Small scientist in science 1st Sec.
1st term
) اليوم / / بتاريخ....1.....(الحصة
Chapter one: Aquatic ecosystem
Water is not just a transparent liquid
It is a medium in which many chemical compounds
May react affecting the quality of water
hydrolysis ( مثال عهي أن انماء وسط يحدث فيه انتفاعالت انكيميائية مثم )انتميؤ
Note
Hydrolysis
Is a chemical reaction in which
Water is used to break down
A compound into ions
Note:
Due to hydrolysis of compounds تفكك المركباتWater affects the balance of
ions of water leading
To
Acidity or alkalinity of water
Dissolving sodium chloride salt in water
Mr. Ibrahim Essa mob: 012 2 520 1990 0111 9 38 1432 Page 1
Small scientist in science 1st Sec. 1st term
Strong acid Weak acid Strong base Weak base
H2SO4 HCN Mg OH Nh4OH
HCl HF Na OH
HNO3 H3PO4 Li OH
H2CO3 NaOH
Explanation of hydrolysis of NaCl
When table salt (NaCl) is added to water
It dissociates into
Sodium ion (Na⁺) and chloride ion (Cl-)
And the salt ions (Na⁺ , Cl ) remain in solution without binding to water
-
ions (H⁺, OH-) making the solution neutral
G.R
Because: the concentration of hydrogen ions (H+) is equal to the
concentration of hydroxide ions (OH-).
strong base وstrong acid مهحىظة انتركيز متساوي عشان االثىيه جاييه مه
neutral انىهائيsolution فال
In the case of sodium bicarbonate salt (NaHCO3) Hydrolysis of the salt
Leads to
1- A decrease in the concentration of hydrogen ions (H⁺)
2- An increase in the concentration of hydroxide ions (OH-)
Results in
Making the salt solution basic
weak acid مهH+ والstrong base اعهي عشان جاي مهOH- مهحىظه تركيز ال
basic انىهائيsolution فال
The opposite happens in ammonium chloride salt (NH4Cl)
When (NH4Cl) dissolves in water it hydrolyses (dissociate)
Mr. Ibrahim Essa mob: 012 2 520 1990 0111 9 38 1432 Page 2
Small scientist in science 1st Sec. 1st term
Leads to
1- A decrease in the concentration of hydroxide ions (OH-)
2- An increase in the concentration of hydrogen ions (H⁺)
Results in
Making the salt solution acidic
weak base مهOH- والstrong acid اعهي عشان جاي مهH+ مهحىظه تركيز ال
acidic انىهائيsolution فال
G.R Water has unique properties
1- Water can dissolve many chemicals
2- can exist in all three states of matter - solid, liquid, and gaseous states
within the range of known temperatures on the Earth's surface
3- Water is essential to the continuation of life on Earth.
Note:
All living cells have a membrane (cell membrane) that separates the organism
from its environment
Water passes from the environment to the inside of the
Living cell through this membrane
Function of the membrane
1- Carrying the substances needed
To produce energy
2- Eliminating ازالةwaste products to the outside.
⯁The hydrosphere on Earth:
The hydrosphere distinguishes Earth from other planets
In the Solar system
About 70% of the Earth's surface is covered by water
About 97% of this water is found in the oceans, seas,
and salt lakes as salt water
About 3% is fresh water
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Small scientist in science 1st Sec. 1st term
The fresh water is found in rivers, freshwater lakes
And groundwater represents approximately 1%
And the reminder part represents
The frozen Water in Polar Regions, mountain peaks and glaciers
earth
land water
30% 70%
Fresh 3% salty
1% 2% 97%
Found in lakes Found in polar
rivers and region
ground water mountain peaks
and glaciers
Note:
Egypt is characterized by its diverse aquatic environments, which include the
Nile River, the Gulf of Suez, the Gulf of Aqaba, the Red Sea, the
Mediterranean Sea, and many salt and freshwater lakes
⯁ Water Cycle in Nature:
Water exists on or near the Earth's surface in a state of continuous change
between its three states
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Small scientist in science 1st Sec. 1st term
\Note:
Water is constantly moving from one place to another in many different
paths that form a nearly closed system called the water cycle in nature or
the hydrologic cycle.
The water cycle as a system is capable of changing the Earth's surface
physically, chemically, and biologically.
Sources of water vapor
1-Evaporation 2-Transpiration 3- Respiration in plants and animals
The water cycle in nature mainly includes:-
1- The process of evaporation which contributes to the formation of
Clouds and the process of rain or snowfall
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Small scientist in science 1st Sec. 1st term
2- Transpiration in plants (biological processes)
3-Respiration in plants and animals
4- Water leakage through the pores of soil and sedimentary rocks to form
groundwater.
Note:
Water vapor in clouds may react chemically with compounds in the air, forming
some acids that falls as acid rain, which decomposes rocks.
Mr. Ibrahim Essa mob: 012 2 520 1990 0111 9 38 1432 Page 6
Small scientist in science 1st Sec. 1st term
⯁ Chemical structure of water:
Water is composed of the two elements
Hydrogen and Oxygen in ratio 2:1 by volume
Oxygen represents 88.89% of the mass
of the water molecule
Hydrogen represents 11.11%
Note:
The two hydrogen atoms are connected to the oxygen atom by two covalent bonds
with an angle of about 104.5 between them.
⯁ Chemical properties of water:
Water does not exist on Earth in a pure form as it contains many Ions and
chemicals that interact with it in different ways.
Three of the main properties of water:
1- Water polarity:
Polarity is the phenomenon that develops
Due to differences in the electronegativity
Between two atoms present in a compound
Electronegativity
Tendency of an atom to attract electrons toward itself
Values of electronegativity of some atoms
Oxygen 3.5
Hydrogen 2.1
Sulfur 2.5
Mr. Ibrahim Essa mob: 012 2 520 1990 0111 9 38 1432 Page 7
Small scientist in science 1st Sec. 1st term
Covalent compounds
Polar Non polar
Ex:H2O Ex:H2S
Boiling point 100° C Boiling point -61°C
Explanation of water polarity
The oxygen atom is characterized by its higher
Electronegativity than the hydrogen atom,
So
The bonding electrons are attracted towards the oxygen atom
Forming
partial negative charge on the oxygen atom
partial positive charge on the hydrogen atom
This is known as the polarity of the water molecule
The polarity of water molecules
Causes water molecules
To
Bond with other water molecules or polar molecules
Of other substances to form hydrogen bonds,
Which
gives water the ability to dissolve many salts
break them(salts) down into hydrated ions
Note
Hydrated ions are ions that have been dissolved in water.
Mr. Ibrahim Essa mob: 012 2 520 1990 0111 9 38 1432 Page 8
Small scientist in science 1st Sec. 1st term
Example
Dissolving sodium chloride salt in water
NaCl (aq) + H₂O(l) → Na⁺(aq) + Cl⁻(aq).
The ability of water molecules to form hydrogen bonds
Results in
Higher boiling point of water at 100° C at normal atmospheric pressure
While
Compounds of similar structure
That can’t form hydrogen bond such as
Hydrogen sulfide which boils at -61°C
2-Hydrolysis (hydration) : سبق شرحها بانتفصيم
A small percentage of water molecules exist in form of ions as hydrogen ions
(H⁺) and hydroxide ions (OH-).
As a result of chemical reactions of water with different compounds, hydrolysis
of some salts, present in natural water, may occur
This hydrolysis affects the balance of these ions in water, leading to
or of the water
3- Acid-base balance (equilibrium(:
The acid-base balance in water depends on the relationship between the
concentrations of hydrogen ions (H⁺) and hydroxide ions (OH-).
This relationship can be recognized by the pH value of the solution
PH scale it is a scale that ranges from 0 to14.
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Small scientist in science 1st Sec. 1st term
Note:
If the concentration of H⁺ increases,
The water becomes acidic
And the pH value is less than 7,
If the concentration of OH- increases
The water becomes basic
And the pH value is greater than 7
While if the concentration of the two ions is Equal
, the water is neutral and the pH value is equal to 7.
PH value: It is the measure of the acidity or basicity of liquids or solutions.
Note:
The pH value of pure water is considered neutral. Give reason
Because: it is PH is about 7
However, this value may vary in natural environments, affecting the organisms
that live in them.
The pH value of water from different sources
1- Seawater The pH value ranges from 7.5 to 8.4,
depending on
1- the region in which the sea is
located
2- the environmental factors
surrounding it
2- Fresh water (rivers and lakes(
The pH value varies from 6.5 to 8.5
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Small scientist in science 1st Sec. 1st term
3- Distilled water
The pH value is around 7 GR
Because it is free of most of the
impurities and ions that contribute to
the acidity or alkalinity of natural water
sources.
4- Groundwater
The pH varies from one region to
another depending on
1-the rock structure of the area.
Groundwater is
either neutral or alkaline, and its pH
value varies GR
due to exposure to salts of certain
rocks
Such as calcium carbonate or
magnesium carbonate.
5- The pH of the clouds
slightly acidic, with values ranging
from 4.5 to 5 GR
due to
the presence of carbon dioxide and
other acidic gases dissolved in the
rain droplets.
Note:
These values of PH can vary depending on different environmental factors,
and human activities in that area which can affect the pH level
When forming clouds or rainwater
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Small scientist in science 1st Sec. 1st term
Tools used in measuring the pH values
A pH meter or pH test strips.
G.R
It is important to closely monitor وراقبSalinity levels as well as the changes in
ionic structure of natural water bodies.
To minimize the negative impacts on water quality and on the health of living
organisms because of hydrolysis of salts and its effects on water
Proper waste disposal انممارسات انسهيمة نهتخهص مه انىفايات
1- Minimizes the addition of harmful salts to water bodies
2- Maintains water quality for wildlife habitats and human consumption.
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