Macro Teaching - Syahrul - Latex

LATEX Latex is the white liquid (milk) produced by a rubber tree.

 Latex

contains 30% of natural rubber polymers and 70% of water that exist in colloidal solution.

 Naturally,

latex will took about a day to solidify and the process is called coagulation of latex.

 Our

folks usually add “cuka getah” to quicken the process. Is the “cuka getah” acid or alkali?

 Sometimes,

coagulation of latex must be prevented for specific use such as in the making of latex foam, mattress and cushion.

Problem statement. 1. 2.

How to quicken the rate of coagulation for latex? What can we do to prevent latex from coagulating?

Experiment 2.8 (page 113)  Apparatus  Beaker  50

cm3 measuring cylinder  Pipette  Glass rod  Materials  Latex 2

mol dm-3 of ethanoic acid.  2 mol dm-3 of ammonium solution.  Litmus paper.

Observation. Ethanoic acid solution  Beaker

A Stirred

Latex

Ammonium solution 

Beaker B

After a day, no coagulation occur.



Beaker C

Discussion:

1.How the natural coagulation of latex can occur?

Positive charge from bacteria’s action

H

+

+ + H+ H H H+ - -

H+ -

-

-

H+ - H

H +

H+ -

-

H

+

-

-

H

+

H - -H+ H+

Neutralized particle rubber

Negative charge

+

+

- H+ H+

Rubber polymer

H H+

H

+

-

H+ H+ H+ - -

+

-

-

-

H+ + - H

H+ + H Protein membrane

H+

-

H+

-

H+ - + H+ H

- H+ H+

H+

+ + H+ H H H+ - -

H+ -

-

-

+ - H

H+ H -

-

+

H+

-

H+

-

H

H+

+ - - + H H H+

- H+ H+

H+

H

+

-

H+ H+ H+ - -

+

-

-

-

H+ + - H

H+ H+ H+

-

H+

-

H+ - + H+ H

- H+ H+

2. How acidic solution can quicken the coagulation process of latex?

ETHANOIC ACID Positive charge from acid

H+

+ + H+ H H H+ - -

H+ -

-

-

+ - H

H+ H -

-

+

H+

-

H+

-

+ - - + H H H+

Neutralized particle rubber

H

H+

- H+ H+

H+

H

+

-

H+ H+ H+ - -

+

-

-

-

H+ + - H

H+ H+ H+

-

H+

-

H+ - + H+ H

- H+ H+

H+

+ + H+ H H H+ - -

H+ -

-

-

+ - H

H+ H -

-

+

H+

-

H+

-

H

H+

+ - - + H H H+

- H+ H+

H+

H

+

-

H+ H+ H+ - -

+

-

-

-

H+ + - H

H+ H+ H+

-

H+

-

H+ - + H+ H

- H+ H+

3. Why alkaline solution able to prevent coagulation to occur?

Ammonium solution / alkaline solution

Rubber particles still remain it negative charges and coagulation can not - OH OH OH- OH OH OH occur. OH + + OH H H + + H H OH H+ H+ OH- H+ H+ + - H H+ + OH H + OH H OH H+ + OH H + OH + OH H - H -H+ + OH OH- H - H+ OH- H+OHH+ H+ + H H+OHOH OH OH H+ H+ H+ H+ - H+ H+ H+ OHH+ H+ H+ OHOHOHOH- OH- OHOH- OH- OHHydroxide ions from alkaline solution will neutralise the acid produced by bacteria.

TEST YOUR UNDERSTANDING  Complete

the given worksheet individually.  Students are given 10 minutes to complete the task.  Discussion on the worksheet.  The answers.

1. Please complete the report on the experiment today at home. 2. Send your report books tomorrow morning. 3. Put them on my desk.