7e

Question 1

how can we make a dispersion more stable

Answer 1

• put more energy into it to form smaller particles
• focus on the surfactant to get a stable microemulsion system ( polymer for steric stabilisation or make them charged )

Question 2

if the CMC = 7.4mM ,, what is 🔺G

Answer 2

🔺G = RT ln(X cmc)

c meaning mole fraction so u want the mole fraction !!

first turn 7.4mM –> 7.4M
7.4mM = 7.4 x10^-3M

then find mole fraction.

7.4x10^-3 / (7.4x10^-3) + 1000/18

= -22121.79 jmol-1
= -22.1 kjmol-1

Question 3

if theres a silver nanoparticle coated in amine functionalised polymer,, why is it more stable at lower than at higher PH

Answer 3

• polymer = steric stabilisation
• amine = NH2 = neutral
• low pH amine = NH3+ = charged
• these repel when they come closer,, meaning theyre more repulsive,, meaning the graph peak is higher = more stable bc molecules are less likely to aggregate.

Question 4

when we are asked to sketch a graph of the attractive,, repulsiove and total interaction energies very with interparticle separation,, what should we think of

Answer 4

that one long lecture with the diff weird graphs

the one where the top bit is repulsive

the lower bit is attractive

interparticle sep is the x acis and interaction energy is the y axis.

Question 5

how can interparticle forces in colloidal silica be controlled using NaCl salt and how does this alter the stability of the dispersion

Answer 5

silica is a charged colloidial dispersion

• adding more salt means the charges attract
• lowering the Ea of that one hill on the graph bc the forces arent repulsive,, meaning the dispersion is less stable bc theres a lower Ea meaning its easy to overcome bc 3/2KT > Ea.