Meghalaya Mbose Class 12 Chemistry — Real Previous-Year Papers

Primary, secondary and tertiary alcohols can be distinguished by (a) Hinsberg's test (b) Tollen's reagent (c) Fehling's solution (d) Lucas test

Phenol is more acidic than ethanol because (a) ethoxide ion is more stable than phenoxide ion (b) phenoxide ion is more stable than ethoxide ion (c) phenol undergoes electrophilic substitution reaction (d) phenol undergoes protonation easily

The most suitable reagent for the conversion of RCH₂OH arrow RCHO is (a) KMnO₄ (b) K₂Cr₂O₇ (c) LiAlH₄ (d) PCC (Pyridinium Chlorochromate)

The compound among the following which gives both iodoform and Fehling's test is (a) ethanol (b) propanone (c) butan-2-ol (d) ethanal

Aldol condensation does not occur between (a) two different aldehydes (b) two different ketones (c) an aldehyde and a ketone (d) an aldehyde and an ester

Which of the following on heating with aqueous KOH, produces acetaldehyde? (a) CH₃CH₂Cl (b) CH₂ClCH₂Cl (c) CH₃CHCl₂ (d) CH₃COCl

Which one of the following is used in Friedel-Crafts acylation reaction? (a) Anhy. AlCl₃ (b) Aq. AlCl₃ (c) NH₂NH₂ (d) NH₂OH

Which one of the following is the correct statement? (a) Alkyl halides are more reactive than aryl halides towards nucleophilic substitution reaction (b) Alkyl halides are less reactive than aryl halides towards nucleophilic substitution reaction (c) Nucleophilic substitution reaction proceeds through carbocation (d) Aryl halides cannot be prepared by electrophilic substitution to arenes

Which complexes do not show geometrical isomerism? (a) Square planar complexes (b) Tetrahedral complexes (c) Octahedral complexes (d) All of the above

Copper sulphate cannot be stored in zinc vessel. This is because (a) EMF of the reaction is negative (b) EMF of the reaction is positive (c) reduction potential value of Zn is more than Cu (d) reduction potential value of Cu is negative

Write the formula of the coordination compound tetraamine aquachlorido cobalt (III) chloride.

Give one example of coordination isomerism.

Arrange the following set of compounds in order of increasing boiling points: 1-chloropropane, isopropyl chloride, 1-chlorobutane

Write the products of the following reaction: CH₃-CH₂-CH₂-CH(Br)-CH₃ xrightarrowAlc.KOH A + B

Complete the following reaction: aniline (benzene ring with an -NH₂ substituent) + Br₂(aq) arrow ?

Why is methanamine a stronger base than ammonia?

10% solution of non-volatile solute in water has a vapour pressure 740 mm at 373 K. Calculate the molar mass of the solute. **OR** What mass of ethylene glycol must be added to 5.5 kg of water to lower the freezing point from 0°C to −10°C? Kf for water = 1.86 K kg mol⁻¹, molar mass of ethylene glycol = 62 g mol⁻¹.

A first-order reaction has a rate constant 1.15×10⁻³s⁻¹. How long will 5 g of this reactant take to reduce to 3 g? **OR** Derive the integrated rate expression of a zero-order reaction.

What is the meaning of the negative sign in the expression E⁰Zn²⁺/Zn = -0.76 V?

Arrange the following in decreasing order of their basic strength: C₂H₅NH₂, (C₂H₅)₂NH, (C₂H₅)₃N, C₆H₅NH₂

Identify the products of the following: CH₃-CH₂-Br xrightarrowKCN A xrightarrowLiAlH₄ B

Identify the products of the following: C₆H₅NH₂ + CHCl₃ + KOH(alc.) arrow ?

The cell in which the following reaction occurs: 2Fe³⁺(aq) + 2I^-(aq) arrow 2Fe²⁺(aq) + I₂(s) has E⁰cell = 0.236 V at 298 K. Calculate the standard Gibbs energy and the equilibrium constant of the cell reaction. [Given, 1F = 96500 C]

(a) What type of deviation from Raoult's law is observed by mixing chloroform and acetone? What causes this deviation? (1+1=2 marks) (b) What is the value of van't Hoff factor, i, for aqueous K₂SO₄ solution, assuming that it undergoes complete dissociation in solution? (1 mark) **OR** (c) What is meant by elevation of boiling point? (1 mark) (d) The boiling point of benzene is 353.23 K. When 1.80 g of a non-volatile solute was dissolved in 90 g of benzene, the boiling point is raised to 354.11 K. Calculate the molar mass of the solute. [Kb for benzene is 2.53 K kg mol⁻¹] (2 marks)

(a) Give one point of difference between order and molecularity of a reaction. (1 mark) (b) The decomposition of HI is expressed by the equation 2HI(g) arrow H₂(g) + I₂(g). If during a certain time interval, the rate of disappearance of HI is 1.8×10⁻³mol L⁻¹s⁻¹, then what will be the rate of appearance of H₂ during the same time interval? (2 marks) **OR** (c) For the reaction, 2NO(g) + O₂(g) arrow 2NO₂(g), the rate equation is given by, r = K[NO(g)]²[O₂(g)]. Calculate the overall order of this reaction. Is this reaction an elementary reaction? Justify your answer. (1+1=2 marks) (d) What is the order of the reaction if its unit of rate constant, k is (i) s⁻¹ and (ii) mol L⁻¹s⁻¹? (1 mark)

(a) Write the mechanism of the following SN1 reaction: (CH₃)₃C-Br xrightarrowaq.NaOH (CH₃)₃C-OH + NaBr (2 marks) (b) Why is t-butyl bromide more reactive towards SN1 reaction as compared to n-butyl bromide? (1 mark) **OR** (c) How would you carry out the following conversions? (1×3=3): (i) Aniline to chlorobenzene (ii) Benzene to diphenyl (iii) But-1-ene to but-2-ene

(a) Write the chemical equation for the preparation of ethoxybenzene by Williamson's synthesis. (1 mark) (b) How do you carry out the following conversions? (1+1=2 marks) (i) Aniline to phenol (ii) Formaldehyde to ethanol **OR** (c) Arrange the following alcohols in decreasing order of acid strength (1 mark): 2-methylpropan-2-ol, propanol, propan-2-ol (d) Predict the product of the following reaction (1 mark): (CH₃)₃C-OH xrightarrow[573K]Cu ? (e) Give the equations only for the conversion of benzene to phenol. (1 mark)

(a) Name four complimentary bases present in a DNA molecule. (1 mark) (b) Name the vitamin whose deficiency causes muscular weakness. (1 mark) (c) Write the structure of products formed when D-glucose is treated with NH₂OH. (1 mark) **OR** (d) What do you mean by denaturation of proteins? (1 mark) (e) What are essential and non-essential amino acids? Give one example of each type. (2 marks)

What is the oxidation number of Fe in [Fe(CN)₆]⁴⁻?

Give one example of a complex having tetrahedral geometry and paramagnetic in nature.

Which one is an inner-orbital complex? [Co(NH₃)₆]³⁺ or [CoF₆]³⁻

According to VBT, which one has the highest paramagnetic character? [Cr(H₂O)₆]³⁺ or [Fe(H₂O)₆]²⁺

What are reducing and non-reducing sugars?

What are epimers?

Name one optically active amino acid and one optically inactive amino acid.

Why are carbohydrates generally optically active?

(a) Write two functions of salt bridge. (1 mark) (b) Calculate the EMF of the cell in which the following reaction takes place: Ni(s) + 2Ag^+(0.002M) arrow Ni²⁺(0.160M) + 2Ag(s) (Given that E⁰cell = 1.05 V) (2 marks) (c) How much electricity in terms of Faraday is required to produce 40 g of Al from Al₂O₃? (F = 96500 C, Atomic mass of Al = 27) (2 marks) **OR** (d) Why does conductivity of a solution decrease with dilution? (1 mark) (e) What is cathodic protection? (1 mark) (f) (i) State Kohlrausch's law. (1 mark) (ii) Given molar conductivities at infinite dilution: λ⁰m(Ba(OH)₂) = 457.6S cm²mol⁻¹, λ⁰m(BaCl₂) = 240.6S cm²mol⁻¹, λ⁰m(NH₄Cl) = 129.8S cm²mol⁻¹. Calculate λ⁰m for NH₄OH. (2 marks)

(a) Why do transition metals generally form coloured compounds? (1 mark) (b) Draw the structures of permanganate ion. (1 mark) (c) Why Cr³⁺ is reducing and Mn³⁺ is oxidizing when both have d⁴-configuration? (1 mark) (d) Give the reaction of potassium dichromate with (i) KI and (ii) H₂S (in acidic medium). (2 marks) **OR** (e) Why do transition metals easily form alloys with other transition metals? (1 mark) (f) Why is silver (Atomic number = 47) considered to be a transition element whereas zinc (Atomic number = 30) is not? (1 mark) (g) Write the balanced chemical equation for the reaction of KMnO₄ with oxalic acid in acidic medium. (1 mark) (h) Write all the reactions occurring during the preparation of potassium permanganate from pyrolusite ore. (2 marks)

(a) Would you expect benzaldehyde to be more reactive or less reactive in nucleophilic addition reactions than propanal? Explain your answer. (2 marks) (b) Identify the products A, B, C and D from the following sequence of reactions (2 marks): CH₃CH₂Br xrightarrow[dry ether]Mg A xrightarrow[(ii) H₃O^+](i) CO₂dry ether B xrightarrow[Δ]NH₃ C xrightarrowBr₂/KOH D (c) Predict the product of the following reaction (1 mark): acetophenone (C₆H₅-CO-CH₃) + CH₃CH₂NH₂ xrightarrowH^+ ? **OR** (d) Write the structures of pentan-2-one and pentan-3-one and give a simple chemical test to distinguish between them. (2 marks) (e) Predict the structures of the products A, B, C and D from the following reactions (1×2=2): (i) benzene xrightarrow[anhy. AlCl₃/CuCl]CO,HCl A xrightarrowHNO₃/H₂SO₄ B (ii) CH₃COOH xrightarrow[(ii) H₃O^+](i) LiAlH₄/ether C xrightarrowanhy. CrO₃ D (f) The pKa values of 4-methoxybenzoic acid, 4-nitrobenzoic acid and benzoic acid are 4.46, 3.41 and 4.19 respectively. Which of these aromatic carboxylic acids is the most acidic and why? (1 mark)