Hydrosphere Contents

2. Properties Of Water

Conclusions

Water has a number of unique chemical and physical properties which enable it to act as a universal solvent and life-giving fluid throughout the world. These properties are: its density; its melting and boiling points; its heat capacity; its heat of vaporisation; its surface tension; its ability to absorb radiation; and its solvent properties.

Questions and answers

1. What atoms does a water molecule comprise of?

question 1 answers

2.At what temperature is freshwater at maximum density and what is the significance of this?

question 2 answers

3. What is significant about the high melting and boiling points of water?

question 3 answers

4. What is the heat capacity of a liquid?

question 4 answers

5. What is heat vaporisation and why is it significant?

question 5 answers

6. What is significant about the surface tension of water?

question 6 answers

7.What is significant about the capacity of water to absorb radiation?

question 7 answers

8.Why is water an excellent solvent of chemical species?

question 8 answers

Question 1 answer

Two hydrogen molecules and one oxygen molecule.

Question 2 answer

The maximum density of water is at 4°C not at freezing point. As lake water cools towards 4°C, it gets heavier and sinks. Below 4°C, the cold water will actually float over the denser 4°C water. The cold surface water cools below 0°C, freezes and forms a layer of ice on the surface of the lake. This insulates the lake from further freezing, so a frozen lake has liquid water at depth. As a result, many organisms that live in lakes can survive sub zero temperatures.

Question 3 answer

Both are unusually high, allowing global distribution of water and associated organism colonisation, from the deserts to polar environments.

Question 4 answer

The heat capacity of a liquid is the amount of energy (heat) required to increase the temperature of that liquid by a given number of degrees. Water has the highest heat capacity of any liquid except ammonia.

Question 5 answer

It is the amount of heat required to convert liquid water into a gas or vapour form. It is the heat released when vapour condenses to form droplets. Heat vaporisation is the mechanism whereby hurricanes and other tropical storms obtain their tremendous destructive energy. It also represents a mechanism which moderates the extremes of the Earth and makes it a suitable place for life to develop.

Question 6 answer

Water has a very high surface tension. The surface tension properties of water is responsible for the shape of liquid water droplets and for the droplet formation in clouds.

Question 7 answer

Water absorbs a large fraction of the energy it receives, particularly in the infra-red range. This in an important component of the natural greenhouse effect and helps to regulate temperature in the atmosphere. Water absorbs quite weakly in the visible light range, allowing photosynthesis at substantial ocean depths.

Question 8 answer

Because of the polar nature of the water molecule, ionic species dissolve in water and become surrounded by a cloud of water molecules. These water molecules separate the charged ions and prevent them from being attracted together and hence form a solid again. The solvent properties of water allow it to be the medium in which many of the main chemical reactions in the biosphere, lithosphere and atmosphere take place.