Determining The freezing Point Of Acetic Acid ! Chemistry 1105

Introduction Today’s Objective Supercool acetic acid Graph the results Acquire acetic acid’s freezing point Measure Supercoiling effect of acetic acid (Materials) Thermistor Ice bath (250 mL Beaker ) Microlab (select: Time vs Temp) Graph data

Glacial Acetic Acid What is it? CH 3 COOH - Ethanonic Acid Glacial = Pure, hydroscopic 100% Acetic Acid vs. 5% In Vinegar Poison. Fatal. Burns Skin/Eyes (itchiness). Inhalation Damage. Flammable. Rinse With Water Thoroughly

Heating Curve For Water Heat Increases the motion of molecules thus Increase in molecular coalitions and Friction Increases In The Above Mentioned Equals An Increase In Disorder, Or Entropy Temperature = Entropy(S) We are going to use this 1`st half

Boiling Point Is the phase transition of any substance affected by Pressure? Yes! Because the liquid and gas phases are in equilibrium but if the pressure changes the substance will try to compensate the external changes in the system. (LeChatelier's principle). Does that mean altitude is a factor? Yes! Because there is less atmospheric pressure In El Paso Takes a little more heat 4-6 O C Lower Than at Sea Level Pressure does not change the boiling of freezing point Why? Melting point and freezing point are defined by the change of state at atmospheric pressure.

Supercooling The liquid cools so fast that the molecules do not have the time to align into the structure of a solid When a super cooled liquid is disturbed, it crystallizes from that point outward. Needs that extra “help” (energy) to start the alignment into a solid. Phenol, Water & Acetic Acid Will Exhibit this Effect is an exception to the freezing curve.

Super Cooling effect

Discussion What will happen if you left drops of water in your test tube and carelessly have add your acetic acid? Freezing point will be different because you mixed water and acetic acid Your experiment will give bad data If acetic acid has a higher freezing point than water, what does that tell you about the procedure? Acetic acid will freeze before water Ice Bath What would be the best equipment to use? Test Tube -a smaller quantity will cool faster

Setting Up Person 1 Use a 250 ml beaker to create an ice Bath Set up MicroLab (TIME VS TEMP) Person 2 (labmate) Find and clean a test tube Completely dry off the test tube (make sure there is no trace of water) Do Not Blow Into the test tube! Moisture in the breathe Before you start the experiment: be sure to rinse the clean test tube with approximately 2 mL of acetic acid.

Set up (Acetic acid) Dry thermistor for each experiment How Much Acetic Acid? One inch (2.5 cm) of the test tube deep Thermistor must not touch the walls of the test tube or beaker Use the same acid for the 3 trials

How it should look Microlab  Time and temperature Check the calibration of thermistor with ice water =Ice water should read Zero Celsius

Procedure (Supercooling) Start analysis with the thermistor outside the test tube. Start at room temperature Put thermistor in test tube, then lower the test tube it to the ice bath Make sure to not move the thermistor When temperature reading is below 10 o c Tap the thermistor tip on the bottom of the test tube As Supercooling effect ends (liquid to solid) Leave the thermistor in (min. 15 seconds) until you get a good line on the graph. Stop experiment and carefully remove the test tube out of the ice bath Do not remove thermistor while the acidic is solid

Procedure (Microlab) Take test tube out Warm up the test tube with hand Remove thermistor after acetic acid is liquid again Failure to do so will result in damage to equipment Graph –click on select domain With the mouse select the part of the curve that is the flat (after the supercooling). Analysis Add a first order linear fit and make sure to display the equation. Change the graph title (ex. Supercool 1) by using right click Print

Analysis Click select domain With the mouse button down choose the part of the curve that is the flat. Then Analysis Add fit screen click ok Type in a label (supercool1) Choose first order and ok

Analysis Go the graph pull down properties and unclick the auto title and type your own Select print from the pull down screen before returning to the original graph This form prints the line fit Change title After print the full graph by clicking zoom out. And print SHOULD HAVE TWO GRAPGHS PRINTED

Report Should include section M1 M2 etc and interface number Close Analyze And Acquire Windows Repeat 2 x each time Same acid Report will be the three full size graphs and 3 zoom graphs The average on one of them Sig Figs and Accuracy counts Empty, Clean, Store All Equipment Clean Up And Turn In Lab Report with MSDS

How should your Graph look? Y=MX+B Select this section Super cooling exp.X (Initials)

Questions?