Water

Question 1

Structure of water

Answer 1

Two hydrogen atoms and one oxygen atom joined by covalent bonds.

Question 2

Charge of water

Answer 2

-The oxygen atom is more electronegative than the hydrogen atoms.

-This means that oxygen has a greater pull on the electron cloud that exists between the atoms.

-Therefore, oxygen acquires a slightly negative charge (δ-), leaving each hydrogen atom with a slightly positive charge (δ+).

-The polarity of water is the main reason for its important biological properties such as solvency, cohesion, and adhesion.

Question 3

The symbol delta δ is used to denote ___

Answer 3

Partial changes in charge

Question 4

Why are water molecules polar?

Answer 4

they have an asymmetrical shape and an electronegative difference

Question 5

What does the polarity of water molecules allow?

Answer 5

-The formation of hydrogen bonds between water molecules: the partially positive hydrogen atoms of one molecule are attracted to the partially negative oxygen atoms of other water molecules.

-This means that most polar or charged compounds can be dissolved in water.

-Such compounds are said to be hydrophilic.

Question 6

What are hydrogen bonds?

Answer 6

-Weak interactions between water molecules

-These are responsible for many important properties of water such as cohesion and adhesion.

Question 7

Examples of hydrophilic compounds

Answer 7

Sugars and most salts

Question 8

Glucose and fructose are both ___

Answer 8

Hydrophilic and can be dissolved in water.

Question 9

Explain what is meant by the term ‘solvent’.

Answer 9

A substance that can dissolve a solute

Question 10

What properties does the polarity or dipolarity of water explain?

Answer 10

1) Cohesion

2) Adhesion

3) Thermal properties

4) Solvent properties

Question 11

Which property of water makes it essential for metabolic reactions?

Answer 11

It is the universal solvent

Question 12

State why it is important for living organisms that glucose is soluble in water.

Answer 12

So it can be transported around the organism

Question 13

What kind of substances are fats and oils?

Answer 13

-Non-polar substances.

-There is no attraction between them and water molecules; instead they repel each other.

-You can’t mix water and oil because oil is hydrophobic.

Question 14

Example of a hydrophobic property in nature.

Answer 14

-Some leaves have a waxy cuticle that has strong hydrophobic properties.

-It causes water to form droplets to minimize contact between the leaf and the water.

Question 15

A hydrophilic substance is one that ___

Answer 15

Is soluble in water.

Question 16

What types of compounds can be dissolved in water?

Answer 16

Polar compounds

Question 17

Cohesion of water

Answer 17

-This is the tendency of water molecules to stick to each other due to the hydrogen bonding between them.

-Each water molecule can potentially form four hydrogen bonds with other water molecules in a tetrahedral arrangement.

Question 18

Describe how water acts as a solvent in the process of digestion.

Answer 18

Dissolves the smaller food molecules / nutrients; allowing them to be more easily absorbed
into the bloodstream

Question 19

Explain the high surface tension of water (cohesion)

Answer 19

-Although hydrogen bonds are weak bonds, the presence of a large number of hydrogen bonds in water gives the cohesive forces great strength.

-This, in turn, is responsible for the high surface tension of water, i.e. the stickiness, due to hydrogen bonding, of water molecules makes the water surface behave as a strong elastic membrane, allowing small organisms or some objects that are denser than water, to float on the water surface.

-Surface tension is also responsible for water droplets adopting a spherical shape, minimizing the ratio of area to volume.

Question 20

Adhesion of water

Answer 20

-This is the interaction that water molecules have with other (different) molecules (e.g. a glass surface) and explains why water molecules stick to other polar compounds by forming hydrogen bonds.

-Forces of adhesion are responsible for capillary action, which is defined as the movement of water molecules and all the things that are dissolved in it within thin spaces without relying on gravity.

-This property of water molecules is essential to allow water to be transported up the stems of plants.

Question 21

Define cohesion and adhesion (how are they different)?

Answer 21

-Cohesion and adhesion describe different properties of water molecules.

-Cohesion is the interaction among water molecules, while adhesion is the interaction between water molecules and a surrounding material or surface.

Question 22

Thermal properties of water

Answer 22

-The hydrogen bonds that hold water molecules together are responsible for the unique thermal properties of water including the high specific heat capacity.

-In order to break down the hydrogen bonds in water, a high amount of energy is needed.

-The high specific heat capacity of water means that the temperature in aquatic ecosystems, for example, ponds, lakes, and seas, does not change rapidly, making these ecosystems stable.

Question 23

Define specific heat capacity

Answer 23

The amount of heat that must be absorbed or released for 1g of a substance to change its temperature by 1°C.

Question 24

Why is water a great coolant?

Answer 24

-Because a large amount of energy is needed to turn liquid water into water vapor.

-This means that water has a high latent heat of vaporization, which can be defined as the amount of heat 1 g of a liquid absorbs to change its state from liquid to gaseous.

-When the water in sweat evaporates on the surface of our skin, it cools down its surface by taking away energy in the form of heat.

-If we compare water to any other substance, it has a high heat of vaporization.

-Related to the high heat of vaporization is the boiling point.