3.2 Water

Question 1

What are polar molecules?

Answer 1

Molecules with regions of positivity and negativity

Question 2

What is a hydroxyl group?

Answer 2

OH

Question 3

How many hydroxyl groups does water contain?

Answer 3

2

Question 4

How do hydrogen bonds form?

Answer 4

Oxygen and hydrogen share electrons unequally when they bond. Oxygen, has a greater share so is more negative.

Hydrogen, has a smaller share so is more positive.

The more negative oxygen atom is attracted to the more positive hydrogen atoms.

Question 5

What are the five reasons why water is important in living organisms?

Answer 5

1. Water acts as a reactant in chemical reactions
2. Water is a solvent in which solutes can dissolve in
3. Water transports substances - due to water being liquid and a solvent, it can transport many types of substances
4. Water acts as a temperature control - due to high specific heat capacity and high latent heat of evaporation
5. Water is a habitat - due to its role in temp control, organisms can survive in it as it provides a stable environment

Question 6

Define specific heat capacity

Answer 6

Energy needed to raise the temperature of 1g of substance by 1 °C

Question 7

Why do hydrogen bonds give water a high specific heat capacity?

Answer 7

H bonds can absorb a lot of energy - so water takes a lot of energy to heat up

Question 8

What is the benefit of water having a high specific heat capacity?

Answer 8

Water doesn’t experience rapid temperature changes. This makes it a stable habitat.

Question 9

What does it mean when water is said to have a high latent heat of evaporation?

Answer 9

A lot of energy is used up when water evaporates

Question 10

What is the benefit of water having a high latent heat of evaporation?

Answer 10

Water acts as a coolant - e.g. when some mammals are too hot and start to sweat, the sweat evaporates and cools the skin’s surface

Question 11

What is cohesion?

Answer 11

Attraction between molecules of the same type

Question 12

Why are water molecules cohesive?

Answer 12

Because they’re polar

Question 13

What is the benefit of water being cohesive?

Answer 13

Being cohesive enables water to flow - so it’s good for transporting substances

Question 14

Why does water’s polarity make it a good solvent?

Answer 14

Many substances in biological reactions are ionic. Due to water’s polarity, the positive side of a water molecules will bind to the anion and the negative side of a water molecules will bind to the cation. This means ions can dissolve in water.

Question 15

What happens to the structure of water when it freezes?

Answer 15

• Becomes less dense
• H bonds fix positions of polar molecules further apart than in liquid state
• This produces a giant, rigid open structure, as each water molecules forms 4 H bonds with other water molecules

Question 16

What is the benefit of water becoming less dense when it freezes for living organisms?

Answer 16

Forms an insulating layer - water below the surface doesn’t freeze