Two elements A and B form compounds having formula AB2 and AB4. When dissolved in 20 g of benzene (C6H6), 1 g of AB2 lowers the freezing point by 2.3 Kwhereas 1.0 g of AB4 lowers it by 1.3 K. The molar depression constant for benzene is 5.1 Kkg mol-1. Calculate atomic masses of A and B.
As We know that:
MB = (Kf x wB x 1000) / (wA X ΔTf)
Now ΔTf = 2.3 , wB = 1.0 , wA = 20, KF = 5.1 (given)
PUTTING THE VALUES IN THE EQUATION
MB = (5.1 x 1 x 1000) / (20 x 2.3) = 110.87 g/mol
Therefore MAB2 = 110.9
For AB4 compound
ΔTf = 1.3 , wb = 1 ,wa = 20
MB = (5.1 X 1 X 1000) / (20 X 1.3) = 196 g/mol
Therefore MAB = 196
Let x be the atomic mass of A & y be the atomic mass of B,
THEN MAB2 = x + 2y = 110.9 ----------------------------------(1)
And MAB = x + 4y = 196 ----------------------------------(2)
Subtracting 2 from 1 ,we get
2y = 196-110.9
y = 85.1 / 2
y = 42.6
Putting the value of y in 1 we get
x = 110.9 - 2 x 42.6
x = 25.7
Therefore atomic mass of A = 25.7 u Atomic mass of B = 42.6 u.
Give simple chemical tests to distinguish between the following pairs of compounds.
(i) Propanal and Propanone
(ii) Acetophenone and Benzophenone
(iii) Phenol and Benzoic acid
(iv) Benzoic acid and Ethyl benzoate
(v) Pentan-2-one and Pentan-3-one
(vi) Benzaldehyde and Acetophenone
(vii) Ethanal and Propanal
A 5% solution (by mass) of cane sugar in water has freezing point of 271 K. Calculate the freezing point of 5% glucose in water if freezing point of pure water is 273.15 K.
How the following conversions can be carried out?
(i) Propene to propan-1-ol
(ii) Ethanol to but-1-yne
(iii) 1-Bromopropane to 2-bromopropane
(iv) Toluene to benzyl alcohol
(v) Benzene to 4-bromonitrobenzene
(vi) Benzyl alcohol to 2-phenylethanoic acid
(vii) Ethanol to propanenitrile
(viii) Aniline to chlorobenzene
(ix) 2-Chlorobutane to 3, 4-dimethylhexane
(x) 2-Methyl-1-propene to 2-chloro-2-methylpropane
(xi) Ethyl chloride to propanoic acid
(xii) But-1-ene to n-butyliodide
(xiii) 2-Chloropropane to 1-propanol
(xiv) Isopropyl alcohol to iodoform
(xv) Chlorobenzene to p-nitrophenol
(xvi) 2-Bromopropane to 1-bromopropane
(xvii) Chloroethane to butane
(xviii) Benzene to diphenyl
(xix) tert-Butyl bromide to isobutyl bromide
(xx) Aniline to phenylisocyanide
A solution of glucose in water is labelled as 10% w/w, what would be the molality and mole fraction of each component in the solution? If the density of solution is 1.2 g mL-1, then what shall be the molarity of the solution?
Henry's law constant for CO2 in water is 1.67 x 108Pa at 298 K. Calculate the quantity of CO2in 500 mL of soda water when packed under 2.5 atm CO2 pressure at 298 K.
Calculate the mass of a non-volatile solute (molar mass 40 g mol-1) which should be dissolved in 114 g octane to reduce its vapour pressure to 80%.
The vapour pressure of pure liquids A and B are 450 and 700 mm Hg respectively, at 350 K. Find out the composition of the liquid mixture if total vapour pressure is 600 mm Hg. Also find the composition of the vapour phase.
Calculate the mole fraction of benzene in solution containing 30% by mass in carbon tetrachloride.
How many mL of 0.1 M HCl are required to react completely with 1 g mixture of Na2CO3 and NaHCO3 containing equimolar amounts of both?
If NaCl is doped with 10-3mol % of SrCl2, what is the concentration of cation vacancies?
Write the reactions of (i) aromatic and (ii) aliphatic primary amines with nitrous acid.
What is crystal field splitting energy? How does the magnitude of Δo decide the actual configuration of d-orbitals in a coordination entity?
What is meant by unidentate, didentate and ambidentate ligands? Give two examples for each.
Differentiate between globular and fibrous proteins.
The rate of a reaction quadruples when the temperature changes from 293 K to 313 K. Calculate the energy of activation of the reaction assuming that it does not change with temperature.
Vapour pressure of pure water at 298 K is 23.8 mm Hg. 50 g of urea (NH2CONH2) is dissolved in 850 g of water. Calculate the vapour pressure of water for this solution and its relative lowering.
Name two poisonous gases which can be prepared from chlorine gas.
Vapour pressure of water at 293 Kis 17.535 mm Hg. Calculate the vapour pressure of water at 293 Kwhen 25 g of glucose is dissolved in 450 g of water.
How would you account for the irregular variation of ionization enthalpies (first and second) in the first series of the transition elements?
Predict the products of electrolysis in each of the following:
(i) An aqueous solution of AgNO3 with silver electrodes.
(ii) An aqueous solution of AgNO3with platinum electrodes.
(iii) A dilute solution of H2SO4with platinum electrodes.
(iv) An aqueous solution of CuCl2 with platinum electrodes.
I Like this solutions
In this question we are calculating the molecular mass of AB2 and AB4 molecule separately,therefore in case molecular mass of AB2 is taken and in other case molecular mass of AB4 is taken
in molality we take the molecular mass of solution in denominator but here there is only molecular mass of compound AB2.Why?