This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Solubility Solutions”.
1. What is defined as the concentration of dissolved solute in a solvent beyond which none of it, if added to the solvent, will increase the concentration further more?
b) Saturation point
c) Solvent capacitance
d) Molar equilibrium concentration
Explanation: Solubility is the maximum amount of solute that can be dissolved in a given solvent at a particular temperature and pressure. It is usually expressed in grams of solute dissolved in 100 grams of the solvent. Any more solute added beyond this forms a supersaturated solution as none of the particles dissolve any more.
2. Which of the following solvents would most likely dissolve 3-Aminopropan-1-ol?
Explanation: The principle of solubility states that ‘like dissolves like’. Following this, it is seen that 3-Aminopropan-1-ol is a highly polar compound since it bears an amine group as well as a hydroxyl group. The polarity of amine group is due to the highly electronegative nature of N atom in N – H and C – N bonds. Since water is the most polar solvent amongst the four, it will dissolve the solute to greatest extent.
3. “The process of dissolution of solute in the solvent takes place even after saturation”. Is this true or false?
Explanation: At saturation point, a dynamic equilibrium is established between the two processes of dissolution and crystallization. These reactions occur at the same rate. When more solute is added beyond saturation point, dissolution of solute takes place but same amount of solute recrystallizes at the same rate. Hence making it look like dissolution does not occur when it actually does.
4. In a saturated solution with endothermic dissolution, how does the concentration of dissolved solute change with increasing then decreasing temperature?
a) Keeps increasing
b) Keeps decreasing
c) Increases and decreases
d) Decreases and increases
Explanation: When a solution is saturated a thermodynamic equilibrium exists between the undissolved solute and dissolved solute. Since the dissolution process here is mentioned as endothermic increasing and decreasing temperatures will decrease and increase the concentration, respectively, as given by Le Chatelier’s Principle of equilibrium.
5. How does the solubility of gas change in a liquid, as described?
a) Increases with decreasing pressure
b) Increases with increasing temperature
c) Decreases with increasing temperature
d) Decreases with increasing pressure
Explanation: In an equilibrium system of gas dissolved in solvent, when pressure over it is increased more and more gas particles are forced into a smaller volume. This also increases the rate at which they strike the surface of the solvent to enter it. Consequently, more gas dissolves with increasing pressure. In the case of increasing temperature, gas particles gain sufficient energy to escape the solvent and solubility decreases.
6. When CO2 is introduced into aerated drinks and sealed, what is the nature of the graph between partial pressure of CO2 and its concentration in the drink?
a) Exponentially increasing
b) Positive slope
c) Negative slope
Explanation: CO2 obeys Henry’s law, which governs the solubility of gases in liquids in relation to its pressure. Henry’s law states that mole fraction of gas in the solution varies directly with its partial pressure over the surface i.e. p ∝ x (mole fraction). The graph is of the form y = mx, a positively sloped straight line passing through the origin.
7. If, at 298 K water is the solvent, and Henry’s law constant for CO2 is 1.67 kbar and the constant of argon is 40.3 kbar, which of the following statements is true?
a) Argon is more soluble than CO2
b) Argon is less soluble than CO2
c) Argon is insoluble in water
d) Argon and CO2 are equally soluble
Explanation: Henry’s law is formulated asp = KH x X (mole fraction). From this, it is seen that as KH increases, mole fraction decreases in order to compensate the increase in partial pressure of the gas. Hence, higher the KH value lower is the solubility. Therefore, argon is less soluble in water than CO2 at 298 K.
8. Which of the following best describes the difficulty in breathing as one climbs to higher altitudes?
a) Henry’s law
b) Raoult’s law
c) Osmotic pressure
d) Relative lowering of atmospheric pressure
Explanation: Henry’s law states that the partial pressure of a gas in vapor phase varies directly with its mole fraction in the solution. At higher altitudes the partial pressure of O2 decreases hence the decrease in its concentration which causes difficulty in breathing.
9. What is the concentration of N2 in a fresh water stream in equilibrium with air at 298 K and 1 atmosphere? Given the value of KH for N2 = 0.00060 mole/kgbar.
a) 0.0474 g/kg
b) 0.0005 g/kg
c) 1316.7 g/kg
d) 13.3 g/kg
KH = 0.00060 mole/kgbar
PN2 = mole fraction of N2 x Pair (from Dalton’s law)
Air consists of 79 mole% N2 and 21 mole% O2.
PN2 = 0.79 x 1 bar= 0.79 bar
Henry’s law –PN2x KH= solubility of N2
0.79 bar x 0.00060 (mole/kgbar) = solubility of N2
Solubility of N2 = 4.74 x 10-4 moles of N2/kg water
Converting moles of N2 to kg of N2 :
Solubility of N2 = 4.74 x 10-4 mole x 28 kg/mole = 0.0133 kg N2/kg water = 13.3 g N2/kg water.
10. What is the substance, present in a larger quantity that tends to establish homogenous bonds with a foreign substance, introduced in smaller quantity?
Explanation: A solution is made up of two parts, the solute and the solvent. Solvent is present in larger quantity which dissolves a solute. The process of dissolution involves formation of homogeneous bonds between the particles of solvent and solute. E.g. salt-water solution is made by dissolving salt, NaCl (solute) in water (solvent).
11. At NTP, the solubility of natural gas in water is 0.8 mole of gas/kg of water. What is the Henry’s law constant for natural gas?
a) 8 kN/m2
b) 7.90 x 10-3 Pa
c) 71.36 bar
d) 105 mmHg
Solubility of natural gas, S = 0.8 mole of gas/kg of water = 0.8 molal
Hence, moles of natural gas in mixture, nNG = 0.8 mole
At NTP, pressure, PNG = 1.01325 bar
Number of moles of water in 1000 g, nw = mass/molar mass
nw = 1000g / (18g/mole) = 55.56 mole
Mole fraction of natural gas in the mixture, XNG = nNG/ (nNG + nw)
XNG = 0.8/(0.8 + 55.56) = 0.0142
Using Henry’s law PNG = KH x XNG
KH = PNG/XNG = 1.01325 bar/0.0142 = 71.36 bar.
12. What is the solubility product expression for silver chromate dissolving in water?
b) [Ag+]2 [Cr2O72-]2
c) [Ag+]2 [Cr2O42-]2
d) [Ag+]2 [CrO42-]2
Explanation: The formula for silver chromate is Ag2CrO4. On the other hand, silver dichromate is formulated as Ag2Cr2O7. If a compound is represented as AXBY then the solubility product expression is written in terms of its molar concentration as [A+]X [B–]Y. Similarly, the solubility product expression for Ag2CrO4 is given as [Ag+]2 [CrO42-]2.
13. What is the molar solubility product for V3(PO4)5 in terms of KSP?
a) S = (KSP/84375)1/8
b) S = KSP1/8
c) S = (KSP/15)1/8
d) S = (KSP/108)1/8
Explanation: The dissociation reaction is represented as V3(PO4)5 → 3V5+ + 5PO43-
If S is the solubility of V5+ and PO43- ions then KSP = [3V5+]3 [5PO43-]5, where the square brackets indicate the molar concentrations of the ions in the solution. KSP can then be written as KSP = [3S] 3[5S] 5 = 33 x 55 x S8 gives KSP= 84375 x S8.
Therefore, on rearranging, S = (KSP/84375)1/8.
14. What characteristic of water accounts for its unique properties as a solvent?
d) Low viscosity
Explanation: Water is a universal solvent. It has the ability to dissolve the greatest number of substances than any other solvent. The highly polar nature accounts for this special feature as the water molecule bears a slightly positively charged hydrogen ion and two highly negatively charged oxygen ions. Since, it becomes attracted to many different types of molecules it is known as the ‘universal solvent’.
15. Which of the following compound releases heat when dissolved in water?
a) Barium chloride
b) Ammonium chloride
c) Lead chloride
d) Calcium chloride
Explanation: Out of the given options calcium chloride is the only salt which releases heat upon dissolving. Barium chloride and ammonium chloride undergo endothermic dissolution which decreases the temperature of water. However, lead chloride is an insoluble salt and does not dissolve.
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