List of top Chemistry Questions

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 \(2.05×10^7 \ ms^{–1}\).
Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess of chlorine is removed by treating with sulphur dioxide. Present a balanced equation for this redox change taking place in water.
The electron energy in hydrogen atom is given by \(E_n = \frac {(–2.18×10^{–18})}{n^2} \ J\). Calculate the energy required to remove an electron completely from the n = 2 orbit. What is the longest wavelength of light in cm that can be used to cause this transition?
The Mn3+ ion is unstable in solution and undergoes disproportionation to give Mn2+ , MnO2, and H+ ion. Write a balanced ionic equation for the reaction.
What is the energy in joules, required to shift the electron of the hydrogen atom from the first Bohr orbit to the fifth Bohr orbit and what is the wavelength of the light emitted when the electron returns to the ground state ? The ground state electron energy is –2.18×10–11 ergs.
Justify giving reactions that among halogens, fluorine is the best oxidant and among hydrohalic compounds, hydroiodic acid is the best reductant.
The compound AgF2 is an unstable compound. However, if formed, the compound acts as a very strong oxidizing agent. Why?
Calculate the wavenumber for the longest wavelength transition in the Balmer series of atomic hydrogen.
  1. The energy associated with the first orbit in the hydrogen atom is –2.18×10–18 J atom–1. What is the energy associated with the fifth orbit ?
  2. Calculate the radius of Bohr’s fifth orbit for hydrogen atom.
The concentration of sulphide ion in 0.1M HCl solution saturated with hydrogen sulphide is 1.0 × 10–19 M. If 10 mL of this is added to 5 mL of 0.04 M solution of the following: FeSO4, MnCl2, ZnCl2 and CdCl2. in which of these solutions precipitation will take place?
What is the minimum volume of water required to dissolve 1g of calcium sulfate at 298 K? (For calcium sulfate, Ksp is 9.1 × 10–6).
How much energy is required to ionise a H atom if the electron occupies n = 5 orbit? Compare your answer with the ionization enthalpy of H atom (energy required to remove the electron from n = 1 orbit).
Consider the reactions:
\(2S_2O_3^{2-}(aq) + I_2(s) \rightarrow S_4O_6^{2-}(aq) + 2I ^- (aq)\)
\(S_2O_3^{2-}(aq) + 2Br_2(l) + 5 H_2O(l) \rightarrow 2SO_4^{2-}(aq) + 4Br ^- (aq) + 10H ^+ (aq)\) 
Why does the same reductant, thiosulphate react differently with iodine and bromine?
What is the maximum concentration of equimolar solutions of ferrous sulphate and sodium sulphide so that when mixed in equal volumes, there is no precipitation of iron sulphide? (For iron sulphide, Ksp = 6.3 × 10–18).
How do you count for the following observations?
  1. Though alkaline potassium permanganate and acidic potassium permanganate both are used as oxidants, yet in the manufacture of benzoic acid from toluene we use alcoholic potassium permanganate as an oxidant. Why? Write a balanced redox equation for the reaction.
  2. When concentrated sulphuric acid is added to an inorganic mixture containing chloride, we get colourless pungent smelling gas HCl, but if the mixture contains bromide then we get red vapour of bromine. Why?
Equal volumes of 0.002 M solutions of sodium iodate and cupric chlorate are mixed. Will it lead to the precipitation of copper iodate? (For cupric iodate Ksp = 7.4 × 10–8).
What is the wavelength of light emitted when the electron in a hydrogen atom undergoes transition from an energy level with n = 4 to an energy level with n = 2?
Consider the reactions: 
  1. H3PO2(aq) + 4 AgNO3(aq) + 2 H2O(l) \(\rightarrow\) H3PO4(aq) + 4Ag(s) + 4HNO3(aq)
  2. H3PO2(aq) + 2CuSO4(aq) + 2 H2O(l) \(\rightarrow\) H3PO4(aq) + 2Cu(s) + H2SO4(aq) 
  3. C6H5CHO(l) + 2[Ag (NH3)2]+(aq) + 3OH- (aq)  \(\rightarrow\) C6H5COO- (aq) + 2Ag(s) + 4NH3(aq) + 2 H2O(l) 
  4. C6H5CHO(l) + 2Cu2+(aq) + 5OH-(aq) \(\rightarrow\) No change observed. 

What inference do you draw about the behaviour of Ag+ and Cu2+  from these reactions?