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Water - Physical and Chemical properties, Uses, Practice problems, FAQs.

Can you imagine life without water?

It’s very obvious, we can’t imagine our lives without water. More than 70% of the Earth's surface is covered by water. It is unsurprising that all living organisms on our blue planet require water. Water is very essential, a local and global resource, a transportation corridor, and a climate regulator. Over the previous two centuries, it has also become the destination for numerous contaminants dumped into the environment, as well as a newly discovered mineral-rich mine. To continue enjoying the benefits of clean water, healthy oceans and rivers, we need to fundamentally change the way we use and treat water.

Table of Contents

  • Chemistry of Water
  • Physical Properties of Water
  • Chemical Properties of Water
  • Uses of Water
  • Practice Problems on Water
  • FAQ's on Water

Chemistry of Water

Water is a simple molecule. Its molecular structure is quite simple. It is made up of two hydrogen atoms and one oxygen atom. A shared pair of electrons bind each hydrogen atom to oxygen covalently. Oxygen also has two electron pairs that are not shared forming a bond angle of  between H-O-bond. Each  bond is polar.

Electronegativity of Oxygen (3.5) > Electronegativity of Hydrogen (2.1) (Values are as per Pauling Scale)

 



 

 

Physical Properties of Water

  • The freezing point of water is or  at  conditions.
  • The boiling point of water is or  at  conditions
  • The heat of vapourisation of water is at at  conditions
  • The heat of fusion of water is  at  at  conditions
  • The specific heat of water is at  conditions
  • The dipole moment of water is approximately  at  conditions
  • Water has a higher specific heat, thermal conductivity, surface tension, dipole moment, and

dielectric constant.

  • Since the density of ice is less than that of water, the ice floats over water.
  • Triple point (solid, liquid, and vapour all the three phases exit together): At , 0.006 atm, water is in equilibrium with ice and vapour.

Chemical Properties of Water

1. Dissociation of Water: Water is quite stable and does not dissociate into its constituent elements even at high temperatures.

2. Amphoteric Nature: It is the ability of a substance to act as an acid as well as a base.

Example:                       

Here, water acts as a Bronsted acid.

                    
Here, water acts as a Bronsted base.
Water undergoes auto-protolysis (self-ionization) as follows:

                    
Amphoteric oxides or hydroxides are formed by several metals, including zinc, tin, lead, aluminium, and beryllium.

3. Oxidising and Reducing Nature: Highly electropositive metals can easily reduce water to evolve dihydrogen gas.

Here, water acts as an oxidising agent.

Here, water acts as a reducing agent.


Water can be oxidised to dioxygen in the presence of fluorine.

4. Hydrolytic Reactions: Water hydrolyses many oxides, halides, hydrides, carbides, nitrides, phosphides, carbonates, etc., to give an acid or a base or both.

Here, water reacts with sulfur dioxide to give the acid as

Here, water reacts with calcium hydride to give the base as

5. Formation of Hydrates with Metals: Water forms three types of hydrates with metals. From aqueous solutions, many salts can be crystallised as hydrated salts. Such an association of water is of different types.
Coordinated Hydrates: In some compounds, water molecules are attached to the metal 
ions through coordinate bonds (complex compounds). These types of hydrates are called coordinate hydrates.

Example:
Hydrogen Bonded Hydrates: In some compounds, water molecules are associated with
hydrogen bonds. These types of hydrates are called hydrogen-bonded hydrates. 

Example: .
Interstitial Hydrates: In some compounds, water molecules occupy the interstitial sites in 
the crystal lattice. These types of hydrates are called interstitial hydrates.
Example:
.


Uses of Water


Water can be used in a variety of ways, both for direct and indirect purposes

  • Direct uses of water are bathing, drinking, cooking, planting water etc
  •  Indirect uses include the processing of wood to manufacture paper and the production of steel for automobiles. Agriculture, industry utilises the majority of the world's water.
  •  Water can dissolve almost anything, this allows it to be an ideal carrier of many chemicals and minerals we need for life.
  • Water is used for various household needs


Practice Problems on Water

Question 1. Explain the redox nature of water.
Answer: Water acts as both 
oxidising and reducing agent.
Highly electropositive metals can easily reduce water to dihydrogen.
(s)
Water is oxidised to  during photosynthesis


Question 2. Water has unusual properties like high freezing point, high boiling point, high heat of vaporisation and high heat of fusion, compared to other chalcogen hydrides. Why?
Answer: The unusual properties like high freezing point, high boiling point, high heat of vaporisation and high heat of fusion, compared to other chalcogen hydrides is due to the presence of significant hydrogen bonding between water molecules.

Question 3. What is the formula and molecular mass of water?
Answer: The formula of water is . The molecular mass of water can be calculated as:
Molecular mass of
 =

Question 4. Why is water considered a universal solvent?
Answer: The chemical composition and physical properties of water are what make it such a universal solvent. The oxygen and hydrogen atoms in water molecules are polarised, with one side (hydrogen) having a positive electrical charge and the other (oxygen) having a negative charge. This enables the water molecule to be attracted to a wide range of polar molecules.


FAQ's on Water

Question 1. What is the  of water at room temperature (298 K)?
Answer: Since water is a neutral solvent, its  value is equal to 7 at standard room temperature.

Question 2. What is bonding?
Answer: Hydrogen bonding is a special class of attractive intermolecular forces that exists due to the dipole-dipole interaction between a covalently bonded hydrogen atom and another highly electronegative atom (like ,  , ).




Question 3. How much freshwater is available to us?
Answer: Humans do not have easy access to the majority of the world's freshwater. Approximately 69 per cent of Earth's freshwater is locked up in the form of ice in glaciers and polar ice caps, and another 30 per cent is locked away in the form of groundwater beneath the surface. Only around 1% of the world's freshwater is readily available for human consumption.

Question 4. What are the main constituents of acid rain?
Answer: Nitrogen oxides and sulfur oxides are the main constituent pollutants which cause acid rain. These oxides react with water, oxygen and other chemicals to form harmful acids which are dangerous for living creatures and majorly responsible for the damage to buildings and monuments

 

 

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