Water is a transparent, tasteless, odorless, and nearly colorless chemical substance that is essential for all known forms of life. It is the most abundant molecule on Earth, covering about 71% of the planet's surface. Here are key aspects of water: **1. **Chemical Composition:** - Water is a simple molecule with the chemical formula H2O, consisting of two hydrogen atoms covalently bonded to one oxygen atom. **2. Physical Properties:** - **State of Matter:** Water can exist in three states: solid (ice), liquid (water), and gas (water vapor), depending on temperature and pressure. - **Density:** Water is densest at around 4 degrees Celsius, causing ice to float on liquid water. **3. Unique Properties:** - **High Heat Capacity:** Water has a high specific heat, meaning it can absorb and store a significant amount of heat energy without a substantial increase in temperature. - **Universal Solvent:** Water is often referred to as the "universal solvent" because it has the ability to dissolve a wide range of substances, facilitating many chemical reactions and biological processes. - **Cohesion and Adhesion:** Water molecules exhibit cohesion (sticking to each other) and adhesion (sticking to other substances), contributing to phenomena like surface tension and capillary action. **4. Role in Biological Systems:** - **Critical for Life:** Water is essential for the survival of living organisms. It serves as a medium for biochemical reactions, participates in cellular processes, and provides a habitat for various organisms. - **Transport Medium:** In organisms, water acts as a transport medium for nutrients, gases, and waste products. **5. Earth's Water Distribution:** - **Oceans:** About 97.5% of Earth's water is found in oceans, primarily as saltwater. - **Freshwater:** Only about 2.5% of Earth's water is freshwater, with the majority locked in glaciers, ice caps, and underground aquifers. **6. Importance in Human Activities:** - **Drinking Water:** Water is essential for human consumption to maintain hydration and support bodily functions. - **Industrial Use:** Water is widely used in industries for processes such as manufacturing, cooling, and transportation. **7. Environmental Significance:** - **Hydrological Cycle:** Water undergoes constant cycling through processes like evaporation, condensation, and precipitation in the hydrological (water) cycle, crucial for sustaining life on Earth. In summary, water is a remarkable and indispensable substance with unique properties that contribute to its role in various natural processes, the sustenance of life, and its essentiality in human activities and industries.

1. Lecture I1I
Aqsa Akhtar
School of Food and Agricultural Sciences
University of Management andTechnology
FST-2101 3(3-0)
Food Chemistry
1

2. Food Constituents :Water
✓ Behavior and properties of water
✓ Introduction & Importance
✓ Structure of water
2

3. Learning Objective
CO 1: Differentiate between major and minor food components and
their functions and physiochemical properties
CLO 1 : Explain the importance of water for shelf stability and
quality of foods
Session Learning Outcomes
SLO 2.1: Understand the structure of water
SLO 2.2: Identify the physical and chemical features of the
water
3

4. Water (moisture) is an inorganic liquid chemical that is colorless,
odorless, tasteless and makes up most of the earth’s hydrosphere
and the fluids in the body of all living beings
Water: Introduction
Monoxide of hydrogen
Nearly 75% of the earth’s
surface is covered by water
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5. ▪ All life requires water
▪ All organisms are made mostly of liquid water
▪ Most of their metabolism requires an aqueous medium
▪ Many organisms live in liquid water or in an environment
dominated by water in its various states
▪ Ex: solid, liquid, or gas
Water: Introduction
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6. Water: Characteristics
For food polymers, water serves as a
structural component and a
plasticizer
Functions to determine the physical
attributes of food products
Direct reactant in hydrolytic processes
Supports critical chemical reactions
as a medium
Universal solvent
Water a predominant constituent of
many foods
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7. Water: Characteristics
▪ Removal of water from foodstuff (dehydration/desiccation) or
binding it with increased concentrations of salts and sugars
therefore, inhibits growth processes of microorganisms, aiding in
preservation and thus longer shelf life
▪ Water also serves as solvent or dispersing medium in wide variety
of foods including milk, juices and other beverages
▪ Water can be dispersed in emulsions in products like butter or
margarine or be the continuous phase of emulsions such as
mayonnaise
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8. 8

9. ▪ Pure water is transparent, colorless, tasteless, and odorless. Water
in a thick layer appears greenish-blue
▪ Pure water is a bad conductor of heat and electricity
▪ Due to the presence of intermolecular hydrogen
bonding among water molecules, water has abnormally high
melting and boiling point
Color & Conductance of Water
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10. pH of Water
Water has a neutral pH of 7, which indicates that it is neither acidic or basic.
The scale ranges from 0 (very acidic) to 14 (very basic)
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11. .
Physical Properties of Water
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12. Polar Nature of Water
▪ Oxygen atoms are electron-seeking
(electronegative), compared to
hydrogen; thus for an oxygen-
hydrogen bond:
✓The oxygen atom has a partial (-)
charge
✓The hydrogen atoms have a partial
(+) charge
▪ Polar character of water allows water
molecules to form hydrogen bonds
Water Structure (1)
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13. ▪ Water molecules consist of two hydrogen atoms joined to an oxygen atom
by covalent bonds
▪ Oxygen is more electronegative than hydrogen
▪ The high electronegativity causes the oxygen atom to pull the shared
pairs of electrons more towards the oxygen atom
▪ As a result, the O–H bond acquires polarity
▪ Oxygen is bonded to the two hydrogen atoms by two O–H covalent
bonds, and there are two lone-pairs of electrons on the oxygen atom
Water Structure (2)
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14. Water Structure (3)
14

15. ▪ It contains two hydrogen atoms covalently bonded with central oxygen
atoms. In a water molecule, its central atom undergoes sp3 hybridization
▪ It is assumed to be the tetrahedral shape of the molecule in which two H
atoms should occupy two concerns of the tetrahedron and the remaining
two corners should occupy two lone pair electrons of the oxygen atom
Water Structure (4)
15

16. Hydrogen Bonding
• The hydrogen bond (H-bond) is a strong bond formed between
polar hydrogen and another heavy atom, usually carbon, nitrogen,
oxygen, or sulfur in biological molecules
▪ In the gas phase the strength of an H bond between two waters
is 22.7 kJ mole
▪ In liquids and solids its strength is greatly dependent on
geometry and the surrounding molecules
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17. Water Density
▪ Has the highest density at 4oC, as Brownian motion slows down
and distance between water molecules starts to reduce
17

18. Structure of Ice (1)
▪ Ice is a tetrahedral lattice where each water makes H-bonds to four
other waters, which lie equidistant from each other at the vertices of a
regular tetrahedron with edge lengths of 0.45 nm
▪ The 2–2 H-bonding symmetry is an important feature of water
▪ Combined with an H–O–H bond angle very close to the ideal
tetrahedral angle of 109.58, and with the tendency for the four
neighboring waters to repel each other electrostatically
18

19. Structure of Ice (2)
19

20. Why Does Ice Floats on Water??
Water’s density is greatest at about 4 °C (39.2 °F), in the liquid phase.
Ice, water’s solid phase, is more buoyant, so it forms at the surface of
water bodies and freezes downward. Lakes and rivers rarely freeze
completely, and the liquid water below can become a winter refuge for
aquatic life
20

21. Polarity of Water
▪ “Like dissolves like” Polar liquids dissolve other polar liquids
▪ Polar liquids will not mix with non-polar substances (i.e. – oil & water
don’t mix)
▪ Substances that repel water = hydrophobic
▪ Substances attracted to water = hydrophilic
21

22. Water as Solvent
22

23. Water Cohesion & Adhesion
▪ Cohesion = Water molecules wanting to stay together, keep water in
puddle, instead of widespread droplets or molecules
▪ Adhesion = Water molecules wanting to stay connected to other
surfaces (glass)
23

24. ▪ Capillary action = Water rising on its own up through a thin
column
▪ Combination of adhesion attracting water molecules to the side of
the column and cohesion pulling more water up into the column
▪ Glass tubes and plant roots are good examples
Water Capillary Action
24

25. Water Heat Capacity
Due to the high heat capacity of water, it can absorb heat either from
physiological reactions or automobile engines
▪ Heat capacity is the amount of heat required to change the
temperature of a given amount of matter by 1°C
▪ The SI unit of heat capacity is joule per kelvin
25

26. Water SurfaceTension
▪ The tension of the surface film of a liquid caused by the attraction of
the particles in the surface layer by the bulk of the liquid, which
tends to minimize surface area
26

27. Forms of Water
.
27

28. ▪ Langmuir or monolayer water (aW between 0 and 0.2)
▪ Monolayer indicates the amount of water that is strongly
adsorbed in specific sites
▪ Capillary water (aW between 0.3 and 0.8)
▪ Capillary water is held in narrow channels between
certain food components because of capillary forces
▪ Loosely-bound water (aW between 0.8 and 1.0)
▪ Molds and yeast start to grow at aW between 0.7 and 0.8
▪ Bacterial growth starts when aW reaches 0.8
Types of Water
28

29. .
• .
Types of Water
29

30. Types of Water
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31. Water Content in Food Samples
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32. ReferenceTerms
▪ Viscosity: A quantity expressing the magnitude of internal friction
in a fluid, as measured by the force per unit area resisting uniform
flow
▪ The enthalpy of vaporization: also known as the heat of
vaporization or heat of evaporation, is the amount of energy that
must be added to a liquid substance, to transform a quantity of that
substance into a gas
▪ Heat of fusion: Quantity of heat necessary to change 1g of a solid
to a liquid with no temperature change
32

33. Take Home Activity
Are nonpolar compounds highly soluble in water?
Why or why not???
A powder dissolves easily in water but not in oil.Are
the molecules in the powder probably polar or
nonpolar? Explain.
33

34. Questions/Discussion 34