Tag: chemical changes

Questions Related to chemical changes

What is the number of moles of oxygen gas evolved by electrolysis of $180\ g$ of water?

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $2.5$

  2. $5.0$

  3. $7.5$

  4. $10.0$

Show answer
Correct Option: B
Explanation:

$2{ H } _{ 2 }O(l)\rightarrow2{ H } _{ 2 }(g)+{ O } _{ 2 }(g)$

moles of water=$\frac { 180 }{ 18 } =10$
1 mole of oxygen for 2 moles of water.
So, 5 moles of oxygen for 10 moles of water.

When water is electrolysed, hydrogen and oxygen gases are produced. If $1.008\ g$ of $H _{2}$ is liberated at cathode, what mass of $O _{2}$ is formed at the anode?

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $32\ g$

  2. $16\ g$

  3. $8\ g$

  4. $4\ g$

Show answer
Correct Option: C
Explanation:

$\dfrac {W _{1}}{W _{2}} = \dfrac {E _{1}}{E _{2}}$
$\dfrac {1.008}{W _{2}} = \dfrac {1.008}{8}$
$\therefore W _{2} = 8\ g$
where, $E _{1}$ and $E _{2}$ are equivalent masses of hydrogen and oxygen respectively.

Zn metal reduces ${SO _{3}}^{2-}$ ions into $H _{2}S$in presence of concentrated $H _{2}SO _{4}$ What weight of Zn is required for
reduction of 6.3 g $Na _{2}SO _{3}$ in presence of concentrated acid.

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. 9.75 g

  2. 13 g

  3. 130 g

  4. 23 g

Show answer
Correct Option: A
Explanation:

eq. of $Zn=$ eq.of ${SO _{3}}^{2-}$
$\frac{w}{65}\times 2 =\frac{6.3}{126}\times 6\Rightarrow w=\frac{6.3}{126}\times \frac{6\times 65}{2}=9.75 g$


$Zn\left( s \right) \left|\ Zn{ { \left( CN \right)  } } _{ 4 }^{ 2- }\ \left( 0.5\ M \right) ,{ CN }^{ - }\left( 0.01 \right)  \right| \left|\ Cu{ \left( { NH } _{ 3 } \right)  } _{ 4 }^{ 2+ }\ \left( 0.5\ M \right) ,{ NH } _{ 3 }\left( 1\ M \right)  \right|\ Cu\left( s \right) $
Given: ${ K } _{ f }$ of $Zn{ { \left( CN \right)  } } _{ 4 }^{ -2\  }=\ { 10 }^{ 16 }$, $\quad \quad \quad$ ${ K } _{ f }$ of $Cu{ \left( { NH } _{ 3 } \right)  } _{ 4 }^{ 2+ }\ =\ { 10 }^{ 12 }$
$\displaystyle \quad \quad \ \ { E } _{ Zn|{ Zn }^{ -2 } }\ =\ 0.76V\ ;\ { E } _{ { Cu }^{ +2 }|Cu }\ =\ 0.34V\ ,\ \dfrac { 2.303RT }{ F } =0.06$
The emf of above cell is:

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $1.22\ V$

  2. $1.10\ V$

  3. $0.98\ V$

  4. $None\ of\ these$

Show answer
Correct Option: A

Calculate the mass of Ag deposited at cathode when a current of 2A was passed through a solution of $Ag{ NO } _{ 3 }$ for 15 min.
(Given : Molar mass of $Ag = 108\ g\ { mol }^{ -\ 1 }$ $\ 1F=96500\ C\ { mol }^{ -1 }$).

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $3.015\ g$

  2. $2.015\ g$

  3. $4.2\ g$

  4. $3.1\ g$

Show answer
Correct Option: B
Explanation:

Given:

Molar Mass of Ag = 108 g/mol

$1F = 96500\ C mol^{−1}$

Reaction at cathode = $Ag + e^-  \rightarrow   Ag(s)$ 

$w = Zlt$

Where, w = Mass deposited at cathode

Z = electrochemical constant

I = current

t = time

Now I = 2amp

$t = 15\ min = 15\times 60 = 900\ seconds$

Z = Eq. wt of substance $/ 96500 = 108/96500$ 

So,

$w = \dfrac{108}{96500} \times 900 \times 2 $

= $2.015g$

The electrochemical equivalent of silver is $0.0011180g$. When an electric current of $0.5$ ampere is passed through an aqueous silver nitrate solution for $200sec$, the amount of silver deposited is:

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $1.1180g$

  2. $0.11180g$

  3. $5.590g$

  4. $0.5590g$

Show answer
Correct Option: B
Explanation:

According to the data given when $1$ e is passed the amount of silver,

deposited is $0.0011180\,g$
$\therefore (0.5\times 200)c$ is passed
then $(0.0011180\times 100)g$
of silver gets deposited 
$=0.11180\,g$

Brine solution on electrolysis will not give__________.

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $NaOH$

  2. ${Cl} _{2}$

  3. ${H} _{2}$

  4. ${O} _{2}$

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Correct Option: D

$H _2(g)$ and $O _2(g)$ , can be produced by the electrolysis of water. What total volume (in $L$) of $O _2$ and $H _2$ are produced at $STP$ when a current of $30$ A is passed through a $K _2SO _4\, (aq)$  solution for 193 minutes?

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. 20.16

  2. 40.32

  3. 60.48

  4. 80.64

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Correct Option: D

During the mid ninteenth century, Daguerro-type portraits were very popular. A portrait image of a person was made on silver plated copper by developing the image with ?

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. Silver bromide

  2. Mercury vapour

  3. 'Hypo' (sodium hypochlorite)

  4. An iodine solution

Show answer
Correct Option: B
Explanation:
The latent image was developed to visibility by several minutes of exposure to the forms given off by heated mercury in purpose made developing box.
So development process of Daguerro-type portraits is done with Mercury Vapour.

Silver can be spread as a thin sheet on another metal by electroplating. The film of silver sticks strongly to the metal. Which of the following metals cannot be properly plated with silver?

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. Copper

  2. Iron

  3. Nickel

  4. Brass

Show answer
Correct Option: B
Explanation:

Iron cannot be property plated with silver it becomes peel if plated with silver are to peeling of silver it cannot properly plated iron.