Tag: chemical changes

Quizzes (7) Questions (139)

Questions Related to chemical changes

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

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?

  1. $32\ g$
  2. $16\ g$
  3. $8\ g$
  4. $4\ g$
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

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.

  1. 9.75 g

  2. 13 g

  3. 130 g

  4. 23 g
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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


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

$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:

  1. $1.22\ V$
  2. $1.10\ V$
  3. $0.98\ V$
  4. $None\ of\ these$
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

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 $Ag = 108\ g\ { mol }^{ -\ 1 }$ $\ 1F=96500\ C\ { mol }^{ -1 }$).

  1. $3.015\ g$
  2. $2.015\ g$
  3. $4.2\ g$
  4. $3.1\ g$
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $

= $2.015g$

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

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:

  1. $1.1180g$
  2. $0.11180g$
  3. $5.590g$
  4. $0.5590g$
Reveal answer Fill a bubble to check yourself
B Correct answer
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 
$=0.11180\,g$

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

$H _2(g)$ 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?

  1. 20.16

  2. 40.32

  3. 60.48

  4. 80.64
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Total charge passed is Q = I * t = 30 A * (193 * 60 s) = 347400 C. The moles of electrons transferred are n(e-) = Q / F = 347400 / 96500 = 3.6 mol. From the electrolysis of water, 2 moles of electrons produce 1 mole of gas total (0.5 mol O2 and 1 mol H2 per 2 moles of electrons, meaning 3 moles of total gas per 4 moles of electrons; specifically, 4 e- give 1 mole O2 (22.4 L) and 2 moles H2 (44.8 L)). Scaling by 3.6 mol of electrons gives (3.6 / 4) * 3 * 22.4 = 60.48 L total gas at STP.

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

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 ?

  1. Silver bromide

  2. Mercury vapour

  3. 'Hypo' (sodium hypochlorite)

  4. An iodine solution
Reveal answer Fill a bubble to check yourself
B Correct answer
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.
Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

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?

  1. Copper

  2. Iron

  3. Nickel

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