2nd PUC Chemistry Model Question Paper 4 with Answers

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Karnataka 2nd PUC Chemistry Model Question Paper 4 with Answers

Time: 3.15 Hours
Max Marks: 70

Part – A

I. Answer ALL of the following. Each questions carries 1 mark. ( 10 × 1 = 10 )

Question 1.
State Henry’s law.
Answer:
Henry’s law states that “The partial pressure of the gas in vapour phase is directly proportional to the mole fraction of the gas in the solution”.
OR
“The mole fraction of the gas in the solution is proportional to the partial pressure of the gas over the solution”.

Question 2.
What is the conclusion drawn when Vant Hoff’s factor of a solution is less than one?
Answer:
The solute in the solution undergoes association
OR
∆T_b or ∆T_f will be half of the normal value and molar mass will be twice the expected value.

Question 3.
How molar conductivity varies with dilution?
Answer:
It increases with dilution.

Question 4.
Mention one criterion for inter-molecular collisions of two reactants to be effective.
Answer:
Proper orientation of molecules.
OR
Energy of activation of molecules.

Question 5.
Name the metal that is refined by Van Arkel method.
Answer:
Zirconium (Zr) or Titanium (Ti).

Question 6.
Name the first noble gas compound prepared by Neil Bartlett?
Answer:
Xenonhexa fluroplatinate (V).

Question 7.

Give an example for Heteroleptic complex.
Answer:
b[Pt (NH₃)₂Cl₂] or any suitable example.

Question 8.
Write the IUPAC name for CH₃– CH(CH₃)-CH₂Cl.
Answer:
1 – chloro – 2 – methyl propane.

Question 9.
Give the name of the product X.
Answer:
Benzaldehyde

Question 10.
Name the storage polysaccharide present in animals.
Answer:
Glycogen.

Part – B

II. Answer any FIVE of the following. Each questions carries 2 mark. ( 5 × 2 = 10 )

Question 11.
a) Give one example for paramagnetic substance.
Answer:
O₂ or Compounds of Cu²⁺ or Fe³⁺ or Cr³⁺ or any suitable example.

b) Which type of binding force existing in ice?
Answer:
Hydrogen binding.

Question 12.
Write anodic and cathodic half-cell reactions taking place in Daniel cell.
Answer:
At anode: Zn(s) → Zn²⁺ + Ze
At cathode: Cu²⁺ + 2e^– → Cu(s)

Question 13.
Show that for first order reaction t_87.5% = 3 t_50%
Answer:

Question 14.
What is lanthanide contraction? What is the cause for it?
Answer:
A steady decrease in the atomic and ionic radii from less lanthanium to lutetium is called lanthanide contrection.
It causes radius of 3rd transister series to be very similar with those of the corresponding members of 2nd transition series.

Question 15.
How do you convert bromoethane into tertiary- butylethyl ether? Give the chemical equation of the reaction.
Answer:
When sodium methoxide in alcohol is heated with ethyl bromide it gives ethers containing substituted alkyl groups.

Question 16.
What is Stephen’s reaction? Give the chemical equation of the reaction.
Answer:
Reduction of nitrites with acidified Sncl conc HCL at room gives aldehydes. In the first step imine hydrochloride obtained which on hydrolysis with boilers water gives aldehyde. This specific type of reduction of nitrites is called Stephen’s Temperature reduction.

Question 17.
What is the therapeutic action of
a) Paracetamol
b) Barbituricacid.
Answer:
a) Decreases body temperature during fever
b) Tranquilizer

Question 18.
What are anionic detergents? Give an example.
Answer:
The sodium salts of sulphonated long chain alcohols
OR
Hydro carbons are called anionic detergents Ex: Sodium lauryl sulphate.

Part – C

III. Answer Any FIVE of the following. Each questions carries 3 mark. ( 5 × 3 = 15 )

Question 19.
Explain the extraction of aluminium from purified alumina by Hall-Heroult process. (3)
Answer:
Pure alumina is dissolved in molten cryolite (Na₃ AlF₆) and mixed with a little CaF₂ which lowers the melting point of the electrolyte. The molten electrolyte is taken in a steel tank lined inside with carbon which acts as Cathode. A number of graphite rods which is suspended in the electrolyte acts as anode.

Electrocytic cell for the extraction of Al
On electrolysis aluminium is discharged at the cathode and oxygen is liberated at the anode.
At cathode :
Al³⁺ + 3e^– → Alcl
At anode:
C_(s)  + O^– → CO_(g) + 2e^–
(melt)
C_(s)  + 2O^2- CO²(g)+ 4e^–
(melt)
Over all reaction : 2Al₂O₃ + 3C → 4Al + 3CO₂

Question 20.
Explain manufacture of nitric acid by Ostwald’s process. (3)
Answer:
The conversion of ammonia in to HNO₃ involves the following steps.
Step -1: oxidation of NH₃ into NO. Ammonia is oxidised by air in the presence of Pt-Rh gauze catalyst at 500k under 9 bar pressure to give nitric oxide.

Step -2: Oxidation of NO to NO₂:
The nitric oxide is oxidised by air at temperature below 100C to give nitrogen dioxide (NO₂).
2NO_(g) + O_2(g) → 2NO_2(g)

Step -3: Formation of Nitric acid.
Nitrogen dioxide is then converted to nitric acid by absorbing NO in water.
3NO_2(g) + H₂O_(L) → 2HNO_3(l) + NO_(g)

Question 21.
a) How is ozonised oxygen prepared? (2)
Answer:
It is prepared by passing silent electric discharge through pure and dry oxygen. 10% of oxygen is converted into ozone.

b) Write the structure of sulphurous acid.
Answer:

Question 22.
a) How does phosphorus react with limited amount of chlorine? Give equation. (2)
Answer:
Phosphorus reacts with limited amount of dry chlorine gas to give PCl₃.
P₄ + 6Cl₂ → 4 PCl₃

b) What is the product obtained by the reaction between fluorine in excess of bromine? (1)
Answer:
Br F₅

Question 23.
a) 3d Transition refer OT and their compounds are good catalysts. Give two reasons? (2)
Answer:

• They have large surface area
• They show variable oxidation states.

b) Give the formula for the calculation of spin only magnetic moment. (1)
Answer:
le = \(\sqrt{n(n+2)}\)BM

Question 24.
Explain the manufacture of potassium dichromate from chromite ore. (3)
Answer:
Manufacture of K₂ Cr₂O₇ from chromite ore involves the following steps.
Step – 1: Chromite ore is heated with sodium carbonate in excess of air to form sodium chromate
4 Fecr₂O₄ + 8 Na₂ CO₃ + FO₂ → 8 Na₂CrO₄ + 2Fe₂O₃ + 8CO₂

Step 2: The yellow solution of sodium chromate is filtered and acidified with H₂SO₄ to give orange solution of sodium dichromate.
2Na₂ CrO₄ + H₂SO₄ → Na₂ Cr₂ O₇ + Na₂SO₄ + H₂O
The less soluble Na₂SO₄ is removed by filtration

Step 3: The solution of sodium dichromate is treated with KCl to form Potassium dichromate.
Na₂ Cr₂ O₇ + 2 KC → K₂ Cr₂ O₇ + 2 NaCl
Solution on cooling gives orange red crystals of K₂ Cr₂ O₇

Question 25.
Using VBT explain, (3)
i) Geometry of the complex
Answer:
Geometry: Octahedral

ii) Type of hybridization, in the complex ion(COF₆)3.
Answer:
Hybridisation: SP³ d²

iii) Is it an inner or outer orbital complex?
Answer:
Type of complex: Outer orbital complex.

Question 26.
a) Draw the structures of cis-trans isomers for [Pt (NH₃)₂.Cl₂].     (2)
Answer:

b) How many ions are produced from the aqueous solution of complex K₃( [Al(C₂O₄)₃]     (1)
Answer:
4 ions

Part – D

IV. Answer Any THREE of the following. Each questions carries 5 mark. ( 3 × 5 = 15 )

Question 27.
a) Calculate the packing efficiency in a Face Centered Cubic lattice. (3)
Answer:
The number of atoms per unit cell in fCC structures is ‘4’
Each atom is considered as one sphere.

So the volume of 4 atoms
(4 sphere) = 4 × \(\frac{3}{4}\) πr² = \(\frac{16}{3}\) πr³
Edge length a = \(2 \sqrt{2} \mathbf{r}\)
The volume of the cubic unit cell = a³ = \((2 \sqrt{2} r)^{3}\)

b) If a metal with atomic mass 209 crystallizes in a simple cubic lattice what is the edge length of its unit cell. (Given d = 91.5 kg m-3). (2)
Answer:

Question 28.
a) 5.8g of a non-volatile solute was dissolved in 100g of carbon disulphide (Molar mass = 76). The vapour pressure of the solution was found to be 190mm Hg.
Calculate the molecular mass of the solute. The vapour pressure of pure carbon disulphide 195 mm Hg. (3)

b) What are azeotropes? Give an example. (2)
Answer:
A solution which boils at constant temperature without any change in composition is called an azeotrope.
Ex: A mixture of 95.5% ethanol and 4.5% water.

Question 29.
a) The resistance of M/10 solution is found to be 2.5 × 103 ohms. Calculate molar conductance(Given Cell constant = 1.15cm^-1).     (3)
Answer:

b) Mention two general methods for prevention of corrosion.   (2)
Answer:

1. Painting
2. Electro chemical methods.

Question 30.
a ) Derive an expression for rate constant of a first order reaction. (4)
Answer:
Consider a first order reaction
R → P
Rate = \(\frac{-\mathrm{d}[\mathrm{R}]}{\mathrm{dt}}\) = K[R]
\(\frac{\mathrm{d}[\mathrm{R}]}{[\mathrm{R}]}\) = -K dt
Interacting the above equation we get
∫\(\frac{\mathrm{d}[\mathrm{R}]}{[\mathrm{R}]}\) = -K ∫dt
In [R] = – Kt + I ………(1)
When t = 0
[R] = [R]₀
Equation (1) becomes In [R]₀ = I
∴ In [R] = -K × t + in [R]₀

b) What is the effect of the positive catalyst on energy of activation? (1)
Answer:
Energy of activation decreases.

Question 31.
a) Mention two factors which effects adsorption of a gas on a solid.
Answer:

1. Surface area of adsorbent.
2. Nature of adsorbent or adsorbate or any suitable factor.

b) Is synthesis of ammonia by Haber’s process, a homogeneous or heterogeneous catalysis? (1)
Answer:
Heterogeneous catalysis.

c) State Hardy-Schulze rule. Among Al₂(SO₄)₃ and (NH₄)₃PO₄ which is better coagulating agent for a negative sol? (2)
Answer:
It states that “The larger the valency of the active ion, the greater is its precipitation action”. Al₂ (SO₄)₃

V. Answer Any FOUR of the following. Each questions carries 5 mark. ( 4 × 5 = 20 )

Question 32.
a) Complete the following reaction and write its name (2)

Answer:

b) Explain Zaitsev rule with an example. (2)
Answer:
Zaitsev rule states that
“During dehydro halogenation reaction, if more than one type of β -Carbon atoms are present, hydrogen atom is mostly removed from β -Carbon atom containing least member of hydrogen atoms.
Example:

c) A Haloalkane when boiled with aqueous KOH which gives an alcohol having inversed configuration. Name the mechanism involved in this reaction. (1)
Answer:
SN²

Question 33.
a) Explain the mechanism involved in the conversion of ethanol into ethene. (3)
Step -1: Formation of protonates alcohol

Step – 2: Formation of Carbocation

Step -3: Elimination of proton from carbocation to form an alkene

b) An organic compound with molecular formula C₆H₆O gives white precipitate with bromine water. Identify the functional group in the organic compound and write the chemical equation for the reaction.
Answer:
The organic compound is phenol

Question 34.
a) Explain Cannizaro’s reaction with an example. (2)
Answer:
Aldehydes which do not have an α – H – atom is heated with strong solution of alate undergo self oxidation and reduction to form alcohol and self of carboxylic acid. Their reaction is called cannizaro’s reaction.
2H – CHO + NaOH → CH₃OH + HCOONA
OR
2C₆H₅CHO + NaOH → C₆H₅CH₂OH + C₆H₅COONa

b) Name the product obtained by the reaction of acetyl chloride with dimethylcadmium. (1)
Answer:
Acetone

c) Explain the reaction between carboxylic acid and PCl₅. (2)
Answer:
Carboxylic acids react with phosphorous pentachloride to formcorresponding acid chlorides.
R – COOH + PCl₅ → R COCl + POCl₃ + HCl

Question 35.
a) Explain carbylamine reaction by taking methyl amine as an example. (2)
Answer:
When a primary amine is heated with chloroform and alcoholic KOH gives isocyanides called carbylamines. This reaction is called carbylamine reaction
R – NH₂ + CHCl₃ + 3 KOH → R – NC + 3KCl + 3H₂O
Ex: CH₃ – NH₂ + CHCl₃ + 3KOH → CH₃ NC + 3KCl + 3H₂O

b) Why do primary amine have higher boiling point than tertiary amines? (1)
Answer:
Due to inter-molecular association OR More hydrogen bonding.

c) Give an example for a coupling reaction of diazonium salt and give its chemical equation. (2)
Answer:
Zenzene diazonium chloride reacts with phenol or anicine to give azodyes. These reactions are called coupling reactions.

Question 36.
a) Deficiency of which vitamin leads to night blindness? (1)
Answer:
Vitamin A

b) Which hormone is responsible for the hyperthyroidism? (1)
Answer:
Thyroxin

c) What is a Zwitter ion of an amino acid? Give its general formula. (2)
Answer:
The amino acid forms dipolar ion called zwitter ion in the aqulous sofuction.

d) What is a nucleotide? (1)
Answer:
Basic unit of nucleic acid containing one sugar unit heterocyclic base and phosphoic acid is called nucleotide.

Question 37.
a) What are Elastomers? Give example. (2)
Answer:
The polymers that have elasticity, like rubber in which polymer chains are held together by the weakest intermolecular forces are referred to as elastomers.
Example: Natural rubber, neoprene, vulcanized rubber.

b) Write the partial structure of nylon 6,6 and Bakelite. (2)
Answer:
Nylon 6.6

Bakelite :

c) What is vulcanization of rubber? (1)
Answer:
The process of heating a mixture of raw rubber with sulphur at a temperature range about 415 K is called Vulcanization of rubber.