SECTION- A
1. What happens when (Do Any Two)(a) Formic acid is heated with Tollen’s reagent?
(b) Acetaldehyde is treated with concentrated NaHSO3 solution?
(c) 2-Pentanone is reacted with iodine in presence of sodium hydroxide?
Ans. (a) Formic acid contains both aldehyde (–CHO) and acidic group (–COOH). Due to presence of aldehydic group, it acts as reducing agent and reduces Tollen’s reagent to metallic silver (silver mirror test) according to the following reaction:
HCOOH + 2[Ag(NH3)2]2+ + 2OH– → 2Ag + CO2 + 2H2O + 4NH3
(b) Sodium hydrogen sulphite adds to aldehydes and ketones to form the addition products.
(c) 2-Pentanone would undergo iodoform reaction with I2 and NaOH as it is a methyl ketone, to give CHI3 (iodoform) and corresponding sodium carboxylate.
2. Answer the following questions: (Do Any Two)
(a) What is the relationship between cell potential and equilibrium constant?
(b) Why hydrogen is used as a Standard electrode?
(c) What is the effect of catalyst on Gibbs energy (ΔG)?
Ans. (a) At equilibrium, the value of cell potential is zero.
(b) Hydrogen is used as a standard electrode because it is an inert electrode and its reduction potential is zero.
(c) There will be no effect of catalyst on Gibbs energy.
3. Answer the following:
(a) In a first order reaction the concentration of reactant is reduced from 0.6 mol L– 1 to 0.2 mol L– 1 in 5 minutes. Calculate the rate constant for the reaction.
(b) What would be the unit of rate equation in case of gaseous reaction?
Ans.(a) Putting the values of both concentrations and time ,we will get rate constant = 0.22 min-1
(b) Unit of rate equation in case of gaseous reaction would be atm s–1.
SECTION- B
4.(a) On the basis of crystal field theory, write the electronic configuration for d4 ion if Δ0 < P.(b) [NiCl4]2− is paramagnetic, while [Ni(CO)4] is diamagnetic, though both are tetrahedral. Why?(Atomic number of Ni = 28)
Ans. (a) On the basis of crystal field theory, for a d4 ion, if ∆o < P, then the complex is a high spin complex formed by the association of weak field ligands with the metal ion. As a result, the fourth electron enters one of the eg orbitals, thereby, exhibiting the electronic configuration t2g3 eg1.
(b) In [NiCl4]2−, Ni is in the +2 state and Cl− which is a weak field ligand does not cause pairing of unpaired 3d electrons. Hence, it is paramagnetic. On the other hand, in [Ni(CO)sub>4], Ni has 0 oxidation state and CO is a strong field ligand which causes pairing of unpaired 3d electrons. Since,no unpaired electrons are present, it is diamagnetic.
OR
4. What is the electronic configuration of Co in [CoF6]3– according to the valence bond theory of coordination compounds. Also predict the magnetic character of the [CoF6]3-.
Ans. Electronic configuration of Co3+ ion is: 3d6 Electronic configuration of sp3d2 hybridised (as F– is a weak field ligand) orbitals of Co3+, with six pairs of electrons from six F– ions:
5. Account for the following:
(a) Why zinc, cadmium and mercury are not regarded as transition metals?
(b) Why Zr and Hf occur in nature together?
(c) In which industry AgBr is used?
Ans.(a) The elements such as Zn, Cd, and Hg are not transition elements because of their electronic configuration. The orbitals of these elements are completely filled both in their ground state as well as in their general oxidation state. Therefore, these elements are not transition elements.
(b) As a consequence of lanthanoid contraction, the atomic radii of (160 pm) and Hf (159 pm) is almost similar. That is why Zr and Hf occur in nature together.
(c) AgBr is widely used in photography industry.
OR
5.(a) Why Cu2+ ion is stable in aqueous solution?
(b) Trivalent Lanthanoid ions are coloured. Why?
(c) CuI2 is not known. Why?
Ans. (a) In an aqueous medium, Cu2+ is more stable because although energy is required to remove one electron from Cu+ to Cu2+ , high hydration energy of Cu2+ compensates for it. Therefore, Cu+ ion in an aqueous solution is unstable. It disproportionates to give Cu2+ and Cu. 2Cu+ (aq) → Cu2+(aq) + Cu(s).
(b) The lanthanide metals are silvery white but the trivalent lanthanide ions show different colours.Colour of the ions depend on the number of unpaired electrons because the elements with (x)f electrons often have a similar colour to those of (14-x)f electrons.The colour of lanthanide ions is due to the presence of partially filled f orbitals. As a result, it is possible to absorb certain wavelength from the visible region of the spectrum. This results in transitions from one 4f orbital to another 4f orbital known as f-f transition.
(c) CuI2 is not known because Cu2+ oxidises I– to I2 as follows:
2Cu+2 + 4I- → Cu2I2 + I2
6. Complete the following equations:
How can you convert the following:
a. Sodium phenoxide to o-hydroxybenzoic acid
b. Acetone to propene
c. Phenol to chlorobenzene
a.
b.
c.
7. Account for the following:
(a) What happens to Δ H and Δ S during adsorption of a gas on solid?
(b) Gelatin is what type of sol?
(c) Give one example of peptising agents.
Ans. (a) During the adsorption of a gas on the surface of a solid there is always a decrease in residual forces of the surface i.e., there is decrease in surface energy which appears as heat. Adsorption, therefore is an exothermic process. Thus, ΔH for adsorption is always negative. Again when a gas is adsorbed,the freedom of movement of its molecules also becomes restricted. This leads to decrease in the entropy of the gas after adsorption. Therefore, ΔS is negative.
(b) Lyophilic type of sol.
(c) Sodium chloride (NaCl) is an example of peptising agent.
8.(a) Write the complete reaction for the following conversions mentioning the necessary conditions:
(i) Toluene to benzaldehyde
(ii) Aldelyde to acetal
(b)Explain why Carbonyl carbon is an electrophilic centre where as carbonyl oxygen is a nucleophilic centre.
Ans.
a.
(a) What is electrochemical series? The cell potential of mercury cell remains constant during its lifetime. Why?
(b) Define cell constant, what is its unit?
(c) Limiting molar conductivity of an electrolyte cannot be determined experimentally. Why?
Ans. (a) Electrochemical series can be defined as the arrangement of various elements in the order of increasing value of their standard reduction potential values. The cell potential of a Mercury cell remains constant throughout it’s life because the overall reaction does not involve any ion in the solution whose concentration may change.
(b) Cell constant of a conductivity cell is defined as the ratio of the distance between the electrodes divided by the area of cross-section of the electrodes. It is denoted by b and can be expressed as:
Cell constant = b = lcm/a cm2
Thus, it is expressed in unit cm-1 or m−1.
(c) In weak electrolyte the conductivity of the solution increases very slowly with dilution of solution and goes on increasing upto infinity. Hence, it can not be measured experimentally.
10. (a)The activation energy of a reaction is zero. Will the rate constant of the reaction depend upon temperature? Give reason.
(b) Write rate law expression and order of the following reaction:
Step 1. H2O2 + I– → H2O + IO– (slow)
Step 2. H2O2 + I– → H2O + IO– + O2 (fast)
(c) Write three points of differences between rate of reaction and rate constant.
Ans.(a) Order of Reaction: First order; Unit of rate constant : s–1.
(b) According to Arrhenius equation:
k = Ae–Ea/RT
If Ea = 0, then wf = A. Frequency factor (a) does not depend upon temperature, therefore, rate constant and rate does not depend on temperature.
Rate = K[H2O2][I–] because step 1 is rate determining step and,
Order = 1 + 1 = 2
(c) Rate of Reaction:
1. It depends upon the concentration of reactant.
2. It is expressed in terms of consumption of reactants or formation of product per unit time.
3. It generally decreases with the progress of the reaction.
Rate Constant:
1. It is independent of the concentration of the reactant.
2. It is proportionality constant in differential form in rate law or rate equation.
3. It does not depend on the progress of the reaction
11. From the following ions which are given:
Cr2+, Cu2+, Cu+, Fe2+, Fe3+, Mn3+
Identify the ion which is:
(a) A strong reducing agent
(b) Unstable in aqueous solution
(c) A strong oxidising agent
Ans.(a) Cr2+ is a strong reducing agent as it is very easily oxidized to more stable Cr3+ (d3) where it attains a stable half-filled t2g configuration.
(b) Cu+ is unstable in aqueous solution because it disproportionates in water to form Cu2+ and Cu.
(c) Mn3+ is a strong oxidising agent because it gets reduced to Mn2+ (d5) in the process and attains an extra stable half-filled d orbital configuration.
SECTION- C
12. Read the passage given below and answer the questions that follow:Properties of Amines
Due to presence of lone pair of electrons in ‘N’ atoms the amines are basic in nature because these lone pair of electrons can be donated to electron deficient compound. Aliphatic amines are stronger bases than ammonia. The basicity increases with the increase in number of alkyl groups attached to the ‘N’ atom. However, the observed basic nature of amines is 2°>1°>3°.
Primary and secondary amines are soluble in water due to hydrogen bonding. Solubility decreases with increase in number of ‘C’ atoms.
(a) Boiling points of amines are less than the alcohols of similar molecular mass. Why?
(b) Amines behave as nucleophiles. Why?
(c) Which reaction is used for the test of primary aromatic amines?
(d) Lower aliphatic amines are soluble in water. Why?
OR
(d) Amines are less soluble in water than alcohols. Why?
Ans. (a) Amines are less polar than alcohols because electronegativity difference between N–H is less than that of O–H. Intermolecular H-bond in amines is weaker than that in alcohols. Hence, boiling point of amines are less than the alcohols of similar molar mass.
(b) Amines contain a lone pair of electrons on nitrogen atom. Therefore they behave as nucleophiles.
(c) Diazo test is used to detect primary aromatic amines.
(d) Lower aliphatic amines are soluble in water because they can form hydrogen bonds with water molecules.
OR
(d) Alcohol molecules form H-bond with water molecules more strongly than amines and therefore solubility of amine is less than that of alcohols.