Chemistry core practical 5

Question 1

Aim

Answer 1

To oxide ethanol using organic techniques reflux and distillation

Question 2

Step 1

Answer 2

Add 20cm3 of acidified dichromate to an ice water bath in a pear shaped flask

Question 3

Step 2

Answer 3

Set up reflux apparatus keeping pear shaped glass in ice cold bath + add anti bumping granules

Question 4

Why add anti bumping granules?

Answer 4

Prevent formation of large bubbles = violent bubbling

Question 5

Step 3

Answer 5

Add 1 cm3 of ethanol drop wise down the apparatus into pear shaped flask

Question 6

Why add ethanol drop wise?

Answer 6

Because the reaction with acidified dichromate is highly exothermic which releases heat

Question 7

Step 4

Answer 7

After, remove the ice cold water bath and let the pear shaped flask reach room temp

Question 8

Step 5

Answer 8

Use a boiling water bath under the flask (with Bunsen burner to ensure it’s always boiling) under the flask

Question 9

Step 6

Answer 9

Distill the products produced using distillation apparatus of colourless organic product

Question 10

What product was collected?

Answer 10

Ethanolic acid because it was the vigorous distillation twice of a primary alcohol (ethanol)

Question 11

Analysis of carboxylic acid includes

Answer 11

Measure pH
Add acidified dichromate to it
Add calcium carbonate
Add magnesium
Add fehling solution

Question 12

pH of distillate

Answer 12

3.5 (Ethanolic acid)

Question 13

Add acidified potassium dichromate solution (orange) results

Answer 13

Remains orange because it cannot be oxidised further to Cr 3+ ions which are green

Question 14

Add calcium carbonate results

Answer 14

Produces carbon dioxide (effervescence)

Question 15

Add magnesium results

Answer 15

Produces effervescence in the form of hydrogen gas which displaced by magnesium from the ethanoic acid

Question 16

Add feelings solution results

Answer 16

Remained blue and did not form a red precipitate because carboxylic acid cannot be further oxidised

Question 17

Fehling s solution

Answer 17

Contains cu 2+ ions dissolved in sodium hydroxide
Positive result (showing it has been reduced = red ppt)

Question 18

Positive fehlings test result

Answer 18

In an aldehyde, can be oxidised again thus reduce Cu 2+ ions to form a red precipitate

Question 19

Negative fehlings test

Answer 19

In carboxylic acid or ketone, cannot be oxidised again so Cu 2+ ions not reduced and remain a blue solution