Water

Question 1

Draw a water molecule – label the atoms and the charge on them. (F)

Answer 1

H-O-H

• H has a partial +ve charge
• O has a partial -ve charge

Question 2

Describe the structure of a water molecule.

Answer 2

An oxygen atom covalently bonded to two hydrogen atoms.

Question 3

Name the bond that can link two water molecules together.

Answer 3

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

• a hydrogen bond is a strong intermolecular force
• it joins together H atoms with O, N or F atoms
• they can be found between water molecules

Question 5

Draw two water molecules and draw and label the bond that links them together. (F)

Answer 5

H-O-H ||||||| H-O-H

Question 6

Define the term “polar”. (F)

Answer 6

Molecules which have regions of negativity and positivity.

Question 7

Explain why water is a polar molecule. (S+C)

Answer 7

Water is a polar molecule because oxygen has a higher electron density than hydrogen as it is more electronegative.

Question 8

Define the term “electronegativity” and “dipole”. (S+C)

Answer 8

Electronegativity: the ability of an atom to attract a pair of electrons in a covalent bond.

Dipole: when there is an unequal sharing of electrons between atoms in a molecule.

Question 9

List the roles water plays in life (at least 5).

Answer 9

• solvent
• transport medium
• coolant
• reactant
• habitat

Question 10

Explain why the polar nature of water allows it to be a useful solvent. (F)

Answer 10

• many compounds are ionic so have +ve and -ve charges
• the partial charges of water are attracted to these
• water molecules cluster around the ions

Question 11

Explain why the polar nature of water allows it to be a transport medium. (F)

Answer 11

• has a high specific heat capacity
• remains a liquid for a large range of temperatures
• good solvent
• can dissolve compounds and then carry them as a liquid

Question 12

Explain why the polar nature of water allows it to be a useful coolant. (F)

Answer 12

• high latent heat of evaporation
• most of the energy going into heating up water is used breaking hydrogen bonds
• when it evaporates, it takes away the heat energy (i.e. sweat)
• because it maintains constant temperatures, allows enzymes to function

Question 13

Explain why the polar nature of water allows it to be a useful reactant. (F)

Answer 13

• metabolic reactions

- condensation and hydrolysis

Question 14

Explain why the polar nature of water allows it to be a useful habitat. (F)

Answer 14

• high specific heat capacity
• difficult to change temperature
• provides a constant environment
• ice floats (due to hydrogen bonding) and forms an insulating layer above the water
• surface tension is strong enough to support small insects

Question 15

Define the term “hydrophilic”.

Answer 15

Attracted to water

Question 16

Define the term “cohesion”.

Answer 16

When molecules are attracted to each other

Question 17

Define the term “hydrophobic”.

Answer 17

Repelled by water

Question 18

Define the term “adhesion”.

Answer 18

When molecules are attracted to other materials