Chapter 3 - Water and Life

Question 1

Properties of Water

Answer 1

• Water is polar due to oxygen being more electronegative
• this creates regions of partial charges
• these regions of partial charges can attract with other water molecules forming hydrogen bonds
• because of the weak nature of hydrogen bonds, which constantly form and break, water can become a liquid

Question 2

Cohesion

Answer 2

the linking together of molecules by hydrogen bonds
- contributes to the transport of water against gravity(up the plant stem) in plants
- Because of high cohesion in water, it therefore has a high level of surface tension

Question 3

Surface Tension

Answer 3

a measure of how difficult it is to stretch or break the surface of a liquid

Question 4

Adhesion

Answer 4

the clinging of one substance to another
- E.g. Hydrogen bonds of water cling/bond to the molecules of cell walls to help counter the downward pull of gravity

Question 5

Kinetic Energy

Answer 5

energy associated with the relative motion of objects,
- Atoms and molecules have kinetic energy because they are always moving

Question 6

Thermal Energy

Answer 6

the kinetic energy due to the random motion of atoms and molecules
- Reflects the total kinetic energy

Question 7

Temperature

Answer 7

a measure in degrees of the average kinetic energy of the atoms and molecules in a body of matter
- Reflects the average kinetic energy

Question 8

Example of relationship between temperature and thermal energy

Answer 8

Boiling water in a pot
- When you heat water the molecules increase in speed and therefore it is measured as an increase in temperature on the thermometer.
- In turn this will increase the thermal energy

- However if you compared the water in the pot to a swimming pool, the pot water will have a higher temperature but the swimming pool has higher thermal energy because there is much more water molecules all moving slower but moving in total more

Question 9

Calorie

Answer 9

the amount of heat it takes to raise the temperature of 1g of water by 1degrees C

Question 10

Specific Heat

Answer 10

the amount of heat that must be absorbed or lost for 1g of that substance to change its temperature by 1 degree C
- A measure of how well a substance resists changing its temperature when it absorbs and releases heat

Question 11

Water’s High Specific Heat

Answer 11

= 1 calorie p/degree C

- Water has a relatively high specific heat to other liquids meaning it needs to absorb a lot of heat for it to change temperature

- As  a result water will change temperature less than other liquids when it gains or loses a given amount of heat

Question 12

Benefits of Water’s High Specific Heat

Answer 12

1. Helps Moderate air temperatures in Coastal areas
   
   2. Stabilizes ocean temperatures, creating ideal environments for marine life

Question 13

Vaporization

Answer 13

molecules who move fast enough can overcome bonds of attraction between other molecules and can depart liquid form and enter the air as gas

Question 14

Heat of Vaporization

Answer 14

the quantity of heat a liquid must absorb for 1g of it to be converted from liquid to gas

- Water, like having a high specific heat also has a high heat of vaporization compared to other molecules - helps again to moderate earths climate

Question 15

Evaporative Cooling

Answer 15

as liquid evaporates, the surface of the liquid remaining behind cools down as the ‘hottest’(quickest moving) molecules have left as gas
○ E.g. sweating in humans,

Question 16

How Can Ice Float on Water

Answer 16

• At temperatures below 0 degrees water freezes because its molecules are moving too slowly to break hydrogen bonds and therefore are locked into crystalline lattices
  
  • The hydrogen bonds which are still linking atoms keep the molecules at far enough distance which makes ice 10% less dense than most molecules

Question 17

Why is Ice Floating Important

Answer 17

• Important for life because if large ice blocks sunk, eventually it could freeze whole oceans
  
  • Instead as the ice floats, it insulates the water below, allowing life to continue living
  • Also provides a solid habitat for organisms

Question 18

Solution

Answer 18

a liquid completly mixed of two or more substances
- includes a solvent(dissolver) and solute(dissolved)

Question 19

Hydration Shell

Answer 19

the sphere of water molecules around a dissolved ion

Question 20

Hydrophilic

Answer 20

any substance which has an affinity(natural liking) for water
- As a result, water adheres to it making items like cotton towels great for drying water off of things

Question 21

Hydrophobic

Answer 21

substances which are nonionic and nonpolar (cannot form hydrogen bonds) seem to repel
- They are major ingredients for cell membranes

Question 22

Molarity

Answer 22

a common measure of solute concentration, referring to the number of moles of solute per litre of solution

Question 23

Molecular Mass

Answer 23

the sum of the masses(number of atoms x atomic mass) of all the atoms in a molecule in Daltons

Question 24

What can Happen during the Dissociation of Water

Answer 24

a hydrogen atom part of a hydrogen bond can leave its electron behind and swap to the other water molecule.
- this turns the hydrogen into a hydrogen ion(gains a positive charge)

- The water molecule which lost the hydrogen is now called a hydroxide ion(OH-)

- The molecule which the hydrogen binds to is now called a hydronium ion(H3O)

Question 25

Acid

Answer 25

a substance which increases hydrogen ions(H+) concentrations in a solution.

• when acids dissolve they donate H+ to decrease the pH

Question 26

Base

Answer 26

a substance which reduces the H+ concentration in a solution to increase pH
- Some bases reduce H+ by directly accepting H+

- Other bases reduce H+ indirectly by dissociating to form H+ which combine with other H+ to form water

Question 27

pH

Answer 27

A measure of Hydrogen ion concentration

• In any aqueous solution at 25 degrees C the product of the H+ and OH- concentrations are constant at 10-14(H+ =10-7, OH- = 10-7)

Question 28

Buffer

Answer 28

a substance that minimizes changes in the concentration of H+ and OH- in a solution
- accepts H+ from a solution where they are in excess and donates them to areas where they have been depleted

Question 29

Ocean Acidification

Answer 29

the process by which the pH of the ocean is lowered when excessive CO2 dissolves in seawater and forms carbonic acid
- prevents animals such as crustaceans from forming exoskeletons