2-Concept and Calculations Review with Equilibrium Concepts
Introduction to Analytical Chemistry
Focus on important chemical concepts and chemical equilibrium.
2A Some Important Units of Measurement
2A-1 SI Units
Adoption of the International System of Units (SI) worldwide.
Based on seven fundamental base units.
Derived units include volts, hertz, coulombs, and joules.
Table 2-1 SI Base Units
Mass: kilogram (kg)
Length: meter (m)
Time: second (s)
Temperature: kelvin (K)
Amount of substance: mole (mol)
Electric current: ampere (A)
Luminous intensity: candela (cd)
Table 2-2 Prefixes for Units
Giga- (G) = 10^9
Mega- (M) = 10^6
Kilo- (k) = 10^3
Deci- (d) = 10^-1
Centi- (c) = 10^-2
Milli- (m) = 10^-3
Micro- (μ) = 10^-6
Nano- (n) = 10^-9
Pico- (p) = 10^-12
Femto- (f) = 10^-15
Atto- (a) = 10^-18
Additional Notes on SI Units
Ångstrom (Å) is a non-SI length unit for very short radiation (1 Å = 0.1 nm).
2A-2 The Mole
The mole (mol) is the SI unit for the amount of a chemical species.
Associated with a chemical formula representing Avogadro’s number (6.022 x 10^23) of particles.
Molar mass (M) is the mass of one mole of a substance in grams.
Distinguishing Between Mass and Weight
Mass is the same regardless of location; weight varies based on gravitational force.
Example: The weight of a space suit on the Moon is 1/6th of its weight on Earth due to lower gravity; however, the mass remains the same.
Molar Mass vs. Molecular Mass
Molar mass of 12C is defined as 12 g (the mass of 6.022 x 10^23 atoms).
The molar mass of elements equals their atomic mass in amu (e.g., oxygen: 15.9994 amu = 15.9994 g).
Sample Problems
Problem 1
Given mass of benzoic acid (MW=122.1 g/mol) in pure acid: 2.00 g
Moles = 0.0164 mol; millimoles = 16.4 mmol.
Problem 2
Mass of Na+ from 25.0 g of Na2SO4 (142.0 g/mol): 8.10 g Na+.
2B Solutions and Their Concentrations
2B-1 Expressing Solution Concentrations
Molar concentration (c_x) = moles of solute per liter of solution (mol L^-1).
Analytical Molarity
Total moles of solute in 1 L of solution (e.g., 1.0 M H2SO4 prepared from 98 g of H2SO4).
Equilibrium Molarity
Concentrations of species at equilibrium; e.g., sulfuric acid dissociating into ions.
The Dilution Formula
C₁V₁ = C₂V₂ (concentration and volume before and after dilution).
Sample Calculation Problems
Sample Problem 1
Molar concentration of ethanol in 2.30 g in 3.50 L: C = 0.0143 M.
Sample Problem 2
Preparation of 500 mL of 0.0740 M Cl- from BaCl2•2H2O (mass = 4.52 g).
Sample Problem 3
Moles in 30.0 g of NaHCO3: 0.3571 mol.
Sample Problem 4
Grams of BaCl2•2H2O needed for 0.108 M BaCl2 in 2.00 L: 52.8 g.
2B-1 Expressing Solution Concentrations
Percent Concentration
Concentrations expressed in percent parts per hundred.
Parts Per Million and Billion
Common conversions for lower concentrations (ppm, ppb).
Sample Problems on Concentrations
Sample Problem 1
Volume of 0.5479 M HCl needed for 100 mL of 0.1000 M HCl: 18.25 mL.
2B-2 Density and Specific Gravity
Density: mass per unit volume (kg/L or g/mL).
Specific gravity: ratio to water's mass.
Sample Problem on Density
Molar concentration of HNO3 from a 70% (w/w) concentration: 16 M.
2C Chemical Stoichiometry
Definition
Stoichiometry: mass relationships among reacting chemical species.
2C-1 Empirical and Molecular Formulas
Empirical formula: simplest ratio of atoms.
Molecular formula: actual number of atoms in a molecule.
2D The Chemical Composition of Aqueous Solutions
Classification of Electrolytes
Strong electrolytes ionize completely; weak electrolytes partially.
2D-2 Describing Acids and Bases
Brønsted and Lowry Theory: acids donates protons; bases accept protons.
Amphiprotic Species
Species acting as both acid and base.
2E Chemical Equilibrium
Equilibrium State
Forward and reverse reaction rates are equal, leading to constant concentrations.
Equilibrium Constant Expressions
Describes concentration relationships among reactants and products.
Key Equilibrium Concepts
Sample Problems
Calculating concentrations, solubility products, dissociation constants for acids and bases.