2.2 Water

Question 1

Fill in the blank. Water is made up of __hydrogen atoms ___ bonded to an ____ atom

Answer 1

Two
Covalently
Oxygen

Question 2

Are electrons shared equally between atoms?

Answer 2

No.

Question 3

What molecule attracts the electrons more strongly?

Answer 3

Oxygen.

Question 4

Are water molecules polar or non-polar?

Answer 4

Polar.

Question 5

Why are water molecules polar?

Answer 5

The shared electrons orbit closer to the oxygen atom than the hydrogen atoms.

Question 6

Why is water described as being polar?

Answer 6

It has a slight charge difference across the different poles of the molecule.

Question 7

Outline which of the two atoms is positive or negative (oxygen and hydrogen.)

Answer 7

The oxygen atom is slightly negative.

The hydrogen atom is slightly positive.

Question 8

Why does water form weak associations with other polar molecules?

Answer 8

Because of the charge difference across the molecule. The slightly negative poles will attract the positive ones, and vice versa.

Question 9

Why are hydrogen bonds stronger than other polar associations?

Answer 9

Due to the high electronegativity of F, O and N. (?)

Question 10

Can water form hydrogen bonds with other water molecules?

Answer 10

Yes.

Question 11

Outline the meaning of the term ‘ thermal properties’.

Answer 11

Water can absorb much more heat before changing state - this requires the breaking of hydrogen bonds.

Question 12

Outline the meaning of the term ‘ cohesive/adhesive properties’.

Answer 12

Water will stick to other water molecules - cohesion.

Water will stick to charged substances (adhesion).

Question 13

Outline the meaning of the term ‘ solvent properties’.

Answer 13

Water dissolves polar and ionic substances - it forms competing polar associations to draw materials apart.

Question 14

Why does water have the capacity to absorb significant amounts of heat before changing state?

Answer 14

It is due to the extensive hydrogen bonding between water molecules.

Question 15

Name the compound often used for comparing thermal properties.

Answer 15

Methane (CH4).

Question 16

Compare the sizes and weights of water and methane.

Answer 16

H20 - 18 dalton

CH4 - 16 dalton

Question 17

Name in total, 2 thermal properties of water, and one thing they result in.

Answer 17

1. Water has the capacity to absorb large amounts of heat energy before changing state.
2. Water has a high specific heat capacity (energy required to raise temperature of 1g by 1 degrees).
   Therefore, water is an effective coolant.

Question 18

Name 4 things water has more of than methane.

Answer 18

1. Higher melting/boiling point.
2. Higher specific heat capacity.
3. Higher heat of vaporisation.
4. Higher heat of fusion.

Question 19

What does water having a high specific heat capacity allow it to do?

Answer 19

It allows it to absorb a lot of thermal energy before it evaporates.

Question 20

Outline cohesive properties.

Answer 20

The ability for like molecules to stick together.

Question 21

Outline adhesive properties.

Answer 21

The ability for dissimilar molecules to stick together.

Question 22

What can cohesive properties of water explain?

Answer 22

Water’s surface tension.

Question 23

Explain why water has surface tension, and what it results in.

Answer 23

The hydrogen bonding between water molecules allows the liquid to resist low levels of external force. The high surface tension makes it sufficiently dense for smaller organisms to move along its surface.

Question 24

What can the adhesive properties of water explain?

Answer 24

Capillary action.

Question 25

Outline capillary action, and what it results in.

Answer 25

Attraction to charged or polar surfaces allows water to flow in opposition of gravitational forces. It is necessary to allow water to be transported up plant stems via a transpiration stream.

Question 26

What kind of solvent is water normally referred to as?

Answer 26

A universal solvent.

Question 27

Why is water a universal solvent?

Answer 27

It has the capacity to dissolve a large number of substances.

Question 28

Why is water able to dissolve any substance containing charged particles?

Answer 28

The polar attraction can weaken intramolecular forces, resulting in the dissociation of atoms.

Question 29

Define hydrophillic.

Answer 29

‘Water loving’ - substances which freely associate and readily dissolve in water.

Question 30

Define hydrophobic.

Answer 30

‘Water hating’ - substances which don’t freely associate or dissolve in water.

Question 31

Fill in the blank. The transport of essential molecules within the bloodstream will depend on their ___ in water

Answer 31

Solubility.

Question 32

Name an example of a water soluble substance.

Answer 32

Sodium chloride.

Question 33

Name an example of a water insoluble substance.

Answer 33

Lipids (eg. fats and cholesterol)

Question 34

Name two other existing properties of water.

Answer 34

1. Water is transparent, allowing light to pass through (important for photosynthesis and vision)
2. Water expands when frozen, becoming less desne (important for life on earth - ice floats and the oceans underneath won’t freeze)

Question 35

What are the benefits and uses of solvent properties in water?

Answer 35

They make water an important medium for metabolic reactions, and make water a good transport medium.