Types of Solution

1
Types of Solution Reactions

• Precipitation Reactions (also called
  double-displacement reaction)
• Acid-Base Reactions
• Oxidation-Reduction Reactions
• System most commonly used by practicing chemists.

2
Precipitation Reactions

• When two solutions are mixed, an insoluble
  substance (precipitate) sometimes forms.
• In other words, a solid forms and separates from
  the solution.

• Example When a yellow aqueous solution of
  K2CrO4 (aq) is added to a colorless aqueous
  solution of Ba(NO3)2, a yellow solid forms.
• What is the equation that describes this
  reaction?
• The reactants have been described K2CrO4 (aq)
  and Ba(NO3)2 (aq).
• Can we predict the products?
• If so, what is the yellow solid?

3

• In the previous example Ba(NO3)2 (aq) and K2CrO4
  (aq) were mixed.
• Remember (aq) means dissolved in water and that
  when dissolved in water an ionic substance breaks
  apart into its constituent ions.

4
Ba(NO3)2 (aq) dissolved in H2O independent
Ba2 and NO3- ions in solution K2CrO4 (aq)
dissolved in H2O independent K and CrO42- ions
Reaction 2K (aq) CrO42- (aq) Ba2 (aq)
2NO3- (aq) ? products
5

• The mixed solution contains the ions
• K CrO2- Ba2 NO3-
• We know our reactants but what is the product or
  products?
• Predicting the products
• When ions form a solid compound, the compound
  must have a zero net charge. Thus the products
  of this reaction must contain both anions and
  cations.
• Most ionic materials contain only two types of
  ions one type of cation and one type of anion
  (for example, NaCl, KOH, Na2SO4, Co(NO3)2).

6

• In our example, the possible combinations from
  the list of ions K, CrO42-, Ba2, and NO3- are
• K2CrO4 KNO3 BaCrO4 Ba(NO3)2

Reactant
Reactant

• Since K2CrO4 and Ba(NO3)2 are reactants our
  products must be KNO3 and BaCrO4.
• But which one is the yellow precipitate?

7

• Products KNO3 and BaCrO4
• Simple Rules for the Solubility of Salts in Water
  (p. 144)
• Most nitrate (NO3-) salts are soluble.
• Most chromate (CrO42-) are only slightly soluble.
• Thus BaCrO4 would be the precipitate.
• What happens to the K and NO3- ions?
• These ions are left in solution they do not form
  a precipitate in this amount of water.

8

• The overall equation for this precipitation
  reaction using the formulas of the reactants and
  products is
• K2CrO4 (aq) Ba(NO3)2 (aq) ? BaCrO4 (s) 2KNO3
  (aq)
• As long as water is present, the KNO3 remains
  dissolved as separated ions.

9

• Memorize the solubility rules in Table 4.1 on
  page 144.
• The phrase slightly soluble used in the
  solubility rules means the tiny amount of solid
  that dissolves is not noticeable.
• The solid appears to be insoluble to the naked
  eye.
• Thus the terms insoluble and slightly soluble are
  often used interchangeably.

10
Describing reactions in solution

• Overall or formula equation
• K2CrO4 (aq) Ba(NO3)2 (aq) ? BaCrO4 (aq) 2KNO3
  (aq)
• Complete ionic equation
• 2K (aq) CrO42- (aq) Ba2 (aq) 2NO3 (aq) ?
• BaCrO4 (s) 2K (aq) 2NO3 (aq)
• In a complete ionic equation, all substances that
  are strong electrolytes are represented as ions.

11

• 2K (aq) CrO42- (aq) Ba2 (aq) 2NO3 (aq) ?
• BaCrO4 (s) 2K (aq) 2NO3 (aq)
• The complete ionic equation shows that only some
  of the ions participate in the reaction.
• Notice the K and NO3 ions are the same before
  and after the reaction.
• They are called spectator ions.
• Net ionic equation
• Ba2 (aq) CrO4 (aq) ? BaCrO4 (s)
• A net ionic equation shows only those solution
  components that are directly involved in the
  reaction.

12

• Three Types of Equations are used to Describe
  Reactions in Solutions
• The formula equation gives the overall reaction
  stoichiometry but not necessarily the actual
  forms of the reactants and products in solution.
• The complete ionic equation represents as ions
  all reactants and products that are strong
  electrolytes.
• The net ionic equation includes only those
  solution components undergoing a change.
  Spectator ions are not included.

13
Acid-Base Reactions

• Arrhenius Definition of Acid and Base
• Acid produces H ions when dissolved in water
• Base produces OH- ions when dissolved in water
• More general definition of acids and bases came
  from Johannes N. BrØnsted (1879-1947) and Thomas
  M Lowry (1874 1936).
• An acid is a proton (H) donor.
• A base is a proton (H) acceptor.
• Includes bases that do not contain OH- ions.

14

• What happens in an acid-base reaction?
• Suppose we mix an aqueous solution of HCl with an
  aqueous solution of NaOH.
• The combined solution contains the ions H, Cl-,
  Na, and OH-.
• We have H and OH- ions which do not exist in
  large quantities in solution so they combine to
  give H2O which is a nonelectrolyte.

15

• Net Ionic Equation when we mix HCl (aq) and NaOH
  (aq)
• H (aq) OH- (aq) ? H2O (l)

16

• What if we mix solutions of an acid that is a
  weak electrolyte with a strong base?
• Remember in solution weak electrolytes do not
  dissociate to any great extent.
• Lets mix together acetic acid (HC2H3O2), a weak
  electrolyte, and potassium hydroxide (KOH), a
  strong base.
• In solution we would have HC2H3O2, K ions, and
  OH- ions.
• We know that KOH is soluble so no precipitation
  occurs.
• What about a reaction between OH- which is a
  proton acceptor and a proton donor, HC2H3O2?
• The OH- ion has a strong affinity for protons so
  it can strip them from the HC2H2O3 molecules.
• The net ionic equation is
• OH- (aq) HC2H3O2 (aq) ? H2O (l) C2H3O2 (aq)

17
Acid-Base Titrations

• Volumetric analysis technique for determining
  the amount of a certain substance by titration.
• Titration involves delivery (from a buret) of a
  measured volume of a solution of known
  concentration (titrant) into a solution
  containing the substance being analyzed (the
  analyte).
• The titrant contains a substance that reacts in a
  known manner with the analyte.

18

• The point in the titration where enough titrant
  has been added to fully react with the analyte is
  called the equivalence point.
• This point is marked by the use of an indicator.
• An indicator is a substance that changes color
  based on the pH of its surroundings.
• The point where the indicator changes color is
  called the endpoint of the titration.
• The goal is to choose an indicator that allows
  the endpoint and the equivalence point to be very
  close together.

19

• Acid-Base Titration
• Commonly used indicator is phenolphathalein.
• Phenolphathalein is colorless in acidic solution
  and pink in basic solution.

Analyte before Titration
Too Far!!! Too Much Titrant Added
Proper Endpoint