[Physics Class Notes] on Properties of Water: Anomalous Expansion of Water Pdf for Exam

Water is an essential part of this planet. It covers almost 71% of the Earth’s surface, of which 95% water is salty that is undrinkable. Only 2% of the water present is fresh and drinkable. Water has a wide range of uses. It is used for the survival of human beings, flora, and fauna. The importance of water can be estimated from the fact that 75% of the human brain is made up of water. Water is not only used for recreations and day-to-day activities but is also used in industries, agriculture, etc.

Chemical Composition of Water

The chemical composition of water is H₂O, which means one molecule of water is made of one oxygen atom and two hydrogen atoms held together by a strong covalent bond. Water is the lightest in gas form, whereas a liquid is much heavier than its solid form. It is a good conductor of electricity and has different properties. Water is colourless, odourless, and tasteless. Apart from these, there are various other properties that make water unique. Water is found everywhere in different forms. At poles, it is found in the form of ice, whereas at other places, it is found in the form of liquid.

Why is Water Unique?

Water is unique when it comes to its physical properties, yet when further research is done on this substance, it seems that even more unusual properties are revealed, like its anomalous behavior, especially when there’s ice involved. The anomalous expansion of water (hereafter referred to as AEW) was first discovered by British scientist W.J.M. Rankine in the year 1859. 

He found that when water is frozen, it occupies more space than when it is in its liquid form. This expansion can be as much as 9% at 0 degrees Celsius (32 degrees Fahrenheit), compared to just 1% for most other substances. The cause of this anomaly is still unknown today, though many hypotheses have been put forward over the years.

One theory suggests that the increased volume is due to the formation of tiny ice crystals; another proposes that water molecules from a more ordered structure, when frozen, take up more space in the process. However, neither of these theories has been proven conclusively.

AEW can have a significant impact on our lives, particularly in the field of architecture. In cold climates, for example, builders have to take AEW into account when designing structures; if they don’t, the buildings may be structurally unsound and could even collapse in severe cases. In addition, AEW can have an impact on the environment. For example, when water expands as it turns to ice, it can put pressure on the banks of rivers and lakes, leading to flooding. In addition, AEW can have an impact on the environment. For example, when water expands as it turns to ice, it can put pressure on the banks of rivers and lakes, leading to flooding. 

Despite its many quirks, water is still an essential part of our lives. It’s important to understand the properties of water in order to make the most efficient use of this vital resource. 

Properties of Water:

1. Amphoteric Nature: It can behave as both – acid and base.

2. Hydrolysis: Water has a very high dielectric constant.

3. Viscosity: It has high viscosity due to the intermolecular force of attraction.

4. Redox Reactions: Water is a great source to obtain dihydrogen.

5. Hydrates Formation: It is defined as the attachment of water molecules with any compound. There are various types of hydrates. They are:

• Coordination hydrates

• Interstitial hydrates

• Hydrogen bond hydrates

There are two properties of water due to the hydrogen bond. They are:

1. Cohesion: Molecules are close to each other because of the collective action of the hydrogen bond. Cohesive forces are responsible for the phenomenon of surface tension between water molecules.

2. Adhesion: It is the bonding of water molecules with other molecules. This characteristic causes capillary action, i.e., the ability of water to flow against gravity in a narrow space.

Anomalous Expansion of Water:

Water shows unnatural behavior, which makes it unique. Between a certain range of temperatures, it shows the anomalous expansion, which has many applications. This helps in the survival of marine life, which is one of the major importance of this behavior of water, in addition to many applications that are discussed.

From the below graph it can be seen.

Hence, it is clear from the graph that density increases as temperature rises from 4 degrees Celsius, and then density decreases after.

Why Does it Happen?

The water molecule is made up of one oxygen and two hydrogen molecules. The water molecules are held together because of the intermolecular force of attraction between them at normal temperatures. The molecules of water in liquid form are always unstable, moving zig-zag inside the container, constantly rearranging themselves.

On cooling the water, zig-zag motion decreases as the molecules lose their energy. On a freezing, the water molecules start squeezing, and water reaches its maximum density. This is caused by the hydrogen bonding between the oxygen atoms that are negatively charged and the hydrogen atom that is positively charged from two different molecules of water. 

The rise in temperature  will cause the ice to form water, not because of the O-O bond but due to H-O bond attraction. The lattice structure of ice prevents the movement of water molecules. But since the H-O bond is not as strong as the O-O bond, it will expand, and hence water will occupy more space. This can be understood with an example: Suppose 5 people are sitting on a seat with their hands folded, but as they start stretching their hands, there is a possibility that the corner one may fall. So, the same goes in the case of water also, as the H-O bond overtakes, it requires more space.

Applications:

This property of anomalous expansion of water has many applications.

• Aquatic Life: This unique property of water helps aquatic life to survive. With a further drop in temperature, water on top forms ice and becomes a bad conductor of heat. This stops the heat from escaping the water body and helps aquatic life to survive. Hence, aquatic life can survive even when the temperature reaches or falls below.

• Bottle Burst: If you put a fully-filled water bottle in the refrigerator and its temperature is below 4 degrees Celsius, then according to the anomalous behavior of water, the water inside t
  he bottle will expand. Therefore, due to no space in the bottle for the expansion of water molecules, water will exert force on the walls of the bottle and it will burst.

• Soft Drinks Bottle: Soft drink bottles are kept in freezers. So, as the temperature drops below 4 degrees Celsius, the drink inside the bottle starts expanding. So, to prevent the molecules from exerting force on the wall and bursting, there is a little space left inside the bottle.

• Pipe Burst: In cold countries, water pipes expand due to the anomalous behavior of water, and hence the water exerts a large amount of force on the pipe wall, and it bursts.

• Breaking of Rocks: Rocks break during winter because as the temperature decreases below, water inside the rocks starts expanding and hence exert a large amount of force on the rocks and results in the breaking of rocks.