Chemistry core practical 5 Flashcards
Aim
To oxide ethanol using organic techniques reflux and distillation
Step 1
Add 20cm3 of acidified dichromate to an ice water bath in a pear shaped flask
Step 2
Set up reflux apparatus keeping pear shaped glass in ice cold bath + add anti bumping granules
Why add anti bumping granules?
Prevent formation of large bubbles = violent bubbling
Step 3
Add 1 cm3 of ethanol drop wise down the apparatus into pear shaped flask
Why add ethanol drop wise?
Because the reaction with acidified dichromate is highly exothermic which releases heat
Step 4
After, remove the ice cold water bath and let the pear shaped flask reach room temp
Step 5
Use a boiling water bath under the flask (with Bunsen burner to ensure it’s always boiling) under the flask
Step 6
Distill the products produced using distillation apparatus of colourless organic product
What product was collected?
Ethanolic acid because it was the vigorous distillation twice of a primary alcohol (ethanol)
Analysis of carboxylic acid includes
Measure pH
Add acidified dichromate to it
Add calcium carbonate
Add magnesium
Add fehling solution
pH of distillate
3.5 (Ethanolic acid)
Add acidified potassium dichromate solution (orange) results
Remains orange because it cannot be oxidised further to Cr 3+ ions which are green
Add calcium carbonate results
Produces carbon dioxide (effervescence)
Add magnesium results
Produces effervescence in the form of hydrogen gas which displaced by magnesium from the ethanoic acid
Add feelings solution results
Remained blue and did not form a red precipitate because carboxylic acid cannot be further oxidised
Fehling s solution
Contains cu 2+ ions dissolved in sodium hydroxide
Positive result (showing it has been reduced = red ppt)
Positive fehlings test result
In an aldehyde, can be oxidised again thus reduce Cu 2+ ions to form a red precipitate
Negative fehlings test
In carboxylic acid or ketone, cannot be oxidised again so Cu 2+ ions not reduced and remain a blue solution
