CBSE Sample Papers for Class 12 Chemistry Paper 7

CBSE Sample Papers for Class 12 Chemistry Paper 7 are part of CBSE Sample Papers for Class 12 Chemistry. Here we have given CBSE Sample Papers for Class 12 Chemistry Paper 7.

CBSE Sample Papers for Class 12 Chemistry Paper 7

Board	CBSE
Class	XII
Subject	Chemistry
Sample Paper Set	Paper 7
Category	CBSE Sample Papers

Students who are going to appear for CBSE Class 12 Examinations are advised to practice the CBSE sample papers given here which is designed as per the latest Syllabus and marking scheme as prescribed by the CBSE is given here. Paper 7 of Solved CBSE Sample Paper for Class 12 Chemistry is given below with free PDF download solutions.

Time Allowed : 3 Hours
Max. Marks: 70

General Instructions

• All questions are compulsory.
• Question number 1 to 5 are very short answer questions and carry 1 mark each.
• Question number 6 to 10 are short answer questions and carry 2 marks each.
• Question number 11 to 22 are also short answer questions and carry 3 marks each.
• Question number 23 is a value based question and carry 4 marks.
• Question number 24 to 26 are long answer questions and carry 5 marks each.
• Use log table, if necessary. Use of calculators is not allowed.

Questions

Question 1.
Write the formula of the compound of phosphorus which is obtained when cone. HNO₃ oxidises P₄.

Question 2.
Write the IUPAC name of the following compound:

Question 3.
What is the effect of adding a catalyst on

1. Activation energy (E_a), and
2. Gibbs energy (ΔG) of a reaction?

Question 4.
Out of

which is an example of allylic halide?

Question 5.
What type of colloid is formed when a liquid is dispersed in a solid? Give an example.

Question 6.
(a) Arrange the following compounds in the increasing order of their acid strength: p-cresol, p-nitrophenol, phenol
(b) Write the mechanism (using curved arrow notation) of the following reaction:
CH₂ = CH₂ \(\underrightarrow { { H }_{ 3 }{ O }^{ + } }\) CH₃ – CH⁺₂ + H₂O

OR
Write the structures of the products formed when Butan-2-ol reacts with the following:
(a) CrO₃
(b) SOCl₂

Question 7.
Calculate the number of unit cells in 8.1 g of aluminium if it crystallises in a face-centered cubic (f.c.c.) structure. (Atomic mass of Al = 27 g mol^-1)

Question 8.
Draw the structures of the following:

1. H₂SO₃
2. HClO₃

Question 9.
Write the name of the cell which is generally used in hearing aids. Write the reactions taking place at the anode and the cathode of this cell.

Question 10.
Using IUPAC norms write the formulae for the following:

1. Sodium dicyanidoaurate (I)
2. Tetraamminechloridonitrito-N-platinum(IV) sulphate

Question 11.

1. Based on the nature of intermolecular forces, classify the following solids: Silicon carbide, Argon
2. ZnO turns yellow on heating. Why?
3. What is meant by groups 12-16 compounds? Give an example.

Question 12.

1. The cell in which the following reaction occurs:
   2Fe³⁺ (aq) + 2I^– (aq) → 2Fe²⁺ (aq) + I₂ (s)
   has E_cell° = 0.236 V at 298 K. Calculate the standard Gibbs energy of the cell reaction. (Given: IF = 96,500 C mol^-1)
2. How many electrons will flow through a metallic wire if a current of 0.5 A is passed for 2 hours? (Given: IF = 96,500 C mol^-1)

Question 13.

1. What type of isomerism is shown by the complex [Co(NH₃)₅ (SCN)]²⁺?
2. Why is [NiCl₄]^2- paramagnetic while [Ni(CN)₄]^2- is diamagnetic? (Atomic number of Ni = 28)
3. Why are low spin tetrahedral complexes rarely observed?

Question 14.
Write one difference in each of the following:

1. Multimolecular colloid and Associated colloid
2. Coagulation and Peptisation
3. Homogeneous catalysis and Heterogeneous catalysis

OR

1. Write the dispersed phase and dispersion medium of milk.
2. Write one similarity between physisorption and chemisorption.
3. Write the chemical method by which Fe(OH)₃ sol is prepared from FeCl₃.

Question 15.
A first order reaction takes 20 minutes for 25% decomposition. Calculate the time when 75% of the reaction will be completed.
(Given: log 2 = 0.3010, log 3 = 0.4771, log 4 = 0.6021)

Question 16.
The following compounds are given to you:
2-Bromopentane, 2-Bromo-2-methylbutane, 1-Bromopentane
(i) Write the compound which is most reactive towards S_N2 reaction.
(ii) Write the compound which is optically active.
(iii) Write the compound which is most reactive towards P-elimination reaction.

Question 17.
Write the principle of the following:

1. Zone refining
2. Froth floatation process
3. Chromatography

Question 18.
Write the structures of compounds A, B and C in each of the following reactions:

Question 19.
Write the structures of the monomers used for getting the following polymers;
(a) Nylon-6, 6
(b) Melamine-formaldehyde polymer
(c) Buna-S

Question 20.
Define the following:

1. Anionic detergents
2. Limited spectrum antibiotics
3. Antiseptics

Question 21.
Give reasons for the following:

1. Red phosphorus is less reactive than white phosphorus.
2. Electron gain enthalpies of halogens are largely negative.
3. N₂O₅ is more acidic than N₂O₃.

Question 22.
Give reasons for the following:

1. Acetylation of aniline reduces its activation effect.
2. CH₃NH₂ is more basic than C₆H₅NH₂.
3. Although – NH₂ is o/p directing group, yet aniline on nitration gives a significant amount of m-nitroaniline.

Question 23.
After watching a programme on TV about the presence of carcinogens (cancer causing agents) Potassium bromate and Potassium iodate in bread and other bakery products, Rupali a class XII student decided to make others aware about the adverse effects of these carcinogens in foods. She consulted the school principal and requested him to instruct the canteen contractor to stop selling sandwiches, pizzas, burgers and other bakery products to the students. Principal took an immediate action and instructed the canteen contractor to replace the bakery products with some protein and vitamin rich food like fruits, salads, sprouts etc. The decision was welcomed by the parents and the students. After reading the above passage, answer the following questions:

1. What are the values (at least two) displayed by Rupali?
2. Which polysaccharide component of carbohydrates is commonly present in bread?
3. Write the two types of secondary structure of proteins.
4. Give two examples of water soluble vitamins.

Question 24.
(a) Account for the following:

1. Transition metals show variable oxidation states.
2. Zn, Cd and Hg are soft metals.
3. E° value for the Mn³⁺/Mn²⁺ couple is highly positive (+1.57 V) as compared to Cr³⁺/Cr²⁺ couple.

(b) Write one similarity and one difference between the chemistry of lanthanoid and actinoid elements.

OR
(a) Following are the transition metal ions of 3d series:
Ti⁴⁺, V²⁺, Mn³⁺, Cr³⁺
(Atomic numbers: Ti = 22, V= 23, Mn = 25, Cr = 24)
Answer the following:

1. Which ion is most stable in an aqueous solution and why?
2. Which ion is a strong oxidising agent and why?
3. Which ion is colourless and why?

(b) Complete the following equations:

1. 2MnO^–₄ + 16H⁺ + 5S^2- →
2. KMnO₄ \(\underrightarrow { heat } \)

Question 25.
(a) A 10% solution (by mass) of sucrose in water has a freezing point of 269.15 K. Calculate the freezing point of 10% glucose solution in water if the freezing point of pure water is 273.15 K.
Given: (Molar mass of sucrose = 342 g mol^-1)
(Molar mass of glucose = 180 g mol^-1)
(b) Define the following terms:

1. Molality (m)
2. Abnormal molar mass

OR
(a) 30 g of urea (M = 60 g mol^-1) is dissolved in 846 g of water. Calculate the vapour pressure of water for this solution if vapour pressure of pure water at 298 K is 23.8 mm Hg.
(b) Write two differences between ideal solutions and non-ideal solutions.

Question 26.
(a) Write the product(s) in the following reactions:

(b) Give simple chemical tests to distinguish between the following pairs of compounds:

1. Butanal and Butan-2-one
2. Benzoic acid and Phenol

OR
(a) Write the reactions involved in the following:
(i) Etard reaction
(ii) Stephen reduction

(b) How will you convert the following in not more than two steps:
(i) Benzoic acid to Benzaldehyde
(ii) Acetophenone to Benzoic acid
(iii) Ethanoic acid to 2-Hydroxyethanoic acid

Answers

Answer 1.

Answer 2.
2-Bromo-3-methylbut-2-en-l-ol

Answer 3.

1. On adding catalyst in a reaction, the activation energy gets reduced and the rate of reaction increases.
2. A catalyst cannot alter the Gibbs energy (ΔG) of a reaction.

Answer 4.

Answer 5.
Gel is formed when a liquid is dispersed in a solid, e.g. cheese, butter etc.

Answer 6.
(a) Order of acidic strength:
p-cresol < phenol < p-nitrophenol

(b) Mechanism of acid catalysed hydration of alkene:
Step 1: Protonation of alkene to form carbocation by electrophilic attack of H₃O⁺:

OR

Answer 7.
1 mole of Aluminium = 27 g
Hence, no. of atoms present in 27 g of Al = 6.022 × 10²³

Answer 8.
1. Structure of H₂SO₃ (Sulphurous acid):

2. Structure of HClO₃ (Chloric acid):

Answer 9.
Mercury cells are used in hearing aids.
Reaction at anode:
Zn (Hg) + 2OH^– → ZnO (s) + H₂O + 2e^–
Reaction at cathode:
HgO + H₂O + 2e^– → Hg (l) + 2OH^–

Answer 10.

1. Na[Au(CN)₂]
2. [Pt(NH₃)₄Cl(NO₂)] (SO₄)

Answer 11.

1. Silicon carbide is a covalent or network solid while argon is a non-polar molecular solid.
2. ZnO shows metal excess defect due to the presence of extra cations, i.e. Zn²⁺ ions in the interstitial sites which on heating changes into yellow due to loss of oxygen.
   • ZnO → Zn²⁺ + \(\frac { 1 }{ 2 }\)O₂ + 2e^–
3. Group 12-16 compounds are imperfect covalent compounds in which there is appreciable ionic character, which depends on the electronegativities of the two combined elements, e.g., ZnS, CdS, etc.

Answer 12.
1. 2Fe³⁺ (aq) + 2I^– (aq) → 2Fe²⁺ (aq) + I₂ (s)
For the given reaction, n = 2, E° = 0.236 V
Using formula
ΔG⁰ = -nFE⁰_cell
= 2 × 96,500 C mol^-1 × 0.236 V
∴ ΔG⁰ = -45.55 KJ mol^-1

2. Given:
I = 0.5 A
t = 2 hrs. = 2 × 60 × 60 s = 7,200 s
Q = I × t = 0.5 × 7200 = 3,600 C
96,500 C electricity flows to produce = 6.022 × 10²³ electrons

Answer 13.

1. [CO(NH₃)₅(SCN)]²⁺ shows linkage isomerism.
2. Since in [NiCl₄]^2-,Cl^– is a weak field ligand and it forms outer orbital complex and has impaired electrons, which imparts paramagnetic character to complex. On the other hand, in [Ni(CN)₄]^2-, CN^– is a strong field ligand, forms an inner orbital complex and has paired electrons which imparts diamagnetic character to it.
3. Low spin tetrahedral complexes are rarely observed because orbital splitting energies for tetrahedral complexes are not sufficiently large for forcing pairing.

Answer 14.
1. Multimolecular colloid and Associated colloids: Multimolecular colloids are formed by the aggregation of a large number of atoms or molecules which generally have diameter less than 1 nm, e.g. sols of gold, etc. While associated colloids are formed by the aggregation of large number of ions in concentrated solutions, e.g. micelles in soap.

2. Coagulation and Peptisation: Coagulation is a process of aggregating together the colloidal particles into large sized particles to form their precipitate while peptisation is a process of converting fresh precipitate into colloidal particles by shaking it with the dispersion medium in the presence of small amount of a suitable electrolyte.

3. Homogeneous catalysis and Heterogeneous catalysis: Homogeneous catalysis is the phenomenon of altering the rate of a reaction when the catalyst has the same phase as the reactants while in heterogeneous catalysis, the catalyst has different phase than that of the reactants.

OR

1. In milk, the dispersed phase is liquid fat particles and dispersion medium is water.
2. Both physisorption and chemisorption depends upon the nature of adsorbent and adsorbate.
3. Fe(OH)₃ is prepared from FeCl₃ by hydrolysis:
   • FeCl₃ + 3H₂O \(\underrightarrow { Hydrolysis }\) Fe(OH)₃ (sol) + 3HCl

Answer 15.

Answer 16.
(i) 1-Bromopentane (CH₃CH₂CH₂CH₂Br) is most reactive towards S_N2 reaction.

Answer 17.

1. Zone refining: This method is based on the principle that impurities are more soluble in melt than in the solid form of metal.
2. Froth floatation process: This method is based on the principle that the metal particles and impurities having different wetting properties.
3. Chromatography: It is based on the principle that different components of a mixture are absorbed on an absorbent to different extent.

Answer 18.

A = Ethanamide
B = Methanamine
C = Methyl isocyanide

A = Nitrobenzene
B = Aniline
C = N-phenylacetamide or Acetanilide

Answer 19.

Answer 20.

1. Anionic detergents. These are the sodium salts of sulphonated long chain alcohols or hydrocarbons.
2. Limited spectrum antibiotics are effective against a single organism or disease, e.g., Streptomycin.
3. Antiseptics are the chemicals which either kill or prevent growth of microbes on living tissues, e.g., Penicillin.

Answer 21.

1. Red phosphorus is less reactive than white phosphorus because white phosphorus possess angle strain where long angles are only 60° making it more reactive. Also, red phosphorus being polymeric is less reactive than white phosphorus which has discrete tetrahedral structure.
2. Electron gain enthalpies of halogens are largely negative due to high effective nuclear charge and smaller size among period. They readily accept an electron to attain noble gas configuration.
3. N₂O₅ is more acidic than N₂O₃ because higher the oxidation state, higher will be acidic character. N₂O₅ has +5 oxidation state and N₂O₃ has +3 oxidation state.

Answer 22.

1. Due to the resonance, the electron pair on nitrogen atom gets delocalised towards the carbonyl group.
2. Because of +I effect in methylamine electron density at nitrogen atom increases whereas in aniline resonance takes place and electron density on nitrogen atom decreases.
3. Due to protonation of aniline/formation of anilinium ion.

Answer 23.

1. Concerned, caring, socially alert, leadership (or any other 2 values)
2. Starch
3. α-Helix and β-pleated sheets
4. Vitamin B/B₁/B₂/B₆/C (any two)

Answer 24.
(a)

1. The variability of oxidation state of transition metals is due to incompletely filled d-orbitals. In transitional elements ns and (n – 1) d electrons have equal energies approximately. Hence in addition to ns electrons, (n – 1) d electrons are also take part in the chemical bonding.
2. Zn, Cd and Hg are soft metals because they do not exhibit covalency due to completely filled d-orbitals. Absence of unpaired d electrons causes weak metallic bonding.
3. Because Mn²⁺ has a stable d⁵ configuration, whereas Cr³⁺ is more stable due to stable t³_2g configuration.

(b) Similarity: Both lanthanoids and actinoids show contraction in atomic radius and both are stable in +3 oxidation state.
Difference: Lanthanoid does not exhibit variable oxidation states, while actinoids show wide range of oxidation states.
OR
(a)

1. Cr³⁺ ion is the most stable, because of its small size and t³_2g configuration.
2. Mn³⁺ is a strong oxidising agent because after gaining one electron it is converted into Mn²⁺ which has a stable d⁵ configuration.
3. Ti⁴⁺ is colourless due to d° configuration, i.e. no unpaired electrons/no electrons in d-orbitals.

(b)

1. 2MnO₄ + 16H⁺ + 5S^2- → 2Mn²⁺ + 8H₂O + 5S
2. 2KMnO₄ \(\underrightarrow { heat } \) K₂MnO₄ + MnO₂ + O₂

Answer 25.

(b)

1. Molality (m). Number of moles of solute dissolved per kg of the solvent.
2. Abnormal molar mass. If the molar mass calculated by using any of the colligative properties and it comes to be different than the theoretically expected molar mass.

OR

23.8 – P_s = 0.0106 × 23.8
23.8 – P_s = 0.2531
So, P_s = 23.8 – 0.2531
∴ P_s = 23.54 mm Hg
(b)

Ideal solution	Non-ideal solution
(i) They obey Raoult’s law over the entire range of concentration.	(i) They do not obey Raoult’s law over the entire range of concentration.
(ii) Neither the heat is evolved or absorbed during dissolution.	(ii) Heat is evolved or absorbed during dissolution.
(iii) Δmix H = 0 Δmin V = 0	(iii) Δmix H ≠ 0 Δmin V ≠ 0

Answer 26.

(b)

1. Tollens’ reagent test. Add ammoniacal solution of sliver nitrate (Tollens’Reagent) in both the solutions taken in flasks separately. Butanal gives silver mirror at the side of the flask whereas butan-2-one does not. Therefore butanal gives Tollens’ test.
2. Ferric chloride test. Add neutral FeCl₃ in both the solutions, phenol reacts with neutral FeCl₃ to form an iron-phenol complex giving violet colour but benzoic acid does not.

OR

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