Water

Question 1

Draw a water molecule with charges

Answer 1

1. 2 hydrogen atoms and 1 oxygen atom arranged in a non-linear shape.
2. Delta + charge on hydrogen and delta - on oxygen
3. Label the bond between hydrogen and oxygen as polar covalent bond

Question 2

Describe structure of a water molecule

Answer 2

A water molecule is composed of 2 hydrogen atoms and 1 oxygen atom. they are bonded by polar covalent bonds.

Question 3

Names the bond that can link two water molecules together.

Answer 3

A hydrogen bond

Question 4

Explain what a hydrogen bond is, which types of atoms it can join together and where they occur in
biology.

Answer 4

The slightly negatively-charged oxygen atoms attract the slightly negatively-charged hydrogen atoms of other water molecules - this attraction is hydrogen bonding.
Hydrogen bonding occurs between a hydrogen atom and another strongly electro-negative atom of a polar covalent bond in the same or another molecule.

Question 5

Draw two water molecules and label the bond that links them together.

Answer 5

1. Draw two water molecules.

2. Dotted line between the oxygen of one and a hydrogen of another and label it hydrogen bond

Question 6

Define the term polar.

Answer 6

The uneven distribution of charge, which results in the atoms within a molecule to have opposing charges. eg, one having a partial negative charge and one having a partial positive charge.

Question 7

explain why water is a polar molecule

Answer 7

Because oxygen is more electronegative than hydrogen- it has a greater pull on shared electrons, the electrons are pulled closer to the oxygen atom which leaves hydrogen with a delta positive charge and oxygen with a delta negative charge.

Question 8

Define the term electronegativity

Answer 8

The measure of the tendency of an atom to attract bonding pairs of electorn

Question 9

Define the term dipole

Answer 9

a molecule that has both positive and negative charges due to uneven distribution of charges.

Question 10

roles water plays in life

Answer 10

1. water is a reactant
2. water is a solvent
3. water transports substances.
4. water helps with temperature control
5. water is a habitat

Question 11

Explain how the polar nature of water makes it’s freezing point 0 and boiling point 100.

Answer 11

because water is polar hydrogen bonds form between the molecules collectively these bonds require a lot energy to break and seperate the water molecules- which is why water has a high boiling point

Question 12

Explain the biological significance of water’s boiling and freezing point

Answer 12

because water’s boiling point 100 degrees it is liquid at most environmental temperatures and provides a stable aquatic environment for animals and a medium for chemical reactions.

Question 13

Explain how the polar nature of water gives it a high specific heat capacity

Answer 13

Hydrogen bonds give water hshc. the hydrogen bonds between molecules can absorb a lot of energy so it takes a lot of energy to heat it up

Question 14

What is high specific heat capacity

Answer 14

The energy needed to raise the temperature of 1 gram of a substance by 1 degrees Celsius.

Question 15

Explain the biological significance having a HSHC

Answer 15

Having an HSFC means a large quantity of energy to raise the temp by 1 degrees. so water temp is fairly stable reducing fluctuations in organisms and environments, cells and aquatic environments slow to freeze.

Question 16

Explain how the polar nature of water gives a high latent heat of vapourisation

Answer 16

It takes a lot of energy to break the hydrogen bonds (polar) between water molecules because hydrogen bonds absorb a lot of energy, so a lot of energy is used up when trying to evaporate it.

Question 17

Explain the biological significance of a High latent heat of vapourisation

Answer 17

Effective as a coolant through sweating , panting and transpiration. As a large amount of energy is expended in evaporating sweat form the skin.

Question 18

Explain how the polar nature of water means that is has a lower density when solid

Answer 18

Water molecules are held further apart in ice than in liquid water because each water molecule form four hydrogen bonds to other water molecules, making a lattice shape. So takes up a greater volume in less space- so ice is less dense than liquid water.

Question 19

Explain the biological significance of having a lower density when solid

Answer 19

Ice floats on water leaving liquid water beneath- so in cold temps ice forms and insulating layer on top of water so the water below doesn’t freeze, and organisms like fish don’t freeze.
High density provides upthrust supporting weight.

Question 20

When is water at it’s highest density

Answer 20

4 degrees celsius

Question 21

Explain how the polar nature of water makes it a good solvent for ionic and polar molecules

Answer 21

As one side of the water molecule is delta +ve and one side is delta -ve they attract to ionic compounds and polar. because the delta +ve side attracts to the negative ion in the compound (Cl-) and levers it out of its solid lattice structure and the many H2Os surround it (sphere of hydration) meaning its’ dissolved. the same happens with the delta -ve side and the +ve ion

Question 22

Explain the biological significance of it being a good solvent for ionic and polar molecules

Answer 22

Enables transport of substances in solution.

Metabolic reactions take place in solution.

Question 23

Hydrophilic

Answer 23

Attracts water

Any charged or polar molecule, group or ion forms electrical bonds with water and dissolves.

Question 24

Hydrophobic

Answer 24

Repels water
Any uncharged or non-polar molecule, group or ion doesn’t form electrical bonds with water and doesn’t dissolve.
Hydrocarbon
Phospholipid have both hydrophobic and hydrophilic regions.

Question 25

Explain how the polar nature of water makes it cohesive

Answer 25

Cohesion is the attraction between molecules of the same type. Water molecules are very cohesive because they have hydrogen bonds between them as they are polar.

Question 26

Explain the biological significance of water being cohesive

Answer 26

Creates water column of transpiration stream and creates a surface on which small organisms are supported

Question 27

Explain how the polar nature of water makes it adhesive

Answer 27

Adhesion is the attraction between water molecules and the molecules of another substance. this is because it forms hydrogen bonds to other polar molecules.

Question 28

Explain the biological significance of water being adheisve

Answer 28

It allows capillary action (water rises up narrow tubes) and moves through narrow spaces as it adheres to the surface of them. E.g when water rises up the xylem vessels and through air spaces between particles in soil.

Question 29

Properties unrelated to being a polar molecule

Answer 29

1. Reactivity
2. Transparency
3. Poor conductivity
4. low viscosity

Question 30

Explain the biological significance of water’s Reactivity

Answer 30

water can take part in reactions, takes part in hydrolysis and condensation reactions and is a major part in photosynthesis

Question 31

Explain the biological significance of Transparency

Answer 31

Allows photosynthesis to happen in aquatic environments . allows light to penetrate cells for photosynthesis in plants.

Question 32

Explain the biological significance of low viscosity

Answer 32

Water molecules slide past each other readily so flows readily. allows transport through vessels e.g. xylem and blood vessels.

Question 33

Using the “polar nature of water” explain the how water can dome above the level of the glass container it is in, the shape of the meniscus in a glass measuring cylinder and capillary action in a narrow glass tube. (S+C)

Answer 33

Because water is cohesive as they form hydrogen bonds as they are polar. so they stick together and are difficult to split apart and so when they rise up over the level of heir container they form a dome this is called surface tension.