Tag: relative formula mass

Questions Related to relative formula mass

$4 g$ 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
$= \displaystyle \frac{(75.53 \times 34.97)+(24.47 \times 36.95)}{100} = \frac{3545.45}{100}$
$=35.45$