CBSE Previous Year Solved Papers Class 12 Chemistry Outside Delhi 2015
Time allowed: 3 hours Maximum Marks: 70
- All questions are compulsory.
- Questions number 1 to 5 are very short-answer questions and carry 1 mark each.
- Questions number 6 to 10 are short-answer questions and carry 2 marks each.
- Questions number 11 to 22 are also short-answer questions and carry 3 marks each.
- Questions number 23 is a value based question and carry 4 marks.
- Questions number 24 to 26 are long-answer questions and carry 5 marks each.
- Use log tables, if necessary. Use of calculators is not allowed.
Question.1. Write the formulae of any two oxoacids of sulphur.
Answer : Oxoacids of sulphur are chemical compounds that contain sulphur, oxygen and hydrogen. Two oxoacids of sulphur are :
(i) Peroxodisulphuric acid : H2S2O8
(ii) Dithionic acid : H2S2O6.
Question.2. Write the IUPAC name of the given compound:
Answer: Ethoxy-2-methyl propane.
Question.3. A delta is formed at the meeting point of seawater and river water. Why?
Answer : River water are a negatively charged colloidal solution whereas sea water contains a number of electrolytes the meeting point of sea water and river water, the electrolytes present in sea water coagulate the colloidal solution of clay resulting in its deposition with the formation of delta.
Question.4. Which would undergo SN1 reactions faster in the following pair:
Question.5. What is the formula of a compound in which the element Y forms ccp lattice and atoms of X occupy 2/3 rd of tetrahedral voids ?
Answer: The formula of the compound is X4Y3.
Question.6. Write one similarity and one difference between the chemistry of lanthanoids and that of actinoids.
(i) Both involve the filling of f-orbital (i.e. 4f and 5f.)
(ii) Both show contraction i.e. Lanthanoide contraction and actinoide contraction.
Question.7. (i) Write down the IUPAC name of the following complex: [Co(NH3)5Cl]2+
(ii) Write the formula for the following complex:
(i) [CO(NH3)5Cl]2+: Pentaamminechloroscobalt(III) ion
(ii) Potassium etrachloridonickelate(II): K2[NiCl4]
Question.8. Write the reagents required in the following reactions :
Arrange the following compounds in increasing order of their property as indicated:
Nucleophiles are negatively charged entity, positivity of carbon is carbonyl group facilitates nucleophilic addition. Thus positivity of carbon in carbonyl group is in order III > I > II. Due to +1 effect of – CH3 group and benzene ring ω -cloud, positivity of carbonyl carbon is so much decrease than (I) and (II). Thus nucleophilic addition order III > I > II.
The stability order II > I > III. Due to +1 effect of —CH3 group electron density of oxygen is more. But in (I) and (II),—I effect of-F is more than -Cl. Thus II is more stabilized than I. Thus acidity order is II > I > III.
Question.9. (i) On mixing liquid X and liquid Y, volume of the resulting solution decreases. What type of deviation from Raoult’s law is shown by the resulting solution ? What change in temperature would you observe after mixing liquids X and Y ?
(ii) What happens when we place the blood cell in water (hypotonic solution) ? Give reason.
Answer : (i) Negative deviation of Raoult s law occurred. There is a elevation of boiling point occurs i. e., temperature of the solution increase.
(ii) When blood cell is placed in water (hypotonic solution), water penetrate to blood cell and blood cell gets bulged and then disrupt.
Question.10. Calculate the time to deposit 1.27 g of copper at cathode when a current of 2A was passed through the solution of CuS04. (Molar mass of Cu = 63.5 g mol-1, 1 F = 96500 C mol-1).
Question.11. A solution is prepared by dissolving 10 g of non-volatile solute in 200 g of water. It has a vapour pressure of 31.84 mm Hg at 308 K. Calculate the molar mass of the solute. (Vapour pressure of pure water at 308 K = 32 mm Hg).
Question.12. (i) Name the method of refining to obtain silicon of high purity.
(ii) What is the role of SiO2 in the extraction of copper ?
(iii) What is the role of depressants in froth floatation process ?
Answer: (i) Zone refining is the method of refining to obtain silicon of high purity.
(ii) Si02 combined with the iron in the copper ore to form iron(II) silicate slag which is easily removed.
(iii) In froth flotation process, depressant prevents the formation of froth. It is used to separate two sulphide ore by preventing the formation of froth of one sulphide ore and allowing the other to form the froth e.g., NaCN a depressant selectively prevents ZnS from coming in froth but allows PbS to come with the froth.
Question.13. (i) Which one of the following is a polysaccharide :
Starch, maltose, fructose, glucose.
(ii) Write one difference between a-helix and β-pleated sheet structures of protein.
(iii) Write the name of the disease caused by the deficiency of vitamin B12.
Answer : (i) Starch is a polysaccharide.
(iii) Pernicious Anaemia caused by the deficiency of Vitamin B12.
Question.14. (i) What type of isomerism is shown by the complex [Cr(H20)6] Cl3 ?
(ii) On the basis of crystal field theory, write the electronic configuration for d ion if ∆0 > P. (iii) Write the hybridization and shape of [CoF6]3-. (Atomic number of Co = 27).
Question.15. How can the following conversion be carried out:
(i) Aniline to bromobenzene
(ii) Chlorobenzene to 2-chloroacetophenone
(iii) Chloroethane to butane.
What happens when
(i) Chlorobenzene is treated with Cl2/FeCl3,
(ii) Ethyl chloride is treated with AgN02,
(iii) 2-bromopentane is treated with alcoholic KOH ?
Write the chemical equations in support of your answer.
Question.16. Examine the given defective crystal:
Answer the following questions :
(i) Is the above defect stoichiometric or non-stoichiometric ?
(ii) Write the term used for this type of defect. Give an example of the compound which shows this type of defect.
(iii) How does this defect affect the density of the crystal ?
Answer : (i) Stoichiometric defect
(ii) Schottky defects e.g. NaCl, CsCl.
(iii) The presence of a large number of Schottky defect in a crystal will lower its density markedly.
Question.18. Write any three differences between Physisorption and Chemisorption.
Question.19. Give reasons of the following:
(i) Phenol is more acidic than methanol.
(ii) The C – O – H bond angle in alcohols is slightly less than the tetrahedral angle (109°28′).
(iii) (CH3)3C – O – CH3 on reaction with HI gives (CH3)3C -I and CH3 – OH as the main products and not (CH3)3C – OH and CH3 -I.
Question.20. Predict the products of the following reactions :
Question.21. (a) Account for the following:
(i) Cu+ is unstable in an aqueous solution.
(ii) Transition metals form complex compounds, (b) Complete the following equation :
Cr2O2-7 +8H+ +3NO– —->
The higher stability of Cu2+ ion in aqueous solution is due to its greater negative than Cu.
It compensates the second ionisation enthalpy of Cu involved in the formation of Cu2+ ions.
(ii) Since transition metals have unfilled or partially filled (sf-orbital thus to satisfy its octate its forms complex compounds.
Question.22. Write the names and structures of the monomers of the following polymers:
Question.23. Seeing the growing cases of diabetes and depression among young children, Mr. Chopra, the principal of one reputed school organized a seminar in which he invited parents and principals. They all resolved this issue by strictly banning junk food in schools and introducing healthy snacks and drinks like soup, lassi, milk, etc. in school canteens. They also decided to make compulsory half an hour of daily physical activities for the students in the morning assembly. After six months, Mr. Chopra conducted the health survey in most of the schools and discovered a tremendous improvement in the health of the students.
After reading the above passage, answer the following questions:
(i) What are the values (at least two) displayed by Mr. Chopra ?
(ii) As a student, how can you spread awareness about this issue ?
(iii) Why should antidepressant drugs not be taken without consulting a doctor ?
(iv) Give two examples of artificial sweeteners.
Answer : (i) The values displayed by Mr. Chopra are :
(a) Care towards nature
(b) Social awareness
(ii) Awareness can be spread by perforating nukkad natak in community, displaying posters, cartoons and slogans and by conducting seminars.
(iii) Antidepressant drugs have lots of side effects like indigestion, headache, stomach aches, drowsiness, weight gain. That is why it should not taken without consultant with doctors.
(iv) Example of artificial sweeteners — Aspartame, Saccharin, Sucralose etc.
Question.24. (a) Account for the following:
(i) Acidic character increases from HF to HI.
(ii) There is a large difference between the melting and boiling points of oxygen and sulphur.
(iii) Nitrogen does not form pentahalide.
(b) Draw the structures of the following:
(i) Which allotrope of phosphorus is reactive and why ?
(ii) How are the supersonic jet aeroplanes responsible for the depletion of ozone layer ?
(iii) F2 has lower bond dissociation enthalpy than Cl2. Why?
(iv) Which noble gas is used in filling balloons for meteorological observations ?
(v) Complete the following equation :
(ii) The exhaust emitted from supersonic jet aeroplane contains C02, NO and other particles which are the killers of stratospheric ozone layer along with the supersonic sound produced by these aeroplanes are destroy ozone layer.
(iii) Due to smaller size and high electro-negativity of fluorine, there are lot more energy require to break the bond of F2 than Cl2. Thus F2 has lower bond dissociation energy than Cl2.
(iv) Helium (He) gas is used in filling balloons for meteorological observations because as it is non-inflammable and light gas.
Question.25. An aromatic compound ‘A’ of molecular formula C7H602 undergoes a series of reactions as shown below. Write the structures of A, B, C, D and E in the following reactions :
(a) Write the structures of main products when benzene diazonium chloride reacts with the following reagents:
(b) Arrange the following in the increasing order of their basic character in an aqueous solution :
C2H5NH2, (C2H5)2NH, (C2H5)3N
(c) Give a simple chemical test to distinguish between the following pair of compounds :
C6H5 – NH2 and C6H5– NH – CH3
+1 effect of three -CH3 group increase the enormous availability of lone pair nitrogen than +1 effect of 2 methyl group than. Thus basicity order I < III < II.
(c) C6H5 — NH2 (Primary amine) and C6H5 – NH — CH3 (Secondary amine) can be distinguished by Hinsberg’s test. In this test amines are allowed to react with Hinsberg’s reagent, benzenesulphonyl chloride (C6H5S02Cl). Primary amines reacts with this reagent to form N-alkylbenzene sulphonyl amide which is soluble in alkali but secondary amines gives sulphonamide which is insoluble in alkali.
26. For the hydrolysis of methyl acetate in aqueous solution, the following results were obtained :
(a) Show that it follows pseudo first order reaction, as the concentration of water remains constant.
(b) Calculate the average rate of reaction between the time interval 10 to 20 seconds%
(Given: log2 = 0.3010, log4 = 0.6021).
(a) For a reaction A + B —> P, the rate is given by Rate = k[A] [B]2
(i) How is the rate of reaction affected if the concentration of B is doubled ?
(ii) What is the overall order of reaction if A is present in large excess ?
(b) A first order reaction takes 30 minutes for 50% completion. Calculate the time required for 90% completion of this reaction.
(a) (i) Since the given reaction has order two with respect to reactant B, thus if the concentration of B is doubled in the given reaction, then the rate of reaction will become four times.
(ii) It the concentration of B is doubled i.e.; [B]2 the overall reaction will be two, because if A is present in large excess, then the reaction will be independent of the concentration of A and will be dependent only on the concentration of B. Order of reaction = 2.