Tag: chemistry

Questions Related to chemistry

It was found from the chemical analysis of a gas that it has two hydrogen atoms for each carbon atoms. At $0^o C$ and $1\ atm$, its density is $1.25\ g$ per litre. The formula of the gas would be ______________.

chemistry the language of chemistry percent composition percentage composition and empirical formula empirical formula, percentage composition and molecular formula

  1. $CH _2$

  2. $C _2H _4$

  3. $C _2H _6$

  4. $C _4H _8$

Show answer
Correct Option: B
Explanation:

$PV=nRT$


$P=\dfrac {dRT}{M}$

$M=\dfrac {1.25\times 0.082\times 273}{1}$

$=27.98$

Molar mass $\equiv 28\ gram/mole$

$\therefore \ $ as empirical formula $=CH _2$

$\therefore \ $ emprical mass $=12+2=14$

$n=\dfrac {28}{14}=2$

$\therefore \ $ Molecular formula $=(CH _2) _2$

$=C _2H _4$

Hence, the correct option is $\text{B}$

When burnt in air, $14.0\ g$ mixture of carbon and sulpher gives a mixture of $CO 2$ and $SO _2$ in the volume ratio of $2:1$, volume being measured at the same conditions of temperature and pressure. Moles of carbon in the mixture is _________.

chemistry the language of chemistry percent composition percentage composition and empirical formula empirical formula, percentage composition and molecular formula

  1. $0.25$

  2. $0.40$

  3. $0.5$

  4. $0.75$

Show answer
Correct Option: C
Explanation:

Consider the mass of $C=x$


mass of $S=14-x$

moles of $C=\dfrac {x}{12};$ moles of $\dfrac {14-x}{32}$

$C+O _2\to CO _2;\quad S+O _2\to SO _2$

moles of $C=$ moles of $CO _2=\dfrac {x}{12}\quad $ moles of $S=$ moles of $SO _2=\dfrac {14-x}{32}$

Given,

$\dfrac {V _c}{V _s}=\dfrac {2}{1}$

$V\alpha $ no. of mole

$\dfrac {\dfrac {x}{12}}{\dfrac {14-x}{32}}=\dfrac {2}{1}$

$\dfrac {x}{12}\times \dfrac {32}{14-x}=\dfrac {2}{1}$

$\dfrac {4x}{42-3x}=1$

$4x=42-3x$

$7x=42$ 

$\boxed {x=6}$

$\therefore \ $ moles of $C$ in mixture $=\dfrac {w}{M}=\dfrac {6}{12}=0.5$

Answer is option $C$

If air is pumped slowly but continuously into a metallic cylinder of strong wall, what would happen to the air inside the cylinder?

chemistry the language of chemistry percent composition percentage composition and empirical formula empirical formula, percentage composition and molecular formula

  1. Temperature of air would increase

  2. Pressure of air would increase

  3. Pressure of air would decrease

  4. Temperature and pressure of air would increase

Show answer
Correct Option: B
Explanation:

Due to continuous pumping number of moles will increase
We know,
$n\propto P$
$n\propto V$
$n\propto \dfrac{1}{T}$
$\therefore$ Pressure will increase.
Option B.

For $10$ min each, at $27^o$C, from two identical holes nitrogen and an unknown gas are leaked into a common vessel of $3$l capacity. The resulting pressure is $4.18$ bar and the mixture contains $0.4$ mole of nitrogen. The molar mass of the unknown gas is?

chemistry the language of chemistry percent composition percentage composition and empirical formula empirical formula, percentage composition and molecular formula

  1. $112$g $mol^{-1}$

  2. $242$g $mol^{-1}$

  3. $224$g $mol^{-1}$

  4. $422$g $mol^{-1}$

Show answer
Correct Option: C

What is the molecular formula of arsenious chloride?

chemistry the language of chemistry percent composition percentage composition and empirical formula empirical formula, percentage composition and molecular formula

  1. $ AsCI _{3}$

  2. $ As _{2}CI _{6}$

  3. $ As _{2}CI _{5}$

  4. $ AsCI _{5}$

Show answer
Correct Option: B

If two compounds have the same empirical formula but different molecular formula, they must have :

chemistry the language of chemistry percent composition percentage composition and empirical formula empirical formula, percentage composition and molecular formula

  1. different percentage composition

  2. different molecular weights

  3. same vapour density

  4. none of these

Show answer
Correct Option: B
Explanation:

If two compounds have the same empirical formula but different molecular formula, they must have different molecular weights.


For example, $CH _2O$ and $C _6H _{12}O _6$ have the same empirical formula but different molecular formula, they have different molecular weights.

Option B is correct.

Calculate the number of molecules present in $0.5$ moles of magnesium oxide $\left( MgO \right) $. 

[Atomic weights :  $Mg=24, O=16$]

chemistry the language of chemistry percent composition percentage composition and empirical formula empirical formula, percentage composition and molecular formula

  1. $14.09\times { 10 }^{ 23 }$ molecules

  2. $3.0115\times { 10 }^{ 23 }$ molecules

  3. $30.12\times { 10 }^{ 23 }$ molecules

  4. $14.09\times { 10 }^{ -23 }$ molecules

Show answer
Correct Option: B
Explanation:
1 mole of MgO contains Avogadro's number of molecules which is $ \displaystyle 6.023 \times 10^{23}$ molecules.

0.5 mole of MgO will contain $ \displaystyle 0.5 \times 6.023 \times 10^{23}=3.0115 \times 10^{23}$ molecules.

Common salt is chemically sodium chloride ($NaCl$).

chemistry substances in common use salts and their properties study of some important salts salts used in daily life

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

The well-known table salt is chemically sodium chloride. Its chemical formula is $NaCl$.

The product of electrolysis of conc. solution of common salt is?

chemistry substances in common use salts and their properties study of some important salts salts used in daily life

  1. $Na+Cl _{2}$

  2. $H _{2}+O _{2}$

  3. $NaOH+H _{2}+Cl _{2}$

  4. $Na+Cl _{2}+O _{2}$

Show answer
Correct Option: C
Explanation:

The ionization of salt:

$NaCl\rightarrow Na^{+}+Cl^{-}$

The half-reaction at the cathode is:

$H _2O+2e^{−}\rightarrow H _2+2OH^{−}$

Here, the reduction is taking place.

The half-reaction at the anode is:

$2Cl^{-}\rightarrow Cl _2+1e^{−}$

Here, oxidation is taking place.

The overall reaction is as follows:

$NaCl+H _2O\rightarrow Na^{+}+OH^{−}+H _2+Cl _2$.

Hence, option $C$ is correct.

Which of the following is not hydroscopic-

chemistry substances in common use salts and their properties study of some important salts salts used in daily life

  1. NaCl

  2. ${\text{MgC}}{{\text{l}} _{2\;\;}}$

  3. ${\text{CaC}}{{\text{l}} _{2\;\;}}$

  4. LiCl

Show answer
Correct Option: D