Chemistry Chapter 14

1
Chemistry Chapter 14

• Mixtures and Solutions

2
14.1 Types of Mixtures

• Objectives
• 1. Compare the properties of suspensions,
  colloids, and solutions
• 2. Identify types of colloids and types of
  solutions
• 3. Describe the electrostatic forces in colloids

3
Suspensions, Colloids and Solutions

• Recall that a mixture is a combination of two or
  more substances in which each substance retains
  its chemical properties
• Heterogeneous mixtures do not blend smoothly
  throughout
• Suspensions and colloids are heterogeneous
• Def a suspension is a mixture containing
  particles that settle out if left undisturbed
• Suspensions can be filtered to pull out the
  suspended particles

4
Electrostatic Forces

• Def a colloid is a heterogeneous mixture of
  intermediate sized particles
• An example is homogenized milk in which the
  components cannot be separated by settling or
  filtration
• If you stir an electrolyte into a colloid, the
  dispersed particles clump together destroying the
  colloid
• Heat also destroys a colloid because it gives
  energy to colliding particles
• Def Brownian motion is the erratic random
  movement of colloid particles

5
Types of Solutions

• Def the Tyndall effect is the phenomenon where
  colloidal particles scatter light even if the
  solution appears clear to the eye
• Recall that a solution is a homogeneous mixture
  that contain a solute and a solvent
• The solute is the substance that dissolves
• The solvent is the dissolving medium
• Solutions can be solid, liquid or gas though most
  exist as liquids
• Def soluble substance dissolves in a solvent
• Def miscible liquids dissolve into each other in
  any proportion
• Def insoluble substances do not dissolve

6
14.2 Solution Concentration

• Objectives
• 1. Describe concentration using different units
• 2. Determine the concentration of solutions
• 3. Calculate the molarity of a solution

7
Units of Concentration

• Def the concentration of a solution is a measure
  of how much solute is dissolved in a specific
  amount of solvent or solution
• Concentration is qualitative if you use words
  such as dilute or concentrated
• Most solutions are described quantitatively using
  percent by mass ( mass), percent by volume (
  vol), molarity (mol/L) and molality (mol/kg)

8
How to Calculate Concentration

• Percent by mass mass of solute x 100
• mass of solution
• Percent by volume vol of solute x 100
• vol of
  solution
• Molality (m) moles of solute
• kg of solvent
• Molarity (M) moles of solute
• liters of
  solution
• We will focus on molarity

9
Molarity

• Use this equation M moles of solute
• 
  liters of soln
• Q What is the molarity of an aqueous solution
  containing 40 g of glucose (C6H12O6) in 1.5 L of
  solution
• 1. find the number of mol of glucose
• 2. divide mol by liters

10

• Q How would you prepare 1L of 1.5 M solution of
  NaCl?
• 1. of means multiply, so 1 L x 1.5 mol 1.5
  mol
• 
  L
• 2. change mol to grams, so 1.5 mol x 58g 85 g
• 
  mol
• 3. so take 85 g NaCl, place it in a 1 L
  volumetric flask and fill to the line with H20

11

• Since moles of solute M x liters, we have a new
  equation M1V1 M2V2 where M1 and V1 are the
  molarity and volume of stock solution M2 and V2
  are the molarity and volume of dilute solution
• This equation lets you take stock solution and
  make less concentrated dilutions
• Q What volume of 3.0 M KI stock solution would
  you use to make 0.3L of 1.25 M solution?

12

• Q What volume of 3.0 M KI stock solution would
  you use to make 0.3L of 1.25 M solution?
• It is very important to keep your 1s and 2s
  straight when plugging into this equation
• of means multiply, so
• 1. (0.3L)(1.25 mol/L) X (3.0M)(x)
• 2. solve
• Challenge If 0.5L of 5.00 M stock solution of
  HCl is diluted to make 2.0 L of solution, how
  much HCl, in grams, is in the solution?

13

• Def mole fraction is the ratio of the number of
  moles of solute or solvent in solution to the
  total number of moles of solute solvent
• XA nA XB nB
• nA nB nA nB
• Mole fraction is dimensionless there are no
  units in the answer because everything cancels
  out
• Q What is the mole fraction of NaOH in an
  aqueous solution that contains 28 of NaOH by
  mass? (Hint assume 100 g, change g to mol and go
  from there)

14
14.3 Factors Affecting Solvation

• Objectives
• 1. Describe how intermolecular forces affect
  solvation
• 2. Define solubility
• 3. Understand what factors affect solubility

15
Intermolecular Forces

• Attractive forces exist among the particles of
  all substances
• When a solid solute is placed in a solvent, the
  solvent particles completely surround the surface
  of the solid solute
• If attractive forces between the solute and the
  solvent particles are greater than the attractive
  forces holding the solute particles together, the
  solvent particles pull the solute particles apart
  and surround them

16

• The surrounded solute particle moves away from
  the solid solute and out into solution
• Def solvation is the process of surrounding
  solute particles with solvent particles to form a
  solution
• like dissolves like is the general rule to
  determine whether solvation will occur in a
  specific solvent
• Bonding and polarity play a role
• Agitation (stirring or shaking), surface area
  (greater surface area dissolves faster)
  temperature (higher temp increases solvation) all
  affect solvation

17
Solubility

• Solubility depends on the nature of the solute
  and solvent
• Def an unsaturated solution is one that contains
  less dissolved solute for a given temperature and
  pressure than a saturated solution
• More solute can be dissolved in an unsaturated
  solution

18
Factors that Affect Solubility

• Def a saturated solution contains the maximum
  amount of dissolved solute for a given amount of
  solvent at a given temperature and pressure
• Solubility is affected by raising the temperature
• For gases, solubility decreases with increased
  temp
• For liquids, solubility increases with increased
  temp due to greater energy and increased particle
  collisions

19

• Def a supersaturated solution contains more
  dissolved solute than a saturated solution at the
  same temperature
• Not every substance can become supersaturated
• To make a supersaturated solution, add solute at
  a high temperature and cool it slowly allowing
  excess solute to remain in solution
• Henrys law states that at a given temp, the
  solubility (S) is directly proportional to the
  pressure (P)
• S1 S2 where S is given in g/L P in any
  units
• P1 P2