1 / 20

Chem. 31 – 9/8 Lecture

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

kaitlin-callery
Download Presentation

Chem. 31 – 9/8 Lecture

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chem. 31 – 9/8 Lecture

  2. 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

  3. Traditional vs. Modern Methods

  4. 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

  5. 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)

  6. 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

  7. 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)

  8. 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)

  9. Unit Conversion – Example Problem • Convert the density of lead from g/cm3 to kg m-3 if density = 11.7 g cm-3.

  10. Concentration Units • General form

  11. Most Commonly Used Concentration Units • Molarity (M) • Mass Fraction (also valid for solids as mass analyte/mass sample)

  12. Most Commonly Used Concentration Units • Mass Fraction – continued • Other Units: Mass/volume units (e.g. mg/mL)

  13. 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

  14. 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?

  15. Preparing Solutions • From scratch 1. Solid to flask 2. Add liquid, dissolve 3. Fill to line

  16. 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

  17. Preparing Solutions • By Dilution 1. Pipet liquid 2. Add liquid, fill to mark

  18. 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

  19. 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)

  20. 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

More Related