2.2 Water Flashcards
(35 cards)
Fill in the blank. Water is made up of __hydrogen atoms ___ bonded to an ____ atom
Two
Covalently
Oxygen
Are electrons shared equally between atoms?
No.
What molecule attracts the electrons more strongly?
Oxygen.
Are water molecules polar or non-polar?
Polar.
Why are water molecules polar?
The shared electrons orbit closer to the oxygen atom than the hydrogen atoms.
Why is water described as being polar?
It has a slight charge difference across the different poles of the molecule.
Outline which of the two atoms is positive or negative (oxygen and hydrogen.)
The oxygen atom is slightly negative.
The hydrogen atom is slightly positive.
Why does water form weak associations with other polar molecules?
Because of the charge difference across the molecule. The slightly negative poles will attract the positive ones, and vice versa.
Why are hydrogen bonds stronger than other polar associations?
Due to the high electronegativity of F, O and N. (?)
Can water form hydrogen bonds with other water molecules?
Yes.
Outline the meaning of the term ‘ thermal properties’.
Water can absorb much more heat before changing state - this requires the breaking of hydrogen bonds.
Outline the meaning of the term ‘ cohesive/adhesive properties’.
Water will stick to other water molecules - cohesion.
Water will stick to charged substances (adhesion).
Outline the meaning of the term ‘ solvent properties’.
Water dissolves polar and ionic substances - it forms competing polar associations to draw materials apart.
Why does water have the capacity to absorb significant amounts of heat before changing state?
It is due to the extensive hydrogen bonding between water molecules.
Name the compound often used for comparing thermal properties.
Methane (CH4).
Compare the sizes and weights of water and methane.
H20 - 18 dalton
CH4 - 16 dalton
Name in total, 2 thermal properties of water, and one thing they result in.
- Water has the capacity to absorb large amounts of heat energy before changing state.
- Water has a high specific heat capacity (energy required to raise temperature of 1g by 1 degrees).
Therefore, water is an effective coolant.
Name 4 things water has more of than methane.
- Higher melting/boiling point.
- Higher specific heat capacity.
- Higher heat of vaporisation.
- Higher heat of fusion.
What does water having a high specific heat capacity allow it to do?
It allows it to absorb a lot of thermal energy before it evaporates.
Outline cohesive properties.
The ability for like molecules to stick together.
Outline adhesive properties.
The ability for dissimilar molecules to stick together.
What can cohesive properties of water explain?
Water’s surface tension.
Explain why water has surface tension, and what it results in.
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.
What can the adhesive properties of water explain?
Capillary action.
