CHM 108 Suroviec Spring 2014 Chapter 4 Part 2
Jan 03, 2016
I. Solution Stoichiometry
According to the following reaction, how many moles of Fe(OH)2 can form from 175.0 mL of 0.227 M LiOH solution? Assume that there is excess FeCl2.
FeCl2(aq) + 2 LiOH(aq) → Fe(OH)2(s) + 2 LiCl(aq)
Determine the number of grams H2 formed when 250.0 mL of 0.743 M HCl solution reacts with 3.41 x 1023 atoms of Fe according to the following reaction.
2 HCl(aq) + Fe(s) → H2(g) + FeCl2(aq)
II. Aqueous Solution and Solubility
Consider salt dissolving in water and sugar dissolving in water.
A. Electrolyte
The way ionic compounds vs. molecular compounds dissolve in water shows the difference between types of solution.
A. Electrolyte
Electrolytes – ions that act at charge carriersSolutes that completely dissociate into ions
are called strong electrolytes
B. Solubility of Ionic Compounds
Most ionic compounds when dissolved in water the solute breaks into ions.
Not true for all ionic compounds
III. Precipitation Reactions
Precipitate: insoluble solid that separates from solution where no solid existed before reaction
Hard water contains Ca2+ and Mg2+
Laundry detergent contains Na2CO3
Examples
1. silver nitrate and potassium chloride2. lead (II) nitrate and potassium chromate3. potassium chromate and silver nitrate4. sodium carbonate and copper (II) chloride5. nickel (II) chloride and potassium hydroxide
IV. Molecular and Ionic Equations
A. Molecular EquationsConsider the following equation:CaCl2 (aq) + Na2SO4 (aq) CaSO4 (s) + 2NaCl
(aq)
B. Ionic Equations
In these equations, see that some of the ions are present on both sides of the arrow
Example
Given:2AgNO3(aq) + MgCl2(aq) 2AgCl (s) + Mg(NO3)2 (aq)
What is the ionic equation? Net Ionic?
IV. Acid and Base Reactions
Bronstead definition of acid: proton donorBronstead definition of base: proton acceptor
A.AcidsHCl (aq) + H2O (l) → H3O+ (aq) + Cl- (aq)
H2SO4 (aq) H+ (aq) + HSO4
- (aq)HSO4
- (aq) H+ (aq) + SO42- (aq)
B. Bases
Proton acceptors
Strong bases ionize completely to OH-
NaOH (s) → Ca(OH)2 →
Weak bases ionize only partially NH3 (aq) + H2O ⇌
V. pH
Concentration scale for acids and bases
Vinegar: [H+] = 1.610-3MPure Water: [H+] = 1.010-7M Ammonia: [H+] = 1.010-11M
pH = -log[H+]
Determine the pH of the above. What is the trend of acids and bases?
VI. Acid-Base Titrations
Commonly used to determine the concentration of a dissolved species or its percentage in a mixture
Titration Measuring the volume
of a standard solution (known concentration) needed to react with a measured quantity of a sample
Titrant (in the buret)
Analyte (in the Erlenmeyer flask)
VI. Acid-Base Titrations
Equivalence point is where the number of moles of acid equals the number of moles of base
The endpoint is indicated by a color change in the acid-base indicator
Example
1. What volume (in mL) of a 1.420 M NaOH solution is required to titrate 25.00 mL of a 4.50 M H2SO4 solution?
2. What volume (in mL) of 0.955 M HCl is required to titrate 2.152g of Na2CO3 to the equivalence point?
VI. Redox Reactions
A. Oxidation Numbers Needed when we are looking at reactions
between 2 nonmetals. The oxidation number of an atom in a
compound is the “charge” that it would have it all shared electrons were assigned to the atom with higher electronegativity.
III. Oxidation-Reduction Reactions
Short name: Redox reactionsElectron exchange
Oxidation is a loss of electrons Reduction is a gain of electrons