3.2 Water

Question 1

What can the unequal sharing of electrons cause?

Answer 1

Atoms with the greater share of negative electrons, will be slightly negative (δ-) compared to the other atom in the bond, which will therefore be slightly positive (δ+).

Question 2

What is meant by a molecule being polar?

Answer 2

They have regions of negativity and regions of positivity.

Question 3

Give two examples of elements that do not share electrons equally in a covalent bond.

Answer 3

Oxygen and hydrogen.

Question 4

Why are hydroxyl groups slightly polar?

Answer 4

They contain the elements hydrogen and oxygen which do not share electrons equally between them.

Question 5

What are hydrogen bonds?

Answer 5

Relatively weak interactions, which break and reform between the constantly moving water molecules.

Question 6

How do polar molecules interact with each other?

Answer 6

Positive and negative regions attract each other to form hydrogen bonds.

Question 7

How can hydrogen molecules be strong despite individual hydrogen bonds being weak?

Answer 7

To be strong, hydrogen bonds occur in high numbers.

Question 8

Why does water have a high boiling point and therefore a high specific heat capacity?

Answer 8

A lot of energy is needed to overcome the strong hydrogen bonds and increase the water temperature to become gaseous.

Question 9

What is specific heat capacity?

Answer 9

Amount of heat needed to raise the temperature of a substance by 1°C

Question 10

Why is ice less dense than water?

Answer 10

Hydrogen bonds fix the positioning of the polar water molecules slightly further apart than the average distance of water molecules in a liquid state. A giant, rigid and open structure is formed that allows ice to float.

Question 11

What is cohesion?

Answer 11

Molecules that are attracted to each other.

Question 12

How does water have cohesive properties and give some examples of cohesion in water.

Answer 12

Molecules are attracted to each other which allows water to move as one mass. This, therefore, allows plants to take up water from their roots and allows us to drink water through a straw.

Question 13

What is adhesion?

Answer 13

Molecules that are attracted to other materials.

Question 14

How does water have adhesive properties and give some examples of cohesion in water.

Answer 14

Water molecules are attracted to other materials, this is why when your hands become wet the water doesn’t run off straight away.

Question 15

Why is water sometimes referred to as having a ‘skin’?

Answer 15

Water molecules are more strongly cohesive to each other than to air, creating surface tension and allowing small insects to inhabit water surfaces.

Question 16

Why does water act as a solvent?

Answer 16

Water is a polar molecule in which many solutes are polar molcules, such as amino acids, proteins, and nucleic acids, in an organism can be dissolved.

Question 17

What mainly makes up the cytosol of prokaryotes and eukaryotes?

Answer 17

Water.

Question 18

Why does water act as a medium and help with transport?

Answer 18

Water is able to dissolve many substances.

Question 19

Why is water a very efficient transport medium within living organisms?

Answer 19

Cohesion and adhesion result in water exhibiting capillary action.

Question 20

What is capillary action?

Answer 20

The process by which water can rise up a narrow tube against the force of gravity.

Question 21

Why does water act as a coolant to help buffer temperature changes during chemical reactions in prokaryotic and eukaryotic cells?

Answer 21

Due to the large amounts of energy needed to overcome the hydrogen bonds. Temperatures in cellular environments can be controlled as enzymes are often active in a narrow temperature range.

Question 22

Why is water stable and therefore provide a constant environment?

Answer 22

Water does not change temperature or become a gas easily.

Question 23

Why can aquatic organisms survive freezing temperatures?

Answer 23

When water freezes, it turns to ice which is less dense than water. This creates a layer of insulation above the water.