M1:05 Water (different to 01a)

Question 1

How are water molecules bonded?

Answer 1

covalently between the hydrogen and oxygenbut water molecules are hydrogen bonded to each other

Question 2

How is water often described?

Answer 2

As a polar molecule

Question 3

Describe a hydrogen bond

Answer 3

a weak interaction that can occur whenever molecules contain a slightly negatively charged atom bonded to a slightly positively charged hydrogen. Water molecules bond

Question 4

What happens in a mixture of pure water in terms of hydrogen molecules and what affect does this have on the water?

Answer 4

hydrogen bonds are constantly being formed and broken, which makes it much more difficult for the molecules to escape as gas.

Question 5

What happens as the temperature falls in water?

Answer 5

there is less kinetic energy so more hydrogen bonds form, and these bonds dont break as easily.

Question 6

What happens as water becomes solid?

Answer 6

the hydrogen bonds formed hold the structure in a semi crystalline forms which is less dense than water, so ice forms on the surface of water.

Question 7

How does water remain stable even when temperature changes dramatically?

Answer 7

as the hydrogen bonds in liquid water restrict the movement of the water molecules so a relatively large amount of energy is needed to increase the temperature of water.

Question 8

What affect does it have that the evaporation of water uses up a relatively large amount of energy?

Answer 8

water evaporating from a surface ‘removes’ heat from the surface, so heat is used in evaporation

Question 9

At what temperature does water stop becoming more dense when it is cooling?

Answer 9

4 degrees

Question 10

How does the fact that ice floats aid the enviroment ?

Answer 10

it means living organisms can survive under it in the winter, prevents whole lakes from freezing

Question 11

Why does water remain spherical and barely wet a waxy surface?

Answer 11

because the hydrogen bonds pull water molecules in at the surface. (cohesion) cohesion also results in the surface tension seen at the surface of a body of water.

Question 12

When will substances dissolve in water?

Answer 12

if the solute is slightly negatively charged is some parts and slightly positively in others. When water molecules cluster arounds the slightly charged parts of the solute moleculeWhich keeps the solute molecules apart, so they are dissolved

Question 13

What happens once a solute is dissolved in water?

Answer 13

the molecules can move around and react with other molecules, which is the basis of most metabolic reactions, that take place in the cytoplasm

Question 14

Why do ions dissolve easily?

Answer 14

As water molecules can cluster around them and separate them.

Question 15

Why is water ideal as a mode of transport?

Answer 15

As it remains liquid over a large temperature range so can act as a solvent for many chemicals

Question 16

Name the importance and an example of water being a solvent

Answer 16

i; metabolic processes in all organisms rely on chemicals being able to react together in a solutioneg; 70-95% of cytoplasm is water, and dissolved chemicals take part in processes such as respiration and photosynthesis in living organisms

Question 17

Name the importance and an example of water being a liquid

Answer 17

im; the movement of materials around organisms require a liquid transport mediumeg; blood in animals, and the vascular tissues in plants use water as a transport medium

Question 18

Name the importance and an example of water being a cohesive product

Answer 18

im; water molecules stick to each other creating surface tension at the water surface , cohesion also makes long, thin water columns very strong and difficult to break eg; transport in the xylem relies on water molecules sticking to each other as they are pulled up by the xylem in the transpiration stream, and some small organisms (eg pond skaters) make use of surface tension to walk on water

Question 19

Name the importance and an example of water being able to freeze

Answer 19

im; water freezes, forming ice on the surface and water beneath becomes isolated and less likely to freeze.eg; organisms such as polar bears live in an enviroment of floating packs and lakes tend not to freeze over completely, so aquatic organisms are not killed as temp falls.

Question 20

Name the importance and an example of water being thermatically stable

Answer 20

im; large bodies of water have fairly constant temperatures, and evaporation of water can cool surfaces by removing heat eg; oceans provide a relatively stable enviroment in terms of temperature and many land based organisms use evaporation as a cooling mechanism eg panting/sweating

Question 21

Name the importance and an example of water being a metabolic substance

Answer 21

im; water takes part as a reactant in some chemical processes eg. water molecules are used in hydrolysis reactions and in the process of photosynthesis