Form 5 chem 一問

A purple layer (1,1,1-trichloroethane) at the bottom and a yellow layer at the top should be observed.

1,1,1-trichloroethane is a non-aqueous organic solvent, when it is added to an aqueous solution of iodine, it extracts most of the halogen(iodine) from the aqueous layer. Iodine gives a purple colour in organic solvent.

Colour changes:
1) 1,1,1-trichloroethane from colourless to purple; 2)aqueous layer from brown to yellow.

Since 1,1,1-trichloroethane is denser than water ( 1.32 g/cm³ for 1,1,1-trichloroethane and 0.998g/cm³ for water), thus ,the purple layer sink and the yellow layer float.





*points to note 1*: most organic solvent with chlorine are denser than water. One example is tetrachloromethane.

*points to note 2*: Another common organic solvent is heptane, which is less dense than water.

concept:
1. organic products are generally more soluble in organic solvents than in water
("有機物"比較易容於"有機溶劑")

2. iodine in organic solvents is purple in colour
(碘於有機溶劑下顯現紫色)

3 1,1,1-trichloroethane is colourless
(1,1,1-三氯乙烷 是透明)

4 1,1,1-trichloroethane should be denser than water-----ps 密度唔清楚
(1,1,1-三氯乙烷 的密度應該 比水高)


所以,
Iodine will desolve mainly in 1,1,1-trichloroethane layer "at the lower part"
and 1,1,1-trichloroethane is from colourless to purple in colour.

ps 唔知係咪係lower part