Tag: chemistry

Questions Related to chemistry

Which is correct about silver plating?

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

  1. Anode - pure $Ag$

  2. Cathode - object to be electroplated

  3. Electrolyte - $Na[Ag(CN) _{2}]$

  4. All of the above

Show answer
Correct Option: D
Explanation:
In silver plating, the object to be plated (e.g., a spoon) is made from the cathode of an electrolytic cell. 

The anode is a bar of silver metal, and the electrolyte (the liquid in between the electrodes) is a solution of silver cyanide, $AgCN$, in water.

When a direct current is passed through the cell, positive silver ions ($Ag^+$) from the silver cyanide migrate to the negative anode (the spoon), where they are neutralized by electrons and stick to the spoon as silver metal.

Hence, option D is correct.

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. ${O} _{2}$

Show answer
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

Show answer
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.