Chapter 4: Calculations Used in Analytical Chemistry

CHE 321: Quantitative Chemical AnalysisDr. Jerome Williams, Ph.D.

Saint Leo University

Overview

• Units & SI System• Moles & Millimoles• Solutions: Expressing Concentration• Stoichiometry

Units & SI System

• Units convey information and serve as guide to solving problems

– Fundamental Units– Derived Units

Table 4-1 p63

Units & SI System

• Measurements based on SI system, which is metric system

– Metric Prefixes– Performing Unit Conversions (see Tutorials)

Table 4-2 p63

Moles & Millimoles

• Mass versus Weight

• Moles are the SI unit for amount of a substance.

• One mole of anything contains Avogadro’s number of particles (chemical formula)

p64

Moles & Millimoles

• Molar Mass is mass in grams of one mole of a substance.

• Calculate molar mass by summing atomic masses of all elements in formula.

• Often more convenient to use unit millimole (Note: 1 mmole is equivalent to 10-3 mole)

p65

Moles & Millimoles

• Review Examples 4.1 & 4.2

• Complete Tutorials

Solutions: Expressing Concentration

• Review definitions of analytical molarity, and equilibrium molarity

– Equilibrium concentrations expressed as molarity– Analytical concentrations use formal concentration

• Review Examples 4.4 – 4.6

• Review Tutorials

Solutions: Expressing Concentration

• Percent Concentration - review definitions & formulas for the following

– Mass (Weight)%– Volume %– Weight/volume %– Parts per Million (ppm)– Parts per Billion (ppb)

• Go over example problems & complete tutorials

Solutions: Expressing Concentration

• Review definitions of p-Functions

pX = - log [ X ]

Solutions: Expressing Concentration

• Review definitions of density and specific gravity

• Density = mass / volume

• M1 V1 = M2 V2

Figure 4-1 p74

Table 4-3 p74

Stoichiometry

• Quantitative relationship among reactants & products in a balanced chemical reaction.

• Review Empirical vs. Molecular Formulas• Review Structural Formulas

Figure 4-2 p76

Suggested Problems

• HW Set 2: 4.1, 4.4, 4.7-4.15 (odd)

• HW Set 3: 4.17, 4.20, 4.23, 4.31, 4.35