11B - Properties of Liquids

Question 1

Def: Define cohesive and adhesive forces.

Answer 1

Cohesive: IMFE’s btw like molecules.
Adhesive: IMFE’s btw unlike molecules.

Question 2

Def: What is viscosity? What does increased viscosity entail? What increases viscosity?

Answer 2

Liquid’s resistance to flow.
A more sluggish flow.
More IMFE’s and cohesive forces.

Question 3

Theory: Relate viscosity with temperature.

Answer 3

Viscosity decreased with increasing temperatures because at higher temp’s, IMFE’s and cohesive forces are weaker.

Question 4

Def: What is surface tension? What increases ST?

Answer 4

Surface tension is the energy required to increase the Surface Area (SA) of a liquid.
Increases with stronger cohesive forces.

Question 5

Theory: Why do liquids tend to “bead”?

Answer 5

Surface molecules experience a net attraction towards the “bulk” (molecules underneath), as their are not molecules above them. Spheres have the lowest surface area to volume area of any shape, so that is the form these surface molecules assume.

Question 6

Def: What is capillary action/rise? Why does it occur?

Answer 6

The ability of a liquid to flow against gravity and spontaneously rise in a narrow tube or porous
structure.
It is due to the adhesive forces of the substance and the container being far greater than the cohesive forces of the substance. It is also dependent on the diameter of the container and force of gravity on the liquid.

Question 7

Def: What is wetting? Why does it occur.

Answer 7

The extent to which a liquid spreads into a thin film on a surface.
Depends on adhesivew forces.

Question 8

Def: What is super-hydrophobicity?

Answer 8

Super-hydrophobic materials are difficult to wet with contact angles of more than 90 degrees. Usually have rough surfaces.