Tag: hydrolysis of salts and the ph of their solutions

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Multiple choice chemistry water drying and dehydrating agents hydrolysis of salts and the ph of their solutions chemical equilibrium and acids-bases

${ H } _{ 3 }{ PO } _{ 4 }$ is a tribasic acid and one of its salt is ${ NaH } _{ 2 }{ PO } _{ 4 }$ What volume of $1M\quad NaOH$ solution should be added to $12g\ { NaH } _{ 2 }{ PO } _{ 4 }$ to convert it into ${ Na } _{ 3 }{ PO } _{ 4 }$? ($at.wt$ of $P=31$)

  1. $100\ ml$
  2. $200\ ml$
  3. $80\ ml$
  4. $300\ ml$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$Na{ H } _{ 2 }{ PO } _{ 4 }+NaOH\rightarrow { Na } _{ 2 }{ HPO } _{ 4 }+{ H } _{ 2 }O\quad \quad -(i)$

Moles$=\cfrac { 12 }{ 120 } $    $\cfrac { 12 }{ 120 } $            $\cfrac { 12 }{ 120 } $
${ Na } _{ 2 }{ HPO } _{ 4 }+NaOH\rightarrow { Na } _{ 3 }{ PO } _{ 4 }+{ H } _{ 2 }O\quad \quad \quad -(ii)$
Moles$=\cfrac { 12 }{ 120 } $     $\cfrac { 12 }{ 120 } $           $\cfrac { 12 }{ 120 } $
Moles of $NaOH$ required $=\cfrac { 12 }{ 120 } +\cfrac { 12 }{ 120 } $
                                              $=0.2$ moles
Now, $Mularity=\cfrac { Moles }{ Vol.of\quad sol\quad in\quad ltrs } $
$\therefore $ Volume of $NaOH$ solution $=\cfrac { 0.2 }{ 1 } $
                                                  $=0.2$ litres
                                                  $=200$ml

Multiple choice chemistry water drying and dehydrating agents hydrolysis of salts and the ph of their solutions chemical equilibrium and acids-bases

The $K _{sp}$ of $Ag _{2}CrO _{4}, AgCl, AgBr$ and $AgI$ are respectively, $1.1\times 10^{-12}$, $1.8\times 10^{-10}$, $5.0\times 10^{-13}$ and $8.3\times 10^{-17}$. Which of the following salts will precipitate last if $AgNO _{3}$ solution is added to the solution containing equal moles of $NaCl, NaBr, NaI$ and $Na _{2}CrO _{4}$?

  1. $Ag _{2}CrO _{4}$
  2. $AgI$
  3. $AgCl$
  4. $AgBr$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
  1. $Ag _2CrO _4\rightleftharpoons 2Ag^++{CrO _4}^{2-}$

    $Ksp=(2s)^2\times s=4s^2$

    $Ksp=(1.1\times 10^{-12})$

    $S=3\sqrt {\cfrac {Ksp}{4}}=6.5\times 10^{-5}$M

    2. $AgCl\rightleftharpoons Ag^++Cl^-$

    $Ksp=S\times S$  ;       $Ksp=1.8\times 10^{-10}$

    $S=\sqrt {Ksp}=1.34\times 10^{-5}$M

    3. $AgBr\rightleftharpoons Ag^++Br^-$

    $Ksp=S\times S$ ;     $Ksp=5\times 10^{-13}$

    $S=\sqrt {Ksp}=0.71 \times 10^{-6}$M

    4. $AgI\rightleftharpoons Ag^++I^-$

    $Ksp=S\times S$  ;    $Ksp=8.3\times 10^{-17}$

    $S=\sqrt{Ksp}=0.9\times 10^{-8}$M

    $\therefore$ Solubility of $Ag _2CrO _4$ is highest, so it will precipitate last.
Multiple choice chemistry water drying and dehydrating agents hydrolysis of salts and the ph of their solutions chemical equilibrium and acids-bases

Dissolution of salt participate in water shows:

  1. Particulate nature of matter.

  2. Continuous nature of matter.

  3. Particle size of salt is very big.

  4. All of these.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The salt will dissolve and water will taste salty. Salt particles dissolve in water because they occupy the spaces between the water molecules resulting in spreading of salt particles throughout the particles of water showing particle nature of matter.

Multiple choice chemistry water drying and dehydrating agents hydrolysis of salts and the ph of their solutions chemical equilibrium and acids-bases

An aqueous solution of zinc sulphate is acidic in nature because______.


  1. $ZnSO _{4}$ ionizes
  2. $SO _{4}^{-2}$ reacts with $H _{2}O$
  3. $Zn^{+2}$ reacts with $H _{2}O$
  4. $Zn^{+2}$ & $SO^{-2} _{4}$ reacts with $H _{2}O$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Zinc sulphate is a salt of a strong acid (H2SO4) and a weak base (Zn(OH)2). When dissolved in water, the zinc ion undergoes hydrolysis with water molecules, releasing hydrogen ions into the solution and rendering it acidic.

Multiple choice chemistry water drying and dehydrating agents hydrolysis of salts and the ph of their solutions chemical equilibrium and acids-bases

KMnO$ _4$ oxidises X$^{n+}$ ion to XO$^- _3$ itself changing into Mn$^{+2}$ in acid solution. $2.68$ $\times$ $10^{-3}$ mole of X$^{n+}$ requires $1.61$ $\times$ $10^{-3}$ mole of MnO$ _4^-$. The value of n is :

  1. $1$
  2. $2$
  3. $4$
  4. $3$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Using the redox equivalence: (n_final - n_initial) * moles_X = (5 - 2) * moles_MnO4. (5 - n) * 2.68e-3 = 3 * 1.61e-3. 5 - n = 1.8. n = 2.

Multiple choice chemistry water drying and dehydrating agents hydrolysis of salts and the ph of their solutions chemical equilibrium and acids-bases

The mass in grams of potassium permanganate (MM = 158) crystals required to oxidise $750\,\,c{m^3}$ of 0.1 M Mohr's salt solution in acidic medium is about 

  1. 11.8

  2. 5.8

  3. 6.0

  4. 2.4
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In an acidic medium, potassium permanganate oxidizes Mohr's salt (iron(II)). The milliequivalents of potassium permanganate must equal the milliequivalents of Mohr's salt. Using normality and volume calculations along with the molar mass of 158 g/mol, the required mass of potassium permanganate is found to be 2.4 grams.

Multiple choice chemistry water drying and dehydrating agents hydrolysis of salts and the ph of their solutions chemical equilibrium and acids-bases

Degree of hydrolysis for a salt of weak acid and strong base can be changed by 

  1. Increasing concentration of salt

  2. Increasing temperature

  3. Adding base

  4. All of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The degree of hydrolysis (h) for a salt of a weak acid and strong base is given by h = sqrt(Kh / C). It depends on the hydrolysis constant (Kh), which is temperature-dependent, and the concentration (C).