Sample Paper Grade 12 Ppt

SAMPLE PAPER

Q1.Write the structure of 3-oxopentanal

Ans. CH3 – CH2 - CO –CH2 – CHO

Q2. What is the order of a reaction whose rate constant has the same units as those of rate of reaction?

Ans. Zero

Q3. Draw figure to show the splitting of d orbitals in an octahedral crystal field.

Q4. Why does nitrogen show catenation properties less than phosphorus?

Ans. Due to more lone pair - lone pair repulsion, N-N is weaker than P-P.

Q 5. Which Xe compound has distorted octahedral shape?

Ans.

Q6. Explain Frenkel defect in crystals.

•

Ans.It occur due to the missing of ions from thenormal lattice site and occupies an interstitial site due to which electrical neutrality and stoichiometry are Maintained.

Q7. Why is Bi (V) a stronger oxidant?

Ans. On moving down the group, the stability of the +5 oxidation state decreases. This is due to the inert pair effect. Thus, Bi (V) is a stronger oxidant.

Q8. Complete the following chemical equation P4(s) +NaOH (aq) +H2O(l) -----→

Ans. P4 + 3NaOH + 3H2O → PH3 + 3 NaH2PO2

Q9. Arrange the following in decreasing order of property indicated against each. Give reason .

• a) H2O, H2S, H2Se, H2Te (boiling point)

• b) NH3, PH3, AsH3, SbH3 (base strength)

Ans.a)

b)

Q10. Give chemical tests to distinguish between the following:

a) Methyl amine and Dimethyl amineb) Benzaldehyde and acetophenone

a) Carbyl amine test or Hinsberg test .

b) Tollen’s test OR lodoform test.

Q11.

a)Chloro acetic acid is more acidic than acetic acid. Give reason.

b)Aniline does not undergo Friedel-Crafts reaction. Give reason

Ans.a) due to –I effect of Cl, it increases the stability

of carboxylate ion. b) Anhydrous act as Lewis acid and from salt

with aniline, in which aniline gets the positive charge and act as deactivating group.

Q12. b) How would you account for the following:

a) Aldehydes are more reactive than ketones towards nucleophilic substitution reactions.

b)The boiling points of aldehydes and ketones are lower than that of the corresponding acids.

Ans. a) explanation on the basis of inductive and

steric effect. b) type of attractive forces in acid H - bonding

type of attractive forces in aldehyde Dipole – Dipole interaction.

Q13.Write two differences between molecularity andorder of a reaction.

Ans. ORDER OF A REACTION• MOLECULARITY OF A REACTIONa)It is sum of the concentration terms on which the rate of reaction

actually depends or it is the sum of the exponents of the concentrations in the rate law equation.

• It is the number of atoms, ions or molecules that must collide with one another simultaneously so as to result into a chemical reaction.

b)It need not be a whole number i.e. it can be fractional as well as zero.• It is always a whole number.c)It can be determined experimentally only and cannot be calculated.• It can be calculated by simply adding the molecules of the slowest

step.

Q14. Write the balanced chemical equation for the reaction of Cl2 with hot and conc. NaOH. Is this reaction a disproportionation reaction?

Ans. 3Cl2 + 6NaOH → 5NaCl + NaClO3 + 3H2O Yes, chlorine from zero oxidation state is

changed to –1 and +5 oxidation states

Q15. Compare the magnetic behaviour of [Ni(CN)4]2− and [NiCl4]2- on the basis of Crystal Field Theory. (Ni = 28)

Ans. Ni(CN)4]2− is diamagnetic and [NiCl4]2- is paramagnetic.

Q16.How would you account for the following?a)Hydrogen fluoride is much less volatile than

hydrogen chloride.b)Interhalogen compounds are very reactive.

Ans. a) Fluorine is more electronegative than

chlorine. Therefore, HF undergoes stronger H-bonding than HCl. Hence, HF is much less volatile than HCl.

b) In interhalogen compounds, X−X bond is ′very weak and can be easily broken. As a result, interhalogen compounds are reactive.

Q17.Complete the following chemical equationsa) Ca3P2(s) + H2O(l) →b)Cu2+(aq) + NH3(aq) → (excess)

Ans a) 3Ca(OH)2 + 2PH3

b) {Cu(NH3)4}2+

Q18. Calculate the efficiency of packing in case of a metal crystal for Face centered cubic.

Ans. • In Face centered cubic (fcc):

As spheres are touching each other, evidently AC = r + 2r + r = 4rAC2 = AB2 + BC2 = a2 + a2 = 2 a2

• AC = / 2 a / 2 a = 4r• a = 4r = 2 /2 r• /2• a = 2 / 2 r• Volume of unit cell = a3 = (2 /2 r)3

• No of sphere in face centered cubic unit cell = 4• total volume of spheres = 4 x (4 π r3 / 3 ) • % efficiency = (volume of sphere/volume of unit cell) x 100• 4 x (4 π r 3 / 3)• % efficiency = ___________ x 100 = 74% (2 /2 r ) 3

Q19. a) Write the formula of Tetraammineaquachloridocobalt (III) chloride.

b) Why is geometrical isomerism not possible in tetrahedral complexes having two different types of unidentate ligands coordinated with the central metal ion?

c) What is meant by the chelate effect? Give an example of chelate compound.

Ans.i) ii) All bond position of the groups are same with

respect to each other . iii) Stability of coordination compound increases if a

bidentate or tridentate ligand is attached to central metal atom and form a 5 or 6 membered ring. This effect is called chelate effect. Ex.

Q20. Account for the following:a)Bond dissociation energy of F2 is less than that

of Cl2 .b)SF4 is easily hydrolyzed whereas SF6 is not

easily hydrolysed.c)N2 is inert at room temperature.

Ans. i) Due to small size of F, more into electronic repulsion b/w lone pairs of electrons.

ii) SF6 is sterically protected by 6 F atom. iii)Due to large bond dissociation energy of

NΞN.

Q21. For the complex [Fe (en)2Cl2] Cl (a) Name the complex. (At. no Fe = 26). (b) What is the hybridisation and the shape of

the complex? (c) Predict the magnetic behavior of the

complex. (d) Draw the geometrical isomers.

Ans. i)Dichloride-bis-(ethylenediamine)lron(III)

chloride . ii) Sp3d2 octahedral

iii) paramagnetic iv) geometrical structure

Q22. How would you obtain the following?a)But -2-enal from ethanalb)Propanone from ethanalc)Benzoic acid from ethylbezene

Ans.1) Ethanol → aldol condensation (reaction). 2) Ethanol with methyl magnesium halide

followed by hydrolysis. 3) Oxidation by KMnO4 / H+

Q23.

Ans.

Q24. Why does PCl3 fume in moisture?b) With what neutral molecule is ClO-

isoelectronic ? Is that molecule a Lewis base? c) When HCl reacts with finely powdered iron, it

forms ferrous chloride and not ferric chloride. Why?

Ans. a) In the presence of (H2O), PCl3 undergoes hydrolysis giving fumes of HCl .

PCl3 + 3H2O→H3PO3 + 3HClb) ClF. Yes,it is Lewis base due to presence of lone

pair of electronsc) Its reaction with iron produces H2. Fe + 2HCl→FeCl2 + H2 ; Liberation of hydrogen

prevents the formation of ferric chloride.

Q25. Discuss the nature of bonding in [Co(C2O4)3]3- on the basis of valence bond theory.

Ans. [Co(C2O4)3]3-

• Explanation• d2sp3, octahedral, diamagnetic

Q26Give reasons:a)p-Nitro benzoic acid has a lower pKa value than benzoic

acid.b)Although amino group is ortho and para directing in

aromatic electrophilic substitution reaction, aniline on nitration gives a substantial amount of meta-nitroaniline..

c)Acetone is highly soluble in water but benzophenone is not.

.

Ans.a) -NO2 group at para position increases the

positive charge on C-1 due to –I and -R effect making the fission of O-H bond easier.

b) Anilinium ion is meta directing.c) Acetone can make hydrogen bonds with

water but benzophenone cannot due to the steric hindrance of two phenyl groups.

Q27.Indicate the steps in the preparation of KMnO4

from pyrolusite ore. Write the ionic equationsfor potassium dichromate reaction with H2S.

Q28.

i) Answer the following :a) What is the basicity of H3PO3 and why?b) Why does fluorine not play the role of a

central atom in interhalogen compound?c) Why do noble gases have very low boiling

points?

ii) Discuss the chemistry involved in Brown ring test for nitrate ion. Give equations also.

Ans.i) a) Basicity 2 due to presence a of 2 OH bond

b) F has smallsize and high electronegativityc) presence of dispersion forces.

ii)

Q29.i)Give example of pseudo first order reactionii.) Express the relation between the half life period of a reactant and its initial concentration for a reaction of nth order.

iii)

Ans.

i)Hydrolysis of cane sugar to produce glucose and fructose

ii) t1/2 α 1/(R)n-1 where n is the order of reaction

iii)

Q30. i.) Explain the mechanism of the reaction of acetaldehyde with HCN.

ii.) Carboxylic acids do not show properties typical of carbonyl compounds. Why?

iii)Carboxylic acids have much higher acidity than phenols. Why?

i)Ans. Mechanism:

Step 1 - Addition of nuclephile CN – to form tetrahedral intermediate, change in hybridization of carbonyl C from sp2 to sp3

Step 2 - Protonation of the intermediate

ii) Due to resonance the positive charge on the carbonyl carbon is less. 1

• iii) The higher acidity of carboxylic acids as compared to phenols is due to the following reasons:

• (1) The conjugate base of carboxylic acid, a carboxylate ion, is stabilised by two equivalent resonance structures in which the negative charge is at the more electronegative oxygen atom. The conjugate base of phenol, a phenoxide ion, has non-equivalent resonance structures in which the negative charge is at the less electronegative carbon atom. Therefore, resonance in phenoxide ion is less stable than in carboxylate ion.

• (2) The negative charge is delocalised over two electronegative oxygen atoms in carboxylate ion whereas it is less effectively delocalised over one oxygen atom and less electronegative carbon atoms in phenoxide ion. Thus, the carboxylate ion is more stabilised than phenoxide ion, so carboxylic acids are more acidic than phenols.