A Fatty Acid Monolayer: Determination of Avogadro's Constant

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Ngoc Pham
Chem162B
Lab #2: Trends in Periodic Table
Date: 01/10/2011
Lab partner: Ian Bauer
Result Section:
Table I: The solubility of the alkaline earth metal ions
| SO42-| CO32-| C2O42-| IO32-|
Mg2+| S| I| S| S|
Ca2+| I| S| S| I|
Sr2+| S| S| S| I|
Ba2+| I| I| I| S|

Key: I- insoluble, S-soluble
Table II: Color of water (Halide) and Halogen (Hexane) layers | Cl2| Br2| I2|
Hexane layer| Clear| orange| Pink |
Water layer | Clear, colorless| Light gold| Light yellow|

Table III: Reactivity of Halogen/Halide Combinations
| Cl-| Br-| I-|
Cl2| X| R| R|
Br2| NR| X| R|
I2| NR| NR| X|
Key: R-reaction occurred, NR-no reaction occurred, X-not tested (there should be no reaction) The redox reactions took place:
Cl2 (aq) + 2Br-(aq) → Cl-(aq)+ 2Br2(aq)
Cl2 (aq) + 2I-(aq)→ Cl-(aq)+ 2I2(aq)
Br2 (aq) + 2I-(aq)→ Br-(aq)+ 2I2(aq)

Answer questions:
Part A
1. Ba2+ > Sr2+ > Ca2+ > Mg2+

2. The ranking above does show a trend in the periodic table. Ba2+ forms the most precipitates in the experiment and shows up on the bottom of the period table, while Mg2+ forms the least precipitates and therefore listed at the top, above the other cations.

3. Atomic size for cation trend: Because Ba2+ atomic size is increasing. It is larger when going down the column. So Ba2+ will be less soluble than Sr2+, Ca2+, and Mg2+. The bigger size (cation ionic size) makes Ba2+more difficult to soluble for solubility depends on hydration of cation (enthalpy of solution) → more precipitates. Part B

4. According to the procedure, we are supposed to look at the color that is seen in the hexane layer. A reaction is indicated if the final hexane color shows presence of a halogen other than the initial. So the data shown in the C l-/ Br2 box shows a dark orange color which means there was not reaction, while the box Br-, Cl2 shows reaction did occur. This means Chloride must be a...
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