12. Charged Colloids in Water Flashcards
What are colloids?
Colloids are mixtures where small particles (< 1µm in diameter) of one substance are suspended in a second medium or continuous phase.
Give two types of colloid
- Solid particles in a liquid
- A liquid within another liquid (emulsions)
Are colloids the same as solutions?
No
Give 4 examples of colloidal interactions
- Cells
- Microbes
- Quantum dots
- Paint
How do colloidal particles behave when in a continuous phase?
They flocculate (stick together) to form an aggregate.
Why do colloidal particles tend to stick together when dispersed in a continuous phase?
Dispersion forces cause a mutual attraction.
What can be done to prevent flocculation in a colloidal interaction?
Short-range repulsion forces can be introduced by decorating the surfaces of colloidal particles with charged groups, and by adding a small amount of salt to the continuous phase.
When added to water, salt is known as an ________.
Electrolyte
What is osmotic pressure caused by?
A concentration difference between two regions of an aqueous solution that results in a chemical potential.
Osmotic pressure acts to try and ________ the concentration in a fluid.
Equalise
Define osmosis
The movement of water molecules from high to low water potential through a semi-permeable membrane to minimise concentration difference.
Give the equation for osmotic pressure between two charged surfaces in an electrolyte
Π = osmotic pressure
n+ = positive ion number density in gap
n- = negative ion number density in gap
n0 = ion number density far from gap
kB = Boltzmann’s constant
T = temperature
Give the equation for osmotic pressure in terms of small potentials
Π = osmotic pressure
n0 = ion number density far from gap
kB = Boltzmann’s constant
T = temperature
Z = atomic number
e = electron charge
V(x) = potential difference
