Chemistry

Electrochemistry and Solutions

206 Questions

Work through advanced chemistry questions focusing on electrochemistry and properties of solutions. Key themes include electrolytic conductivity, colloidal solutions, and solubility products. These concepts are frequently tested in JEE advanced, NEET, and university level chemistry competitive examinations.

Colloidal solutionsMolar conductivitySolubility productElectrolytic conductivityHydrolysis of saltsEquivalent conductivity

Electrochemistry and Solutions Questions

Multiple choice evs experiments with water water and its types hard and soft water what floats - what sinks

The molecular formula of a commercial resin used for exchanging ions in water softening is $C 8H _7SO _3 $ (Mol. wt. 206). Water would be the maximum uptake of $Ca^{2+} $ ions by the resin when expressed ____ in mole per gram of resin.

  1. $\dfrac{2} {309} $
  2. $\dfrac{1} {412} $
  3. $\dfrac{1} {103} $
  4. $\dfrac{1} {206} $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The chemical reaction for softening water can be given as:-


$2C _8H _7(SO _3)Na+Ca^{+2}\longrightarrow [C _8H _7(SO _3)] _2Ca+2Na^{+}$

$\therefore$  $2$ moles of resin$\equiv1$ mole of $Ca^{2+}$

$\therefore$  Mass of resin = $206\times 2=412g$

For $412g$ of resin, $1$ mole of $Ca^{2+}$ is required.

$\therefore$  Maximum uptake of $Ca^{2+}$ ions $= \cfrac {1}{412}$ mole/gram of resin.

Multiple choice chemistry nitrogen and sulfur ammonia-properties and uses ammonia compounds of nitrogen - ammonia

The formula of Ammonium Sulphate is:

  1. $N{H} _{4}S{O} _{4}$
  2. ${(N{H} _{4})} _{2}S{O} _{4}$
  3. $N{H} _{4}{(S{O} _{4})} _{2}$
  4. $N{H} _{2}{(S{O} _{4})} _{2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ammonium sulfate is made by treating ammonia, often as a by-product from coke oven, with sulfuric acid: 

$2 NH _3$ + $H _2SO _4 \rightarrow$   $(NH _4) _2SO _4$
Option "B" is correct.

Multiple choice chemistry nitrogen and sulfur ammonia-properties and uses ammonia compounds of nitrogen - ammonia
The dissolution of ammonia gas in water does not obey Henry's law. On dissolving, a major portion of ammonia molecules reacts with ${H} _{2}O$ to form ${NH} _{4}OH$ molecules. ${NH} _{4}OH$ again dissociates into ${NH} _{4}^{+}$ and ${OH}^{-}$ ions. In solution therefore, we have ${NH} _{3}$ molecules, ${NH} _{4}OH$ molecules and ${NH} _{4}^{+}$ ions and the following equilibrium exist:

${NH} _{3}(g)$ $ \rightleftharpoons{NH} _{3}(l)+{H} _{2}O{(l)}\rightleftharpoons  {NH} _{4}OH{(aq)}\rightleftharpoons  {NH} _{4}^{+}{(aq)}+{OH}^{-}{(aq)}$

Let, ${c} _{1}$ ${(mol/L)}$ of ${NH} _{3}$ pass in liquid state which on dissolution in water forms ${c} _{2}$ ${(mol/L)}$ of ${NH} _{4}OH$. The solution contains ${c} _{3}$ ${(mol/L)}$ of ${NH} _{4}^{+}$ ions.

Concentration of undissociated ammonium hydroxide is________.
  1. ${c} _{1}+{c} _{2}$
  2. ${c} _{2}-{c} _{3}$
  3. ${c} _{1}+{c} _{3}$
  4. ${c} _{1}-{c} _{2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

${NH} _{3}(g)$$\rightleftharpoons {NH} _{3}(l)+{H} _{2}O\rightleftharpoons  {NH} _{4}OH\rightleftharpoons  {NH} _{4}^{+}+{OH}^{-}$

$c _1$                                                $c _2$                $c _3$
So, remaining moles of undissociated ammonium hydroxide, $NH _4OH=  c _2-c _3$

Multiple choice chemistry nitrogen and sulfur ammonia-properties and uses ammonia compounds of nitrogen - ammonia

Select the correct options about the solubility of the following species in $ H _2O$ and $ NH _3 $(aq).
$AgF, AgCN, AgCl, Agl, CaF _2, CaCl _2 $ :

  1. $AgF$ and $CaCl _2 $ are soluble in $H _2O$
  2. $AgCN$ and $AgCl$ are soluble in $NH _3$
  3. $AgI$ and $CaF _2$ are soluble in $ H _2O $ and $ NH _3 $ (aq) both

  4. None of these
Reveal answer Fill a bubble to check yourself
A,B Correct answer
Explanation

A. $AgF$ and $CaCl _2$ are polar compounds. Hence, they are soluble in water which is a polar solvent. Thus, the option A is correct.

B. $AgCN$ and $AgCl$ form complexes with ammonia as ammonia is a very good ligand. Hence, $AgCN$ and $AgCl$ are soluble in ammonia. Thus, the option B is correct.

C. $CaF _2$ and $AgI$ are insoluble in water. Thus, the option C is incorrect.

Multiple choice some important compounds of magnesium and calcium the s-block elements chemistry

Solubility product of $\displaystyle { Mg\left( OH \right)  } _{ 2 }$ at ordinary temperature is $\displaystyle 1.96\times { 10 }^{ -11 }$. $\displaystyle pH$ of a saturated solution of $\displaystyle { Mg\left( OH \right)  } _{ 2 }$ will be

  1. 10.53

  2. 8.47

  3. 6.94

  4. 3.47
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\displaystyle { Mg\left( OH \right)  } _{ 2 }\rightleftharpoons M{ \underset { S }{ g }  }^{ 2+ }+2{ \underset { 2S }{ OH }  }^{ - }$
$\displaystyle { K } _{ sp }{ Mg\left( OH \right)  } _{ 2 }=\left[ { Mg }^{ 2+ } \right] { \left[ { OH }^{ - } \right]  }^{ 2 }$
$\displaystyle \Rightarrow \quad { K } _{ sp }{ Mg\left( OH \right)  } _{ 2 }=4{ S }^{ 3 }$
$\displaystyle 1.96\times { 10 }^{ -11 }=4{ S }^{ 3 }$
or $\displaystyle S={ \left[ \frac { 1.96\times { 10 }^{ -11 } }{ 4 }  \right]  }^{ 1/3 }$
or $\displaystyle S={ \left( 4.9\times { 10 }^{ -12 } \right)  }^{ 1/3 }$
$\displaystyle \therefore \quad S=1.69\times { 10 }^{ -4 }$
So, concentration of $\displaystyle \left[ { OH }^{ - } \right]=2S $
$\displaystyle \therefore \quad \left[ { OH }^{ - } \right] =3.38\times { 10 }^{ -4 }$
$\displaystyle \Rightarrow \quad pOH=-\log { \left[ { OH }^{ - } \right]  } $
$\displaystyle =-\log { \left[ 3.38\times { 10 }^{ -4 } \right]  } $
$\displaystyle \therefore \quad pOH=3.471$
$\displaystyle pH=14-pOH$
$\displaystyle =14-3.471$
$\displaystyle \therefore \quad pH=10.529$

Multiple choice some important compounds of magnesium and calcium the s-block elements chemistry

What is the chemical formula of triple superphosphate?

  1. $Ca(H _2PO _4).2H _2O$
  2. $Ca{(H _2PO _4)} _2.H _2O$
  3. $Ca(H _2PO _4).3H _2O$
  4. $CaSO _4.3H _2O$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Triple Superphosphate is manufactured in a two stage process. First, sulphuric acid is reacted with phosphate rock, to produce phosphoric acid. Gypsum is a by-product of the stage and is removed. Secondly, the phosphoric acid is reacted with phosphate rock resulting in triple superphosphate.
Calcium superphosphate is an inorganic compound with the chemical formula $Ca{ ({ H } _{ 2 }P{ O } _{ 4 }) } _{ 2 }$. It is commonly found as the monohydrate $Ca{ ({ H } _{ 2 }P{ O } _{ 4 }) } _{ 2 }.{ H } _{ 2 }O$ . Both salts are colourless solids. They are used mainly as superphosphate fertilizers.

Multiple choice some important compounds of magnesium and calcium the s-block elements chemistry

Single super phosphate contains:

  1. 20% $P _2O _5$
  2. 16 to 18% $P _2O _5$
  3. 20 to 25% $P _2O _5$
  4. 10 to 46% $P _2O _5$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Single superphosphate (SSP) contains 16-18% ${ P } _{ 2 }{ O } _{ 5 }$, 11-12% sulfur, and 20% calcium. SSP is manufactured by reacting rock phosphate with sulfuric acid. SSP does not have a great influence on soil pH.

Multiple choice some important compounds of magnesium and calcium the s-block elements chemistry

$ MgCl _2 \cdot 6H _2O$ is obtained from carnalite. Which of the following is true?

  1. $ MgCl _2 \cdot 6H _2O$ is left behind in the fused mass
  2. $ MgCl _2 \cdot 6H _2O$ solidifies when fused mass is cooled to 176 deg C
  3. $KCl$ remains in the fused state
  4. Solvent extraction is used to extract $KCl$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Carnalite ($ KCl \cdot MgCl _2 \cdot 6H _2O$) is fused and cooled to 176 deg C.  Potassium content solidifies and $ MgCl _2 \cdot 6H _2O$ remains infused state. Fused mass is separated from deposited $KCl$ and is allowed to cool. The remaining $KCl$ is separated by deposition of carnalite crystals, which crystallizes out first.
$ MgCl _2 \cdot 6H _2O$ is left behind in the fused mass.

Multiple choice some important compounds of magnesium and calcium the s-block elements chemistry

$MgO$ when mixed with a saturated solution of $MgCl _2$ sets to a hard mass known as 'sorel cement'. The composition of sorel cement is $MgCl _2.nMgO.xH _2O$. The value of $n$ is:

  1. 2

  2. 5

  3. 3

  4. 1
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

There are two types of sorel cement 3 phase and 5 phase.

$MgCl _2.3Mg(OH) _2.8H _2O$ is 3 phase sorel cement.

Multiple choice chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

Concrete is produced from a mixture of cement, water and small stones. Small amount of gypsum, $CaSO _4\cdot 2H _2O$ is added in cement production to improve the subsequent hardening of concrete. 
The elevated temperature during the production of cement may lead to the formation of unwanted hemihydrate $CaSO _4\cdot \frac { 1 }{ 2 }H _2O$ according to reaction.

$CaSO _4\cdot 2H _2O(s)\rightarrow CaSO _4\cdot \frac { 1 }{ 2 }H _2O(s) + \frac { 3 }{ 2 }H _2O(g)$
The $\Delta _f H^{ \ominus }$ of $CaSO _4\cdot 2H _2O(s),\ CaSO _4\frac { 1 }{ 2 }H _2O(s),\ H _2O(g)$ are $-2021.0  kJ  mol^{ -1 }$, $-1575.0  kJ  mol^{ -1 }$ and $-241.8  kJ  mol^{ -1 }$ respectively. The respective values of their standard entropies are $194.0$, $130.0$ and $188.0  J  K^{ -1 }  mol^{ -1 }.$ 
$R = 8.314  J  K^{ -1 }  mol^{ -1 } = 0.0831  L  bar  mol^{ -1 }  K^{-1}$
Answer the follwoing questions on the basis of above information.
The value of equilibrium constant for reaction is:

  1. 0

  2. <1

  3. >1

  4. =1
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\Delta H^{ \ominus } = \Delta H^{ \ominus } _ { P } - \Delta H^{ \ominus } _{ R }; (for\quad 1\quad mol)$
$= \left[ -1575.0 kJ mol^{ -1 }-\frac { 3 }{ 2 } \times 241.8 \right] -\left[ -2021.0 kJ mol^{ -1 } \right] $
$= +83.3 kJ mol^{ -1 }$
For 1 Kg $CaSO _4\cdot 2H _2O$
Numebr of moles $=\frac { 1000}{ 172 }$
$= 5.81$
$\therefore$ Heat change for $5.81\quad mol\quad of\quad CaSO _4\cdot 2H _2O = 5.81\times 83.3 kJ mol^{ -1 }$
$=484 kJ mol^{ -1 }$
$\Delta G = \Delta H - T\Delta S$
$= 17.92 kJ$ ........ $(\Delta S = S _P - S _R)$
$\Delta G = -nRTln K$
$\therefore$ $K = e^{ -\Delta GlnRT } < 1$

Multiple choice chemistry water too little to waste pollution of water water pollution planet earth

Maximum prescribed limit of $Cu$ in drinking water is:

  1. 2 ppm

  2. 1 ppm

  3. 3 ppm

  4. 5ppm
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The Food and Nutrition Board(FNB) recommends dietary copper intakes for adults is 1.5-3.0 mg as Cu is an essential macronutrient. 

If excess Cu in drinking water can cause gastrointestinal tract disturbances and chronic ingestion can cause liver toxicity. 

Thus, the correct option is $C$