Lesson 3 - Water

Question 1

Which part of water molecule is negative and which is positive

Answer 1

The Oxygen is partially negative
The hydrogen is partially positive

Question 2

What is electronegativity

Answer 2

the measure of an atom’s pull on a bonded pair of electrons

Question 3

Main properties of water and their uses

Answer 3

• a metabolite in many metabolic reactions: condensation and hydrolysis reactions
• an important solvent in which metabolic reactions occur
• has a relatively high heat capacity, buffering changes in temperature
• has a relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporisation
• has strong cohesion between water molecules; this supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air

Question 4

Which bonds are stronger, covalent or hydrogen bonds?

Answer 4

Covalent

Question 5

Because water is cohesive it results in…

Answer 5

Surface tension

Question 6

Surface tension allows…

Answer 6

Provides habitats for organisms, e.g. the pond skater

Question 7

Name 2 practicals that show surface tension

Answer 7

Floating pins
Penny practical

Question 8

Electronegativity meaning

Answer 8

The measure of an atom’s pull on a bonded pair of electrons

Question 9

Name the intermolecular bonds and intramolecular bonds in a molecule water

Answer 9

intermolecular bonds - between molecules (hydrogen bond)
intramolecular bonds - within the molecule in between the atoms (covalent bond)

Question 10

Cohesion definition

Answer 10

Water to water attraction

Question 11

Adhesion definition

Answer 11

Water to xylem vessel

Question 12

Hydrophobic definition

Answer 12

Not attracted to water (e.g. fats/oils)

Question 13

Hydrophilic definition

Answer 13

Attraction for water

Question 14

How is water a solvent

Answer 14

• It dissolves charged ionic molecules, such as salt (NaCl)
• It also dissolves other polar molecules, such as glucose (sugar), that can form hydrogen bonds with the water molecules (contains OH groups)

Question 15

Condensation reactions

Answer 15

a chemical reaction in which water is produced when smaller molecules are joined to form a larger molecule

Question 16

Hydrolysis reactions

Answer 16

a chemical reaction in which a water molecule is needed to break up a large molecule into smaller molecules

Question 17

water is a solvent and a metabolite… how is it used as a transport medium in animals

Answer 17

plasma in the blood (watery solution) transports dissolved substances eg. sugars, urea, salts, ions

Question 18

water is a solvent and a metabolite… how is it used as a transport medium in plants

Answer 18

xylem vessels transport water and dissolved minerals. Phloem transports water and dissolved sucrose and amino acids

Question 19

Definition of a high specific heat capacity

Answer 19

A large amount of energy is required to raise the temperature by 1 degrees

Question 20

Positives about water having a high specific heat capacity

Answer 20

water buffers changes in temperature and so it is thermostable, providing a stable environment for aquatic organisms.

Question 21

Does water have a small or large latent heat of vaporisation?

Answer 21

A large amount of energy is required to evaporate water

Question 22

Density and freezing (apply to water)

Answer 22

• As water freezes it expands (water molecules are held further apart by hydrogen bonds) therefore frozen water is less dense than liquid water therefore floats
• The frozen ice layer insulates the water below it therefore the water below doesn’t freeze (allowing sustained life below)

Question 23

Positives of water being transparent

Answer 23

Light travels through water allowing aquatic plants/algae to photosynthesise