List of top Chemistry Questions asked in CBSE Class XI

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?
Calculate:
  1. ∆GΘ and 
  2. the equilibrium constant for the formation of NO2 from NO and O2 at 298 K
\(NO (g) + \frac 12O_2 (g) ⇋ NO_2 (g)\)
where,
 ∆fGΘ (NO2) = 52.0 kJ/mol
∆fGΘ (NO) = 87.0 kJ/mol
∆fGΘ (O2) = 0 kJ/mol.
How do you account for the formation of ethane during chlorination of methane?
At 1127 K and 1 atm pressure, a gaseous mixture of CO and CO2 in equilibrium with soild carbon has 90.55% CO by mass
\(C(s) + CO_2(g) ⇋ 2CO(g)\)
Calculate Kc for this reaction at the above temperature.
Bromine monochloride, BrCl decomposes into bromine and chlorine and reaches the equilibrium:
\(2BrCl (g) ⇋ Br_2 (g) + Cl_2 (g)\)
for which Kc = 32 at 500 K. If initially pure BrCl is present at a concentration of 3.3 × 10–3 mol L–1, what is its molar concentration in the mixture at equilibrium?
What is meant by the term bond order? Calculate the bond order of: \(N_2\), \(O_2\), \(O_2^+\) and \(O_2^-\) .
Equilibrium constant, Kc for the reaction
\(N_2 (g) + 3H_2 (g) ⇋ 2NH_3 (g)\)
At 500 K is 0.061 At a particular time, the analysis shows that composition of the reaction mixture is 3.0 mol L–1 N2, 2.0 mol L–1 H2 and 0.5 mol L–1 NH3. Is the reaction at equilibrium? If not in which direction does the reaction tend to proceed to reach equilibrium?
One of the reaction that takes place in producing steel from iron ore is the reduction of iron(II) oxide by carbon monoxide to give iron metal and CO2.
\(FeO (s) + CO (g) ⇋ Fe (s) + CO_2 (g);\ K_p = 0.265\  \text {atm}\) at 1050 K
What are the equilibrium partial pressures of CO and CO2 at 1050 K if the initial partial pressures are: \(P_{CO}\) = 1.4 atm and \(P_{CO_2}\) = 0.80 atm?
(a) How many subshells are associated with n = 4 ? (b) How many electrons will be present in the subshells having ms value of \(-\frac{1}{2}\) for n = 4 ?
Indicate the number of unpaired electrons in : (a) P, (b) Si, (c) Cr, (d) Fe and (e) Kr.
Define hydrogen bond. Is it weaker or stronger than the van der Waals forces?