3.1 The Chemistry of Water

Question 1

What are these properties of water and how do they make water essential for life? (3.1):
cohesion/adhesion/surface tension of water

Answer 1

• Cohesion: Molecules of the same kind sticks together. Water sticks to water, its cohesive nature and high surface tension allows itself to move up the tree.
• Adhesion: Water sticks to other molecules. H2O sticks to other molecules, making the tree trunks, stem, etc.
• Surface tension: Water has high surface tension due to cohesion.

Question 2

What are these properties of water and how do they make water essential for life? (3.1):high specific heat

Answer 2

• Amount of energy required to increase the T of 1g of substance by 1˚C
• Difficult to raise or decrease temperature of water

Question 3

What are these properties of water and how do they make water essential for life? (3.1):
high heat of vaporization

Answer 3

• Amount of heat a liquid must absorb for 1g to be converted to gaseous state
• Evaporative cooling: Surface of an object gets cooler when molecules turn from l to g, where molecules that move fast turns into gas.
• Ocean example: In summer, the temperature is very high, parts of the H2O evaporates, leaving cooler molecules behind, which keeps the surface of the heat relatively cool.

Question 4

Why is ice less dense than liquid water? Why is this important for life? (3.1)

Answer 4

• When H2O is cooled down, the molecular motion is slow and the H-bonds are forming and it’s harder to break. In ice, water molecules are apart from each other in a fixed distance, it forms a lattice structure with a lot of space, resulting in its floating nature.
• It is important because in wildlife nature, the surface of ocean/lake/ponds/rivers cool down in the winter and turns into ice and it floats on top of the water, helps life to survive

Question 5

Why is water so important?

Answer 5

• Life is based on water as water is an excellent solvent. Solute dissolves in solvent to make solution. Substances are more likely to react when they are dissolved in water.
• Huge amount of life and cells depends on molecules interacting with each other, and it’s easier when dissolved in water

Question 6

Hydrogen bonds

Answer 6

Formed between a partial positive H and a partial negative atom, usually O or N

Question 7

Why is water a good solvent?

Answer 7

Due to its nature and ability to form H-bonds with other things that have charge. Hydrophilic atoms/molecules are ions and polar molecules that stays in solution and interacts with H2O.

Question 8

Hydrophobic

Answer 8

Uncharged and non-polar molecules that don’t dissolve in water. It interacts with each other in hydrophobic interactions. Tries its best to move away from hydrophilic substances.

Question 9

Why is water the essential of life?

Answer 9

• Water is cohesive. H2O sticks to H2O through H-bond, resulting in surface tension. Cohesion and surface tension moves H2O up (against gravity) from the roots to tree trunk and stems.
• Water is also adhesive. H2O sticks to other molecules. Through adhesion, H2O sticks to different molecules that makes up the tree trunks, stem, etc.
• H-bond allows tree to move H2O up.

Question 10

Cohesion

Answer 10

Molecules of the same kind stick together

Question 11

Surface tension

Answer 11

How hard is it to break the surface of a liquid.

Question 12

Special thermal properties of water

Answer 12

• Molecular motion of water slows down in low temperature, more H-bonds formed, and the motion speeds up in high temperature, causing more H-bonds to break.
• Vapourization: Water vapourizes due to H2O molecules are moving too fast, energy is absorbed and H-bonds break, causing the liquid to be warm.

Question 13

Specific heat of water

Answer 13

• Amount of E required to increase T of 1g of substance by 1˚C.
• Water has high specific heat, makes it hard to increase and decrease T
• In winter, large bodies of water cooled down, forming H-bonds, releasing heat to the environment, stabilizing planet temperature.