NEB Class 12 Science Chemistry Question Paper 2080

What is the molarity of 1.1 g/mL H₂SO₄ solution having specific gravity 15% (w/w)?

Which of the following is not a primary standard substance?

The degree of ionization of an electrolyte depends on

Electron pair donors are

Which theory put forward the concept of secondary valency for explanation of co-ordination compounds?

Zinc is not considered as a typical transition metal due to

Which of the following compound is known as Schweitzer's reagent?

Primary aliphatic amine and primary aromatic amine can be distinguished by

Chloro group in chlorobenzene is

Oxidation of which alcohol gives ketone?

Which of the following is not a phenol?

Titrimetric analysis involves the measurement of volume of solution in order to determine concentration of solution.

a) What is meant by standardization? [1]

b) Write any four qualities of primary standard substance. [2]

c) Give any two examples of secondary standard substance. [1]

d) Calculate the mass of Na₂CO₃ required to prepare 250 mL of its 0.1 N solution. [1]

OR

Define the following terms related to titration. [1+1+1+1+1]

a) Equivalence point b) Indicator c) End point d) Acidimetry e) Normality factor

Sorensen, in 1909, proposed a more practical measure of acid concentration called pH.

a. Define pH. [1]

b. Calculate the pH of 1M acetic acid. To what volume 1L of this solution is diluted so that the pH of the solution that is formed is twice of its original value. ($K_a = 1.8\times10^{-5}$). [4]

One of the characteristics of transition elements is to show colour in its compounds.

a) Why do transition elements show colour in their compounds? [1.5]

b) Salts of Zn²⁺ are colourless but those of Cu²⁺ are blue in colour. Why? [2]

c) Potassium permanganate has pink colour. [1.5]

Copper has been extensively used by human kind from ancient period for many purposes.

a) Name any two important ores of copper found in Nepal. [1]

b) Copper matte is produced during smelting process. Write the reactions involved during this process. [2]

c) Discuss how copper is electro-refined. [2]

You are given 2-methylpropan-2-ol, propan-1-ol and propan-2-ol in three separate test tubes.

a) Classify them as 1°, 2° and 3° alcohol. [1]

b) Which method would you apply to distinguish them? Name the method. [1]

c) Write all the reactions involved in the method. [3]

Bromination of phenol is one of the important electrophilic substitution reactions of phenol.

a) Discuss why ortho-, para- substituted products are formed by phenol during electrophilic substitution reaction. [3]

b) Write with reaction which product is formed if phenol is reacted with bromine water. [1]

c) What happens if the bromination of phenol is performed with solution of Br₂ in CCl₄? [1]

OR

a) An organic compound (A) has 76.6% carbon and 6.38% hydrogen. Its vapour density is 47. It gives positive FeCl₃ test. The compound (A) upon treatment with CO₂ and NaOH at 140°C under pressure gives (B). The compound (B) on acidification gives (C) which if reacted with acetyl chloride gives a well-known analgesic (D). Identify (A), (B), (C) and (D) with the involved reactions. [4]

b) Give a reaction to show that carboxylic acid is more acidic than phenol. [1]

Haloalkane mainly gives nucleophilic substitution reaction in which more reactive nucleophile displaces halide.

a) Write any three differences between $S_N1$ and $S_N2$ reaction. [3]

b) Convert chloroethane into 1-aminopropane. [2]

Consider a reaction:

$A \xrightarrow{PCl_5} B \xrightarrow{NH_3,\,\Delta} C \xrightarrow{KCN} D \xrightarrow{dil.\,HCl} E$

The compound A is a primary alcohol which has positive iodoform test. Identify A, B, C, D and E. [5]

Titration involving potassium permanganate is called permanganometric titration.

a) Why KMnO₄ is not a primary standard substance? [1]

b) KMnO₄ solution is acidified with dilute H₂SO₄ but not with dilute HCl or HNO₃. Why? [1]

c) Why KMnO₄ is called self-indicator? [1]

d) KMnO₄ acts as auto catalyst in permanganometric titration. Discuss. [1]

e) 2.5 g of dolomite was dissolved in 80 mL (f=1.05) N HCl. The resulting solution was made up to 250 mL. 30.2 mL of N/10 NaOH solution was required to neutralize 25 mL of diluted solution. Calculate the percentage composition of CaCO₃ and MgCO₃ in dolomite. (Ca=40, Mg=24, C=12 and O=16). [4]

OR

Write short notes on:

a) Lewis acid-base concept [2]

b) Common ion effect and solubility product [2]

c) Choice of indicator in acid-base titration [2]

d) Hydrolysis of salt. [2]

a) Identify A, B, C and D in the following reaction sequence. [4]

$CH_3CH_2OH \xrightarrow{} A \xrightarrow{Mg/\text{ether}} B \xrightarrow{HCHO} C \xrightarrow{H^+} D$

b) An alkene (A) while performing Baeyer's test was found to give a dihydric alcohol (B), $C_2H_6O_2$. The compound (B) undergoes stepwise oxidation with $K_2Cr_2O_7/H^+$ to give a dicarboxylic acid (C), $C_2H_2O_4$ as a final product. Identify (A), (B) and (C) with related reactions. Mention one application of compound (B). [4]

Show your familiarity with the following reactions. [2+2+2+2]

a) Reimer-Tiemann reaction

b) Diazotization reaction

c) Coupling reaction