Lab 5: Silver Nanoparticles
Method:
Sodium Borohydride reduction of Silver Nitrate
Sodium Citrate Cap
More Sodium Citrate
Other Notes:
-Nanoparticles of 100nm or less have different properties that bulk materials
-Electron movement is limited because of nanoparticle size
-Surface effects are more important to nanoparticles because of high surface to volume
ratio
-Local Surface Plasmon Resonance is most important surface effect
> Wave-like oscillations of electrons
>Correspond to specific frequencies
>Causes nanoparticles of different sizes to be different colors
-High surface to volume ratio makes them useful for chemical catalysis (antibacterial
agents)
-Surface of silver nanoparticles are actually Silver Oxide
-Monodisperse samples have sharper absorbance peaks
-Capping controls kinetics of process, not thermodynamics
-As a result, drop size and stir speed matter
-Hydrazine acted as reductant for second silver nitrate addition
Calculations:
Standard Curve based on previous literature
Equal Addition Calculation
Lab 6: Chemical Kinetics
Method:
Iodine Clock Reaction
Create Triiodide by oxidizing iodide with hydrogen peroxide
React triiodide formed with thiosulfate in presence of starch
With hydrogen peroxide in excess, and iodide being regenerated conditions are
held constant to measure reaction rate
Once thiosulfate is used up, triiodide will form complex with starch signaling end
Time taken for thiosulfate to be used up is equal to reaction rate for iodide
Since reactants are in excess, they are lumped into Keff
Iodination of Acetone
Reaction Triiodide with Acetone with acid to iodinate the acetone
Change the concentrations of each reactant to determine reaction order with
respect to each
Change to deuterated hydrogen to determine rate determining step
Other notes:
-Thiosulfate reaction is too fast to matter
-Non-elementary reaction rate law cannot be determined from stoichiometry
-Look however how to write rate law for slow second step (determined by deuterium
experiment)
Calculations:
KH/KD
Lab 7: Titrations
Method:
Addition of acid to soda ash to determine amount of sodium bicarbonate
Addition of EDTA to cough drop to determine amount of Zinc present
Addition of thiosulfate to triiodide starch complex in excess to determine amount of
ascorbic acid present
Other Notes:
-acid-base titrations can be used for concentration, molecular weights, and equilibrium
constants
-Monitored with either indicator or pH probe (potentiometric titration)
-Soda Ash is a weak base being titrated by a strong acid
-Soda Ash is a water softener because it can dissolve calcium or magnesium carbonate
-Color change based on formation of a complex is a complexometric titration
-Zinc Gluconate is in cough drops and readily releases Zn 2+ upon consumption
-Unlike other transition metals, zinc ions are colorless
-Xylenol orange is yellow in the absence of zinc, and red in the presence of zinc
-EDTA is a chelating agent, and forms a colorless complex with zinc
-Pre-mix zinc solution with xylenol orange, add EDTA until color change (must be at pH
5.5 because the formation constant is greater than 106
-Iodate and iodide in acidic conditions produce triiodide
-this triiodide reacts in excess with the ascorbic acid in the vitamin c tablet
-the excess triiodide forms a colored complex with starch
-thiosulfate is used to titrate excess triiodide back to iodide
-amount of triiodide in excess (equal to thiosulfate added) is subtracted from total
amount of triiodide calculated from iodate reaction to get ascorbic acid reacted
Calculations:
-Mol of titrant is equal to moles of titrand at equivalence point
Lab 8: Microstates in Matlab
Microstate: the arrangement of each molecule in a system in a single instant
Configuration: An arrangement where particles have set quanta (can include multiple
microstates)
Ensemble: All possible microstates in a system
Microstate in red, Configuration in green
-Microstates increase when quanta and particles are added (heat and entropy)
Boltzmann Distribution
-Increasing particles and not quanta increases entropy and decreases temperature
-Increasing quanta and not particles increases entropy and temperature
-Increasing both increases entropy and decreases temperature
-At high temperatures, change in entropy decreases
>1/T=dS/dE