NEB Class 12 · Past paper
The complete NEB Class 12 2076 exam paper for Chemistry, all 33 questions with solved model answers.
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C in C2H2 gets sp hybridization, why?
In ethyne, $\ce{C2H2}$ ($\ce{H-CC-H}$), each carbon is bonded to only two groups (one H and the other C) and forms a triple bond. To arrange two sigma bonds linearly and leave two unhybridised p orbitals for the two pi bonds of the tripl...
Distinguish between titration error and normality factor.
Titration error: the difference between the observed end point and the true equivalence point of a titration; it makes the measured titre slightly wrong and is minimised by choosing a proper indicator and adding titrant dropwise near the...
Write the conjugate acid and base of NH3.
On the Bronsted-Lowry idea: Conjugate acid of $\ce{NH3}$ (add a proton): $\ce{NH4+}$ (ammonium ion). $$\ce{NH3 + H+ - NH4+}$$ Conjugate base of $\ce{NH3}$ (remove a proton): $\ce{NH2-}$ (amide ion). $$\ce{NH3 - NH2- + H+}$$
How many coulombs are required to produce i) 80 gm of calcium from molten CaCl2 ii) 50 gm of aluminium from molten Al2O3?
(i) 80 g Ca ($\ce{Ca^2+ + 2e- - Ca}$): moles $$ \begin{aligned} &= 80/40 \ &= 2 \end{aligned} $$ ; electrons $$ \begin{aligned} &= 2\times2 \ &= 4\ \text{mol} \ Q &= 4\times96500 \ &= 386000\ \text{C};(3.86\times10^{5}\ \text{C}) \e...
State the first law of thermodynamics.
First law of thermodynamics (conservation of energy): energy can neither be created nor destroyed but only changed from one form to another; the total energy of an isolated system stays constant.
For a closed system, $\Delta U = q + w$, where $\Delta U$ is the change in internal energy, $q$ the heat absorbed and $w$ the work done on the system.
Calculate the entropy change (dS) and free energy change (dG) for the conversion of ice into water at equilibrium when the enthalpy change (dH) is 9 kJ/mol.
At the melting point (0 degrees C = 273 K), ice and water are in equilibrium, so the change is reversible and $$\Delta G = 0$$ Since $$ \begin{aligned} \Delta G &= \Delta H - T\Delta S \ &= 0 \end{aligned} $$ at equilibrium, $$ \begin{a...
You are given a rate law Rate = K[A]^2[B]. By how many times will the rate increase or decrease if i) concentration of A is doubled while that of B remains constant ii) concentration of A is kept constant and that of B is doubled?
Rate $=k[A]^2[B]$. (i) [A] doubled, [B] constant: the rate depends on $[A]^2$, so $$ \begin{aligned} \frac{r'}{r} &= (2)^2 \ &= 4 \end{aligned} $$ The rate becomes 4 times (increases fourfold). (ii) [A] constant, [B] doubled: the rate d...
How is sodium benzoate converted into acetophenone?
Convert sodium benzoate to benzene (decarboxylation), then do Friedel-Crafts acylation: $$ \begin{aligned} \ce{C6H5COONa + NaOH ->[CaO][\Delta] C6H6 + Na2CO3} \ \ce{C6H6 + CH3COCl ->[anhyd. AlCl3] C6H5COCH3 + HCl} \end{aligned} $$ The product $\ce{C6H5COCH3}$ is acetophenone.
Explain why chlorobenzene is less reactive than benzene in electrophilic substitution reactions.
Although the lone pair on chlorine can donate into the ring (making it o/p directing), chlorine is also strongly electronegative and withdraws electron density by the inductive effect ($-I$). The inductive withdrawal outweighs the weak resonance donation, so the ring in chlorobenzene has less electron density than benzene.
A less electron-rich ring attracts the electrophile less strongly, so chlorobenzene undergoes electrophilic substitution more slowly (it is deactivated) than benzene. Also, the partial double-bond character of the $\ce{C-Cl}$ bond (resonance) holds the chlorine firmly.
What product would you obtain when phenol is treated with i) Benzene diazonium chloride ii) Phthalic anhydride?
(i) With benzene diazonium chloride (coupling in mild alkali) gives an orange azo dye, p-hydroxyazobenzene: $$\ce{C6H5N2Cl + C6H5OH -> C6H5-N=N-C6H4OH + HCl}$$
(ii) With phthalic anhydride (heated with conc. $\ce{H2SO4}$) gives the dye/indicator phenolphthalein (two phenol units condense with the anhydride, with loss of water).
Identify the major products A and B giving their IUPAC names: Methoxymethane -(excess HI, heat)-> A -(sodium phenoxide, heat)-> B.
A: methoxymethane cleaved by excess HI gives iodomethane (both parts become the iodide): $$\ce{CH3-O-CH3 + 2HI -> 2CH3I + H2O}$$ A $= \ce{CH3I}$, IUPAC name iodomethane.
B: iodomethane with sodium phenoxide (Williamson synthesis) gives methoxybenzene: $$\ce{C6H5ONa + CH3I -> C6H5-O-CH3 + NaI}$$ B $= \ce{C6H5OCH3}$, IUPAC name methoxybenzene (anisole).
An organic compound C3H6O does not give a silver mirror with Tollen's reagent but gives a yellow precipitate with NaOH and I2. Identify the compound and write the reactions involved.
$\ce{C3H6O}$ that gives no silver mirror (so it is not an aldehyde) but gives a yellow precipitate of iodoform (so it has a $\ce{CH3CO-}$ group) is propanone (acetone), $\ce{CH3COCH3}$.
Iodoform reaction: $$\ce{CH3COCH3 + 3I2 + 4NaOH -> CHI3(s) + CH3COONa + 3NaI + 3H2O}$$ It does not react with Tollen's reagent because ketones are not oxidised by it.
Why is the nitro group called an ambident group?
An ambident group is one that can attach to another atom through either of two different atoms in it. The nitrite/nitro group has two donor atoms, nitrogen and oxygen. When it bonds through nitrogen it gives a nitro compound (
What happens when aniline is i) treated with benzene diazonium chloride ii) heated with chloroform in presence of alc. KOH?
(i) With benzene diazonium chloride (coupling) gives a yellow azo dye, p-aminoazobenzene: $$\ce{C6H5N2Cl + C6H5NH2 -> C6H5-N=N-C6H4-NH2 + HCl}$$
(ii) With chloroform and alcoholic KOH (carbylamine reaction) gives foul-smelling phenyl isocyanide: $$\ce{C6H5NH2 + CHCl3 + 3KOH -> C6H5NC + 3KCl + 3H2O}$$
Write down the functional isomer of methyl methanoate. What product would you expect when the isomer is heated with P2O5?
Methyl methanoate is $\ce{HCOOCH3}$ ($\ce{C2H4O2}$, an ester). Its functional isomer (same formula, different group) is ethanoic acid, $\ce{CH3COOH}$ (a carboxylic acid). On heating ethanoic acid with the dehydrating agent $\ce{P2O5}$, w...
What are lipids? Name the products formed when simple lipids undergo hydrolysis.
Lipids are naturally occurring organic compounds (fats and oils) that are esters of long-chain fatty acids with glycerol (triglycerides); they are insoluble in water but soluble in organic solvents and serve as stored energy.
On hydrolysis (acidic, or alkaline as in saponification) a simple lipid gives glycerol and fatty acids (or the sodium salts of the fatty acids, i.e. soap, in alkaline hydrolysis).
What is meant by i) invert sugar ii) non-reducing sugar?
i) Invert sugar: the equimolar mixture of glucose and fructose obtained by hydrolysis of sucrose. It is called invert sugar because the sign of optical rotation changes (inverts) from right (sucrose) to left (the mixture, because fructose is strongly laevorotatory).
ii) Non-reducing sugar: a sugar that cannot reduce Tollen's or Fehling's reagent because its reducing (anomeric) groups are locked in the glycosidic linkage, e.g. sucrose.
Mention an important function of each of the following: i) DDT ii) Nitrogen fertilizer iii) tranquilizers iv) broad spectrum antibiotics.
i) DDT: a powerful insecticide, used to kill mosquitoes and other insect pests (controls malaria-spreading insects).
ii) Nitrogen fertilizer: supplies nitrogen to plants for the synthesis of proteins and chlorophyll, promoting leafy growth (e.g. urea).
iii) Tranquilizers: drugs that reduce anxiety and mental tension and induce calm/sleep (used to treat stress and mental disorders).
iv) Broad spectrum antibiotics: drugs effective against a wide range of both Gram-positive and Gram-negative bacteria (e.g. chloramphenicol, tetracycline).
Name the monomers of bakelite and state the polymerisation process for it.
Monomers of bakelite: phenol ($\ce{C6H5OH}$) and formaldehyde (methanal, $\ce{HCHO}$).
Polymerisation process: bakelite is formed by condensation polymerisation (step-growth). Phenol and methanal first react to give ortho and para hydroxymethylphenols:
$$\ce{C6H5OH + HCHO ->[H+/OH-] HO-C6H4-CH2OH}$$
These hydroxymethylphenols then condense with one another, losing water at each step, to build a cross-linked three-dimensional network resin, which is bakelite.
How is granulated zinc obtained? Write an important application.
Granulated zinc is obtained by melting ordinary zinc and pouring the molten metal in a thin stream into cold water; it solidifies at once into small irregular granules. Application: granulated zinc has a large surface area, so it is used...
Why is silver nitrate solution used for staining the fingers of voters during an election?
The organic matter and proteins of the skin reduce $\ce{AgNO3}$ to finely divided metallic silver, which is black and firmly bound to the skin, so the mark cannot be washed off and lasts for several days. Because the stain is permanent (...
What is meant by i) quenching of steel ii) annealing of steel?
i) Quenching (hardening): heating steel to redness and then cooling it suddenly by plunging into water or oil. This makes the steel very hard and brittle.
ii) Annealing: heating steel to redness and then cooling it very slowly. This makes the steel soft and less brittle (relieves internal stresses and increases ductility).
It is better to express concentration in molality rather than molarity, why? X gm of a metal (equivalent weight = 12) was completely dissolved in 100 cc of N/2 HCl. The volume was made up to 500 cc. It is found that 25 cc of the diluted acid solution required 17.5 cc of N/10 NaOH for complete neutralization. Find the value of X.
Why molality: molality is based on the mass of solvent, which does not change with temperature, whereas molarity uses volume, which changes as temperature (and hence density) changes. So molality gives a temperature-independent concentra...
Mention the important applications of the standard hydrogen electrode. The standard electrode potentials for Fe^3+/Fe^2+ and I2/I- are +0.77 V and +0.54 V respectively. i) Draw the standard cell notation. ii) Identify the anode and cathode from the current drawn. iii) Write the cell reaction. iv) Calculate the standard cell potential.
Applications of SHE: it is the primary reference electrode assigned $E^\circ = 0$ V, used to measure the standard electrode potentials of other electrodes and to build the electrochemical series; it also helps determine pH and the feasibility of redox reactions.
Since $E^\circ(\ce{Fe^3+}/\ce{Fe^2+})=0.77$ V is higher than $E^\circ(\ce{I2}/\ce{I-})=0.54$ V, the iron couple is reduced (cathode) and the iodide couple is oxidised (anode).
i) Cell notation:
$$\ce{Pt | I- | I2 || Fe^3+, Fe^2+ | Pt}$$
ii) Anode (oxidation) $=$ the $\ce{I2}/\ce{I-}$ electrode; cathode (reduction) $=$ the $\ce{Fe^3+}/\ce{Fe^2+}$ electrode.
iii) Cell reaction:
$$\ce{2Fe^3+ + 2I- -> 2Fe^2+ + I2}$$
iv)
$$ \begin{aligned} E^\circ_{cell} &= E^\circ_{cathode} - E^\circ_{anode} \ &= 0.77 - 0.54 \ &= \textbf{0.23 V} \end{aligned} $$
.
State enthalpy of combustion. If the heats of formation of CO2, H2O and C6H12O6 are -395, -269.4 and -1169 kJ/mol respectively, calculate the heat of combustion of glucose.
Enthalpy of combustion: the enthalpy change when one mole of a substance is completely burnt in excess oxygen. For glucose: $$ \ce{C6H12O6 + 6O2 - 6CO2 + 6H2O} $$ . $$ \begin{aligned} \Delta Hc &= [6,\Delta Hf(\ce{CO2}) + 6,\Delta Hf(...
Write the chemistry of corrosive sublimate.
Corrosive sublimate is mercuric chloride, $\ce{HgCl2}$, a white poisonous solid. Preparation: it is made by heating mercury with excess chlorine: $$\ce{Hg + Cl2 - HgCl2}$$ or by heating mercuric sulphate with sodium chloride: $$\ce{HgSO4...
Starting from a Grignard reagent, how would you prepare i) propan-1-ol ii) propan-2-ol? Mention the chemical test to distinguish them. Write down the structural formula of neo-pentyl alcohol and its IUPAC name.
i) Propan-1-ol is prepared by adding a Grignard reagent to methanal and then hydrolysing. The Grignard reagent adds to methanal: $$\ce{C2H5MgBr + HCHO - C2H5CH2OMgBr}$$ and acidic hydrolysis gives the primary alcohol: $$\ce{C2H5CH2OMgBr ...
How is trichloromethane prepared in the laboratory? Why is it discouraged to use chloroform as an anaesthesia?
Laboratory preparation of trichloromethane (chloroform): warm ethanol (or acetone) with bleaching powder and water (haloform reaction). Bleaching powder supplies $\ce{Cl2}$ and $\ce{Ca(OH)2}$: $$ \begin{aligned} \ce{CH3CH2OH + Cl2 -> CH3CHO + 2HCl} \ \ce{CH3CHO + 3Cl2 -> CCl3CHO + 3HCl} \ \ce{2CCl3CHO + Ca(OH)2 -> 2CHCl3 + (HCOO)2Ca} \end{aligned} $$ The chloroform is distilled off and purified.
Why discouraged as anaesthesia: on exposure to air and light chloroform is slowly oxidised to the extremely poisonous gas phosgene (carbonyl chloride): $$\ce{2CHCl3 + O2 ->[light] 2COCl2 + 2HCl}$$ Phosgene is toxic, so chloroform is unsafe as an anaesthetic (it is now stored in dark bottles with a little ethanol to destroy any phosgene).
An aliphatic compound A reacts with SOCl2 to give B. B heated with ammonia produces C. C further heated with Br2/KOH yields D. D gives E when treated with NaNO2/HCl at low temperature. E is a primary alcohol which gives a positive iodoform test. Identify A, B, C, D and E and write the reactions involved.
E is a primary alcohol giving the iodoform test, so E = ethanol, $\ce{CH3CH2OH}$ (the only primary alcohol that responds to iodoform). Working back: - D $$ \ce{-[NaNO2/HCl]} $$ E: a primary amine gives an alcohol with nitrous acid, so D ...
Describe the laboratory method of preparation of pure and dry nitrobenzene. Identify the major products A, B, C and D in the sequence: A -(PCl5, heat)-> B -(H2, Pd/BaSO4)-> C -(alc. KCN)-> D. The compound C can be obtained by oxidation of toluene in the presence of CeO2/H+.
Nitrobenzene: benzene is warmed with a nitrating mixture of conc. $\ce{HNO3}$ and conc. $\ce{H2SO4}$ at 55 to 60 degrees: $$\ce{C6H6 + HNO3 ->[conc. H2SO4] C6H5NO2 + H2O}$$ The product is washed with water and dilute $\ce{NaOH}$, dried over anhydrous $\ce{CaCl2}$ and distilled (b.p. 211 degrees) to give pure, dry nitrobenzene.
Reaction sequence: since C is obtained by oxidation of toluene, C = benzaldehyde, $\ce{C6H5CHO}$. Then:
$$ \begin{aligned} \ce{C6H5COOH + PCl5 -> C6H5COCl + POCl3 + HCl} \ \ce{C6H5COCl + H2 ->[Pd/BaSO4] C6H5CHO + HCl} \ \ce{2C6H5CHO ->[alc. KCN] C6H5CH(OH)COC6H5} \end{aligned} $$
a) How is propanone prepared from i) 2,2-dichloropropane ii) isopropyl alcohol iii) propyne? Give suitable reactions for the conversion of ethanoic acid into i) methane ii) methyl ethanoate. b) Write the structural formula of primary, secondary and tertiary amines from C3H9N. How would you apply Hoffmann's method to separate them?
a) Propanone from: i) 2,2-dichloropropane (hydrolysis of gem-dihalide):
$$ \ce{CH3CCl2CH3 + 2NaOH(aq) -> CH3COCH3 + 2NaCl + H2O} $$
ii) isopropyl alcohol (oxidation):
$$ \ce{CH3CH(OH)CH3 ->[K2Cr2O7/H2SO4] CH3COCH3} $$
iii) propyne (Markovnikov hydration):
$$ \ce{CH3C#CH + H2O ->[HgSO4/H2SO4] CH3COCH3} $$
Ethanoic acid conversions: i) to methane (decarboxylation with soda-lime):
$$ \ce{CH3COONa + NaOH ->[CaO][\Delta] CH4 + Na2CO3} $$
ii) to methyl ethanoate (esterification):
$$ \ce{CH3COOH + CH3OH <=>[conc. H2SO4] CH3COOCH3 + H2O} $$
b) Amines of $\ce{C3H9N}$:
Hoffmann's separation: treat the mixture with diethyl oxalate; the primary amine gives a solid oxamide, the secondary gives a liquid oxamic ester, the tertiary does not react. Distil off the tertiary amine first, then hydrolyse the residue with $\ce{NaOH}$ to regenerate the primary amine (from the solid) and the secondary amine (from the liquid), and separate them by distillation.
State Ostwald's dilution law. What is the limitation of this law? Define the terms i) ionic product of water ii) common ion effect iii) degree of ionisation iv) pH value. What will be the resultant pH when 200 ml of aqueous HCl (pH = 2) is mixed with 300 ml of an aqueous solution of NaOH (pH = 12)?
Ostwald's dilution law: for a weak electrolyte, $K = \dfrac{\alpha^2 C}{1-\alpha}$ (for very weak electrolytes $\alpha=\sqrt{K/C}$), so the degree of ionisation increases on dilution. Limitation: it holds only for weak electrolytes; it f...
Write short notes on any two: i) Chemistry of the rusting of iron ii) Extraction of blister copper from copper pyrites iii) Lewis concept of acid and base iv) Laboratory preparation of ethoxyethane.
iii) Lewis concept of acid and base: a Lewis acid is an electron-pair acceptor (has a vacant orbital), e.g. $\ce{BF3}$, $\ce{AlCl3}$, $\ce{H+}$; a Lewis base is an electron-pair donor (has a lone pair), e.g. $\ce{NH3}$, $\ce{H2O}$, $\ce{OH-}$. An acid-base reaction is the formation of a coordinate (dative) bond: $$\ce{BF3 + NH3 -> F3B<-NH3}$$ This concept is wider than the Bronsted idea because it explains reactions that involve no proton transfer.
iv) Laboratory preparation of ethoxyethane: ethanol is heated with excess conc. $\ce{H2SO4}$ at 140 degrees (continuous etherification): $$ \begin{aligned} \ce{C2H5OH + H2SO4 -> C2H5HSO4 + H2O} \ \ce{C2H5HSO4 + C2H5OH ->[413 K] C2H5OC2H5 + H2SO4} \end{aligned} $$ The distillate is washed with dilute $\ce{NaOH}$ and $\ce{CaCl2}$ solution, dried over anhydrous $\ce{CaCl2}$ and sodium wire, and distilled (b.p. 308 K).
In ethyne, (), each carbon is bonded to only two groups (one H and the other C) and forms a triple bond. To arrange two sigma bonds linearly and leave two unhybridised p orbitals for the two pi bonds of the tripl...
On the Bronsted-Lowry idea: Conjugate acid of (add a proton): (ammonium ion). Conjugate base of (remove a proton): (amide ion).
(i) 80 g Ca (): moles ; electrons $$ \begin{aligned} &= 2\times2 \ &= 4\ \text{mol} \ Q &= 4\times96500 \ &= 386000\ \text{C};(3.86\times10^{5}\ \text{C}) \e...
First law of thermodynamics (conservation of energy): energy can neither be created nor destroyed but only changed from one form to another; the total energy of an isolated system stays constant.
For a closed system, , where is the change in internal energy, the heat absorbed and the work done on the system.
At the melting point (0 degrees C = 273 K), ice and water are in equilibrium, so the change is reversible and Since at equilibrium, $$ \begin{a...
Rate . (i) [A] doubled, [B] constant: the rate depends on , so The rate becomes 4 times (increases fourfold). (ii) [A] constant, [B] doubled: the rate d...
Convert sodium benzoate to benzene (decarboxylation), then do Friedel-Crafts acylation:
The product is acetophenone.
Although the lone pair on chlorine can donate into the ring (making it o/p directing), chlorine is also strongly electronegative and withdraws electron density by the inductive effect (). The inductive withdrawal outweighs the weak resonance donation, so the ring in chlorobenzene has less electron density than benzene.
A less electron-rich ring attracts the electrophile less strongly, so chlorobenzene undergoes electrophilic substitution more slowly (it is deactivated) than benzene. Also, the partial double-bond character of the bond (resonance) holds the chlorine firmly.
(i) With benzene diazonium chloride (coupling in mild alkali) gives an orange azo dye, p-hydroxyazobenzene:
(ii) With phthalic anhydride (heated with conc. ) gives the dye/indicator phenolphthalein (two phenol units condense with the anhydride, with loss of water).
A: methoxymethane cleaved by excess HI gives iodomethane (both parts become the iodide): A , IUPAC name iodomethane.
B: iodomethane with sodium phenoxide (Williamson synthesis) gives methoxybenzene: B , IUPAC name methoxybenzene (anisole).
that gives no silver mirror (so it is not an aldehyde) but gives a yellow precipitate of iodoform (so it has a group) is propanone (acetone), .
Iodoform reaction: It does not react with Tollen's reagent because ketones are not oxidised by it.
(i) With benzene diazonium chloride (coupling) gives a yellow azo dye, p-aminoazobenzene:
(ii) With chloroform and alcoholic KOH (carbylamine reaction) gives foul-smelling phenyl isocyanide:
Methyl methanoate is (, an ester). Its functional isomer (same formula, different group) is ethanoic acid, (a carboxylic acid). On heating ethanoic acid with the dehydrating agent , w...
Monomers of bakelite: phenol () and formaldehyde (methanal, ).
Polymerisation process: bakelite is formed by condensation polymerisation (step-growth). Phenol and methanal first react to give ortho and para hydroxymethylphenols:
These hydroxymethylphenols then condense with one another, losing water at each step, to build a cross-linked three-dimensional network resin, which is bakelite.
The organic matter and proteins of the skin reduce to finely divided metallic silver, which is black and firmly bound to the skin, so the mark cannot be washed off and lasts for several days. Because the stain is permanent (...
Applications of SHE: it is the primary reference electrode assigned V, used to measure the standard electrode potentials of other electrodes and to build the electrochemical series; it also helps determine pH and the feasibility of redox reactions.
Since V is higher than V, the iron couple is reduced (cathode) and the iodide couple is oxidised (anode).
i) Cell notation:
ii) Anode (oxidation) the electrode; cathode (reduction) the electrode.
iii) Cell reaction:
iv)
.
Enthalpy of combustion: the enthalpy change when one mole of a substance is completely burnt in excess oxygen. For glucose: . $$ \begin{aligned} \Delta Hc &= [6,\Delta Hf(\ce{CO2}) + 6,\Delta Hf(...
Corrosive sublimate is mercuric chloride, , a white poisonous solid. Preparation: it is made by heating mercury with excess chlorine: or by heating mercuric sulphate with sodium chloride: $$\ce{HgSO4...
i) Propan-1-ol is prepared by adding a Grignard reagent to methanal and then hydrolysing. The Grignard reagent adds to methanal: and acidic hydrolysis gives the primary alcohol: $$\ce{C2H5CH2OMgBr ...
Laboratory preparation of trichloromethane (chloroform): warm ethanol (or acetone) with bleaching powder and water (haloform reaction). Bleaching powder supplies and :
The chloroform is distilled off and purified.
Why discouraged as anaesthesia: on exposure to air and light chloroform is slowly oxidised to the extremely poisonous gas phosgene (carbonyl chloride): Phosgene is toxic, so chloroform is unsafe as an anaesthetic (it is now stored in dark bottles with a little ethanol to destroy any phosgene).
E is a primary alcohol giving the iodoform test, so E = ethanol, (the only primary alcohol that responds to iodoform). Working back: - D E: a primary amine gives an alcohol with nitrous acid, so D ...
Nitrobenzene: benzene is warmed with a nitrating mixture of conc. and conc. at 55 to 60 degrees: The product is washed with water and dilute , dried over anhydrous and distilled (b.p. 211 degrees) to give pure, dry nitrobenzene.
Reaction sequence: since C is obtained by oxidation of toluene, C = benzaldehyde, . Then:
a) Propanone from: i) 2,2-dichloropropane (hydrolysis of gem-dihalide):
ii) isopropyl alcohol (oxidation):
iii) propyne (Markovnikov hydration):
Ethanoic acid conversions: i) to methane (decarboxylation with soda-lime):
ii) to methyl ethanoate (esterification):
b) Amines of :
Hoffmann's separation: treat the mixture with diethyl oxalate; the primary amine gives a solid oxamide, the secondary gives a liquid oxamic ester, the tertiary does not react. Distil off the tertiary amine first, then hydrolyse the residue with to regenerate the primary amine (from the solid) and the secondary amine (from the liquid), and separate them by distillation.
Ostwald's dilution law: for a weak electrolyte, (for very weak electrolytes ), so the degree of ionisation increases on dilution. Limitation: it holds only for weak electrolytes; it f...
iii) Lewis concept of acid and base: a Lewis acid is an electron-pair acceptor (has a vacant orbital), e.g. , , ; a Lewis base is an electron-pair donor (has a lone pair), e.g. , , . An acid-base reaction is the formation of a coordinate (dative) bond: This concept is wider than the Bronsted idea because it explains reactions that involve no proton transfer.
iv) Laboratory preparation of ethoxyethane: ethanol is heated with excess conc. at 140 degrees (continuous etherification):
The distillate is washed with dilute and solution, dried over anhydrous and sodium wire, and distilled (b.p. 308 K).