List of top Chemistry Questions

Arrange benzene, n-hexane and ethyne in decreasing order of acidic behaviour. Also give reason for this behaviour.
Assuming complete dissociation, calculate the pH of the following solutions: (a) 0.003 M HCl (b) 0.005 M NaOH (c) 0.002 M HBr (d) 0.002 M KOH
It has been found that the pH of a 0.01M solution of an organic acid is 4.15
Addition of HBr to propene yields 2-bromopropane, while in the presence of benzoyl peroxide, the same reaction yields 1-bromopropane. Explain and give mechanism.
In any period, the valency of an element with respect to oxygen
Ethyl acetate is formed by the reaction between ethanol and acetic acid and the equilibrium is represented as:
\(CH_3COOH (l) + C_2H_5OH (l) ⇋ CH_3COOC_2H_5 (l) + H_2O (l) \)
  1. Write the concentration ratio (reaction quotient), Qc , for this reaction (note: water is not in excess and is not a solvent in this reaction)
  2. At 293 K, if one starts with 1.00 mol of acetic acid and 0.18 mol of ethanol, there is 0.171 mol of ethyl acetate in the final equilibrium mixture. Calculate the equilibrium constant. 
  3. Starting with 0.5 mol of ethanol and 1.0 mol of acetic acid and maintaining it at 293 K, 0.214 mol of ethyl acetate is found after sometime. Has equilibrium been reached?
Predict which of the following reaction will have appreciable concentration of reactants and products:
  1. \(Cl_2 (g) ⇋ 2Cl (g): \  K_c = 5×10_{–39}\)
  2. \(Cl_2 (g) + 2NO (g) ⇋ 2NOCl (g); \ K_c = 3.7×10^8\)
  3. \(Cl_2 (g) + 2NO_2 (g) ⇋ 2NO_2Cl (g); \  K_c = 1.8\)
Dihydrogen gas used in Haber’s process is produced by reacting methane from natural gas with high temperature steam. The first stage of two stage reaction involves the formation of CO and H2. In second stage, CO formed in first stage is reacted with more steam in water gas shift reaction,
\(CO (g) + H_2O (g) ⇋ CO_2 (g) +H_2 (g)\)
If a reaction vessel at 400°C is charged with an equimolar mixture of CO and steam such that \(P_{co}= P_{H_2O} = 4.0\) bar, what will be the partial pressure of H2 at equilibrium? Kp= 10.1 at 400°C.
The ionization constant of phenol is 1.0 × 10–10. What is the concentration of phenolate ion in a 0.05 M solution of phenol? What will be its degree of ionization if the solution is also 0.01M in sodium phenolate?
At 473 K, equilibrium constant Kc for decomposition of phosphorus pentachloride, PCl5 is \(8.3 ×10^{-3}\). If decomposition is depicted as,
\(PCl_5 (g) ⇋ PCl_3 (g) + Cl_2 (g)\)   \(∆_r H^Θ = 124.0\  kJ mol^{–1}\)
  1. write an expression for Kc for the reaction.
  2. what is the value of Kc for the reverse reaction at the same temperature?
  1. what would be the effect on Kc if
    1. more PCl5 is added
    2. pressure is increased
    3. the temperature is increased ?
The ionization constant of HF, HCOOH and HCN at 298K are 6.8×10–4,1.8×10–4 and 4.8×10–9 respectively. Calculate the ionization constants of the corresponding conjugate base.
The pH of a sample of vinegar is 3.76. Calculate the concentration of hydrogen ions in it.
The concentration of hydrogen ions in a sample of soft drink is 3.8 × 10–3 M. What is its pH?
Classify the following species into Lewis acids and Lewis bases and show how these act as Lewis acid/base: (a) OH– (b) F– (c) H+ (d) BCl3
Describe the effect of: 
  1. addition of H2
  2. addition of CH3OH
  3. removal of CO
  4. removal of CH3OH 

on the equilibrium of the reaction:
\(2H_2(g) + CO (g) ⇋ CH_3OH (g)\)

The species: H2O, HCO3–, HSO4– and NH3 can act both as Brönsted acids and bases. For each case give the corresponding conjugate acid and base.
Write the conjugate acids for the following Brönsted bases: NH2–, NH3 and HCOO–.
What will be the conjugate bases for the Brönsted acids: HF, H2SO4 and HCO3–?
Dihydrogen gas is obtained from natural gas by partial oxidation with steam as per following endothermic reaction:
\(CH_4 (g) + H_2O (g) ⇋ CO (g) + 3H_2 (g)\)
  1. Write as expression for Kp for the above reaction.
  2. How will the values of Kp and composition of equilibrium mixture be affected by
    1. increasing the pressure
    2. increasing the temperature
    3. using a catalyst?
Which of the following reactions will get affected by increasing the pressure? Also, mention whether change will cause the reaction to go into forward or backward direction.
  1. \(COCl_2 (g) ⇋ CO (g) + Cl_2 (g)\)
  2. \(CH_4 (g) + 2S_2 (g) ⇋ CS_2 (g) + 2H_2S (g)\)
  3. \(CO_2 (g) + C (s) ⇋ 2CO (g)\)
  4. \(2H_2 (g) + CO (g) ⇋ CH_3OH (g)\)
  5. \(CaCO_3 (s) ⇋ CaO (s) + CO_2 (g)\)
  6. \(4NH_3 (g) + 5O_2 (g) ⇋ 4NO (g) + 6H_2O(g)\)
Which of the following are Lewis acids? H2O, BF3, H+, and NH4+.
What effect does branching of an alkane chain has on its boiling point?
What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species: HNO2, CN– , HClO4,F–,OH–,CO and S2–
In the alkane \( H_3C-CH_2-C(CH_3)_2-CH_2-CH(CH_3)_2\) , identify 1°,2°,3° carbon atoms and give the number of H atoms bonded to each one of these.
What are the necessary conditions for any system to be aromatic?