Humboldt State University ® Department of Chemistry

Richard A. Paselk

Science 331 - Fall 2005

"Chemistry" Final Study Guide

Second Session

Review Midterm Study Guide. Expect 50% of Final to be material from the Midterm Study Guide.

Review web notes, examples etc.

Terms (be able to define/describe): Define/describe: solution, salt, solvent, solute, saturated solution, phase change, boiling, solid, boiling point (bp), heat of vaporization/condensation, melting point (mp), heat of melting/solidification, Arrhenius acid/base definition, Brønsted acid/base definition, "empirical" acid/base definition, heating/cooling curve. Law of Conservation of Energy, temperature, mixture, pure substance, homogeneous mixture, heterogeneous mixture, energy, heat,

Be able to draw/interpret heating/cooling curves (for example, the plot for heating ice until it is turned to liquid water and then to steam, the cooling curve is symmetrical and oposite).

Chemical Reactions: Be able to balance simple equations by inspection such as we have done in class. Remember the important considerations of conservation of mass. For chemical equations, conservation of mass means that we must have the same numbers of the same kinds of atoms on both side of the equation.

Be able to predict the products and balance simple fuel oxidation reactions (burning). (e.g. CH₄ + 2 O₂ CO₂ + 2 H₂O)

Acids & Bases: What are acids? Bases? What are the charecters of acids and bases. Hydrogen ion, proton, hydroxide ion. Define/describe: Arrhenius acid model, Brønsted model, Empirical model, hydronium ion (H₃O⁺), strong acid/base (100% dissociated when < 1M), weak acid/base (less than 100% dissociated when < 1M).

• Acids and bases which you must know:
  • Acids: Hydrochloric acid = HCl; Nitric acid = HNO₃; S ulfuric acid = H₂SO₄; Acetic acid = CH₃COOH = HC₂H₃O₂
  • Bases: Sodium hydroxide = NaOH; Potassium hydroxide = KOH; Ammonium hydroxide = NH₄OH
• Be able to write equations for the dissociation of acids and bases (e.g. HCl H⁺ + Cl^-)
• the reaction of acids and bases (e.g. HCl + NaOH H₂O + Na⁺ + Cl^-)

Note that for "organic" acids (acids with carbon) we will see a common element = -COOH, a carbon with two oxygens, one of which has a hydrogen attached. The hydrogen on the oxygen is then the acidic hydrogen. (Alcohol, with a -COH is not acidic.)

pH and pH scale

• Note that acids have low pH (< 7), bases high pH (>7) and neutral solutions have a pH of 7 (in reality a range of pH values near 7 are generally considered neutral).
• pH scale commonly represented from 1 -14
  • pH 1 corresponds to 0.1 M hydrogen ion concentration (approximately the concentration of human stomach acid, or a 1:100 dilution of concentrated HCl ["pool acid"]).
  • pH 14 corresponds to 0.1 M hydroxide ion concentration (approximately the concentration of 4 grams of sodium hydroxide [lye] disolved in a liter of water).

The History of the Earth and Deep Time:

How old is the Universe? Earth? How long ago did the Precambrian end? What marks the end of the precambrian and the beginning of the currrent Eon? (The modern fossil record of multicellular animals with hard parts began with the Cambrian.) What are some of the major occurances in the Precambrian? Note the relative lengths of the major divisions in Universe/Earth history

What often happens to mark the end of a major geological period (mass extinction, e.g. the end of the Cambrian, or the Cretaceous).

Note that Precambrian occurances are listed in notes and Phanerozoic times are summarised on HSU NHM exhibits website.

How do we know how old things are?

Look at three different age ranges:

Universe

1. Stellar Life Cycle: Stars burn hydrogen at particular rates depending on how big (bright) they are. Oldest globular clusters stars with ages between 11 By and 18 By.
2. Hubble Constant: Universe is "expanding." That is all galaxies are going away. If calculate how long it has been since they were in same place, then Universe 12-14 By old by recent calculations.
3. WMAP Satellite: Measures of microwave background pattern, etc. Calculations give an age of 13.7 By ±1%.

Earth and Solar System

1. Rock layers. Layers in sedimentary rock generally will be seasonal, like tree rings. Again can extend range by looking for overlaps. Determined Earth must be 100's of millions of years old in nineteenth century.
   • Different biological organisms are characteristic of each time period-determine relationships of deposits by comparing organisms.
2. Glacial Ice. Count layers, like in tree rings (below). Very deep ice-fields go back over 200,000 years.
3. Radiometric dating. Depends on rate of decay of radioisotopes. For ancient time use long half-life isotopes such as ²³⁸U.

Archeology

1. Tree rings. Note that can go past oldest living tree if older wood which overlaps is available (e.g. in old buildings, preserved in bogs, at archeological sites). Limited to about 10,000 y so far.
2. Radiometric dating. Depends on rate of decay of radioisotopes. For "recent" times use short half-life isotopes such as ¹⁴C.

Be able to determine age of sample given amount decayed and half-life as done in class (Lecture 11).

Rates of Chemical Reactions

How are chemical reaction rates effected by temperature? concentration? Explain why each relationship should be true.

Gases

Gases are characterized by four properties

1. Amount of substance, n 
   1. In moles, where one mole is 6.03 x 10²³ particles. For gases, one mole =
      1. 6.03 x 10²³ atoms for Noble gases
      2. 6.03 x 10²³ molecules for other gases
2. Volume, V (in Liters)
3. Pressure, P (in atm, though often measured in mmHg)
4. Temperature (in K, where Kelvins = °C + 273)

Describe/define: Boyle's Law, Charles Law

Boyle's Law (PV = k)

• How does gas volume change with pressure?
  • Volume is inversely proportional to pressure.
    • Example: If a gas occupies 0.5 L at a pressure of one atmosphere, what will its volume be at two atmospheres? at one-half atmosphere?
      • Solution 1: For two atmospheres, P has doubled, so volume will be halved, V = 0.25 L.
        • Quantitatively, find constant, 0.5 * 1 = 0.5; V * 2 = 0.5, so V= 0.5/2 = 0.25L
      • Solution 1: For one-half atmosphere, P has halved, so volume will be doubled, V = 1 L.
        • Quantitatively, find constant, 0.5 * 1 = 0.5; V * 0.5 = 0.5, so V= 0.5/2 = 1L

Charles Law (V = k'T, where T is in absolute temperature, e.g. Kelvins).

• How does gas volume change with temperature?
• Volume is directly proportional to absolute temperature (temperature in Kelvins for the metric system).
  • Example: If a gas occupies 0.5 L at 27°C what will its volume be at 327°C? at 150 K?
    • Solution 1: Find initial and final temperatures; 27 + 273 = 300 K, 327 + 273 = 600 K
      • New temperature is double initial temperature, so volume will be double, V = 1 L.
    • Solution 2: Find initial and final temperatures; 27 + 273 = 300 K, 150 K
      • New temperature is half the initial temperature, so volume will be half, V = 0.25

 

How did the study of gases result in the concept of "absolute zero"? (Can't have negative volumes.)

Sci 331 Home

© R A Paselk

Last modified 2 December 2005