Pathway 4: Chapter 7 Study Pack

Part A: Properties of Solutions Answers
Part B: Dissolving Process
Part B1: Factors Affecting Rate of Dissolving Answers
Part C: Intermolecular Forces Answers
Part D: Units of Concentration of Solutions Answers
Part D1: Solution Preparation Problems Answers
Part V: Chapter 7 Vocabulary

Part A: Properties of Solutions
Back in Chapter 3 a solution was introduced as a homogeneous mixture of a solute and solvent and you included them in your matter chart for Part G of Chapter 3. A solution is defined as a homogeneous mixture of two or more substances. The two new words that are introduced are solute and solvent. Although we usually think of solutions to be liquids, Table 14.1 Corwin 6^th lists some common examples of solutions whose physical state correspond to that of a solvent.

Chapter 7 starts with six properties of a true solution which are not listed in chapter 4 as a separate list. You will write five of these six properties for Part A of Chapter 7 Path 4 Exam:

1. It is homogeneous mixture of two or more components, solute and solvent

2. It has variable composition, that is, the ratio of solute and solvent may be varied.

3. The dissolved solute is molecular or ionic in size

4. It may be colored or colorless but it is usually transparent

5. The solute remains uniformly distributed throughout the solution and will not settle out with time (every drop has exactly the same concentration)

6. The solute generally can be separated from the solvent by purely physical means (for example evaporation or distillation)

Part A: Solution Properties

List five of the six properties of a true solution:

(1)

(2)

(3)

(4)

(5)

(6)

Part B: Dissolving Process

Part B1: Factors Affecting Rate of Dissolving

Part B & B1 covers the dissolving process and a discussion of solubility and temperature plus solubility and pressure of a gas in a solution is as follows.

The following answers the first question:

State two factors greatly affecting the solubility of a gas in a liquid:

(1) Temperature (increased temperature of a solvent also generally increases the kinetic energy of the solute and the gas solute acquire more of a tendency to escape from the solvent. Therefore, Cooling the solvent increased the solubility of a gas in a liquid solvent.)

(2) Pressure (increasing the pressure (partial pressure) of a gas solute increases the solubility proportionally of that solute in the liquid (Henry’s Law)

The properties of liquids dissolved in liquids focus on the main property which is polarity. Now is the time to review polar covalent bonds chapter 6. Polar covalent bonds depend on the electronegativities of the two elements.

If two elements differ in electronegativity between 0.4 and 1.7, then polar covalent bonds are formed. If the difference between the two atoms is greater than 1.7 then ionization takes place. A solution containing ions must be dissolved by polar molecules as a solvent.

Next you must understand the three dimensional geometry of the molecules to determine if a molecule is polar. Molecules with polar covalent bonds have dipoles, which are vectors, created by the polar covalent bonds When they are summed, if there is a net moment of force the molecule is polar. However, it is possible for a compound to have polar covalent bonds and be nonpolar when the net summation of the vectors total zero.

The “Like Dissolves Like Rule” depends on the polarity of the molecules of the solute and the solvent (Table14.3 Corwin 6^th is the same as Table 13.3 on page 378..

What is the main factor affecting the solubility of a liquid in a liquid:

(3) Nature of the solute and solvent: the like dissolves like rule. The general principle that solubility is greatest when the polarity of the solute is similar to that of the solvent

From Corwin’s 6^th edition

The discussion of the dissolving leads to the rate of dissolving, which is the next question in Section B1 of Chapter 7 (They do not list #3 below.).

State four factors which governs the rate of dissolving a solid in a liquid:

1. Particle Size (increased surface area increases rate of solution i.e powders have greater surface area than crystals
and will dissolve faster)

2. Temperature (increased temperature of solvent generally increases rate of solution, except gases in liquids is opposite)

3. Concentration of Solution- when the solute and solvent are first mixed the rate of dissolving is at a maximum, as saturation approaches the rate of dissolving slows

4. Agitation or stirring-the effect of agitation is kinetic which increases the rate of solution.

Part B1: Factors Affecting Rate of Dissolving

State two factors greatly affecting the solubility of a gas in a liquid and explain:

(1)

(2)

What is the main factor affecting the solubility of a liquid in a liquid and explain the rule:

(3)

State four factors which governs the Rate of dissolving a solid in a liquid:

(1)

(2)

(3)

(4)

Part C: Intermolecular Forces

1. Describe the different type of interparticle forces that can occur between atoms, molecules, and ions.

2. Distinguish between the forces called intermolecular forces.

3. What forces are referred to as van der Waals forces?

4. Draw a flow chart or diagram to summarize these intermolecular forces and show an example.

Type of Interaction	Factors Responsible For Interaction	Approximate Energy (kJ/mol)	Example
Ion-dipole
Dipole-dipole
Hydrogen Bonding, X—H…:Y
Dipole-induced dipole
Induced dipole-induced dipole (London dispersion forces)

5. What are London Forces?

Part D: Concentration of Solutions
General Words:

Specific Words/Terms of Concentration:

There are three measurements of solutions in preparation problems of which two will be given and the third will be asked in Part D for preparing a solution in a laboratory. The three are: mass of solute, volume of solution (not volume of solvent-you should know the difference), and the concentration of the solution.

There are six methods of measuring the concentration of a solution: Molarity, Weight (Mass) Percent, Volume Percent, Molality, Parts Per Million, and Normality. Problems for Part D will focus mainly on Molarity, but Weight percent is also fair game. The other four methods of measuring concentration will not be asked in Part D.

Part D1: Preparation of Solutions Calculations

If the problem states the mass of the solute and the volume of the solution prepared is given, then the Molarity is unknown for one problem type. The other common problem is how to make a known volume of a known concentration of a solution and you have to find the mass.

1. How many grams of solute are needed to prepare 250 ml of a 0.0100 M KMnO₄?

2. 20 grams of AgNO₃ were placed in a 250 ml volumetric flask, calculate the Molarity of the Solution.