12th Chemistry Pre-Board Paper PDF (2022-23) - BJM Carmel Academy

**BJM CARMEL ACADEMY** **CBSE SENIOR SECONDARY SCHOOL** FIRST PRE BOARD EXAMINATION (2022-23) SUBJECT: CHEMISTRY (043) ======================== Class: XII Marks: 70 ==================== Name: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Time: 3hrs. ==============...

**BJM CARMEL ACADEMY** **CBSE SENIOR SECONDARY SCHOOL** FIRST PRE BOARD EXAMINATION (2022-23) SUBJECT: CHEMISTRY (043) ======================== Class: XII Marks: 70 ==================== Name: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Time: 3hrs. ============================================================================================== **[General Instructions]:-** **Read the following instructions carefully.** a. There are 35 questions in this question paper with internal choice, b. SECTION A consists of 18 multiple choice questions carrying 1 mark each. c. SECTION B consists of 7 very short answer questions carrying 2 marks each. d. SECTION C consists of 5 short answer questions carrying 3 marks each. e. SECTION D consists of 2 case-based questions carrying 4 marks each. f. SECTION E consists of 3 long answer questions carrying 5 marks each. g. All questions are compulsory. h. Use of calculators and log tables is not allowed. **SECTION -- A** **The following questions are multiple-choice questions with one correct answer. Each question carries 1 mark. There is no internal choice in this section.** 1\) The formation of cyanohydrins from propanone is which type of reaction - a\) Electrophilic Substitution c) Electrophilic addition b\) Nucleophilic reaction d) Nucleophilic addition 2\) Charge carried by 1 mole of electron is - a\) 6.023 x 10^23^C b) 9.65 x 10^4^C c) 1.6 x 10^−19^C d) 6.28 x 10^19^C 3\) At a given temperature osmotic pressure of a concentrated solution of a substance - a\) is higher than that of a dilute solution. b\) is lower than that of a dilute solution. c\) is same as that of a dilute solution. d\) cannot be compared with osmotic pressure of dilute solution. 4\) The half life of a first order reaction is 69.35 sec. The values of rate constant of the reaction is - a\) 1.0 S^-1^ b) 0.1 S^-1^ c) 0.01 S^-1^ d) 0.001 S^-1^ 5\) Recemisation occurs in - a\) S~N~2 reaction c) Neither S~N~2 nor S~N~1reaction b\) S~N~1 reaction d) S~N~2 reaction as well as S~N~1 reaction 6\) Which of the following are used to convert RCHO into R. CH~2~OH -- a. Ether b) LiAlH~4~ c) KOH d) RMg X followed by hydrolysis 7\) The source of nitrogen in Gabriel Synthesis of amines is - a. Sodium azide c) Potassium cyanide b. Sodium nitrite d) Potassium pthalimide 8\) Which of the following acid is vitamin -- a. Aspartic acid b) Ascorbic acid c) Adipic acid d) Saccaric acid 9\) Total number of unpaired electrons present in Co^3+^ (atomic number = 27) is - a. 2 b) 7 c) 3 d) 4 10\) Which of the following oxidation state is common for all lanthanoids -  a) +2 b) +3 c) +4 d) +5 11\) What is the correct IUPAC name of the given compound? a. 2, 2 -- Dimethylbutanoic acid c) 2-Ethyl -- 2 -- Methylpropanoic acid b. 2 -- Carboxyl -- 2 - Methylbutane d) 3 -- methylbutane carbonylic acid 12\) Which of the following compounds is oxidized to Methyl ethyl ketone - 13\) In Leclanche dry cell, the Cathode is - a\) Zn container b) MnO~2~ c) Graphite rod d) NH~4~Cl 14\) Amylopectin is insoluble in water and constitute about - a\) 15 -- 20% of starch c) 50 -- 70 % of starch b\) 20 -- 40 % of starch d) 80 -- 85 % of starch **Assertion Reason type question.** **Given below are two statements as Assertion (A) Reason (R). Select the most appropriate answer from the option given below:** a. Both A and R are true and R is the correct explanation of A. b. Both A and R are true and R is not the correct explanation of A. c\) A is true but R is false. d\) A is false but R is true. 15\) **A:** Phenol on oxidation with chromic acid gives benzoquinone. **R:** Pure phenol is colourless but turn pink due to oxidation to phenoquinone. 16\) **A:** Reducing sugars undergo mutarotation. **R:** During mutarotation, one pure anomer is converted into an equilibrium mixture of two anomers. 17\) **A:** Ce^4+^ is used as an oxidising agent in volumetric analysis. **R:** Ce^4+^ has a tendency to attaining +3 oxidation state. 18\) **A:** Hoffmann's bromamide reaction is given by primary amines. **R:** Primary amines are more basic than secondary amines. **SECTION- B** **This section contains 7 questions with internal choice in one question. The following questions are very short answer type and carry 2 marks each.** 19\) A first order reaction has a rate constant 1.15 x 10^-3^ S^-1^. How long will 5g of this reactant take to reduce to 3g? 20\) What are essential and non essential amino acid? Give two examples of each type. **OR** What is the effect of denaturation on the structure of proteins? 21\) Give the structural formula and IUPAC name of the following compounds: i\) BHC ii) DDT **OR** What are ambident nucleophiles? Explain with an example. 22\) \[Fe(CN)~6~\]^-2^ and \[Fe(H~2~O)~6~\]^2+^ are different coloured in dilute solution. Why? 23\) The conductivity of 0.20M solution of KCl at 298 k is 0.025 Scm^-1^. Calculate its molar conductivity? 24\) Why is molecularity applicable only for elementary reaction and order is applicable for elementary as well as complex reaction? 25\) Carry out the following conversion - a\) Benzoic acid to aniline b) Bromomethane to ethanol **SECTION- C** **This section contains 5 questions with internal choice in two questions. The following questions are short answer type and carry 3 marks each.** 26\) How do you convert the following? i\) Benzoic acid to Benzaldehyde iii) Acetic acid to methane ii\) Ethyne to Ethanol **OR** How will you prepare carboxylic acids from: i\) Aldehyde ii) Grignard reagent iii) Amide 27\) Write the name, the structure and magnetic behavior of each one of the following complexes. i\) \[Ni(CN)~4~\]^-2^ ii) Ni(CO)~4~\] iii) \[Co(NH~3~)~4~Cl~2~\]Cl At. No. Ni = 28 Co = 27 28\) Calculate freezing point of a solution when 3 g of CaCl~2~ (M = 111 g/mol) was dissolved in 100 g. of water, assuming CaCl~2~ undergoes complete ionization. (K~f~ for water = 1.86 k kg mol^-1^) 29\) Give explanation for each of the following: i\) Why are amines less acidic than alcohols of comparable molecular masses? ii\) Why do primary amines have higher boiling point than tertiary amines? iii\) Why are aliphatic amines stranger bases than aromatic amines? 30\) How will you bring the following conversions: i\) Toluene to benzyl alcohol. ii\) Benzene to biphenyl iii\) But -- l -- ene to but -- 2 - ene **SECTION- D** **The following questions are case-based questions. Each questions has an internal choice** **and carries 4 marks each. Read the passage carefully and answer the questions** **that follow.** 31\) Carbohydrates, Proteins, nucleic acids etc. form the basis of life and are responsible for the growth and maintenance of living systems. Therefore, they are referred to as biomolecules. Carbohydrates are widely distributed in nature. Carbohydrates are optically active polyhydroxy aldehyde or ketones or the compounds which produce such units on hydrolysis. Glucose, fructose, Sucrose, Starch, Cellulose, etc. are some naturally occurring carbohydrates. They act as the major source of energy for animals and human beings. i\) Which carbohydrate provide instant energy to the body? ii\) Which disaccharide is found only in animals and not in plants? iii\) Write the names of two monosaccharides obtained on hydrolysis of lactose sugar. 32\) **Read the following passage and answer the following questions**. i. What type of liquid form the ideal solution? ii. Give one example of ideal solution. iii. Write two charactristics of non-ideal solution. **OR** **SECTION- E** **The following questions are long answer type and carry 5 marks each. Two questions have an internal choice.** 33\) Calculate E.m.f. and ∆G for the following cell at 298 k: Mg~(s)~\|Mg^2+^~(0.01m)~\|\| Ag^+^~(0.0001m)~\|Ag~(s)~. Given: E^o^mg^2+^/mg = −2.37v, E^o^Ag^+^/Ag = +0.80v. **OR** Conductivity 00.00241m acetic acid is 7.896 x 10^-5^ S cm^-1^. Calculate its molar conductivity. If λ^o^m for acetic acid is 390.5 S cm^2^mol^-1^. What is its dissociation constant? 34\) How will you prepare the following compounds from benzene? You may use any inorganic reagent and any organic reagent having not more than one carbon atom. i. methyl benzoate iii) p-nitro benzoic acid ii\) m-nitrobenzoic acid iv) phenylacetic acid p-nitrobenzaldehyde **OR** Show how each of the following compounds could be converted to benzoic acid -- i\) Ethylbenzene iv) Phenylethene ii\) Acetephenone v) Toluene iii\) Bromobenzene 35\) Assign reasons for the following: i\) The enthalpies of atomization of transition elements are high. ii\) The transition metals and many of their compounds act as good catalyst. iii\) From element to element, the actinoid contraction is greater than the lanthanoid contraction. iv\) The E^o^ value for the Mn^s+^/Mn^2+^ couple is much more positive than that of Cr^3+^/Cr^2+^. v\) Sc(Z = 21) does not exhibit variable oxidation states and yet it is regarded as a transition element. \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--