Colloids & Nanoparticles

Question 1

What is a colloid?

Answer 1

A colloid is a mixture of solute and solvent in which the solute particles are between 1-1000 nm, the particles do not settle to the bottom

Question 2

When does a change of state occur?

Answer 2

When an attractive force dominates, particles come closer together or when a kinetic motion causes the particles to move further apart

Question 3

What is a sol?

Answer 3

A type of colloid where solid particles are dispersed in a liquid

Question 4

Define an aerosol.

Answer 4

A type of colloid in which solid or liquid particles are dispersed in a gas.

Question 5

Define foam.

Answer 5

A type of colloid where gas particles are dispersed in liquid.

Question 6

What is an emulsion?

Answer 6

A type of colloid where liquid particles are dispersed in a liquid.

Question 7

What is a solution?

Answer 7

A solution is a homogenous of two or more substances,

Question 8

What is a suspension?

Answer 8

A mixture containing large, dispersed solid particles that can settle out or be separated by filtration.

Question 9

What is the tyndall effect?

Answer 9

when a light beam is shone through a liquid colloid and the relatively large particles scatter light.

Question 10

Name the three types of mixtures possible

Answer 10

colloids, suspensions and solutions

Question 11

why can the large surface area of particles be toxic?

Answer 11

increased surface area means more potential for binding to toxics acting as a vectors

Question 12

How do you calculate surface area of a sphere?

Answer 12

4pie rsquared

Question 13

How do you calculate surface area of a rod or tube?

Answer 13

2(pir2) + 2pirh

Question 14

Name the two forces in colloids

Answer 14

Electrostatic stabilization and steric stabilization

Question 15

What is electrostatic stabilization?

Answer 15

it stabilizes the colloids by having a lot of charges on the surface, same charges will repel

Question 16

What is steric stabilization?

Answer 16

Something on the surface of the particles that prevents them getting too close, attraction force of Van der waals and electrostatic repulsion are balanced

Question 17

What is the neutralization reaction?

Answer 17

Acid + base -> salt + water

Question 18

Describe the difference between a hard acid and a soft acid?

Answer 18

A hard acid is where all of the acid groups dissociate (all H+s come off) whereas a soft acid is where only part of it dissociates

Question 19

Name the 3 stages in where a colloid goes from a stable system to phase separation?

Answer 19

sedimentation, flocculation and coagulation

Question 20

what is a micelle?

Answer 20

particle of colloidal dimensions that exists in equilibrium with the molecules or ions in solution from which it is formed

Question 21

Describe the structure of a micelle

Answer 21

composed of amphillic macromolecules, made of hydrophilic and hydrophobic blocks.

Question 22

Whats the difference between biomass and biochar?

Answer 22

Biomass = plant material we start with
Biochar = what is produced from the plant material

Question 23

Define wettability

Answer 23

The spread of water on a surface

Question 24

Describe the difference between superhydrophobic and superhydrophillic in terms of wettability?

Answer 24

Superhydrophobic means the water droplets won’t spread at all
Superhyrophillic means the water will spread across the surface evenly

Question 25

Why should various methods of particle size analysis be considered? (3)

Answer 25

- material suppliers and employers use many different types of instruments - use a different technique, likely to get a different answer - important to understand how analysis methods differ to compare data

Question 26

What does stokes law calculate?

Answer 26

The velocity of sedimentation

Question 27

Name 3 methods used to calculate particle size

Answer 27

- sieves - laser diffraction - dynamic light scattering - manual microscopy - automated microscopy

Question 28

Advantages of laser diffraction in calculating particle size? (3)

Answer 28

- uses a low power beam (non intrusive) - fast typically 3 mins to measure - precise and wide range

Question 29

Disadvantages of laser diffraction in calculating particle size? (3)

Answer 29

- expensive - volume measurement assumes spherical particles when they may be different shapes - must be different in refractive indices between particles and suspending medium

Question 30

What size do particle's diameters in a colloid range between?

Answer 30

1-1000nm

Question 31

How does high temperatures alter the physical state of a substance (solid/liquid/gas/) ?

Answer 31

particles move faster by kinetic energy causing a transition from solid > liquid > gas

Question 32

How does low temperatures alter the physical state of a substance (solid/liquid/gas/) ?

Answer 32

particles move less and attractive forces bring them back together gas > liquid > solid

Question 33

Why do colloids often have a milky colour?

Answer 33

particles large enough to scatter light causing it to bend

Question 34

Describe the properties of a solution?

Answer 34

it is ALWAYS transparent and light can pass through with no scattering from solute particles. e.g. sugar and water

Question 35

Name the balanced two forces in any colloidal system

Answer 35

Attractive force of van der waals and Electrostatic repulsion

Question 36

Describe sedimentation

Answer 36

When particles are heavier and there is a gravity effect where they start to settle first and as the concentration increases they start to agglomerate

Question 37

Describe flocculation

Answer 37

The charge is suddenly neutralized and the particles come together very quickly and then this agglomerate will have a higher density and will therefore settle out

Question 38

What does laser diffraction do?

Answer 38

It converts scattered light to particle size distribution

Question 39

How does laser diffraction measure particle size?

Answer 39

> particles pass through a laser beam and the light scattered by them is collected over a range of angles > the angle of diffraction is inversely related to particle size

Question 40

What does dynamic light scattering measure?

Answer 40

Diffusion constant and therefore you msut use stokes Einstein law to calculate particle size

Question 41

Name 3 features of a colloid

Answer 41

- particle size must be in the range of 1 - 1000nm - mixture composed of particles in a dispersing medium - tyndall effect, shining a beam through the colloid causes the larger particles to scatter light which makes the substance appear cloudy