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Chemistry NEB Grade 12 Model Question 2079-2023

Chemistry | NEB Grade 12 Model Question 2079-2023

Hi, Students of grade XII-12 out there! Today, we’ve brought you Chemistry NEB Grade 12 Model Question 2079-2023 with subject code: 3021 and you can download the neb grade xii (12) Chemistry subject question paper of the year 2079-2023 in PDF format. Please check and download pdf file grade 12 Chemistry Model question paper of the year 2023-2079 Nepal. The model question provided below – Chemistry neb grade xii-12 of the year 2079-2023 for the board exam 2079 and onwards. And it is based on the latest NEB Syllabus for 2079. We will be adding more model question papers of grade xii-12 later on. Scroll down to Download Chemistry NEB Grade 12 Model Question 2079-2023 in pdf format which is 722 kb in size. Enjoy!

Chemistry NEB Grade 12 Model Question Paper 2079-2023

NATIONAL EXAMINATIONS BOARD [NEB]
NEB Grade XII-12
2079-2023
Model Question
Chemistry
Subject Code – 3021
Time – 3 hrs
Full Marks – 75

The candidates are required to give their answers in their own words as far as practicable. The figures in the margin indicate full marks.

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Attempt all the questions

Group A

Rewrite the correct options of each questions in your answer sheet. (11×1= 11)

1. Identify the equivalent weight of K2Cr2O7 in the following reaction?

(Cr =52, K=39)
K2Cr2O7 + 3H2SO4 + 5(COOH) 2 K2SO4 + Cr2 {SO4)3 + 10CO2 + 8H2O

A) 49
B) 294
C) 98
D) 108

2.In a solution that is at equilibrium, what happens to the concentration of H+ ions if the concentration of OH- ions is increased?

A) The concentration of H+ ions increases
B) The concentration of H+ ions decreases
C) The concentration of H+ ions stay the same
D) It depends on the initial concentration of H+ ions

Check this  too …

NEB Grade 12 Chemistry Model Question Solution 2079-2023.

3. Assuming the rate of a reaction is doubled for every 10oC rise in temperature how many times increases the rate of temperature rises from 100C to 1000C?

A) 112 times
B) 400 times
C) 512 times
D) 614 times

4. forthe given reactions
i. C + O2→ CO2, Δ H = – x KJmol-1
ii. 2CO + O2→ 2CO2, Δ H = – y KJmol-1 The enthalpy of formation of CO becomes

A) 2y-x
B). 2x-y
C) 𝑦−2𝑥2
D) 𝑥−2𝑦2

5. What product would be obtained if red hot copper wire reacts with steam?

A) CuO
B) Cu2O
C) Cu2O2
D) Cuo2

6. For which manufacturing process, Bessemer converter is used?

A) Pig iron
B) Steel
C) Wrought iron
D) Cast iron

7. When Sodium phenoxide reacts with methyl bromide it gives

A) Cresol
B) Toluene
C) benzene
D) Anisole

8. Identify the X in the following reaction:

A) Na2S
B) Sn/HCl
C) LiAlH4
D) Na/H2

9. Which of the following reagents can be used to distinguish between a phenol and a carboxylic acid?

A) KOH
B) Na
C) NaOH
D) NaHCO3

10. The colorless sweet smelling liquid compound A which exposed in air forms poisonous phosgene and also react with acetone gives sleep-inducing drug. Predict the product when the compound A reduced in a neutral medium?

A) Methylene chloride
B) Methane
C) Ethyne
D) Ethane

11. Oxygen containing organic compounds upon oxidation forms a carboxylic acid as the major organic product with its molecular mass higher by 14 units. Identify the organic compound.

A) A primary alcohol
B) An aldehyde
C) A ketone.
D) A secondary alcohol

Group B

Short answer questions (8×5= 40)

12. The addition of solution of required concentration in a reaction mixture yields profitable products and saves reactants.

a) A solution of HCl is labelled 2M. Clarify its meaning?
b) In which aspects molarity is different from molality?
c) List the significance of normality factor in preparation of standard solution?
d) Liquor ammonia kept at a corner of your chemistry lab is 25% (w/w) NH3 and its specific gravity is 0.91. Find the molarity of liquor ammonia. [1+1+1+2]

13.

a) Write down the differences between rate of reaction and rate constant. (2)
b) For the reaction 2A+B→product, following data were obtained

Experiment[A] moleLitre-1[B] moleLitre-1Initial rate, moleLitre-1 S-1
10.500.501.6×10-4
20.501.003.2×10-4
31.001.003.2×10-4

Find,
i) order with respect to A and B. (1)
ii) the value of the rate constant of the reaction (1)
iii) the rate of reaction when the concentration of A and B is 0.5M and
0.4 M, respectively. (1)
Or
Four metals A, B, C and D react in the following way:

B displaces only A from solution. Only D and Cdisplaces hydrogen from 1M HCl solution. None of the metals will displace C from solution. Answer the followings:

i) Make the activity series of four metals with hydrogen (1)
ii) The standard potential for the following electrodes are:
C+++ 2e- C,Eo= -0.76V
D++++ e- D++,Eo= +0.77V
a) Construct the galvanic cell by pointing out cathode and anode. (2)
b) With 1M solution of the ions, what will be EMF of cell? (1)
c) Will the reaction occur: C++ + 2D++ → C + D+++. Occur? Give reasons. (1)

14. An ammonia solution is added to the sulphate of coinage metal A, the blue Precipitates (B) which appears dissolves in excess of reagent to form deep blue Solution(C). Answer the followings:

a) Identify A, B and C with sequence of chemical reaction. (3)
b) Predict the electronic configuration of this metal A. (1)
c) Select the suitable methods for the purification of metal A? (1)

15. What is meant by d-d electron transitions? List the characteristics of transition metals. 1+4=5

16. Write down the structural formula and IUPAC name of tertiary alcohol with formula C4H10O. How would you apply Victor Meyer’s method for the distinction of 1- propanol and 2- propanol ? Explain. 1+4

17. An organic compound X reacts with methyl magnesium bromide followed by acidic hydrolysis yields the compound Y. The compound Y On oxidation with acidified KMnO4 yields Z. All three gives positive iodoform test. Answer the followings:

a). Predict the compounds X , Y and Z with sequence of reaction and give their IUPAC names. (3)
b) Make the product by reacting Z with dilute NaOH? (2)
OR
An organic compound(X) when heated with acetone gives hypnotic and nervous sedatives drugs and form carbonyl chloride when it exposes to air
a) Predict the organic compound (X) (1)
b) Write the reactions for the formation of (X) from ethanol. A (2)
c) Predict compound the new compound by treating (X) withconcnitric acid? (1)
d) Convert (X) into acetylene. (1)

18.

a) Nitro group in nitrobenzene is meta-directing group towards electrophilic substitution reaction, why? How does nitrobenzene react with?i) Zn/ NH4Cl ii) LiAlH4 (2+2)
b) What are the isomers of formula C2H7N? (1)

19. Give an example of the following reactions 1×5=5

(a) RiemerTiemann’s reaction
(b) Perkin’s condensation reaction
(c) Williamson’s ether synthesis
(d) Cannizzaro’s reaction
(e) Sandmeyer’s reaction

Group C

Long answer questions (3 x 8 =24)

20. The expressions of Ostwald’s dilution law is, ∝ = √𝐾𝑎/𝐶
a) Derive it.
b) What information can you obtain from this expression?
c) Will strong electrolytes obey this expression, why?
d) 0.1M ethanoic acid is 1.34% ionized. Find its dissociation constant. (3+ 2+1+2)

Or

a) Hess’ law is applied to calculate different types of enthalpy of reaction.
i) Illustrate the Hass law of constant heat summation.
ii) Standard enthalpy of combustion of c (g); H2 (g) and C2H2 (g) are -394 KJ mol-1, -286 KJ mol-1 and -1300 KJ mol-1 respectively. Calculate enthalpy of formation of acetylene. (2+4)

b) Draw the energy profile diagram of exothermic and endothermic reaction. (1+1)

21. An organic compound C2H4O2 has two functional isomers A and B. Isomer A changes blue litmus into red and B has fruity smell.
a) Give the reaction for the formation of A by using Grignard’s reagent. (1)
b) Convert the isomer A into isomerB? (2)
c) Write a suitable test reaction to distinguish A frommethanoic acid. (1)
d) Arrange the following in the decreasing order of their acidic strength and give reason for your answer.
CH3COOH, ClCH2COOH, FCH2COOH, C6H5COOH (2)
e) Identify A and B of the following reactions. (2)
OR
Amines are formally derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group which may respectively be called alkyl amines and aryl amines.
a) Give a test to distinguish alkyl amine and aryl amine. (2)
b) How can you separate ethylamine and dimethylamine present in mixture byHoffmann’s method? (3)
c) Arrange the following amines In terms of increasing order of basic strength. (1)
Propyl amine,ethyl methylamine, trimethylamine.
d) Convert: ethanamine to methanamine (2)

22.

a. How are cement classified on the basis of hardening and setting behavior? (2)
b. Differentiate between
i. paper and pulp (2)
ii. artificial and natural radio activity (2)
iii .addition and condensation polymer (2)

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