ gram atoms
  2. $32$ gram atoms
  3. $14$ gram atoms
  4. $36$ gram atoms
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  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. $275 \times 200 \times 10^{-4}\, g$
Reveal answer Fill a bubble to check yourself
B Correct answer
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