Uploaded by Naeem Akhtar Samoon

Basic Chemistry Lab Exercise

Basic Chemistry Lab Exercise
Colloids are the dissolved state of substances that either do not pass, or pass very slowly through
a parchment paper or animal membrane. A few examples of colloids are starch, glue and gelatin.
A colloid is not a substance, but it depicts a particular state of a substance that depends upon the
size of its particles. The size of a particle in a colloidal system is between 1-100 nm. A colloidal
system is a two phase heterogeneous system in which one phase is called the dispersed phase
and the other is called the dispersion medium.
Dispersed phase: It is the component present in a small proportion.
Dispersion medium: It is the component present in excess.
For example, in a colloidal solution of silver in water, silver is the dispersed phase and water is the
dispersion medium.
Depending upon the nature of the interaction between the dispersed phase and dispersion medium
sols can be classified into two types.
1. Lyophilic sols
2. Lyophobic sols
The word meaning of lyophilic means ‘liquid-loving’ or ‘solvent- attracting’. This means that in
this colloidal solution there is a strong attraction between the dispersed phase and dispersion
medium, i.e., the dispersed phase has great affinity for the dispersion medium that results in
the extensive solvation of the colloidal particles. In such solids, the dispersed phase does not
easily precipitate and the sols are quite stable. These sols are reversible in nature. The
dispersed phase obtained by the evaporation can be easily converted to the sol state by
simply agitating it with the dispersion medium. Additional stabilisers are not required during
their preparation. If water is used as the dispersion medium, lyophilic sols are called
hydrophilic sols. Starch, gum, gelatin, egg albumin etc. are examples of lyophilic sols.
The word lyophobic means ‘liquid-hating’. That means in these sols, there is little or no
interaction between the dispersed phase and the dispersion medium ie, dispersed phase has
little affinity for dispersion medium. These sols are easily precipitated by the addition of small
amounts of electrolyte, by heating or by shaking, therefore these sols are relatively less
stable than lyophilic sols. They need stabilising agents for their preparation. If water is used
as the dispersion medium, lyophobic sols are called hydrophobic sols. Examples of lyophobic
sols include sols of metals and their insoluble compounds like sulphides and oxides.
Beaker (250 ml), Watch Glass, Porcelain Dish, Measuring Cylinder (100 ml), Pippete (10 ml),
Graduated Pippete (20 ml)
Egg, Sodium chloride (5g), Ferric chloride (2 g), Aluminium chloride (2g), Starch/gum (500
mg), Arsenious oxide (0.2 g)
I. Egg Albumin Sol
(i) Prepare 100 mL of 5% (w/v) solution of NaCl in water in a 250 mL beaker.
(ii) Break one egg in a porcelain dish and pipette out the albumin and pour it in sodium chloride
solution. Stir well to ensure that the sol is well prepared.
II. Starch/gum Sol
(i) Measure 100 mL of distilled water with the help of a measuring cylinder and transfer it to a 250
mL beaker and boil it.
(ii) Make a paste of 500 mg starch or gum in hot water and transfer this paste to 100 mL of boiling
water with constant stirring. Keep water boiling and stirring for 10 minutes after addition of paste. To
judge the efficacy of the prepared sol, you may compare it with the original paste prepared.
B. Preparation of Lyophobic Sol
I. Ferric hydroxide/Aluminium hydroxide
(i) Take 100 mL of distilled water in a 250 mL beaker and boil it.
(ii) Add 2g of ferric chloride/aluminium chloride powder to boiling water and stir it well.
(iii) Take 100 mL of distilled water in another 250 mL beaker and boil it.
(iv) Pour 10 mL of ferric chloride/aluminium chloride solution prepared in step (ii) drop by drop into
the boiling water with constant stirring. Keep the water boiling till brown/ white sol is obtained.
II. Arsenious Sulphide Sol
(i) Transfer 100 mL of distilled water to a beaker of 250 mL capacity.
(ii) Add 0.2 g of arsenious oxide to it and boil the content of the beaker.
(iii) Cool and filter the solution.
(iv) Pass hydrogen sulphide (H2S) gas through the filtered solution till it smells of H2S. (Use Kipp’s
apparatus to pass hydrogen sulphide gas).
(v) Expel H2S gas from the sol by slow heating and filter it.
(vi) Label the filtrate as arsenious sulphide sol.
(a) While preparing colloidal solutions of starch, gum, ferric chloride, aluminium chloride etc., pour
the paste or solution gradually into the boiling water with constant stirring. Addition of these
substances in excess may cause precipitation.
(b) Arsenious oxide is poisonous in nature; so wash your hands immediately every time after
handling this chemical.