A1.1 Water

COMPLETE

What is a Water molecule ?

A polar molecule made of 1 oxygen and 2 hydrogen atoms.

Where is the Negative pole ?

Area with more electrons, around the oxygen atom.

Where is the Positive pole ?

Area with fewer electrons, near the hydrogen atom nuclei of water molecules.

Why is Cohesion of water molecules is high ?

H-bonds make water molecules attract each other more strongly. It causes surface tension.

Why is Water density lower than ice ?

The extra hydrogen bonds cause cold water molecules to move apart slightly

Why is water a good solvent?

The polar water molecules dissolve so many substances.

Why does Water have dipolarity ?

Because water molecule contains both positive and negative charges.

Why is Water a good coolant in sweat ?

it has a high specific heat capacity

Why is Water good for transport ?

it can easily dissolve glucose, sodium chloride, oxygen, and many amino acids.

Where did the first cells originate from ?

The first molecular cells reacted with each other in a liquid solvent ( water )

Why is water a substance in which life depends on ?

After many years of evolution most molecules of life are still dissolved in water . This allows processes of life to happen as molecules can move around and interact ( when water is in a liquid state )

What happened during formation of the first cells ?

In formation of first cells water became enclosed in a membrane, different substances dissolved in this membrane allowing chemical reactions to occur between solutes.

Describe the structure of a water molecule

There are covalent bonds between hydrogen and oxygen bonds because they share electrons

Why are there polar covalent bonds in water ?

Because of the unequal sharing of electrons in the bonds.

What charges do the molecules in water have ?

Hydrogen= partial positive Oxygen = Partial negative

Describe the location of the polar covalent bond in a water molecule

2 hydrogen atoms are on the same side of molecule and form one pole, singular oxygen atom forms the other pole

What is a hydrogen bond?

A weak bond formed between polar water molecules.

Explain sharing of electrons between atoms in a water molecules

Oxygen has 6 valence electrons and it shares 1 with each of the hydrogen molecules so they have a full shell of 2

Consequences of collective strength of hydrogen bonds between water molecules

As a collective unit the high numbers of hydrogen bonds gives water its unique properties ( make it vital for living things )

Why are there many hydrogen bonds per unit volume of water ?

A hydrogen bond is also known as a weak intermolecular force. Water molecules are small therefore there are many per unit volume of water

How do hydrogen bonds form between water molecules ?

It forms when a positive hydrogen atom is attracted to a negative atom of another polar molecule

Explain the partial charges of oxygen and hydrogen in a water molecule

TBC

Define cohesion

Attraction between molecules of the same type ( 2 hydrogens )

How does water move through the xylem of a plant ?

Water is sucked upwards from the roots to the leaves along tubular vessels in xylem tissues. This continues like a stream as there are continuous columns of water travelling upwards.

How is tension created in a plant ?

There is tension in roots from attraction between soil particles and water. There is tension in leaves as water is lost through evaporation. Tension is also experienced between the cell walls and water molecules Water moves upwards as pulling forces in leaves are greater than forces in roots

How is tension in a plant broken ?

Many hydrogen bonds must be broken simultaneously at one point along the vessel

How is surface tension created?

Cohesive forces affect water molecules equally in all directions, except at the surface where only inward forces are present. The inward forces cause the surface to contract into the smallest possible surface area.

What benefit does surface tension have to living molecules ?

It allows living organisms to use water surfaces as a habitat (pond skaters )

Why is it possible for objects to float on water ?

Cohesion between water molecules due to hydrogen bonds is greater than attractions between water and floating objects

Define adhesion

attraction between molecules of different substances

What is an ion ?

A charged particle

What is polarity?

Having positively & negatively charged areas because of uneven electron distribution

What's the difference between a cation and an anion ?

Cations are positively charged ions whilst anions are negatively charged ions.

Why is water attracted to molecules that are polar or charged ?

A1.1.4

TBC

What is capillary action?

The ability of a liquid to flow against gravity up a narrow tube

What happens to hydrogen bonds during capillary action?

As water is drawn up the change from air filled to water filled creates many hydrogen bonds so there is a release in energy. Hydrogen bonds are also formed between the glass and water causing a further release in energy

How is capillary action useful in plants ?

water adheres to cellulose in cell walls so any wall that begins to dry will be hydrated as long as a water source is available

What is the cause of capillary action in soil ?

The attraction of water to many chemicals in the soil. If soil is porous water is drawn through by capillary action wetting it.

Examples of capillary action in plants:

• When water evaporates from leaf cell walls adhesion forces will allow water to be drawn out of the nearest xylem vessel. This keeps walls moist.

• If xylem were to become air filled adhesion between water and the wall will help to refill the vessel with water

What is a solvent?

The liquid that particles dissolve in

What is a solute?

the substance that is dissolved

What is a solution?

a mixture of solute and solvent

What is solvation?

the interaction between a solvent and the dissolved solute

Why is water able to dissolve charged and polar molecules ?

The polar nature of water means it forms shells around both charged and polar molecules. This prevents them from clumping together.

Water's negative pole is attracted to positive ions. Water's positive pole is attracted to negative ions.

It forms hydrogen bonds with polar molecules

Define hydrophilic

Substances that are chemically attracted to water ( water loving )

Define hydrophobic

Water fearing substances that are attracted to other hydrophobic substances

What substances are hydrophilic?

• Substances with both polar molecules e.g glucose

• Ions e.g sodium and chloride

• Substances that water adheres to e.g cellulose

What substances are hydrophobic?

• non polar

• no positive or negative charges ( not an ion )

• Lipids e.g fats and oils

Why is water the medium for metabolism ?

All reactions occur in the cytoplasm which is a complex aqueous solution of dissolved substances ( water is the solvent ) The solutes in the cytoplasm can move and interact. This means enzymes can catalyse specific chemical reactions.

When refering to metabolisms this refers to all reactions that are catalysed in the cytoplasm.

What are the 2 transport systems in plants ?

• Mineral ions transported in cell sap

• Sucrose and other photosynthesis products are transported in phloem sap

What substances gets transported in blood ?

• sodium chloride

• amino acids

• cholesterol

• glucose

• oxygen

• fats

How is glucose transported ?

It is transported around the body in blood plasma as it is a polar molecule therefore is soluble in water.

How is sodium chloride transported ?

It is transported around the body in blood plasma as it is an ionic compound that will dissolve to form it's separate ions

How are amino acids transported ?

Amino acids are comprised of both hydrophobic and hydrophilic regions which means it has varying solubility. It is soluble enough to be dissolved in blood plasma.

How is oxygen transported?

Due to the water levels in plasma it cannot transport enough O2 around the body as the solubility of oxygen decreases. Bound to hemoglobin

How is fat transported around the body ?

Non polar and therefore insoluble in water. They are coated in a small phospholipid layer which allows fat droplets to be transported in blood plasma

How is cholesterol transported in the blood?

by lipoproteins as it is an insoluble non polar molecule

What is a physical property?

A characteristic of a material that can be observed or measured without changing its chemical structure

What physical properties of water are important for animals in aquatic habitats ?

• High specific heat capacity

• High surface tension

• Thermal conductivity

• Solvent properties

Why does Water has high specific heat capacity ?

some heat is used to break H-bonds so more is needed to raise the temperature.

What is buoyancy?

The ability of a fluid to exert an upward force on an object placed in it

Effect of buoyancy

If density of object is lower than that of the fluid the buoyancy force acting of the object will be greater than the force due to gravity and the object will float.

What causes buoyancy?

The difference in pressure gives rise to a different force

What is viscosity?

the resistance of a liquid to flow

What causes viscosity?

Due to internal friction between the particles of a fluid

Effect of viscosity

The more viscous a fluid the greater the friction and therefore the resistance to flow

Compare viscosity of air to water and blood

The viscosity of air is 50x smaller than that of water at the same temperature

• Blood doesn't flow as easily as water because the solutes increase viscosity

Define thermal conductivity

Rate at which heat passes through an object

What materials are useful as heat insulators and why ?

Fats and oils

Because they conduct heat 25% as quickly as water and 5% air.

Define specific heat capacity

it is the amount of energy needed to raise the temperature of 1 kg of a substance by 1 degrees celsius

Outline a benefit to life of water's high specific heat capacity.

Temperatures of water remains stable in comparison to air temperatures so aquatic habitats are more thermally stable than terrestrial habitats

• Also allows birds and mammals to maintain constant body temperatures

Describe how the ringed seal interacts with the physical properties of water in their habitats

• Spends time submerged in water

• Forages for food in water but rears their young on land -Water is more viscous than air so must use more energy to move through it

Describe how the black-throated loon interacts with the physical properties of water in their habitats

• Flies

• Forages for food in water but rears their young on land

• Air is less dense so provides a less buoyant force

• expends more energy to stay aloft

• Easier to maintain a temperature as air acts as an insulator whilst water conducts heat away from submerged animals

Explain the hypothesis that asteroids are responsible for the origin of water on earth

Water was delivered to earth by colliding asteroids

• There is evidence that there was a much heavier rate of bombardment than once every 20 million years

• The asteroids contained a lot of water

State 2 reasons why water was retained on early earth

• Distance from the sun ensures that sunlight never raises temperatures high enough for water to boil. ( liquid water is retained easier than water vapour due to cohesive forces from hydrogen bonding )

• Earth has relatively strong gravity which holds oceans and atmospheric gases tight. Very little water vapour escapes from atmosphere into space

What is the Goldilocks zone?

Habitable zone around a star where conditions are suitable for life.

Why is the presence of water fundamental to search for extra-terrestrial life?

Liquid water is essential to all known life forms on earth