1.6 and 1.7

Question 1

why does solid water float on liquid water?

Answer 1

This is because the density of ice is less than that of liquid water and so ice floats on water.

• the hydrogen bonding in solid H2O causes OPEN SPACES in the structure of ice

Question 2

What are the properties of water

Answer 2

• great solvent power as it is highly polar and dissolves many ionic substances and polar substances (some non polar gases by dispersion forces)
• high heat of fusion/ vaporization ( this is because we need to break a significant amount of hydrogen bonds around water molecules
• high surface tension and capillarity

Question 3

Define surface tension

Answer 3

the resistance of liquid to increase its surface area

• magnitude of force that controls the shape of the liquid
• a measure of the amount of energy needed to expand the surface area of a liquid

Question 4

Describe characteristics of surface tension?

Answer 4

• surface molecules packed more closely than bulk (the molecules below then)
• energy is needed to move extra molecules to surface (means not favorable to have more molecules on the surface; more surface area)
• surface tension is higher for substances with strong intermolecular attraction eg. water, mercury (means more energy is needed to put molecules to the surface)

Question 5

Why does surface tension occur?

Answer 5

the liquid surface has a net attraction downwards, thus causes fewer molecules at surface = smallest surface area

• molecules on the surface attracted to molecules below them, beside them but NOT above them unlike molecules in the bulk sample

Question 6

Why are liquid droplets spherical in shape?

Answer 6

it is the shape with the least surface area

Question 7

true or false: molecules at surface experience overall INWARD attraction; contract surface making it act like skin

Answer 7

true

Question 8

Define Viscosity

Answer 8

It is the measure of a liquids’ resistance to flow (harder for molecules to move past their neighbors)

Question 9

Characteristics of viscosity

Answer 9

• increases with stronger intermolecular forces
• increases with chain length (extent of contact)
• usually decreases with temperature (supplying thermal energy increases KE of particles)

Question 10

true or false: liquids are most stable when there are fewest molecules on the surface

Answer 10

true

Question 11

Define Capillary action

Answer 11

the spontaneous rising of liquid through a narrow gap against gravity (eg. water moving away from the direction of gravity)

Question 12

When does Capillary action occur?

Answer 12

when adhesive forces (attractive forces between unlike molecules) are greater than cohesive forces (intermolecular forces which occur between the same substances; resist separation)

Question 13

Define volatility

Answer 13

it is the tendency of a liquid to become a gas

- increases as temperature increases