Additional Topics

Chromatography Chromatography is a separation technique used to separate components of a mixture, and this separation can be based on: Intermolecular forces (This is the one that would be tested on) Size Charge Paper chromatography: Here’s what’s needed: Chromatography paper (this is the stationary phase) A solvent/solution (this is the mobile phase) A mixture (usually a dye) A container to perform the chromatography, with a lid.

Here’s how it works: First place line in pencil about two centimeters from the bottom of the paper Next place a dot of dye (marker, ink, etc…) along the center of the line that you drew Next place the paper into solvent but make sure that the line, and dot are above the solvent. (Close the lid to allow solvent vapors to interact with the paper). Allow the solvent to travel through the paper until it reaches close to the end of the paper. Once the solvent travels through your mark, it will separate the dye into its constituent parts. After the solvent has reached its final point, draw a line with your pencil marking the distance that both the dye and the solvent traveled. Just based on the location of the dye, you can tell which component (based on color) is more attracted to the mobile phase. The color that travels the furthest has intermolecular forces most similar to the mobile phases…”likes dissolve likes”. The color that doesn’t travel as far is more attracted to the stationary phase (the paper). Next, you could calculate an Rf value (retention factor) = distance travels by the solute/distance travels by the solvent. A higher Rf indicates a higher attraction to the mobile phase.

Column Chromatography Here’s what’s needed: A chromatography column Glass wool (to prevent solids from flowing through) Sand (to help build a level surface of silica gel) Solvent (mobile phase: added before stationary phase to keep sand even.) Silica gel (stationary phase) Concentrated sample (A mixture to be separated). Here’s how it works: Set up the column Drain the mobile phase down to the stationary phase Add a concentrated sample to the column Drain the mobile phase to the top of the column Gently add additional mobile phase and the column is now ready to run.

Alloys Alloy– a metallic material that contains more than one element (Two or more metals, or a metal and a nonmetal). (information on pgs. 1082- 1086 of your text) Alloy Characteristics – stronger than their individual component metals, conductive (retain the “sea” of mobile electrons, but they become less malleable due to their new structure. The density tends to lie between the component metals. Often the surface of the metal alloy is changed through a chemical reaction…example, a chemically inert oxide layer in steel.

Types of Alloys Substitutional Alloys – One metal atom with a similar radii (usually within 15% of each other) substitutes for another in the crystal structure. Examples: A copper-nickel alloy contains two metal atoms with the same metallic radii 135 pm. Brass: copper and zinc Interstitial Alloys – small, usually nonmetallic, atoms fit in between the metallic atoms of a crystal. Examples: Steel: Iron, carbon, and other metals such as chromium, manganese, and vanadium.

AP Question! (c)

Work Here is the formula in your textbook: W = -PΔV P is the external pressure that the car piston pushes against When the gas expands within the piston. Use this conversion factor 101.3 J = 1 L atm for the following problem: A piston within a cylinder equipped with a piston expands with an external pressure of 1.58 atm. If the initial volume is 0.485 L and a final volume is 1.245 L, how much work, in J, is done? W = -1.58 atm (1.245 L – 0.485 L)= -1.20 L atm = -122 J

The Plan!!! Monday – Setting 90 min aside (Part 1 AP Exam) Tuesday – Setting 105 min aside (Part 2 AP Exam) Wednesday –Thursday – Go over the Mock AP Exams and Analyze Your Score and Posters Friday – Finish going over Mock AP analyze your overall score. Posters Final thoughts!