Louisiana Tech University, Chemistry 102 POGIL Exercises
Chapter 12(1). Solutions: Solutes and solution process
Why?
Many types of solutes (gases, liquids, solids) in solution find many applications. E.g. are CO2 in
soft drinks, salt to melt ice, and water transport through osmosis in plants. Therefore, it is important to
understand the properties of solution and solution process. The solubility of solutes in solvent depends
on the balance of intermolecular forces, and the enthalpy (heat) & entropy (order) changes for in the
solution. You need a conceptual understanding of these processes in order to predict solution behavior
and improve your critical thinking skills.
Learning Objectives
Understand chemical solution process and properties
 Solubility and intermolecular forces
 Enthalpy and entropy in dissolving gases, liquids and solids
 Solubility and Equilibrium: Applying Le Chaterlier’s principle
 Effect of temperature on solubility
 Effect of pressure in dissolving gases in liquids: Henry's Law (12.4)
 Describe the compositions of solutions in terms of weight percent, mass fraction, parts per million,
parts per billion, parts per trillion and molarity (Section 12.5).
Success Criteria
1. Predict solubility based on properties of solute and solvent (Section 15. 1).
2. Interpret the dissolving of solutes using enthalpy and entropy changes (Section 15.2).
3. Differentiate among saturated and supersaturated solutions (Section 15.3).
4. Describe how ionic compounds dissolve in water (Section 15-3).
5. Predict how temperature affects the solubility of ionic compounds (Section 15.4).
6. Predict the effects of T and P on the solubility of gases in liquids (Section 15.4-5).
Resources
Chemistry: A Molecular Approach, 2nd Edition-Nivaldo J. Tro - Pearson Prentice Hall
Prerequisites
Differentiate polar and nonpolar covalent compounds and ionic compounds.
Polar and nonpolar molecules: “like dissolves like.”
Intermolecular forces: hydrogen bonding, dipole-dipole and London dispersion.
Molality(m) and Mole fraction
New Concepts
Solubility Intermolecular Forces
The three types of forces between the solute and the solvent are solute-solute and solventsolvent and solvent-solute must be considered in the solution process. These interactions could be ionion, ion-dipole, hydrogen bond, dipole-dipole between ionic and/or polar compounds. They could be
London dispersion forces between non-polar molecules of the solvents and/or the solute.
Enthalpy Factors
Covalent compounds
Enthalpy of solution, Hsoln: Could be broken into three steps: Hsoln=H1+H2+H3
1. Breaking solute-solute (energy is absorbed, H1)
2. Breaking solvent-solvent (energy is absorbed, H2)
3. Making solvent-solute attractions (energy is released, H3)
Ionic compounds
1. Breaking solute-solute (energy is absorbed, H1) related to lattice energy (Hllattice) for ionic solids
2. Breaking solvent-solvent (energy is absorbed, H2)
3. Making solvent-solute attractions between ions and water dipoles (energy is released, H3)
Appropriate equation for the heat of solution for ionic compound is:
Hsoln = Hlattice +Hhyd
Hlattice is defined as the energy required separate ions in the solid to gaseous ions.
Hhyd is defined as the energy released when gaseous ions are put in water solution.
Hhyd=Hhyd(cations)+Hhyd(anions),
Entropy Factors
Entropy of solution, Ssoln: Could be broken into three steps: Ssoln =Sfinal-Sinitial
Sfinal = entropy of solution; Sinitial = entropy of solute (S1) + entropy of solvent (S2)
1. Entropy solute (S1)
2. Entropy of solvent (S2)
3. Entropy of solution (S3 or Sfinal)
4. Entropy solution: Ssoln=Sfinal-Sinitial= S3 -(S1 + S2)
Combined Enthalpy and Entropy Effects
Effect of both Hsoln and Ssoln on solubility:
Gsoln = Hsoln -TSsoln
As you will learn more in chapter 17,
Gsoln, Gibbs free energy (G) for the solution process should be negative if the solution process is
spontaneous.
Either Hsoln is – or Ssoln + situation would make Gsoln, -(negative).
Summary of observations during solution process
•
•
•
•
Materials with similar polarity are soluble in each other. Dissimilar ones are not.
Polar substances with similar forces are likely to be soluble in each other.
Non-polar solutes dissolve in non-polar solvents.
Stronger solute-solvent attractions favor solubility, stronger solute-solute or solvent-solvent attractions
reduce solubility.
• Negative Hsoln and positive Ssoln favors solubility. With a positive Hsoln only when Ssoln is positive
and temperature is high enough to make Gsoln Negative material will be soluble.
Non-polar solute -Non-polar solvent: Solid iodine (I2) dissolves in liquid bromine (Br2).
Non-polar solute - Polar solvent: O2, N2, H2, and CO2 are not very soluble in water.
Polar Solute - Polar Solvent- Solute (NH3) and solvent (H2O) dissolves readily.
Ionic Solute - Polar Solvent- NaCl dissolves in water readily
Solution terminology
Miscible - liquids that dissolve in each other. Immiscible - liquids that do not dissolve.
Saturated solution-A solution that contains as much it can hold.
Unsaturated solution-A solution that contains less than maximum amount.
Supersaturated solution-A solution that contains more than maximum amount.
Temperature and Pressure Effects on Solubility:
Liquid and solid solutes: Pressure has no effect. Temperature effect depends on Hsoln.
Pressure and Dissolving Gases in Liquids: Henry's Law
Sg = kHPg; where Sg is the solubility, kH is the Henry’s the Law constant,
Pg is partial pressure of gas
Effect of temperature and pressure on solubility of solutes: could be explained in terms of La
Chaterlier principle applied to solubility equilibrium.
Solution concentration:
a) Molarity (M): moles of solute /Liters of solution
b) Molality (m): moles of solute /kg of solvent
c) Mole fraction (a): moles of solute (a)/solvent(b)/ moles of a + b
d) Mass percent (% weight): (mass of solute/mass of solution)*100= w/w%
e) Volume percent (% volume) :(volume of solute/volume of solution)*100= v/v%
f) "Proof"; 2 x v/v%
g) ppm and ppb: (mass of solute/mass of solution)*106, ppb= 109
Chapter 12 GHW#1 Printed Name:_____________________ Group Name:__________
Key Questions
1. What are the main factors affecting a solubility of a solute in a solvent?
2. Arrange the following inter-particles forces in liquids and solids in the order of increasing strength:
ion-ion, ion-dipole, hydrogen bond, dipole-dipole and London dispersion
3. Identify the most important type of inter-particle force for each of the following compounds:
a) NaCl(s) or NaCl(l)
b) N2(l) or N2(s)
c) N2(g)
d) Na(s) and Na(l)
e) H2O(l) or H2O(s)
f) CH3CH2OH(l) or CH3CH2OH(s)
4. Which of the above inter-particle force could be named as intermolecular force?
5. What types of inter-particle forces (solute-solute:H1, solvent-solvent: H2, solvent-solute:H3)
are involved when
a) CH3CH2OH(l): dissolved in water: H1 =
; H2 =
For covalent compounds: Hsoln=H1+H2+H3
;H3=
b) Na2SO4(s) dissolved in water: H1 =
;H3 =
; H2 =
Ion-ion inter-particle forces in solids are called Lattice Energy. ( this is related to H1)
Ion-water inter-particle forces are called Hydration Energy (this is related to H2 and; H3)
For ionic compounds; Hsoln = Hlattice +Hhyd
6. Assign the entropy (most +, + or least +) for solute:S1, solvent: S2, solution(solvent-solute):S3,
following: (Indicate which one is highest, intermediate and lowest order)
a) CH3CH2OH(l): dissolved in water: S1 =
; S2 =
;S3=
b) For Na2SO4(s) dissolved in water:
; S2 =
;S3 =
S1 =
7. Why sand is insoluble in both polar and nonpolar solvents?
8. How does temperature and pressure affect the solubility of following?
a) NH4NO3(solid) in water with positive Hsoln:
b) CO2 gas in water:
9. Deep sea divers may experience a condition called the "bends" if they do not readjust slowly to the
lower pressure at the surface. Using the diagram on pressure dependence solubility of gases on water
explain this phenomenon.
10. Define following solution concentration units:
a) Molarity (M)
b) Molality (m)
c) Mole fraction (a)
d) Mass percent (% weight)
e) Volume percent (% volume)
f) "Proof"
g) ppm and ppb
11. Compare the advantages and disadvantages of these solution concentration parameters.
12. Determine the number of moles of solute present in 416 mL of 3.75 M HBr solution.
(Atomic weights: Br = 79.9, H = 1.008).
13. Determine the mass (g) of solute required to form 25 mL of a 0.1881 M H2O2 solution. (Atomic
weight - O = 16.00, H = 1.008).
14. A concentrated solution of AgNO3 is 21.9% by weight and the density is 1.220 g/cm3. How many
grams of the solution are required to prepare 150.0 mL of a 0.200M solution?
(Atomic weights: Ag = 107.87, N = 14.01, O = 16.00).
15. A solution of carbon tetrachloride, CCl4, in benzene (C6H6) is 0.010 m. What mass (g) of CCl4 is in
50.0 g of benzene?
(Atomic weights: C = 12.01, H = 1.008, Cl = 35.45).