Chemistry #expch001 Important Questions
Ch. 16. Solutions and environmental Chemistry #expch_016
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- Which of the following requirement is satisfied by a phase change of the first order?
a) there are changes of volume and entropy
b) the first-order derivative of the Gibbs function changes discontinuously
c) both of the mentioned d) none of the mentioned
Answer: (c)
Explanation
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We describe a first-order phase transition of a simple system in a process where the volume is kept constant. We show that, unlike what happens when the pressure is constant,
(i) the transformation extends over a finite temperature (and pressure) range,
(ii) each and every extensive potential (internal energy U, enthalpy H, Helmholtz energy F, and Gibbs energy G), and the entropy S is continuous across the transition, and
(iii) the constant-volume heat capacity does not diverge during the transition and only exhibits discrete jumps.
2.What is the mathematical formula for Boyle-Van’t Hoff law ?
(a)p ∝ C
(b)p ∝ nV
(c)p ∝ 1V
(d)π ∝ nV
Answer: (d)
Explanation
How presentation will benefit audience: Adult learners are more interested in a subject if they know how or why it is important to them.
Presenter’s level of expertise in the subject: Briefly state your credentials in this area, or explain why participants should listen to you.
The van’t Hoff-Boyle’s law states that at constant temperature the volume of an ideal gas is inversely proportional to the pressure of the gas.
Van’t Hoff Boyle Law of solution :
→ At constant temperature the osmotic pressure (⊓) of a delute solution is directly proportional to its molar concentration (C) or inversely proportional to volume (V) of the solution.
Explanation : π∝C but C=Vn
∴π∝Vn→π∝V1
Or say πV= constant [ n is no. of moles of solute dissolved in liters ]
Van’t Hoff Charle’s Law of solution :
→ The concentration remaining constant, the osmotic pressure (π) of a dilute solution is directly proportional to absolute temperature (T) of the solution.
Explanation : π∝T
Tπ= constant.
- Under which of the following conditions, will the solute dissolve spontaneously in water ?
(a)ΔH(hydration) > ΔH(lattice)
(b)ΔH(hydration) < ΔH(lattice)
(c)ΔH(hydration) = ΔH(lattice)
(d)ΔH(hydration) + ΔH(lattice) = 0
Answer: (a) - Which of the following is the false statement ?
(a)According to Raoult’s law, vapour pressure of the solution varies directly as the mole fraction of the solvent.
(b)The equation for the osmotic pressure (π) is π=CRT, where C is molarity of the solution
(c)The correct order of osmotic pressure of 0.01 M aqueous solution of each given substance to BaCl2 > KCl > CH3COOH > Sucrose
(d)Two solutions of sucrose having the same molality but different solvents have identical depressions in freezing point.
Answer: (d)
Explanation
Example objectives
At the end of this lesson, you will be able to:
Save files to the team Web server.
Move files to different locations on the team Web server.
Share files on the team Web server.
- Which of the following expresses the osmotic pressure of solution ? (π = Osmotic pressure, C = Concentration of solution)
(a)π = RTC
(b)π = CTR
(c)π = CRT
(d)π = CRT
Answer: (c) - Colligative properties can be used for calculating:
a)The density of a compound
b) The lattice energy of a compound
c) The molecular mass of a compound
d) All of the above
Answer:(c) - Which law explains the following statement ?
“Solutions having identical volume and number of particles possess identical osmotic pressure “.
(a)Boyle-Van’t Hoff law
(b)Raoult’s law
(c)Henry’s law
(d)Avogadro-Van’t Hoff law
Answer:(d)
Explanation
The van’t Hoff-Boyle’s law states that at constant temperature the volume of an ideal gas is inversely proportional to the pressure of the gas. Where P is the pressure, V is the volume.
Statement of van’t Hoff-Avogadro’s law : At given temperature, equal volumes of the solutions having the same osmotic pressure contain number of solute particles.
Explanation : The equal number of moles of the substances contain equal number of molecles.
Henry’s law, statement that the weight of a gas dissolved by a liquid is proportional to the pressure of the gas upon the liquid. The law, which was first formulated in 1803 by the English physician and chemist William Henry, holds only for dilute solutions and low gas pressures.
Raoult’s law is a relation of physical chemistry, with implications in thermodynamics. Proposed by French chemist François-Raolult’s in 1887, it states that the partial pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component (liquid or solid) multiplied by its mole fraction in the mixture.
In consequence, the relative lowering of vapor pressure of a dilute solution of nonvolatile solute is equal to the mole fraction of solute in the solution.
- Two solutions of a substance (non electrolyte) are mixed in the following manner. 480 mL of 1.5 M first solution + 520 mL of 1.2 M second solution. What is the molarity of the final mixture?
a) 1.20 M
b) 1.344 M
c) 1.50 M
d) 2.70 M
Answer: b
Explanation
Molarity of a mixture, Mmix can be calculated by:
Mmix = (M1V1 + M2V2) / (V1 + V2)
= (1.5 x 480) + (1.2 x 520)/(480 + 520)
= 720+624/1000 = 1.344 M
- The density (in g mL–1) of a 3.60 M sulphuric acid solution that is 29% H2SO4 (Molar mass = 98 g mol–1) by mass will be:
a) 1.45
b) 1.64
c) 1.88
d) 1.22
Answer : d
Explanation
The relation between Molarity, M and mass percent (%) is given by:
M = (% x 10 x d) / MW
Where:
MW = molecular weight of solute
d = density of solution
Therefore:
d = M x MW / (% x 10) = 3.60 x 98 / 29 x 10 = 1.216 g mL-1
- Density of a 2.05 M solution of acetic acid in water is 1.02 g/mL. The molality of the solution is:
a) 1.14 mol kg-1
b) 3.28 mol kg-1
c) 2.28 mol kg-1
d) 0.44 mol kg-1
Answer: c
Explanation
Molarity of acetic acid solution = 2.05 M
Therefore the number of moles of acetic acid in 1 L solution = 2.05 mol
mass of acetic acid in 1 L solution = no. of moles x molar mass = 2.05 mol x 60 g mol-1 = 123 g
Note: molar mass of acetic acid is 60 g mol-1
Density, d = mass of solution / volume of solution
Hence:
mass of solution = density x volume of solution = 1.02 g mL-1 x 1000 mL = 1020 g
mass of solvent = mass of solution – mass of solute = 1020 – 123 = 897 g = 0.897 kg
molality, m = no. of moles / mass of solvent (in Kg) = 2.05 mol / 0.897 kg = 2.285 mol kg-1
- A 5.2 molal aqueous solution of methyl alcohol, CH3OH is supplied. What is the mole fraction of methyl alcohol in the solution?
(a) 0.050
(b) 1.100
(c) 0.190
(d) 0.086
Answer: d
Explanation
molality of aqueous solution = 5.2 mol kg-1
Therefore, the number of moles of methyl alcohol in 1 kg of solvent (water) = 5.2 mol
And the number of moles of solvent (water) = weight / molar mass = 1000 g / 18 g mol-1 = 55.55 mol
Hence:
Mole fraction of methyl alcohol = nMeOH /nMeOH + nwater = 5.2 / 55.55 + 5.2 = 0.08559
- Molal boiling point constant is the ratio of the elevation in the boiling to:
a) Molarity
b) Mole fraction of solvent
c) Molality
d) Mole fraction of the solute
Answer: c
13.The solubility of a substance in a solvent depends on
(a) Temperature
(b) Pressure
(c) Nature of solute and solvent
(d) All of the above
Answer: (d)
FACTORS AFFECTING SOLUBILITY
Temperature
Particle size
Agitation
Pressure
Nature of solute and solvent
- Choose the correct example for a non-ideal solution??
(a) Benzene + Toluene
(b) Ethanol + Hexane
(c) Chlorobenzene +Bromobenzene
(d) Hexane + Heptane
Answer: (b)
15.Which condition holds for the ideal solution?
(a) Change in volume in zero
(b) Change in volume is non-zero
(c) Change is enthalpy is non-zero
(d) None of the above
Answer: (a)
16.Which of the following is not the consequence of ozone layer depletion?
(a) Increased ultraviolet rays
(b) Cyanobacteria are sensitive to UV radiation and would be affected by its increase.
(c) Malignant melanoma-Another form of skin cancer
(d) None of these
Answer: (d)
17.Who discovered the ozone layer?
(a) Henri Buisson & Charles Fabry
(b) Carl Sagan & Charles Fabry
(c) G.M.B Dobson
(d) Carl Sagan & G.M.B Dobson
Answer: (a)
The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson.
18.What is the average concentration of ozone in the ozone layer of the atmosphere? (PPSC 2020)?
(a) Nearly 20ppm
(b) Greater than 10 ppm
(c) Less than 10ppm
(d) none of these
Answer: (c)
Explanation: The concentration of ozone is about 10 ppm in the ozone layer and only 0.3 ppm in the entire atmosphere.
19- CFCs (chlorofluorocarbons) are greenhouse gases that have caused a rise of 3 degree C in the global temperatures in the past century. Name the CFC that is used in refrigerators.?
(a) Carbon dioxide
(b) Methane
(c) Ammonia
(d) Freon
Answer: (d)
20- Find the secondary pollutant among these?
PAN
N2O
SO2
CO2
Answer: (a)
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