Discuss the principle of estimation of halogens, sulphur and phosphorus present in an organic compound.
Estimation of halogens
Halogens are estimated by the Carius method. In this method, a known quantity of organic compound is heated with fuming nitric acid in the presence of silver nitrate, contained in a hard glass tube called the Carius tube, taken in a furnace. Carbon and hydrogen that are present in the compound are oxidized to form CO2 and H2O respectively and the halogen present in the compound is converted to the form of AgX. This AgX is then filtered, washed, dried, and weighed.
Let the mass of organic compound be m g.
Mass of AgX formed = m1 g
1 mol of Agx contains 1 mol of X.
Therefore, Mass of halogen in m1 g of AgX = (Atomic mass of X x m1 g) / (Molecular mass of AgX)
Thus, % of halogen will be = (Atomic mass of X x m1 x 100) / (Molecular mass of AgX x m)
Estimation of Sulphur
In this method, a known quantity of organic compound is heated with either fuming nitric acid or sodium peroxide in a hard glass tube called the Carius tube. Sulphur, present in the compound, is oxidized to form sulphuric acid. On addition of excess of barium chloride to it, the precipitation of barium sulphate takes place. This precipitate is then filtered, washed, dried, and weighed.
Let the mass of organic compound be m g.
Mass of BaSO4 formed = m1 g
1 mol of BaSO4 = 233 g BaSO4 = 32 g of Sulphur
Therefore, m1 g of BaSO4 contains 32 x m1 / 233 g of sulphur
Thus, percentage of sulphur = 32 x m1 x100 / 233 x m
Estimation of phosphorus
In this method, a known quantity of organic compound is heated with fuming nitric acid. Phosphorus, present in the compound, is oxidized to form phosphoric acid. By adding ammonia and ammonium molybdate to the solution, phosphorus can be precipitated as ammonium phosphomolybdate.
Phosphorus can also be estimated by precipitating it as MgNH4PO4 by adding magnesia mixture, which on ignition yields Mg2P2O7.
Let the mass of organic compound be m g.
Mass of ammonium phosphomolybdate formed = m1 g
Molar mass of ammonium phosphomolybdate = 1877 g
Thus, percentage of phosphorus = (31 x m1 x 100 %) / (1877 x m)
If P is estimated as Mg2P2O7,
Then percentage of phosphorus = (62xm1x100%) / (222xm)
What are hybridisation states of each carbon atom in the following compounds ?
(i) CH2=C=O,
(ii) CH3CH=CH2,
(iii) (CH3)2CO,
(iv) CH2=CHCN,
(v) C6H6
Explain the terms Inductive and Electromeric effects. Which electron displacement effect explains the following correct orders of acidity of the carboxylic acids?
(a) Cl3CCOOH > Cl2CHCOOH > ClCH2COOH
(b) CH3CH2COOH > (CH3)2CHCOOH > (CH3)3C.COOH
Write bond line formulas for : Isopropyl alcohol, 2,3-Dimethyl butanal, Heptan-4- one.
Give condensed and bond line structural formulas and identify the functional group(s) present, if any, for :
(a) 2,2,4-Trimethylpentane
(b) 2-Hydroxy-1,2,3-propanetricarboxylic acid
(c) Hexanedial
Indicate the σ and π bonds in the following molecules :
(i) C6H6,
(ii) C6H12,
(iii) CH2Cl2,
(iv) CH2=C=CH2,
(v) CH3NO2,
(vi) HCONHCH3
Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles:
(a) CH3COOH + HO- → CH3COO- + H2O
(b) CH3COCH3 + C-N → (CH3)2 C (CN) (OH)
(c) C6H5 + CH3C+O → C6H5COCH3
For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion.
Which of the following represents the correct IUPAC name for the compounds concerned?
(a) 2,2-Dimethylpentane or 2-Dimethylpentane
(b) 2,4,7-Trimethyloctane or 2,5,7-Trimethyloctane
(c) 2-Chloro-4-methylpentane or 4-Chloro-2-methylpentane
(d) But-3-yn-1-ol or But-4-ol-1-yne
Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation.
(a) C6H5OH
(b) C6H5NO2
(c) CH3CH=CHCHO
(d) C6H5–CHO
(e) C6 H5 - C+H2
(f) CH3CH = CHC+H2
Which of the following carbocation is most stable ?
How do you account for the formation of ethane during chlorination of methane?
What will be the minimum pressure required to compress 500 dm3 of air at 1 bar to 200 dm3 at 30°C?
What are the common physical and chemical features of alkali metals?
Calculate the molecular mass of the following:
(i) H2O
(ii) CO2
(iii) CH4
Assign oxidation number to the underlined elements in each of the following species:
(a) NaH2PO4
(b) NaHSO4
(c) H4P2O7
(d) K2MnO4
(e) CaO2
(f) NaBH4
(g) H2S2O7
(h) KAl(SO4)2.12 H2O
What is the basic theme of organisation in the periodic table?
Explain the formation of a chemical bond.
Choose the correct answer. A thermodynamic state function is a quantity
(i) used to determine heat changes
(ii) whose value is independent of path
(iii) used to determine pressure volume work
(iv) whose value depends on temperature only.
A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.
a) What is the initial effect of the change on vapour pressure?
b) How do rates of evaporation and condensation change initially?
c) What happens when equilibrium is restored finally and what will be the final vapour pressure?
Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.
Explain the formation of H2 molecule on the basis of valence bond theory.
Compare the relative stability of the following species and indicate their magnetic properties:
O2,O2+,O2- (superoxide), O22-(peroxide)
What is meant by the term bond order? Calculate the bond order of: N2, O2,O2+,and O2-.
Dinitrogen and dihydrogen react with each other to produce ammonia according to the following chemical equation:
N2(g) + H2(g) → 2NH3(g)
(i) Calculate the mass of ammonia produced if 2.00 × 103 g dinitrogen reacts with 1.00 × 103 g of dihydrogen.
(ii) Will any of the two reactants remain unreacted?
(iii) If yes, which one and what would be its mass?
The pH of 0.1M solution of cyanic acid (HCNO) is 2.34. Calculate the ionization constant of the acid and its degree of ionization in the solution.
Describe the change in hybridisation (if any) of the Al atom in the following reaction.
Out of benzene, m-dinitrobenzene and toluene which will undergo nitration most easily and why?
Calculate the mass percent of different elements present in sodium sulphate (Na2SO4).
Calculate the energy required for the process
The ionization energy for the H atom in the ground state is 2.18 ×10–18 J atom–1
What would have happened if the greenhouse gases were totally missing in the earth's atmosphere? Discuss.