2. ACKNOWLEDGEMENT
I would like to express my greatest appreciation to the all individuals who have helped and supported me
throughout the project. I am thankful to my chemistry teacher for her ongoing support during the project,
from initial advice, and provision of contacts in the first stages through ongoing advice and
encouragement, which led to the final report of this chemistry project. A special acknowledgement goes to
my colleagues who helped me in completing the project by exchanging interesting ideas and sharing their
experience. I wish to thank my parents as well for their undivided support and interest who inspired me
and encouraged me to go my own way, without whom I would be unable to complete my project .At the
end, I want to thank my friends who displayed appreciation to my work and motivated me to continue
my work.
3. CERTIFICATE
This is to certify that ABHAY PANDEY of class XII 'A' has
successfully completed the project work on chemistry for class XII in
the year 2020-2021. It is further certified that this project is the
individual work of the candidate.
Signature:
Date -
4. COAGULATION
Coagulation is a process which involves coming together of colloidal particles so as to change into large sized particles which ultimately settle
as a precipitate or float on the surface.
Coagulation of lyophobic solutions:
Coagulation of lyophobic sols can be done by the following methods:
By electrophoresis - The colloidal particles move towards oppositely changed electrodes get discharged and precipitate.
By mixing two oppositely charged sols - Oppositely charged sols when mixed together in almost equal proportion, neutralise their charges and
get partially or completely precipitated.
By Boiling- When a sol is boiled the adsorbed layer is disturbed due to increased number of collisions with the molecules of the dispersion
medium. This reduces the charge on the particles and they ultimately settle down in the form of a precipitate.
By Persistent dialysis - On prolonged dialysis, traces of the electrolyte present in the sol are removed almost completely. Colloids become
unstable and coagulate.
By addition of electrolyte - When excess of electrolyte is added, colloidal particles precipitate as colloids interact with ions carrying charge
opposite to that present on themselves. This causes neutralisation leading to their coagulation.
A negatively charged ion when added to a positively charged sol causescoagulation. The negatively charged ion is called coagulating
ion/flocculative ion as it neutralises the colloid to cause coagulation.
5. COAGULATION OF LYOPHILIC SOLUTIONS
Lyophilic sols are stable because of charge and solvation of colloidal particles. So we remove these two factors to coagulate them. This is done by
o Addition of an electrolyte
o Addition of a suitable solvent
HARDY-SCHULZE RULE-
The quantity of the electrolyte which is required to coagulate a definite amount of a colloidal solution depends upon the valency of the ion having
a charge opposite to that of the colloidal particles. This observation oh Hardy and Schulze are known as Hardy Schulze law.
o For negative sols, when positive ions are added
Al3+> Ba2+>Na+ is the order in terms of flocculating power
o For positive sols, when negative ions are added
[Fe(CN)6] 4-> PO43->SO42->Cl- is the order in terms of flocculating power
6. CURDLING OF MILK
Curdling is the breaking of an emulsion into different composition using physical and chemical processes .
Fresh milk is an example of a colloid,consisting of fat and protein particles floating in a water based solution .the
colloidal suspension scatters light,causing milk to appear white.the protein molecules mainly casein repel each other
so they naturally distribute evenly through the liquid,milk is slightly acidic. When the pH is lowered even more by
the addition of another acidic ingredient the protein molecules stop repelling each other.This allows them to stick
together or coagulate into the clumps known as curds.The watery liquid that remains is called whey.
7. HOW SOUR MILK CURDLES
◼ When milk goes “off” or turns sour, it is because acids produced by bacteria lower the pH of milk so the proteins can clump
together. The increased acidity of the milk also causes it to taste sour. The bacteria living in milk naturally produce lactic acid as
they digest lactose so they can grow and reproduce. This occurs whether milk is fresh or pasteurized. You won’t notice the effect on
flavor until enough acid has been produced. Refrigerating milk slows the growth of bacteria. Similarly, warm milk helps bacteria
thrive and also increases the rate of the clumping reaction.
