Question

1. In lab (seperating benzocaine and triphenylmethanol using diethyl ether and 10% HCl as extraction solvents ), the addition of 6M NaOH to the aqueous layer must be performed when the beaker is in an ice/water bath. why?

2. how do you test the pH of a solution using litmus paper in organic labs?

3. a student's solution violently bumped in their RBF while it was on the rotary evaporator. This has caused the student to loss most of their product. As you help this student, they tell you that they added 35ml of their solution yo their 50ml round bottom flask. you note no issues with the rotary evaporator settings and equipment
WHAT IS THE PROCEDURE ERROR?

Answer 1

Answer 1

Addition of 6M NaOH (too concentrated) to a solution that contains HCl will result in neutralization reaction between acid and base. This reaction is exothermic in nature and hence will generate heat. This heat may cause bumping as well as burning of diethyl ether present in the solution.

To avoid this, beaker is kept in ice bath or cold water bath so that the heat released by the neutralization can be stopped from raising the temperature of solution.

Answer 2

Solution to be tested is taken in a testube. Dip red litmus paper in the solution and pull out. Observe the color change, if there is no change then, solution is either acidic or neutral. If it turned blue, then solution is basic.

Repeat the procedure with blue litmus paper for same solution. If color changes then it is acidic and if no color change is seen, then solution is basic or neutral.

Compare the results of blue and red litmus paper:

	Red litmus paper	Blue litmus paper	Results
	No color change	No color change	solution is neutral
	No color change	Color changed to red	Solution is acidic
	Color changed to blue	No color change	Solution is basic

Answer 3

The error is that solution added has exceeded the limit of Round bottom flask.

For samples undergoing distillation, the round bottomed flask must be half filled. It is because,

firstly it is to be held in slanting position.

Secondly, the sample will undergo boiling and hence vapors will be formed. so, there must be space for the vapors.

Hence, bumping is the result of overfilling of the flask.