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All questions of Equilibrium for NEET Exam

 In a buffer solution containing equal concentration of B and HB, the Kb for B is 10–10. The pH of buffer solution is : [2010]
  • a)
    10
  • b)
    7
  • c)
    6
  • d)
    4
Correct answer is option 'D'. Can you explain this answer?

Nilotpal Gupta answered
For the buffer solution containing equal concentration of B and HB
pH = pKa + log 1
pH = pKa = 4
The octahedral complex ion [ CoCl2(NH3)4]+ i.e., tetra amminedichloro cobalt (III) ion exists as cis and trans isomers.

The values of Kp1 and Kp2 for the reactions
are in the ratio of 9 : 1. If degree of dissociation of X and A be equal, then total pressure at equilibrium (1) and (2) are in the ratio :
  • a)
    3 : 1
  • b)
    1 : 9
  • c)
    36 : 1
  • d)
    1 : 1
Correct answer is option 'C'. Can you explain this answer?

Gaurav Kumar answered
Given reaction are
Let the total pressure for reaction (i) and (ii) be P1 and P2 respectively, then
After dissociation,  
At equilibrium (1–α) α α
[Let 1 mole of X dissociate with α as degree of dissociation ]
Total number of moles =   1– α + α + α = (1+α)
Thus  
We have,
Dividing (i) by (ii), we get
i.e. Option (c) is correct answer.

Equimolar solutions of the following substances were prepared separately. Which one of these will record the highest pH value ? [2012]
  • a)
    BaCl2
  • b)
    AlCl3
  • c)
    LiCl
  • d)
    BeCl2
Correct answer is option 'A'. Can you explain this answer?

Aniket Chawla answered
(AlCl3, LiCl & BeCl2) ) all these solutions are acidic due to cationic hydrolysis, where as BaCl2, is salt of strong base and strong acid, hence its solution will almost neutral i.e., pH ≈ 7.

At 100°C the Kw of water is 55 times its value at 25°C. What will be the pH of neutral solution? (log 55 = 1.74) [NEET Kar. 2013]
  • a)
    6.13
  • b)
    7.00
  • c)
    7.87
  • d)
    5.13
Correct answer is option 'A'. Can you explain this answer?

Krish Khanna answered
Kw at  25°C = 1 × 10–14 At 25ºC
Kw = [H+] [OH] = 10–14 At 100°C (given) Kw = [H+] [OH] = 55 × 10–14
∵ for a neutral solution [H+] = [OH]
∴ [H+]2 = 55 × 10–14
or [H+] = (55 × 10–14)1/2
∵  pH = – log [H+]
On taking log on both side – log [H+] = –log (55 × 10–14)1/2
pH =  – 0.87 + 7      
=  6.13

Buffer solutions have con stant acidity and alkalinity because [2012]
  • a)
    these give unionised acid or base on reaction with added acid or alkali.
  • b)
    acids and a lkalies in these solutions are shielded from attack by other ions.
  • c)
    they have large excess of H+ or OH ions
  • d)
    they have fixed value of pH
Correct answer is option 'A'. Can you explain this answer?

Yash Modi answered
Buffer solutions are those whose pH is almost constant due to the presence of mechanisms to control its fluctuation. This is due to the presence of excess of either excess of H+ or OH- etc. so that there is no effect when some of either of them may enter from outside. Eg. blood in human body is at constant pH of about 7.4. It uses H+ and HCO3- ions to regulate any change in it's pH (like during respiration)

Which one of the following orders of acid strength is correct? [2003]
  • a)
    RCOOH > HC ≡ CH > HOH > ROH
  • b)
    RCOOH > ROH > HOH > HC≡CH
  • c)
    RCOOH > HOH > ROH > HC ≡ CH
  • d)
    RCOOH > HOH > HC ≡ CH > ROH
Correct answer is option 'C'. Can you explain this answer?

The higher is the tendency to donate proton, stronger is the acid. Thus the correct order is R – COOH > HOH > R – OH > CH ≡ CH depending upon the rate of donation of proton.

The dissociation equilibrium of a gas AB2 can be represented as : [2008]
The degree of dissociation is ‘x’ and is small compared to 1. The expression relating the degree of dissociation (x) with equilibrium constant Kp and total pressure P is :
  • a)
    (2Kp/P)
  • b)
    (2Kp/P)1/3
  • c)
    (2Kp/P)1/2
  • d)
    (Kp/P)
Correct answer is option 'B'. Can you explain this answer?

For the reaction
=  x3 [(1–x) can be neglected in denominator
The partial pressure at equilibrium are calculated on the basis of total number of moles at equilibrium.
Total number of moles
= 2 (1–x) + 2x + x  = (2 + x)
where P is the total pressure.
Since x is very small so can be neglected in denominator Thus, we get

Which has the highest value of pH? [2002]
  • a)
    CH3COOK
  • b)
    Na2CO3
  • c)
    NH4Cl
  • d)
    NaNO3
Correct answer is option 'B'. Can you explain this answer?

Amrita Gupta answered
Explanation:

The pH of a solution is a measure of its acidity or alkalinity. It is a scale that ranges from 0 to 14, where pH 7 is considered neutral. A pH less than 7 is acidic, while a pH greater than 7 is alkaline.


To determine which compound has the highest value of pH among the given options, we need to understand the nature of these compounds and their behavior in water.


a) CH3COOK (Potassium acetate):
Potassium acetate is a salt of a weak acid (acetic acid) and a strong base (potassium hydroxide). When it dissolves in water, it undergoes hydrolysis.

The hydrolysis of potassium acetate produces acetate ions (CH3COO-) and potassium ions (K+).

The acetate ion is the conjugate base of the weak acid acetic acid, which means it can accept protons (H+) from water and increase the concentration of hydroxide ions (OH-) in the solution.

The presence of hydroxide ions increases the pH of the solution, making it slightly alkaline. However, the pH of potassium acetate solution is not as high as the other options.


b) Na2CO3 (Sodium carbonate):
Sodium carbonate is a salt of a weak base (carbonic acid) and a strong base (sodium hydroxide). When it dissolves in water, it dissociates into carbonate ions (CO32-) and sodium ions (Na+).

The carbonate ion is a strong base and can accept protons from water, increasing the concentration of hydroxide ions (OH-) in the solution.

As a result, the presence of hydroxide ions significantly increases the pH of the solution, making it highly alkaline.

Therefore, sodium carbonate has the highest value of pH among the given options.


c) NH4Cl (Ammonium chloride):
Ammonium chloride is a salt of a weak base (ammonia) and a strong acid (hydrochloric acid). When it dissolves in water, it dissociates into ammonium ions (NH4+) and chloride ions (Cl-).

The ammonium ion is a weak acid and can donate protons to water, increasing the concentration of hydronium ions (H3O+).

The presence of hydronium ions decreases the pH of the solution, making it slightly acidic.


d) NaNO3 (Sodium nitrate):
Sodium nitrate is a salt of a strong acid (nitric acid) and a strong base (sodium hydroxide). When it dissolves in water, it dissociates into nitrate ions (NO3-) and sodium ions (Na+).

The nitrate ion is a neutral species and does not significantly affect the pH of the solution.

Therefore, sodium nitrate does not have a particularly high or low pH value.


In conclusion, among the given options, sodium carbonate (Na2CO3) has the highest value of pH.

Calculate the pOH of a solution at 25°C that contains 1× 10–10 M of hydronium ions, i.e. H3O+.
  • a)
    4.000
  • b)
    9.0000 [2007]
  • c)
    1.000
  • d)
    7.000
Correct answer is option 'A'. Can you explain this answer?

Arpita Nambiar answered
To calculate the pOH of a solution at 25°C, you need to know the concentration of hydroxide ions (OH-) in the solution.

The pOH is defined as the negative logarithm (base 10) of the hydroxide ion concentration. The formula to calculate pOH is:

pOH = -log[OH-]

If you do not have the concentration of hydroxide ions, you will need additional information to calculate it.

Equal volumes of three acid solutions of pH 3, 4 and 5 are mixed in a vessel. What will be the H+ ion concentration in the mixture ? [2008]
  • a)
    1.11 × 10–4 M
  • b)
    3.7 × 10–4 M
  • c)
    3.7 × 10– 3 M
  • d)
    1.11× 10–3 M
Correct answer is option 'B'. Can you explain this answer?

Prisha Singh answered
[H3O]+ for a solution having pH = 3 is given by [H3O]+ = 1×10–3 moles/litre  
Similarly for solution having pH = 4, [H3O]+ = 1 × 10–4 moles/ litre and for pH=5 [H3O+] = 1×10–5 moles/ litre Let the volume of each solution in mixture be IL, then total volume of mixture solution  L = (1 + 1 + 1) L =3L
Total [H3O]+ ion present in mixture solution = (10–3 + 10–4 + 10–5) moles Then [H3O]+ ion concentration of mixture solution
=  0.00037 M = 3.7 ×10–4 M.

If the concentration of OH ions in the reaction decreased by   times, then equilibriumconcentration of Fe3+ will increase by : [2008]
  • a)
    8 times
  • b)
    16 times
  • c)
    64 times
  • d)
    4 times
Correct answer is option 'C'. Can you explain this answer?

Dipika Das answered
For this reaction Keq. is given by
If (OH) is decreased by times then forreaction equilibrium constant to remain constant, we have to increase the concentration of [Fe3+] by a factor of 43 i.e 4× 4 × = 64. Thus option (c) is correct answer.

Equimolar solutions of the following were prepared in water separately. Which one of the solutions will record the highest pH ? [2008]
  • a)
    SrCl2
  • b)
    BaCl2
  • c)
    MgCl2
  • d)
    CaCl2
Correct answer is option 'B'. Can you explain this answer?

Pooja Saha answered
The highest pH will be recorded by the most basic solution. The basic nature of hydroxides of alkaline earth metals increase as we move from Mg to Ba and thus the solution of BaCl2 in water will be most basic and so it will have  highest pH.

What is the correct relation ship between the pHs of isomolar solutions of sodium oxide (pH1), sodium sulphide (pH2), sodium selenide (pH3) and sodium telluride (pH4)? [2 00 5]
  • a)
    pH1 > pH2 > pH3 > pH4
  • b)
    pH1 > pH2 ≈  pH3 > pH4
  • c)
    pH1 < pH2 < pH3 < pH4
  • d)
    pH1 < pH2 < pH3 ≈ pH4
Correct answer is option 'A'. Can you explain this answer?

Shruti Chauhan answered
The solution formed from isomolar solutions of sodium oxide, sodium sulphide, sodium selenide H2O, H2S, H2Se & H2Te respectively.
As the acidic strengh increases from H2O to H2Te thus pH decreases and hence the correct of pHs is pH1 > pH2 > pH3 > pH4.

The solubility product of AgI at 25ºC is 1.0 × 10–16 mol2 L–2. The solubiliy of AgI in  10–4 N solution of KI at 25ºC is approximately(in mol L–1) [2003]
  • a)
    1.0 × 10–8
  • b)
    1.0 × 10–16
  • c)
    1.0 × 10–12
  • d)
    1.0 × 10–10
Correct answer is option 'C'. Can you explain this answer?

Rhea Sarkar answered
Ksp for AgI = 1 × 10–16 In solution of KI, I would be due to the both AgI and KI, 10–4 solution KI would provide = 10–4 I
AgI would provide, say = x I (x is solubility of AgI)
as x is very small ∴ x2 can be ignored
∴      10–4 x = 10–16

The value of equilibrium constant of the reaction
[2008]
The equilibrium constant of the reaction
  • a)
  • b)
  • c)
    16
  • d)
Correct answer is option 'B'. Can you explain this answer?

Niti Patel answered
Given : Equilibrium constant (K1) for the reaction
  To find equilibrium constant for the following reaction
For this multiply (i) by 2, we get
[Note: When the equation for an equilibrium is multiplied by a factor, the equilibrium constant must be raised to the power equal to the factor]
Now reverse equation (iii), we get
[Note: For a reversible reaction, the equilibrium constant of the backward reaction is inverse of the equilibrium constant for the forward reaction.] Equation (iv) is the same as the required equation (ii), thus K2 for equation (ii) is i.e.
option (b) is correct.

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