Water: An Introduction
The most important resource also necessary for the core sustainable development of a human is water. Before we discuss water, let’s get to know some key statistics about water. Here are a few:
An average person uses 101 gallons of water per day, i.e., 380 liters of water used per day.
68% of the Earth’s freshwater is trapped in glaciers
85% of our human brain is made of water
What is Water?
Water, also known as \[H_{2}O\] is a substance composed of the chemical elements hydrogen(\[H_{2}\]) and oxygen (\[ O_{2} \]). As the polar inorganic compound, water is a colorless, tasteless and odorless liquid. Water being the most studied chemical compound is known as the universal solvent. It is the only substance to exist in all three states of matter – solid, liquid, and gas. Life on earth has been believed to originate in the world’s water bodies such as oceans, rivers, lakes.
How is a Water Molecule Formed?
A water molecule is formed with the chemical bond of hydrogen and oxygen. Water is the best example of a polar covalent bond. Meaning, the chemical bond in which electrons unequally share the atoms. Every water molecule covalently bonds with two atoms of hydrogen and one atom of oxygen, reaction can be written as follows:
\[H_{2} + O_{2} \rightarrow H_{2}O \]
What are the States of Water?
As stated, water is the only substance to exist in all three states of matter – solid, liquid, and gas. The first state of water, in solid, is ice. As a solid-state substance, water is available in a hard, amalgamated crystal called ice and loosely amalgamated crystal called snow. The most commonly visible state of water, which is the second state, on the Earth’s atmosphere is liquid, known as “water.” The third state of water, in the gaseous form, is called water vapor or steam. This is the state of water when clouds are formed – by minute droplets of water suspended in the air.
What is the Relation between the Hydrological Cycle and the States of Water?
A hydrological cycle is the general cycle of nature where the water flow is regulated in different states of water, making it portable for all life forms on Earth. This is strengthened due to the availability of water in all the states. Additionally, the process of evaporation, precipitation, and condensation makes it easier to transport water across different landforms.
The liquid state of water from water bodies – oceans, rivers, lakes, etc. is converted into a gaseous state called water vapor due to the process of evaporation. The water further condenses together to form tiny droplets of water vapor called clouds. Furthermore, the clouds precipitate as liquid state water known as rain. This liquid state water is used for different purposes by life forms, and the remaining water gets collected back into the water bodies.
What are the Properties of Water?
The properties of the compound – water can be classified into:
Physical properties
Chemical properties
Electrical properties
Thermal properties
Let’s go ahead and focus on the physical and chemical properties of water:
Physical Properties of Water
Appearance: As you are aware now, water is a colorless, odorless, and tasteless liquid in its natural state. The crystal structure of water in hexagonal.
Boiling Point of Water: The boiling point is defined as the temperature at which the vapor pressure of the liquid is equal to the pressure surrounding the liquid, and thus the liquid changes to vapor. It is known to us that the boiling point of water is 100°C.
Freezing Point of Water: The freezing point is the temperature at which the substance changes state from liquid to solid. So, for water, the point at which liquid state water turns to solid-state ice is the freezing point of water, which is 0°C or 32°F.
Specific Heat Capacity: Water has a high specific heat capacity of 4.2 joules per gram at 25°C. This is due to the extensive hydrogen bonding between the water molecules.
Density of Water: The density of water is about 1 gm/cc and it varies with temperature in an unusual pattern. The density of water in different states – solid and liquid. In solid-state, the density is 0.9gm/cc
Viscosity of Water: The viscosity is defined by the resistance to deformation at a given rate. In other words, the thickness of the liquid –e.g., syrup and water. The viscosity of water is 0.89 cP(centi-poise).
Surface Tension of Water: Surface tension is the tendency of the fluid to shrink in a minimum surface area. Water has a high surface tension of 72 mN/m at 25°C. Because of this high surface tension of water, insects can walk on the surface of the water without any discomfort.
Refractive Index of Water: In simpler words, the refractive index is the number that describes how fast the light reached the material. The refractive index of water is 1.333 at 20°C.
Compressibility of Water: Compressibility is defined as the function of temperature and pressure and its effect on the substance. For water, the compressibility at 0°C is \[5.1 \times 10 - 10 Pa - 1\], and it reduces to \[ 4.4 \times 10 - 10 Pa - 1\] till 45°C. As the pressure is increases, the compressibility decreases further.
Dielectric Constant of Water: Dielectric constant is a measure of how easily the material is polarized by an electric field. The dielectric constant of water is very high, which is at 78.6. This constant plays a very important role in water, being a universal solvent.
Chemical Properties of Water
Chemical Formula: The chemical formula of water is \[H_{2}O\]. As described earlier, the molecule of water is formed by the covalent bond of hydrogen and oxygen atoms.
Amphoteric Nature of Water: Amphoteric nature is one of the most important properties of water. Amphoteric means the ability of the substance to act as an acid or base. Water in the natural state is neither acidic nor basic. The main reason is its ability to donate and accept protons. However, rainwater is slightly acidic, with a pH between 5.2 and 5.8.
Solvency of Water: Water is described as the universal solvent. This is because of the chemical composition and physical attributes, along with its high dielectric constant, which makes it the most solvent substance. The availability of positive and negative charges with hydrogen and oxygen respectively allows it to attract with other molecules of compounds, disrupting their molecular forces and allowing them to disintegrate and dissolve.
The chemical compound that consists of two hydrogens and one oxygen atom is known as water. Water is generally referred to as the liquid state of that compound while the solid phase is referred to as ice and the gas is referred to as steam. A supercritical fluid is also formed by water under special conditions. In Chemistry, the formula of water is \[H_{2}O\].
Formula of Water
\[H_{2}O\] is the chemical formula of water consisting of two elements which are hydrogen and oxygen. In order to form water, two molecules of hydrogen combine with one molecule of oxygen. Water is also known as the universal solvent which indicates that it has the property to dissolve many substances.
The Physical Properties of Water
Some of the physical properties of water are-
The molecules in water have hydrogen bonding between them.
The boiling and melting point of water are 100° and 0° C respectively.
The three states water can have are- solids, liquids, and gas.
Water has a polar nature because of which it can dissolve almost every substance and is hence called the universal solvent.
In the solid state, water possesses a crystalline structure which is a cage-like structure in the form of 3-D. The crystalline structure of water has many voids due to which the density of ice is less than water and hence can float on water.
The density of water is known to be as .0.99 g/ml, at 4° C.
The Physical Properties of Water
The important chemical properties of water are-
Amphoteric Nature of Water - Water can act as both an acid and a base which means water can act as both a proton donor and a proton acceptor.
\[H_{2}O(l)+NH_{3}(aq) \Leftrightarrow NH_{4}^{+} (aq)+OH^{-}(aq)\]- Acidic Behaviour
\[H_{2}O(l)+H_{2}S(aq) \Leftrightarrow H_{3}0^{+} (aq) + Hs^{-}(aq)\]- Basic Behaviour
Self-Ionisation (Auto-Protolysis of Water) - The ionisation of water takes place in the process of autoprotolysis of water which means in order to form a hydroxide ion \[OH^{-}, H_{2}O\] deprotonates (proton removal).
\[2H{2}O \Leftrightarrow H^{2}O^{+} + OH^{-}\]
Hydrolysis - The dielectric constant of water is very high which means it has a strong tendency to hydrate. In the presence of hydration shells around it, water has strong reactions with the ions of salts.
\[SiCl_{4} + 2H{2}O \rightarrow SiO_{2} 4HCl \]
Redox reactions - Dihydrogen can be obtained by water as it is a great source and can be reduced when it is reacted with a highly electropositive metal like Sodium.
\[H_{2}O + Na \rightarrow 2NaOH + H_{2}\]
FAQs on Properties of Water
1. What is the structure of water?
The structure of water is a bent molecule structure. In the structure, one oxygen atom is bonded with 2 hydrogen atoms. Since the oxygen atom is highly electronegative, the bonds present in the structure are polar. The shared pair of electrons are attracted towards the oxygen atoms to a greater extent than the hydrogen atoms. This results in the formation of a pair of opposite charges or dipoles. The hydrogen atoms acquire one partial positive charge while the oxygen atoms acquire the partial negative charges. The bond angle of H-O-H is is slightly smaller than the ideal \[sp^{3}\] hybridized atomic orbital and is 104.5° in the case of water. The structure of water has a tetrahedral geometry. To know about the states of water, students can visit Vedantu’s study material on the Form of water.
2. How many types of water are present in nature?
Water is known to exist in two types-
Soft Water - When the water is free from the salts of magnesium and calcium, it is known as soft water.
Hard Water - When the water consists of salts of magnesium and calcium in the form of chlorides, hydrogen carbonates, and sulfates, it is known as hard water. The hardness of water can be further classified into permanent and temporary hardness. Temporary hardness occurs due to the presence of calcium bicarbonate \[Ca(HCO_{3})_{2}(aq)\] and magnesium bicarbonate \[Mg(HCO_{3})_{2}(aq)\] while the permanent hardness is due to the presence of magnesium and calcium chlorides, nitrates and sulfates.
3. How to remove temporary and permanent hardness from hard water?
In order to remove the temporary hardness of water, the water is boiled which leads to the formation of carbonate precipitate from the bicarbonates that can be separated. Permanent hardness as the name suggests is difficult to remove and does not form lather as well therefore it cannot be removed by boiling water. To remove the permanent hardness, the hard water is treated with \[Na_{2} HCO_{3}\] which is also known as washing soda.
4. What is heavy water?
Heavy water is also known as \[D_{2}O\] in chemistry since it is made up of deuterium. Deuterium is the isotope of hydrogen. Heavy water is used in nuclear reactors as a moderator in order to slow down neutrons so that they react more to fissile uranium-235 as compared to uranium-238. Heavy water cannot be drunk and is not suitable for drinking purposes. If someone drinks heavy water, the metabolic processes in his body will slow down.
5. What is demineralized water?
When there are no minerals present in the water and only consist of the \[H^{+} and OH^{-}\] ions, it is known as demineralized water. Demineralized water can be used to sanitize equipment and is also used in some food processing applications. The demineralized water is not at all advisable to drink since it lacks all the ions and minerals which are required for proper body growth.
