PHD ENTRANCE TEST (MOST ASKED MCQs)

Answer (a) mixture of o− and p−bromotoluenes

given N=N0/5

T=[(2.303 X T½ )log(N/N0)]/0.693

12953

Among many colorimetric methods for carbohydrate analysis, the phenol-sulfuric acid method is the easiest and most reliable method. It has been used for measuring neutral sugars in oligosaccharides, proteoglycans, glycoproteins, and glycolipids. This method is used widely because of its sensitivity and simplicity

Ist order, r1=k[A]

r1/r2=K1/K2

The substituent on the benzene ring has an effect on the reactivity of the aromatic ring. Effects such as inductive effect wherein the electronegativity of the substituent attached is greater which therefore pulls the electron density towards itself. For example, Nitrogen, Oxygen and halogens are more electronegative than the Carbon on the ring therefore, it pulls the electron density towards itself and therefore deactivating the ring. Deactivation of the ring implies that the reaction would be slower and activating the aromatic ring on the other hand means that the reaction would be faster. Another thing to consider in nucleophilic aromatic substitution is the site of where nucleophilic attack takes place. There are different orientation of reaction depending how substituted the ring is. It could be ortho, meta or para to the substituent (if it’s monosubstituted). So when these two factors that are taken into consideration are combined, it will then tell us the reactivity and where the nucleophile will attack/or direct the new substituent and also tell us which of the product will form in majority.

The four principle classes of pericyclic reactions are termed: Cycloaddition, Electrocyclic, Sigmatropic, and Ene Reactions

Beckmann rearrangement consists generally of an alkyl migration anti-periplanar to the expulsion of a leaving group to form a nitrilium ion. This is followed by solvolysis to an imidate and then tautomerization to the amide

Answer

Correct option 16 mins

For a first-order reaction, we have: t_75%​=2t_50%​

Given: t75%​=32 min

Substituting the values in the above expression, we get-

32 min =2 t50%​

t50%​=16 mins

Hence, 50% of the reaction would have been completed in 16 mins.

Photoisomerization is the photochemical cis-trans isomerization of organic molecules with a double bond in their structure. This reaction is a common photo-reaction

Phytochemistry is the study of phytochemicals, which are chemicals derived from plants. Phytochemists strive to describe the structures of the large molecule.

Thiophene is cyclic, planar, the sulfur atom present in it is sp2 hybridized

Cerium(IV) salts, especially cerium(IV) sulfate, are often used as standard reagents for volumetric analysis in cerimetric titrations.

0.46 V

Xylene exists in three isomeric forms. The isomers can be distinguished by the designations ortho- (o-), meta- (m-) and para- (p-), which specify to which carbon atoms (of the benzene ring) the two methyl groups are attached.

The McLafferty rearrangement is a well-known process in mass spectrometry

Isodiaphers are a set of nuclides that have a different number of protons and neutrons, but there is the same difference between the protons and neutrons

Metals:

In metals, the conduction band is either partially filled or the valence band is partially empty. There are electrons that behave as free electrons as they shift to higher energy levels by acquiring energy above the Fermi level in the conduction band. There is no forbidden energy gap in the metals. Since there is no forbidden gap, the number of electrons available for the conduction is more increasing the conductivity of the material. Metals behave as a conductor because of the movement of the free electrons when a small amount of electric current is applied.

Insulators:

In insulators, the valence band is completely filled while the conduction band is empty. This results in a large energy gap. Since the energy gap between the conduction band and the valence band is more, there is no movement of electrons from the valence band to the conduction band.

Semiconductor:

In a semiconductor, the valence band is completely filled with electrons while the conduction band is empty. The energy gap between the bands is less. For electrons to jump from the valence band to the conduction band, room temperature needs to be maintained. If the temperature is 0K, there is no transfer of electrons from the valence band to the conduction band.

Answer (a) CN− and NO+

Vanadium pentoxide has an orthorhombic structure with Space group Pmmn and lattice parameters of a = 11.51 Å, b=4.37 Å, and c=3.56 Å.

Pure V2O5 is a diamagnetic layered semiconductor with many applications such as catalysis

C=0.1M , %α=0.001

Ka=Cα^2

0.1 x (0.001/100)^2

=1x 10^-11

Terpenes are linear or cyclic compounds composed of isoprene units which can be saturated…

Osmium tetroxide oxidizes alkenes to give glycols through syn addition. A glycol, also known as a vicinal diol

Answer

Correct option 16 mins

For a first-order reaction, we have: t_75%​=2t_50%​

Given: t75%​=32 min

Substituting the values in the above expression, we get-

32 min =2 t50%​

t50%​=16 mins

Hence, 50% of the reaction would have been completed in 16 mins.

NCI-funded research delivers a breakthrough discovery with paclitaxel (Taxol), a cancer drug from the bark of the Pacific yew tree that expands treatment options for patients with breast and ovarian cancers

Answer (a) Metal sulphides are thermodynamically more stable than CS2

Answer (a) X4Y3

Basic buffer has a basic pH and is prepared by mixing a weak base and its salt with strong acid. The aqueous solution of an equal concentration of ammonium hydroxide and ammonium chloride has a pH of 9.25

Potassium bromide (KBr, spectroscopic grade) is typically used as the window material because it is transparent in the IR, between 4000–400 cm-1

Answer (b) lesser energy difference between 5f and 6d than between 4f and 5d orbitals

From left to right on the periodic table, acid-base character of oxides and hydroxides go from basic to acidic.

We know that NH3 has a bond angle of 107 ∘ . This bond angle is less as compared to the tetrahedral angle, owing to the increase in the repulsion to bond pairs. This happens due to the presence of lone pairs of nitrogen.

Now on reacting with HCl, NH3 results in the formation of NH4Cl. The reaction is given below:

NH3 + HCl→ NH4Cl

In this case, NH4+ has no longer any lone pair at nitrogen. Hence, the ammonium ion is perfectly tetrahedral, just like the CH4. So, now the bond angle is 109.5 ∘ .

Therefore, we can say that when NH3 is treated with HCl, H — N — H the bond angle increases.

Amine is heated with alcoholic potassium hydroxide and chloroform. If a primary amine is present, the isocyanide is formed. The reaction is known as carbylamine reaction. (HERE ALL MAY BE WRONG) CHECK ANSWER PLZ.

-2.303RTlogK=-nfE

log K =9.369

k=10^9.369 ==2.3 x 10^9

Answer (c) anomers

2HI(g) ——–> H2  + I2(g)

a                              0          0

a(1-0.5)                 0.25a    0.25a

k=(0.25a x 0.25a) / (0.5a)^2

=0.25

Chemical Tests for the Detection of Alkaloids:

1. Mayer’s test:
2. Dragendorff’s test:
3. Wagner’s test:
4. Marme’s test:

the most characteristics absorption band in the spectrum of 2-hexanone is that from the stretching vibration of carbonyl double bond C=O, at 1716 cm^-1.  It is a very strong band comparing to the others on the spectrum. A strong absorbance band in the 1650-1750 cm^-1 region indicate that a carbonyl group (C=O) is present. Within that range, carboxylic acids, esters, ketones and aldehydes tend to absorb in the higher wavenumber/frequency end (1700-1750 cm^-1), while conjugated unsaturated ketones and amides tend to absorb on the lower wavenumber/frequency end (1650-1700 cm^-1).

no negative marking please check answer yourself.

A metallocene is a compound typically consisting of two cyclopentadienyl anions bound to a … “Group 4 Transition Metal Sandwich Complexes.

Transition metals can form unstable intermediate products with suitable reactants. These intermediate products lower the activation energy of the reaction which makes the reaction faster. So, transition elements are the most efficient catalysts.

The acid anhydride functional group results when two carboxylic acids combine and lose water (anhydride = without water). Symmetrical acid anhydrides are named like carboxylic acids except the ending -acid is replaced with -anhydride. This is true for both the IUPAC and Common nomenclature.

Answer (c) Chlorides of both beryllium and aluminium have bridged chloride structures in solid phase

The two polynucleotide chains or strands of DNA are linked up by hydrogen bonding between the nitrogenous base molecules of their nucleotide monomers.

 Adenine-Thymine (two hydrogen bonds) and Cytosine-Guanine (three hydrogen bonds).

Answer (b) RSiCl3

Cellulose is a polysaccharide composed of a linear chain of β-1,4 linked d-glucose units with a degree of polymerization ranged from several hundreds to over ten thousands, which is the most abundant organic polymer on the earth

(3S,4R,5R)-1,3,4,5,6-Pentahydroxyhexan-2-one

The idea of “green” solvent implies to reduce the environmental impact resulting from its use in chemical processes. In this sense, water can be considered as a potentially green solvent since is non-toxic to health and the environment. Moreover, it is the safest and least expensive solvent.

Azurite is a soft, deep blue copper mineral produced by weathering of copper ore deposits. The blue of azurite is exceptionally deep and clear. Specimens tend to lighten in color over time due to weathering of the specimen surface into malachite; this is why they are found together.

they are mainly Green and blue pigment

SN1 usually gives a mixture of products with inversion and retention of configuration Thus it leads to racemisation.
SN2 reaction takes place through a back-side attack, which inverts the stereochemistry of the carbon atom i.e   Complete inversion of configuration takes place.

During the reversible process, the system is in thermodynamic equilibrium with its surroundings. On being reversible, it does not leave any change in either the system or the surroundings. Since it takes an infinite time for a reversible process to finish, hence, perfectly reversible processes are not possible.
a process is called reversible when the surroundings are always in equilibrium with system.
So, the correct answer is “Option C”.

For non-polar side chains, the amino acids are: Alanine (A), Valine (V), Leucine (L), Isoleucine (I), Proline (P), Phenylalanine (F), Methionine (M), Tryptophan (W), Glycine (G) and Cysteine (C).

Neutral Amino acids: Glycine, Alanine, leucine, Isoleucine, valine, phenylalanine, Proline, methionine, serine, threonine, tyrosine, cysteine, glutamine, asparagine, tryptophan.

Acidic amino acids: Aspartic acid, glutamic acid

Basic amino acids: Lysine, histidine, Arginine

We know that for a reaction if K/Q​<1, the reaction proceeds in backward direction. Hence, the reaction mixture forms more reactant species.

Answer (c) reduces permanganate to Mn2+

Answer (b) o-nitrophenol

Halides of alkaline earth metals form hydrate so they are hygroscopic in nature. Due this nature they can be used as water absorbing compounds.
Thats why they can act as dehydrating agents and can absorb moisture from air.

Increase (or decrease) in temperature will change the value of K for reaction.
Addition of catalyst, increase in pressure and removal of one of the products will not change the value of K for reaction.
The value of K (the equilibrium constant) for reaction depends only on  temperature and is independent of the pressure or concentrations of reactants/products, presence of catalyst etc.

External pressure (P)=4 bar=3.95 atm

Initial volume (V1​)=4L

Final volume (V2​)=1L

No. of moles (n)=0.001 mole

R=8.314L−atmK−1mol−1

For an isothermal process,

Work done (W)=−PΔV

∴W=−3.95×(1−4)=11.85L.atm=1200.7605=1.2×10^3 J

Hence the work done for the given process is 1.2×10^3J.

The working pH range for indicators is as follows:

Phenolphthalein- 8.3-10.0

Litmus- 5.0-8.0

Methyl red- 4.2- 6.3

Methyl orange- 3.1-4.4