Water

Question 1

What does a molecule of water consist of?

Answer 1

Two Hydrogen atoms covalently bonded to 1 Oxygen atom

Question 2

Why is Water Dipolar?

Answer 2

Oxygen is slightly negative (indicated by δ–) and the hydrogens slightly positive (indicated by δ+). This is known as a dipole. This creates different charged regions, making water a polar molecule. Because it has two charged regions, it is dipolar.

Question 3

What Causes Oxygen and Hydrogen to gain a slight charge?

Answer 3

Each hydrogen shares a pair of electrons with the oxygen. The oxygen has a greater
affinity for electrons than the hydrogens, so it ‘pulls’ the electrons closer

This makes the oxygen slightly negative (indicated by δ–) and the
hydrogens slightly positive (indicated by δ+)

Question 4

State the 8 Properties of Water.

Answer 4

Cohesion
Surface tension
High specific heat capacity
High latent heat of vaporization
Good solvent Amphoteric
Liquid at room temperature
Capillarity

Question 5

Why are Hydrogen Bonds important?

Answer 5

Many of the properties of water are due to its ability to
form hydrogen bonds.

Question 6

How do Hydrogen Bonds form?

Answer 6

The slight negative charge on the oxygen atom makes it
attract the slightly positive hydrogen atom of another
water molecule

Question 7

Explain the Property of Cohesion.

Answer 7

water molecules stick together enabling water flow

Question 7

Explain the Property of Surface tension and how it is a biological role of water.

Answer 7

water behaves as though it has skin on its surface. This allows water skater insects to walk on water without sinking in. The surface tension of water because water forms hydrogen bonds that holds
the water layers together

Question 8

Explain the Property of High specific heat capacity and how it is a biological role of water.

Answer 8

a lot of energy is required to raise 1g of water by 1oC. This stops rapid water temperature changes and is thus good for aquatic animals

Question 9

Explain the Property of High latent heat of vaporization and how it is a biological role of water.

Answer 9

it takes a lot of heat to make water 8evaporate.

Question 10

Explain the Property of water being a Good solvent.

Answer 10

water dissolves ionic and polar substances like salts, organic
molecules (e.g. amino acids), alcohol and others as it is polar itself. These
polar substances are hydrophilic (friends with water) while hydrophobic
molecules are repelled by water (afraid of water!). The positive end of a
water molecule will be attracted to a negative ion and the negative end to a
positive ion meaning that the ion gets surrounded by water molecules and
hence dissolves.

Question 11

Explain the Property of Amphoteric.

Answer 11

acts as an acid (H+) and an alkali (OH-).

This allows water to act like a buffer – a substance the prevents changes in pH
when acid or base is added

Question 11

Explain the Property of Liquid at room temperature as a biological role of water.

Answer 11

water provides a liquid environment within cells and aquatic organisms.

Question 12

Explain the Property of Capillarity as a biological role of water.

Answer 12

water can move up a narrow tube against gravity by capillarity
or capillary action. Water molecules stick to the side of the tube by adhesion.
This allows for water transport in organisms (xylem and circulatory system)

Question 13

Water + insoluble liquid =?

Answer 13

Insoluble liquids can form emulsions
(tiny droplets of one liquid suspended
in another liquid).

Question 14

Water + insoluble solid=?

Answer 14

Insoluble solids form suspensions
(solids mixed in a liquid where they
will separate if not stirred).

Question 15

Why is Water a good solvent? e.g sodium chloride

Answer 15

NaCl is a ionic substance made up of positive Na + ions and Negative Cl - ions

These can therefore attract the dipolar water molecules

Na + attracts the slightly negative Oxygen atoms in the water molecule

Cl - attracts the slightly Positive Hydrogen atoms in the water molecule

The molecules form a layer around the ions and break the ionic substances apart

Question 16

Why are Non-polars molecules such as lipids insoluble?

Answer 16

Because the do not attract the water molecules