Question on Carboxylic Acids

Which is the carboxylic acid that reduces Tollen’s Reagent?

Answer:

Tollen’s Reagent gets reduced by -CHO (aldehyde) functional groups. The carboxylic acid that has this functional group present in its structure is formic acid.

Question on Acids & Bases

With how many moles of NaOH will one mole of H₃BO₃ react?

Answer:

H₃BO₃ is a monobasic acid. So, one mole of  H₃BO₃ will react with one mole of NaOH.

Question on Solid State

Heat is added to an amorphous solid. Will the visible change be equivalent to (a) adding heat to ice cube or (b) adding heat to a chocolate bar? Why?

Answer:

Amorphous solids do not have a sharp melting point. So adding heat to an amorphous solid will make it melt and the visible change will be equivalent to adding heat to a chocolate bar.

Question on Markovnikov Addition

What is the name of the Hydrocarbon with the molecular formula C₄H₈ that gives the same product on Markovnikov’s and anti-Markovnikov’s addition of aqueous HBr?

Answer:

Markovnikov’s Addition is that where the negative part of the addendum gets added to that carbon of the alkene having less number of hydrogen atoms (the one which is more substituted) and the reverse happens in anti-Markovnikov’s addition.

For a molecule to give the same product on both the modes of addition, it must be a symmetrical one. With the above argument and the molecular formula provided, the hydrocarbon should be but-2-ene.

Question on Stoichiometry

How many grams of Calcium Chloride are formed when 1g each of Calcium and Chlorine are allowed to react completely?

Answer:

According to the following reaction 1 mole of Ca will react with 1 mole of Cl₂.

Ca + Cl₂ = CaCl₂

1g of Ca is 1/40 moles and 1g of Cl₂ is 1/71 moles. Cl₂ is the limiting reagent in this reaction and will be completely consumed to produce 1/71 moles of CaCl₂.

1/71 moles of CaCl₂ is ((1/71) * 111)g = 1.56g

Question on Isomerism

For the molecular formula C₅H_8, how many structural isomers that are cyclic alkenes and with no ethyl group are possible?

Answer:

There are six isomers that satisfy the conditions mentioned in the question. They are given below.

 

Question on Freezing Point

What will be the freezing point of an 1 molal Sulphuric Acid solution if K_f of water is 1.8 K.Kg/mol?

Answer:

The depression in freezing point DT_f = i * K_f * m where “i” is the number of particles present in the solution for every particle dissolved and “m” is the molality of the solution. One mole of Sulphuric acid will dissociate to give two moles of H⁺ and one mole of SO₄^2- ions.

DT_f = i * K_f * m = 3 * 1.86 * 1 = 5.58

So, the freezing point of the solution will be, 0 - 5.58 = -5.58°C

Question on Cell emf

The Standard Reduction Potentials of Pb²⁺/Pb and Cu²⁺/Cu couples are -0.76V and +0.34V respectively. What will be the standard emf of the cell constructed with the two couples mentioned above?

Answer:

From the SRPs given in the question it could be found that, for the cell to be spontaneous Pb²⁺/Pb should act as the anode and Cu²⁺/Cu should act as the cathode. Also,

E^o_Cell = E^o_Cathode - E^o_Anode = 0.34 - (-0.76) = 0.34 + 0.76 = 1.1V

Question on Nomenclature

If isopropyl alcohol is a secondary alcohol, what kind (primary, secondary or tertiary) is isobutyl alcohol?

Answer:

Isobutyl alcohol is a primary alcohol.

Question on Hydrocarbons

What is the name of the hydrocarbon having molecular formula C₄H₈ which on treatment with aqueous HI produces an alkyl halide, that is optically inactive?

Answer:

The hydrocarbon is 2-methylprop-1-ene. The reaction is as follows;

Question on Basic Strength

Which one of the two compounds given below is a stronger base and Why?

Answer:

In Trisilyl Amine the lone pair of electrons in Nitrogen atom are delocalised into the vacant d-orbitals of Silicon, due to which the availability of electron density on nitrogen atom in that molecule is decreased and hence wont be able to act as a strong base in comparison to Trimethyl Amine. So, Trimethyl Amine is the stronger base among the compounds given.

Question on Photochemical Halogenation

How many dichloro isomers are obtained on photochlorination of neopentane?

Answer:

2 dichloro isomers are obtained. They are given below.

Question on Isotopes

With two isotopes of carbon, C¹² and C¹³ and with three isotopes of oxygen, O¹⁶, O¹⁷ and O¹⁸, how many number of carbon dioxide molecules can be formed that have even number as molecular weight?

Answer:

Six carbon dioxide molecules can be formed. They are given below.

C¹²O¹⁶₂, C¹²O¹⁷₂, C¹²O¹⁸₂, C¹²O¹⁶O¹⁸, C¹³O¹⁶O¹⁷ and C¹³O¹⁷O¹⁸

Question on Structure of Alkane

How many tertiary carbon atoms are present in the following alkane molecule?

Answer:

A tertiary carbon is the one connected to three other carbon atoms. The molecule given in the question has no such carbon atoms.

Question on Qualitative Analysis

Few drops of Barium Chloride are added to aqueous solutions of the following 2 compounds.

(1) Sodium Shulphate

(2) Sodium Carbonate

Which one of the compounds given above forms a white precipitate that is insoluble in dilute HCl?

Answer:

The answer is Sodium Sulphate. Sodium Sulphate reacts with Barium Chloride to give Barium Sulphate while Sodium Carbonate will give Barium Carbonate.

If Barium Sulphate and Barium Carbonate react with HCl the reactions would be as follows;

BaSO₄ + 2HCl = BaCl₂ + H₂SO₄

BaCO₃ + 2HCl = BaCl₂ + H₂CO₃

HCl can not release H₂SO₄ from BaSO₄ as H₂SO₄ is a stronger acid than HCl whereas it can release H₂CO₃ from BaCO₃ as H₂CO₃  is a weaker acid than HCl. So Sodium Sulphate forms a white precipitate with Barium Chloride that is insoluble in dilute HCl.

Question on pH of a solution

What will be the pH of the solution obtained by mixing equal volumes of 0.1M HOAc with 0.1M NaOH if pKa of HOAc = 4.74?

Answer:

Equal volumes of 0.1M NaOH and 0.1M HOAc react to give 0.05M NaOAc. An aqueous solution of NaOAc will be basic as it is a salt of a weak acid and a strong base.

The pH of an aqueous solution of a weak acid and a strong base is calculated as follows;

pH = ½ pK_w + ½ pK_a + ½ log C = ½ (14) + ½ (4.74) + ½ log (0.05) = 8.72 

(pK_w = 14 at 25°C)

Question on Isomerism

How many chiral carbons are present in the molecule shown below?

Answer:

A chiral carbon is the one whose valencies are satisfied by 4 different groups. There are five carbons in the molecule given.

Out of the five carbons, 2 and 4 are chiral as they are having their valencies satisfied by four different groups. Carbon 3 will also be optically active depending on the configuration of carbons 2 and 4.