Lecture 2

Question 0

What is the electronegativity of oxygen?

Answer 0

3.5

Question 1

What is electronegativity?

Answer 1

The ability of an atom to attract electrons.

Question 2

What is the electronegativity of hydrogen?

Answer 2

2.1

Question 3

What is the angle between the two O - H covalent bonds in a water molecule?

Answer 3

105°

Question 4

What is hydrogen bond?

Answer 4

The difference in electronegativities of O and H creates a dipole in a water molecule. This makes a slight negative charge on the oxygen end and a slight positive charge on the hydrogen end. The attraction between an oxygen atom on one molecule and a hydrogen atom on another is called the hydrogen bond.

Question 5

What are six main characteristics of water due to hydrogen bonding?

Answer 5

High specific heat
High latent heat of fusion
High latent heat of vaporization
High surface tension
High dissolving power
High transparency to light

Question 6

What is specific heat?

Answer 6

The amount if heat required to raise the temperature of 1g of water by 1°C.

Question 7

What is the specific heat of water?

Answer 7

1 calorie/g-°C = 4.2J/g-°C

Question 8

How is the climate in coastal areas related to the high specific heat of water?

Answer 8

Water can hold a lot of heat, and quite resilient in changing its temperature.
This is why coastal areas are warmer in winter and cooler in summer compared to inland areas.

Question 9

What is latent heat of fusion?

Answer 9

The amount of heat required to melt 1g of ice into liquid water.

Question 10

What is the latent heat of fusion for water?

Answer 10

0.333kJ/g = 6.02kJ/mol

Question 11

What is latent heat of vaporization?

Answer 11

The amount of heat required to vaporize 1g of liquid water.

Question 12

What is the latent heat of vaporization for water?

Answer 12

2.250kJ/g

Question 13

What does the large amount of energy needed for phase changes in water tell you about the hydrogen bond?

Answer 13

Pulling apart hydrogen molecules by breaking hydrogen bonds require a lot of energy!

Question 14

How does high surface tension of water play a role in the biosphere?

Answer 14

Plants can take up water.
Cell membranes
Small animals can walk across water!

Question 15

When more salts are dissolved in water, how does the water’s freezing point change?

Answer 15

The freezing point of water decreases as the salinity increases.

Question 16

When more salts are dissolved in water, how does the water’s temperature of maximum density change?

Answer 16

The temperature of max density decreases as the salinity increases.

Question 17

What are the freezing point and the temperature of maximum density for pure water?

Answer 17

Freezing pt: 0°C

Max density: 4°C

Question 18

Why is water a good solvent?

Answer 18

The dipole of water molecules are attracted to positive or negative charges of ions. Because of the attraction, water molecules surrounds (hydrates) the ion, keeping the ions dissolved in water.

Question 19

Why is ocean dark except at the surface?

Answer 19

The water absorbs light. At 100m depth, only the light around the wavelength of blue visible light penetrates through.