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Chem. 31 – 9/8 Lecture. Announcements. As far as I know the labs are full (sect. 3 still to add one person in 2 nd meeting) However, if you are high on the list to be added, check the labs again as space may open Homework and Quiz text problems: for your benefit, not to turn in
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Announcements • As far as I know the labs are full (sect. 3 still to add one person in 2nd meeting) • However, if you are high on the list to be added, check the labs again as space may open • Homework and Quiz • text problems: for your benefit, not to turn in • additional problems: for points (1.1 due this Wednesday • quiz on Wednesday • corrected diagnostic quiz also due Wednesday • quiz in lab next Thursday and following Monday
Chapter 1 – Measurements and Titrations No measurement is valuable unless it is given with units and some measure of uncertainty Units – Chapter 1 Uncertainty – Chapters 3 and 4
Units of Measure • Most Basic – SI base units (important ones) Measure Unit_____ Length meter (m) Mass kilogram (kg) (only one with multiplier) Time second (s) Temperature Kelvin (K) Amount Mole (mol)
Units of Measure • Directly Derived from Base Units • Volume: cube volume = l3 so units = m3 • Density = m/V so kg/m3 • Pressure = force(kg·m/s2)/area(m2) = kg/(s2·m) l
Units of Measure • Other metric units (not directly in SI units) • Density (g/cm3) • Pressure (Pascals or Pa = kg/(s2·m)) • Non-metric units (used commonly) • For pressure 1 atmosphere (atm) = 101300 Pa • English/Other system (not emphasized here)
Units of Measure • Metric Multipliers (ones you should know) Name Abbreviation Multiplier Kilo k x103 Centi c x10-2 Milli m x10-3 Micro m x10-6 Nano n x10-9 Analytical chemists like small quantities. An instrument that can detect 1 fg (1 x 10-15 g) is better than an instrument that can detect 1 pg (1 x 10-12 g)
Unit Conversion – Example Problem • Convert the density of lead from g/cm3 to kg m-3 if density = 11.7 g cm-3.
Concentration Units • General form
Most Commonly Used Concentration Units • Molarity (M) • Mass Fraction (also valid for solids as mass analyte/mass sample)
Most Commonly Used Concentration Units • Mass Fraction – continued • Other Units: Mass/volume units (e.g. mg/mL)
Conversion between Concentration Units – Example Problem What is the molarity of a H2O2 solution that is listed as 25% H2O2 by mass and has a density of 1.07 g mL-1? MW (H2O2) = 34.0 g mol-1
Preparing Solutions • From Scratch (direct from solids) Let’s say we want 100 mL of 0.100 M FeCl3. What equipment do we need? How do we make the solution?
Preparing Solutions • From scratch 1. Solid to flask 2. Add liquid, dissolve 3. Fill to line
Preparing Solutions • By Dilution What if we need 20.0 mL of 0.00200 M FeCl3? How do we make it? If direct by weighing, mass FeCl3 = 0.0065 g (not very accurate) By Dilution from 0.100 M FeCl3
Preparing Solutions • By Dilution 1. Pipet liquid 2. Add liquid, fill to mark
Stoichiometry • Stoichiometry refers to ratios between moles of reactants and products in chemical reactions • The ratio of moles of reactants and products is equal to the ratio of their stoichiometric coefficients Example: aA + bB ↔ cC + dD Moles A/moles B = a/b
Stoichiometry • Example problem: How many moles of H2O2 are needed to completely react with 25 mL of 0.80 M MnO4-? Reaction: 5H2O2(aq) + 2MnO4- +6H+↔ 2Mn2+ + 5O2(g) + 8H2O(l)
Stoichiometry • Remember: there are two (common) ways to deliver a known amount (moles) of a reagent: • Mass (using formula weight) • Volume (if molarity is known) • Titrations = A practical way of using stoichiometry with precise measure of added volume