Tag: chemistry

Questions Related to chemistry

Which of the following will not produce an electrolytic solution upon addition of water?
chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

  1. $N _2(g)$

  2. $HCl(g)$

  3. $KOH(s)$

  4. $NaI(s)$

  5. $CaCl _2(s)$

Show answer
Correct Option: A
Explanation:

When water is added, HCl, KOH, NaI and $CaCl _2$ will produce an electrolytic solution. However, $N _2$ will not produce an electrolytic solution on addition of water. Nitrogen is a homo-nuclear diatomic molecule which does not dissociate into aqueous solution.

Electrolysis of which of the following compound will give $KOH$?

chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

  1. Aqueous $KCl$ solution

  2. Fused $KCl$

  3. Fused potassium

  4. Aqueous potassium

Show answer
Correct Option: A
Explanation:

Electrolysis of aqueous $KCl$ solution will give $KOH$. This is similar to the preparation of $NaOH$ by electrolysis of aqueous $NaCl$ solution. The electrolysis of fused $KOH$ will give potassium metal.

A solution containing one mole per lite of each $Cu(NO {3}) _{2}; AgNO _{3}; Hg _{2}(NO _{3}) _{2}$ and $Mg(NO _{3}) _{2}$ is being electrolysed by using inert electrodes. The values of standard electrode potentials (reduction potentials) are $Ag/ Ag^{+} = 0.80\ volt, 2Hg/ H _{2}^{2+} = 0.79\ volt, Cu/ Cu^{2+} = + 0.24\ volt, Mg/ Mg^{2+} = -2.37\ volt$. With increasing voltage, the sequence of deposition of metals on the cathode will be___________.

chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

  1. $Ag, Hg, Cu$

  2. $Cu, Hg, Ag$

  3. $Ag, Hg, Cu, Mg$

  4. $Mg, Cu, Hg, Ag$

Show answer
Correct Option: A
Explanation:

Higher the standard reduction potential, higher will be the tendency to undergo reduction so, more fast will be its deposition on electrode (cathode) .

$E^o _{Ag/Ag^+}=0.80V\ E^o _{2Hg/Hg _2^{2+}}=0.79V\quad \downarrow (Reduction\quad potential\quad decreases)\ E^o _{Cu/Cu^{2+}}=0.24V$    
Order of deposition= $Ag> Hg> Cu$

The emf of a cell containing sodium/ copper electrodes is $3.05\ V$, if the electrode potential of copper electrode is $+0.34\ V$, the electrode potential of sodium is:

chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

  1. $-2.71\ V$

  2. $+ 2.71\ V$

  3. $-3.71\ V$

  4. $+3.71\ V$

Show answer
Correct Option: A
Explanation:
$E _{cell}^{\circ}=E _{cathode}^{\circ}-E _{anode}^{\circ}$
$\Rightarrow3.05=0.34-(-2.71)$
$=3.05$
$\therefore$ Electrode potential of Sodium is $-2.71V$

The resulting solution obtained at the end of electrolysis of concentrated aqueous solution of $NaCl:$

chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

  1. Turns blue litmus into red

  2. Turns red litmus into blue

  3. Remains colourless with phenolphthalein

  4. The colour of red or blue litmus does not change

Show answer
Correct Option: B
Explanation:

During the electrolysis of aqueous sodium chloride solution, the products are $NaOH , Cl _2$ and $H _2$.
$NaCl(aq) + H _2O(l) \rightarrow Na^+ (aq) +OH^-(aq) +\frac{1}{2} H _2(g) +\frac{1}{2}Cl _2(g)$
Due to formation of base, it turns res litmus into blue.

Which of the following batteries are responsible for direct environmental hazard?

chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

  1. Alkaline dry cell

  2. Mercury cell

  3. $Ni-Cd$ battery

  4. Lithium battery

Show answer
Correct Option: A,B,C
Explanation:

Alkaline batteries are prone to leaking potassium hydroxide, a caustic agent that can cause respiratory, eye and skin irritation. Potassium, if it leaks, can cause severe chemical burns thereby affecting the eyes and skin.

Mercury can even be absorbed through the skin. These harmful substances permeate into the soil, groundwater and surface water through landfills and also release toxins into the air when they are burnt in municipal waste combustors.

For humans, both lead and cadmium can be taken only by ingestion or inhalation.  Moreover, cadmium is easily taken up by plant roots and accumulates in fruits, vegetables and grass. The impure water and plants in turn are consumed by animals and human beings, who then fall prey to a host of ill-effects.

Since Li-ion batteries contain less of toxic metals than other types of batteries which may contain lead or cadmium, they are generally categorized as non-hazardous waste. 

A, B and C are correct options.

An acidic solution of $C{u^{2 + }}$ salt containing $0.4\,g$ of $C{u^{2 + }}$ is electrolysed until all the copper is deposited. The electrolysis is continued for seven more minutes with the volume of solution kept at 100 ml and the current at $1.2$ amp. Find the volume of gases evolved at anode and Cathode at NTP during the entire electrolysis. 

chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

  1. $78.20\,ml,\,\,99.78\,ml$

  2. $58.48\,ml,\,\,78.20\,ml$

  3. $98.56\,ml,\,\,58.24\,ml$

  4. $78.20\,ml,\,\,58.48\,ml$

Show answer
Correct Option: C
Explanation:
Solution:- (C) $98.56 mL, \; 58.24 \; mL$
Assuming ${Cu}^{+2}$ salt to be $CuS{O} _{4}$, the reactions occuring at the electrodes would be-
At anode:-
${H} _{2}O \longrightarrow 2 {H}^{+} + \cfrac{1}{2} {O} _{2} + 2 {e}^{-}$
At cathode:- 
${Cu}^{+2} + 2 {e}^{-} \longrightarrow Cu$
Equivalent weight of ${Cu}^{+2} = 31.5 \; g$
$0.4 \; g$ of ${Cu}^{+2} = \cfrac{0.4}{31.5} = 0.0127 \; g$ equivalent
At the same time the oxygen deposited at anode.
Equivalent weight of oxygen $= 8 \; gm$
Mass of oxygen deposited $= 0.0127 \times \cfrac{8}{32} = 0.0031 \text{ mol}$
After the complete deposition of copper, the reactions would be-
At anode:-
${H} _{2}O \longrightarrow 2 {H}^{+} + \cfrac{1}{2} {O} _{2} + 2 {e}^{-}$
At cathode:-
$2 {H} _{2}O + 2{e}^{-} \longrightarrow {H} _{2} + 2 {OH}^{-}$

Given:-
$I = 1.2 \; A$
$t = 7 \text{ min} = 7 \times 60 = 420 \; s$
Amount of charge passed $= I \times t \ = 1.2 \times 7 \times 60 = 504 \; C$
Therefore,
Amount of oxygen liberated $= \cfrac{1}{96500} \times 504 = 0.00523 \; g$ equivalent $= \cfrac{8}{32} \times 0.00523 = 0.0013 \text{ mol}$
Amount of hydrogen liberated $= 0.00523 \; g$ equivalent $= \cfrac{1}{2} \times 0.00523 = 0.0026 \text{ mol}$
Now,
Gas evolved at anode $= {O} _{2}$
Total no. of moles of ${O} _{2}$ evolved $= 0.0031 + 0.0013 = 0.0044 \text{ mol}$
$\therefore$ Volume of gas evolved at anode $= 0.00447 \times 22400 = 98.56 \; mL$
Gas evolved at cathode $= {H} _{2}$
Total no. of moles of ${H} _{2}$ evolved $= 0.0026 \text{ mol}$
$\therefore$ Volume of gas evolved at cathode $= 0.0026 \times 22400 = 58.24 \; mL$
Hence the volume of gases evolved at anode and cathode at NTP during the entire electrolysis $98.56 \; mL$ and $58.24 \; mL$ respectively.

During electrolysis of brine solution, product obtained at cathode and anode are:

chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

  1. hydrogen and chlorine gas respectively

  2. chlorine and hydrogen gas respectively

  3. sulphate and chlorine gas respectively

  4. sodium and hydrogen gas respectively

Show answer
Correct Option: A
Explanation:

$At\ cathode:{ 2H } _{ 2 }O+{ 2e }^{ - }\rightarrow { H } _{ 2 }+{ 2OH }^{ - }\ At\ anode:{ 2Cl }^{ - }\rightarrow { Cl } _{ 2 }+{ 2e }^{ - }$

Conductivity of $NaCl$ is more:

chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

  1. in a aqueous solution than in alcohol

  2. in alcohol than in a aqueous solution

  3. both in aqueous solution and in alcohol

  4. none of the above

Show answer
Correct Option: A
Explanation:

 The conductivity of NaCl is more in an aqueous solution than in alcohol.
Water is a highly polar solvent. In water, NaCl completely dissociates into sodium ions and chloride ions.
$\displaystyle NaCl \rightarrow Na^+  +  Cl^-$
The electrical conductivity of aqueous NaCl solution is due to a presence of these ions.
Alcohol is less polar than water. Hence, the degree of ionization of NaCl in alcohol is much lower than that in water.   Hence, a lesser number of current carrying ions are present in alcohol. Hence, $NaCl$ in alcohol has lower conductivity than $NaCl$ in an aqueous solution.

3%solution of glucose is isotonic with 1% solution of a non-volatile non-electrolyte substance the molecular mass of the substance would be 

chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

  1. 30

  2. 60

  3. 90

  4. 120

Show answer
Correct Option: B
Explanation:

since the two solution are isotonic,

therefore, $C _1 RT = C _2 RT$
$C _1 = C _2$
let  mass of solution = 100 g
so mass of glucose = 3g
and mass of non-volatile substance = 1g
so, we get
$\dfrac{3}{180} = \dfrac{1}{M}$
$M = 60$
hence, molecular mass of non-volatile substance = 60