Chem Lab Notes

Topics: Chemistry, Rate equation, Temperature Pages: 3 (1034 words) Published: May 7, 2014
1. Phase changes
a. Determine the melting point of a substance
b. The temperature at which the solid melts is called the melting point c. Furthermore, addition of heat causes the temperature of the liquid to increase until it reaches its boiling point. d. Stearic acid is a solid at room temperature.

e. Melting stearic acid and recording when crystallization occurs; the temperature will remain constant at the freezing point until the liquid to solid phase change is complete. f. When crystallization is complete, the temperature will decrease until thermal equilibrium with the surroundings is reached. g. RESULT: determine the freezing point of the substance, interpret the changes in temperature h. Part of the graph that represents cooling of the liquid?

i. Solidification?
i. What is happening to the kinetic energy of the stearic acid molecules as the liquid cools? i. During crystallization?
j. Changes are exothermic or endothermic?
k. Freezing temperature of stearic acid?
2. Rate Law Determination of the Crystal Violet Reaction
a. Observe the reaction between crystal violet and sodium hydroxide. b. One objective is to study the relationship between concentration of crystal violet and time elapsed during the reaction. i. CV+ (purple) + OH-  CVOH (colorless)

c. Rate law: rate= k[CV+]m[OH-]n
i. K is the rate constant
ii. M is the order with respect to crystal violet
iii. N is the order with respect to hydroxide ion
d. Use a spectrophotometer to monitor the absorbance of the concentration of the crystal violet with time e. Absorbance vs time
i. A linear plot here indicates a zero order reaction with respect to crystal violet, where k = -slope f. ln(absorbance) vs time
i. a linear plot here indicates a first order reaction with respect to crystal violet, where k = -slope g. 1/absorbance vs time
i. A linear plot here indicates a second order reaction with respect to crystal violet, where k = slope. h. Once the order has been determined, find the...
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