Properties of water

Question 1

‘Hydrogen Bonds’

Answer 1

Form between the changed ends of molecules. Covalent bonding within water molecules distorts electrical charge on water molecule creating dipole molecule.

Question 2

Surface tension in water

Answer 2

High level

Question 3

Dipolar

Answer 3

A water molecule is said to be dipolar because it has a positive and a negative pole as a result of the uneven distribution of electrons within it
The dipole nature within a water molecule creates attractive forces known as hydrogen bonding, allowing them to stick together

Question 4

Unique properties of water

Answer 4

• High heat capacity
• Higher melting and boiling point relative to other hydrogen compounds

Question 5

Bonding of H2O

Answer 5

Covalent

Question 6

Asymmetrical shape

Answer 6

Two hydrogen molecules are at one end, separated by 105 degreed when in the gaseous or liquid phase and 109.5 degrees when ice

Question 7

Oxygen end of molecule

Answer 7

Negatively charged

Question 8

Hydrogen end of molecule

Answer 8

Positively charges

Question 9

Dipole structure of water

Answer 9

Produces an electrostatic bond (hydrogen bond) between water molecules with cluster together

Question 10

Clumps of water molecules

Answer 10

Act to increase the viscosity of water

Question 11

Breaking hydrogen bonds

Answer 11

More energy is required than normal to break up hydrogen bonds

Question 12

As temperature decreases….

Answer 12

• Atoms or molecules move closer
• Density increases because there is more mass (atoms) in the same volume
• Until formation of ice moves them apart
• Maximum density caused by hydrogen bonding

Question 13

What controls density?

Answer 13

Temperature

Question 14

Water dissolves salts by:

Answer 14

• Halite (NaCl) ionic bond
• Surrounding the atoms in the salt molecule
• Neutralising the ionic bond holding the molecule together
• Dissolved salts form cations and anions

Question 15

What lowers the freezing point of water

Answer 15

Adding salt- salt ions intefere with the formations of the hexagonal structure of ice

Question 16

Hydration

Answer 16

The process of water surrounding an ion

Question 17

Seawater salinity

Answer 17

The temperature of maximum density is at the freezing point

Question 18

Surface Cooling

Answer 18

Dense water sinks and surface cooling >4C increases density and promotes overturning. Sinking water is replaced by upwelling

Question 19

Lakes 0-4C

Answer 19

• Cooling <4C lowers density
• Stratified cold layer promotes surface freezing
• Deep water isolated from the surface and remains ‘warm’ throughout winter

Question 20

Density changes in lakes

Answer 20

Causes biannual overturning, and prevent lakes from totally freezing

Question 21

Seasonally fresh water

Answer 21

Reaches maximum density twice a year; while freezing (autumn) and whilst thawing (spring)
e.g. overturning in lakes

Question 22

When sea water freezes to form sea ice…

Answer 22

Salt is rejected during freezing as salt ions interfere with the formation of the hexagonal structure of ice

Question 23

Salt ejection

Answer 23

Leads to salty brine solution- aids overturning circulation- thermocline
- Density of water increases as salinity increases