Water

Question 1

What type of bonding holds the hydrogen and oxygen molecules together?

Answer 1

Covalent bonds

Question 2

What type of bonding holds water molecules together?

Answer 2

Hydrogen bonds

Question 3

Explain how water is bonded (using electrons in your answer).

Answer 3

Each oxygen atom shares electrons with two hydrogen atoms. The oxygen atom has a greater affinity for for the electrons than the hydrogen’s so it pulls them closer (the electrons are not evenly distributed along the covalent bond). Making the O slightly negative (δ-) and the hydrogens slightly positive (δ+) which creates charged regions.

Question 4

What is a water molecule?

Answer 4

A polar molecule (it has polarity - its dipolar)

Question 5

Explain hydrogen bonding.

Answer 5

They are weak bonds between a slightly positively charged hydrogen atom and a slightly negatively charged atom in another molecule (in this case its oxygen). Hydrogen bonding gives water some of its useful properties. They provide water’s stable structure.

Question 6

What is a solute?

Answer 6

The thing that dissolves.

Question 7

What is a solvent?

Answer 7

A substance capable of dissolving another substance.

Question 8

What is specific heat capacity (SHC)?

Answer 8

The amount of energy (heat) required to raise 1kg of water through 1 degree centigrade.

Question 9

What is water’s (SHC) like?

Answer 9

High (4.2kJ) due to the H-bonds which helps keep the temperature of large bodies of water constant (most of the thermal energy absorbed is used to break hydrogen bonds and change state so less energy is available to inc. the temp.) - it can buffer (resist) changes in temperature.

Question 10

What is Latent heat of Vaporisation?

Answer 10

The amount of energy required to change the state of 1 kg of a material without changing its temperature.

Question 11

What is water’s latent heat of vaporisation like?

Answer 11

It is high. Water changes state when the hydrogen bonds holding water together are broken. This allows water molecules on the surface to escape into the air as a gas. It is especially difficult because hydrogen molecules continually attract other water molecules, continually making and breaking bonds.

Question 12

What effect does water having a high latent heat of vaporisation have?

Answer 12

Large bodies of water can be cooled with minimal loss of water. Useful for living organisms as they can use water loss through evaporation (via sweating or panting in animals or the transpiration stream in plants) to cool down without loosing too much water - when water evaporates it carries heat energy away from a surface .

Question 13

Why is water such a good solvent?

Answer 13

It has polarity so if the solute is an ionic compound the slightly positively charged end of the water molecule will be attracted to the negative ion and vice versa because opposites attract. Water molecules will surround the solute keeping the solute apart - its dissolved.

Question 14

What does hydrophilic mean?

Answer 14

Will dissolve in water.

Question 15

Examples of water being a good solvent?

Answer 15

Movement of minerals to lakes and seas, absorption of dissolved minerals, transport of dissolved substances (via the blood and lymph in animals), removal of metabolic waste such as urea and ammonia in urine, 70-95% of cytoplasm is water and that is where the basis on metabolic reactions occur.

Question 16

What is cohesion?

Answer 16

The attraction between molecules of the same type (eg. two water molecules).

Question 17

Is water cohesive?

Answer 17

Yes, very - due to the hydrogen bonds and therefore its polarity.

Question 18

What properties does water have due to the fact its cohesive?

Answer 18

Helps water flow meaning its great for transporting substances, high surface tension when it comes into contact with air, makes long thin water columns very strong and difficult to break.

Question 19

Examples of use of water because its cohesive?

Answer 19

Water being pulled up through the xylem in the transpiration stream due to the molecules sticking together (it can flow), surface tension which is the reason why sweat forms droplets form and why insects can walk on the surface of a pond.

Question 20

What is adhesion?

Answer 20

When a substance (eg. water) can stick to other things

Question 21

Why is water such a good lubricant?

Answer 21

Because its cohesive and adhesive which makes it viscous. Eg. synovial fluid (lubricates many vertebrae joints, pleural fluid (minimises friction between lungs and thoracic cage - ribs - during breathing), mucus (permits easy passage of faeces down the colon and lubricates the penis and vagina during intercourse).

Question 22

Give info about waters molecular mobility.

Answer 22

Constant making and breaking of H-bonds because they are so weak which allows osmosis to take place.

Question 23

What is waters transparency like?

Answer 23

Is transparent (lets light through) and has high transmission, so photosynthesis is possible in shallow areas.

Question 24

Give info about waters density as it freezes.

Answer 24

When it cools its density increases until it gets to 4 degrees then it decreases as the water molecules move further apart to provide space for all four H-bonds to fit (it expands) this makes ice float on water, the max no. of hydrogen bonds are formed as it reaches freezing point

Question 25

What benefits does ice floating on water have for the ecosystem?

Answer 25

It insulates the water below so it doesnt freeze allowing organisms underneath to maintain their environment, provides space for penguins and polar bears to walk on.

Question 26

When is calcium used?

Answer 26

In bone formation.

Question 27

When are sodium and potassium used?

Answer 27

In nervous transmition.

Question 28

When is magnesium used?

Answer 28

As part of the structure of chlorophyll.

Question 29

When is chlorine used?

Answer 29

Chloride is used to maintain the correct functioning of the stomach (HCL), used in osmotic balance.

Question 30

When is nitrate used?

Answer 30

In amino acids and DNA.

Question 31

When is phosphate used?

Answer 31

In phospholipids and ATP.

Question 32

What are the five main properties of water and the mnemonic to remember them?

Answer 32

Metabolite, Solvent (most reactions take place in a solution), High Heat Capacity and Large Latent Heat of Vaporisation (temp. control), Cohesion (My sofa has large cushions)

Question 33

What is a metabolite?

Answer 33

Any substance involved in metabolism/reactions

Question 34

What reactions is water involved in that makes it a metabolite?

Answer 34

A hydrolysis reaction requires a water molecule to break a bond, a condensation reaction releases a water molecule as a new bond is formed.Eg. amino acids to polypeptides, releasing of energy via ATP.

Question 35

How does evaporation of water cool down an organism?

Answer 35

When water evaporates it carries heat energy away from a surface and helps to lower the temperature eg. when humans sweat.

Question 36

Why is having a high specific heat capacity beneficial to organisms?

Answer 36

It makes water a good habitat because the the temperature underwater is more likely to be more stable than on land, water inside organisms maintains a stable temperature helping them to maintain a steady internal body temperature (so enzymes can work).

Question 37

Why does water form droplets?

Answer 37

Because of cohesion which causes water to clump together.