List of top Chemistry Questions asked in CBSE Class XI

Discuss the principle of estimation of halogens, sulphur and phosphorus present in an organic compound.
The following data are obtained when dinitrogen and dioxygen react together to form different compounds: 
          Mass of dinitrogen                Mass of dioxygen 
(i)              14 g                                            16 g 
(ii)             14 g                                             32 g 
(iii)            28 g                                             32 g 
(iv)            28 g                                             80 g 
  1. Which law of chemical combination is obeyed by the above experimental data? Give its statement.
  2. Fill in the blanks in the following conversions: 
    (i)1 km = ...................... mm = ...................... pm 
    (ii) 1 mg = ...................... kg = ...................... ng 
    (iii) 1 mL = ...................... L = ...................... dm3
A sample of drinking water was found to be severely contaminated with chloroform, CHCl3, supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass).
  1. Express this in per cent by mass.
  2. Determine the molality of chloroform in the water sample.
What is the concentration of sugar (C12H22O11) in mol L–1 if its 20 g are dissolved in enough water to make a final volume up to 2L?
What is the difference between distillation, distillation under reduced pressure and steam distillation?
Describe the method, which can be used to separate two compounds with different solubilities in a solvent S.
Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles. 
(a) \(CH_3COOH+HO^{–6} \rightarrow CH_3COO^–+H_2O\) 
(b) \(CH_3COCH^{3+} C^–N\rightarrow (CH_3)_2C(CN)(OH)\)
(c) \(C_6H_6 + CH_3C+O^+ \rightarrow C_6H_5COCH_3\)
Calculate the concentration of nitric acid in moles per litre in a sample which has a density, 1.41 g mL–1 and the mass per cent of nitric acid in it being 69%.
What are electrophiles and nucleophiles? Explain with examples.
Which of the two, \(O+2NCH_2CH_2O^- \,or \,CH_3CH_2O^–\)is expected to be more stable and why?
Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions:
  1. \(2AgBr (s) + C_6H_6O_2(aq) \rightarrow 2Ag(s) + 2HBr (aq) + C_6H_4O_2(aq)\)
  2. \(HCHO(l) + 2[Ag (NH_3)_2] ^+ (aq) + 3OH^ - (aq) \rightarrow 2Ag(s) + HCOO ^- (aq) + 4NH_3(aq) + 2H_2O(l)\)
  3. \(HCHO (l) + 2Cu^{ 2+}(aq) + 5 OH^ - (aq) \rightarrow Cu_2O(s) + HCOO ^- (aq) + 3H_2O(l)\)
  4. \(N_2H_4(l) + 2H_2O_2(l) \rightarrow N_2(g) + 4H_2O(l)\)
  5. \(Pb(s) + PbO_2(s) + 2H_2SO_4(aq) \rightarrow  2PbSO_4(s) + 2H_2O(l)\)
Yellow light emitted from a sodium lamp has a wavelength (λ) of 580 nm. Calculate the frequency (ν) and wavenumber (v) of the yellow light
Give the IUPAC names of the following compounds:
IUPAC names of compounds
(f) Cl2CHCH2OH
An ion with mass number 37 possesses one unit of negative charge. If the ion conatins 11.1% more neutrons than the electrons, find the symbol of the ion.
Calculate the oxidation number of Sulphur, chromium, and nitrogen in
\(H_2SO_5\), \(Cr_2O_7^{2−}\) and \(NO_3^−\). Suggest structure of these compounds. Count for the fallacy.
Write bond line formulas for, Isopropyl alcohol, 2,3-Dimethylbutanal, Heptan-4-one.
Indicate the σ and π bonds in the following molecules. \(C_6H_6, C_6H_{12}, CH_2Cl_2, CH_2=C=CH_2, CH3NO2, HCONHCH_3.\)
A certain particle carries 2.5 × 10–16 C of static electric charge. Calculate the number of electrons present in it.
How many electrons in an atom may have the following quantum numbers?
  1. n = 4, ms = – \(\frac 12\)
  2. n = 3, l = 0
Consider the reactions: 
(a) \(6 \,CO_2(g) + 6H_2O(l) \rightarrow C_6H_{12}O_6(aq) + 6O_2(g)\) 
(b) \(O_3(g) + H_2O_2(l) \rightarrow  H_2O(l) + 2O_2(g)\) 
Why it is more appropriate to write these reactions as: (a) \(6\,CO_2(g) + 12H_2O(l) \rightarrow  C_6H_{12}O_6(aq) + 6H_2O(l) + 6O_2(g)\) 
(b) \(O_3(g) + H_2O_2(l) \rightarrow H_2O(l) + O_2(g) + O_2(g)\) 
Also suggest a technique to investigate the path of the above (a) and (b) redox reactions.
  1. An atomic orbital has n = 3. What are the possible values of l and ml?
  2. List the quantum numbers (ml and l) of electrons for 3d orbital.
  3. Which of the following orbitals are possible?
    1p, 2s, 2p and 3f
Which of the following are isoelectronic species i.e., those having the same number of electrons?
\(Na^+, K^+, Mg^{2+}, Ca^{2+}, S^{2–}, Ar\)
Whenever a reaction between an oxidising agent and a reducing agent is carried out, a compound of lower oxidation state is formed if the reducing agent is in excess, and a compound of higher oxidation state is formed if the oxidising agent is in excess. Justify this statement giving three illustrations..
The mass of an electron is 9.1 × 10–31 kg. If its K.E. is 3.0 × 10–25 J, calculate its wavelength.
Calculate the wavelength of an electron moving with a velocity of \(2.05×10^7 \ ms^{–1}\).