chapter three 2016 كامل ان شاء الله لاتنسونا من الدعاء 1

Chapter 3 The EXPERT

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Vaporization

Condensation

Chapter three

a) The vaporization process

continues until the vapour pressure

equals saturated water vapour pressure.

b) When the number of water molecules

which evaporate from the liquid is equal to the number of

water molecules in the condensed vapour, so there is a

state of equilibrium.

The equilibrium system

Is apparently a stationary system but in reality

dynamic.

Vapour pressure

Is the pressure due to water vapour in air at a certain

temperature.

Saturated water vapour pressure:

Is the maximum water vapour pressure in air at a

certain temperature


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NaCl + AgNO3 NaNO3 + AgCl

Mg + 2HCl MgCl2 +H2

1- The reaction between magnesium and hydrochloric acid is

a complete reaction?

………………………………………………………………

………………………………………………………………

…………………………….…………………………………

Chemical reactions can be divided into

Reversible

(Incomplete)

Reactions.

Complete

(irreversible)

reactions.

Complete (irreversible)

reactions.

They are reactions in which one of the products escape

from the system (gas evolves or a precipitate is

formed ), so the products cannot combined with each

other once more reforming the reactants, under the

conditions of the experiment.


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CH3COOH + C2H5OH CH3COOC2H5 + H2O

Acetic acid ethanol ethyl acetate water

Ethyl acetate is neutral but when we add blue litmus paper it

changes to red

Due to the presence of acetic acid (CH3COOH) where the

reaction is reversible

The previous reaction moves in both directions {forward & backward}

1- The forward direction is:

CH3COOH + C2H5OH CH3COOC2H5 + H2O

2- The backward direction is:

CH3COOC2H5 + H2O CH3COOH + C2H5OH

Both the reactants and products are always found in the

reaction medium.

Reversible

(Incomplete) Reactions.

They are reactions in which the reaction proceed in

both directions; forward and backward. And both the

reactants and products are always found in the

reaction medium.

Forward

Backward


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The equilibrium position remains unchanged since all reactants

and products are still found in the system and as long as the

reaction conditions are not changed.

The concentration unit is expressed as mole / liter

The time unit is expressed as second or minute.

During the complete chemical

reaction , the concentration of the

reactants decrease and the

concentration of the products

increases .

Chemical equilibrium

in reversible reactions

It is a dynamic system takes place when the forward

reaction equals the rate of backward reaction .The

concentrations of the reactants and products are not

changed.

Rate of chemical

reactions

Is the change in concentration of the reactants or

products per unit time.

Conc.

Time

Products

Reactants


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In case of reversible reactions, the

increase in the concentration of the

products and decrease in the

concentration of the reactants proceed

until an equilibrium state is established.

1- Very fast: The reaction between silver nitrate and sodium chloride to form

silver chloride instantly.

2- Comparatively slow: The reaction between oil and caustic soda (NaOH) to give soap

and glycerol.

3- Very slow reaction: Iron rusting which needs several months to take place.

Conc.

Time

Reactants

Products


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A-Type of bonding in the reactants

Ionic reactants Undergo very fast reactions,

BEC. IT TAKES PLACE BETWEEN IONS, WHERE IONS OF

REACTANTS COMBINE WITH EACH OTHER AS SOON AS

THEIR SOLUTIONS ARE MIXED.

THE REACTION BETWEEN SODIUM CHLOORIDE AND

SILVER NITRATE

Covalent bonded reactants Undergo slow reactions. `

Bec. It takes place between molecules as in case of organic

compounds

B-Surface area exposed to the reaction

By increasing the surface area of the reactants the rate of the

chemical reaction increases and vice versa

1-Nature of the reactants includes

B-Surface area exposed

to the reaction

A-Type of bonding in

the reactants


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1- Put two equal masses of Zinc metal ,one of them in form of

powder and the other in form of a block

2- Place each of them in two test tubes

3- Add to each test tube equal volume of diluted hydrochloric

acid

The reaction with Zinc powder is completed in a shorter time

than that with Zinc block.

Nickel powder is used oil hydrogenation rather than nickel block? Iron fillings rust faster than iron block? ……………………………………………………………………

……………………………………………………………………

……………………………………………………………………

……………………………………………………………………

Steps

Observation

As the surface area exposed to the reaction

increases the rate of the reaction increases

Conclusion

Illustrates the effect of the surface area exposed to the

reaction on the rate of the chemical reaction.


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By increasing the No. of the reacting molecules ((the greater

the concentration)).

The chance of collisions per unit volume increases.

So the rate of the reaction increases.

At constant temperature, the rate of chemical reaction is

directly proportional to the product of multiplication of

the reactant concentrations; each is raised to the power of

the number of molecules or ions in the balanced chemical

equation.

2- Concentration of reactants

Guldberg and waag.

They are two scientists that established a low

expressing the relation between the rate of the

chemical reaction and concentration of reactants,

this law is ((law of mass action))

Law of mass action


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To clarify the law of mass action, perform the following experiment.

To show the effect of concentration on the rate of the

reaction

1- Add iron (III) chloride (faint yellow) gradually

To ammonium thiocyanate solution (colorless)

The color of the solution turns red

Due to the formation of iron (III) thiocyanate

FeCl3 + 3NH4SCN Fe(SCN)3 + 3NH4Cl

2-if an excess amount of iron (III) chloride is added the red color

of the solution increases, indicating the formation of more iron

(III) thiocyanate

Clarifying the law of mass action

Steps

Observation

Iron (III)

chloride

Faint

yellow

Ammonium

thiocyanate

(Colorless)

Iron (III)

thiocyanate

Red

Ammonium

Chloride (Colorless)

Forward

Backward


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3-when the rate of backward reaction (r2) equals the forward

reaction (r1) in the above reaction, an equilibrium state established

and both reaction rates are expressed as the following:

r1 [FeCl3] [NH4SCN]3

r1 = k1 [FeCl3] [NH4SCN]3

r2 [Fe(SCN)3] [NH4Cl]3

r2 = k2 [Fe(SCN)3] [NH4Cl]3

r1 = r2 ((at equilibrium)) k1 [FeCl3] [NH4SCN]

3 = k2 [Fe(SCN)3] [NH4Cl]

3

2

1

k

k = Kc =

3

43

3

43

]SCNNH][FeCl[

]ClNH][[Fe(SCN)

Kc =the equilibrium constant of the reaction

Calculate the Kc of the reaction I2 + H2 2HI

Providing that the concentration of I2 , H2 , and HI at equilibrium

are 0.221 , 0.221 and 1.563 mole / liter

……………………………………………………………………

……………………………………………………………………

……………………………………………………………………

……………………………………………………………………

1- The small values of equilibrium constant Kc ( 1) means that: a) the concentration of the products are less than the

concentration of the reactants which

b) the reaction is not proceed well towards the formation of the

products

c) The reversible reaction has an effective role (is dominant).

K1 = rate constant of

forward reaction

K2 = rate constant of

backward reaction


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The solubility of silver chloride in water AgCl(s) Ag

+(aq) + Cl

-(aq)

KC = [Ag+] [Cl

-] = 1.7 x 10

-10

From the value of Kc in the above reaction indicates that : silver

chloride is sparingly soluble in water

2-The high values of equilibrium constant Kc ( ) indicates that: a- the reaction proceeds almost to its end .This means that the

b- Forward reaction is the predominant reaction.

c- The concentration of the products are greater than the

concentration of the reactants.

H2(g) + Cl2(g) 2HCl(g) KC = 4.4 x 1032

3- The concentration of water , solid substances and precipitates ,

should not appear in the equilibrium constant equation

Bec. The concentrations remain constant whatever their quantities

(is considered as a constant because it does not significantly

varied in the reaction.)

The effect of temperature on the rate of the chemical reaction can

be explained in the light of collision theory

3- Effect of temperature on

the rate of reaction

Collision theory This theory assumes that: to have a chemical

reaction, molecules of the reactants must collide

with each other.


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1- Only molecules of very high velocity can react

Since their kinetic energy is high enough to break the bonds

within the molecules so that the chemical reaction can take

place.

2-the molecules must have a minimum amount of energy to react

during collision called Activation energy

3-The rate of many chemical reactions is doubled by increasing

the reaction temperature 10o C.

The rate of chemical reaction increases as the temperature increases?

Due to increasing the proportion of activated molecules which

react by collision

Activation energy The minimum amount (quantity) of energy that must

be gained by a molecule to react at collision

Activated molecules They Are molecules which have kinetic energy that

equals or exceeds the activation energy.


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1-bring a flask filled with nitrogen dioxide gas

(Reddish brown) and place it in cooling mixture

2-remove the flask from the cooling mixture and keep it at room

temperature (25oC)

3-put the flask in a basin filled with hot water

Illustrates the effect of the temperature on a

reaction at equilibrium

Steps

The intensity of the color decreases

gradually until the reddish brown color

disappears

Observation

The reddish brown color starts to appear

gradually

Observation

The intensity of reddish brown color

increases

Observation

NO2

N2O4 N2O4

NO2

Cooling mix. Hot water Room temp.


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1-In case of an exothermic reaction in equilibrium state

Decrease in temperature move the reaction to the forward

direction. And vice versa

2- In case of an endothermic reaction in equilibrium state

Increase in temperature move the reaction to the forward

direction. And vice versa

2NO2 N2O4 + Heat

1- The concentration of a substance in the solution is given in

a terms of molarity and expressed by placing the substance

between two square brackets [ ]

2- If the reactants or products are in the gaseous state, the

concentration the concentration is expressed by using their

partial pressure.

Ammonia gas is prepared by the reaction between its elements

in industry according to the following reaction:

N2 + 3H2 2NH3, H = - 92 KJ

From the previous reaction we conclude that:

1-four molecules react to form two molecules

2-the formation of ammonia gas is accompanied by a decrease

in the volume.

Conclusion

Cooling

Heating

4- Effect of pressure

High pressure

Cooling


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3-by applying pressure and cooling the rate of ammonia

formation increases.

Increasing the pressure or cooling on a gaseous reaction under

equilibrium, shift the direction of reducing the pressure.

In this case, the equilibrium constant is expressed by the symbol

Kp to indicate that the concentrations of the substances are

expressed by the partial pressure. ) (.

KP = )H(P)N(P

)NH(P

2

3

2

3

2

*the equilibrium constant of the above reaction can be also

expressed in terms of molar concentration

Calculate the (Kp) of the reaction N2(g) + 2O2(g) 2NO2(g)

Provided that the pressures are 2,1 and 0.2 atm. for NO2 ,O2 and

N2 Respectively.

……………………………………………………………………

……………………………………………………………………

……………………………………………………………………

Conclusion


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The change in any of the conditions of a chemical

equilibrium such as concentration, pressure or

temperature causes shift of the equilibrium in the

direction which will oppose this change .

Using pressure vessels (Barsto) in cooking? Bec. It increases the rate of the chemical reaction and cooking

by increasing the temperature in a short time.

It is advised not to heat the cylinder in order to obtain more butane gas? Bec. The pressure inside the cylinder increases by increasing the

temperature which leads to explosion

The rate of ammonia gas formation increases by increasing the pressure and decreasing the temperature according to the following equation

N2 + 3H2 2NH3, H = - 92 KJ

Le Chatelier

A French scientist formulated a rule predicts the

effect of different factors such as concentration,

temperature and pressure on the systems under

equilibrium.

Le Chatelier's principle


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Bec. The reaction is exothermic and volumes of products is less

than that of reactants , so by increasing pressure and decreasing

the temperature forward reaction increases and ammonia gas

formation increases ((according to Le Chatelier's principle ))

Endothermic reaction Exothermic reaction

A + B+Heat AB A + B AB+ Heat

A + B AB A + B AB

A + B AB- Heat A + B-Heat AB

By heat moves forward

By cooling moves backward

By heat moves backward

By cooling moves forward

By increasing the pressure the

reaction moves to the smallest

volume

By decreasing the pressure the

reaction moves to the largest

volume

The catalyst has no effect on a

reaction under equilibrium

If volumes of reactants and

products are equal the change in

pressure has no effect

5- Effect of Catalysts

Catalysts

Substances that cause a change in the rate of

chemical reaction without itself are being changed".

I.e. without affecting the position of equilibrium.


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Slow reactions in industry can't be proceeded at a faster rate by heating?

Bec. It is very expensive; due to the additional cost of the used

fuel for heating so the cost of products increases.

1- They are needed in small quantities.

2- They change the reaction rate without affecting the position

of equilibrium.

3- They decrease the activation energy.

4- They accelerate the backward and forward reactions at the

same time.

1- Catalysts are used in more than 90 % of the industrial

processes such as : Food and petrochemical industries

2- Catalysts are also used in catalytic converters used in

modern cars to convert the gaseous combustion products,

which cause air pollution , into safe products .

Catalysts are metals, metal oxides or compounds.

Properties of catalysts

Enzymes

They are high molecular weight proteins produced in

living cells act as catalysts for many biological and

industrial processes


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The catalyst doesn’t affect the equilibrium of reversible reactions?

Bec. It changes the rate of reaction, and doesn’t affect the

equilibrium position.

And accelerate the backward and forward reactions at the

same time

Some chemical reactions are affected by light, as

1- the photosynthesis process: In which chlorophyll in plants absorbs light and form

carbohydrates in the presence of CO2 & H2O

2- and Photographic films

It contains silver bromide in a gelatinous layer.

When light falls on such films, silver ions accept

electrons from bromide ions and converted into silver

metal

Bromine is absorbed in the gelatinous layer.

The increase in light intensity is associated with an

increase in the amount of silver formed.

Ag+ + e- Ag

6- Effect of light


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Ionic substances Covalent compounds

1-they are dissolved in water

and (+ve) and (-ve) ions are

liberated

2-their solutions conduct

electricity

3-their (+ve) and (-ve) ions are

attracted by electrostatic

attraction forces.

Ex. sodium chloride

1-the bonds between their

molecules are covalent

2-they also are ionized in

water but with different degree

3-Ex.

a-hydrogen chloride gas is

ionized in nearly 100%

b-ethanoic acid undergoes

ionization at a much less

extent

Applications of the law of mass action in ionic equilibrium

Steps

Test the electrical conductivity of pure ethanoic and

hydrogen chloride gas dissolved in benzene.

Observation

The lamp in both cases will not illuminate.

Conclusion

The two solutions don’t contain ions to conduct

the electric current.


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Steps

1-dissolve 0.1 mole of hydrogen chloride gas in

one liter of water

2-also dissolve 0.1 mole of pure ethanoic acid in

one liter of water

3-test the electrical conductivity of each solution.

Observation

The lamp gives strong illumination with

hydrochloric acid and weak illumination with

ethanoic acid

Conclusion

Hydrochloric acid solution contains a large no.

of ions, while the second contains little no. of

ions

Test for the effect of dilution on both solutions of

hydrochloric gas and ethanoic acid

Steps

1-dilute each solution to 0.01 molar

2-test the electric conductivity

3-dilute each solution to 0.001 molar

4-test the electric conductivity again.

Observation

The illumination of the lamp isn’t affected in

case of dilution of hydrochloric acid but

increases in case of dilution of ethanoic acid


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Ionization constants of some weak acids.

Acid Chemical formula Ionization const.(Ka)

Sulphurous H2SO3 1.7 × 10-2

Hudrofluric HF 6.7× 10-4

Nitrus HNO2 5.1× 10-4

Acetic (ethanoic) CH3COOH 1.8× 10-5

Carbonic H2CO3 4.4× 10-7

Boric H3BO3 5.8× 10-10

So they can be arranged according to their strength as the

following:

H2SO3 HF HNO2 CH3COOH H2CO3 H3BO3

Conclusion

1-strong electrolytes as HCl are completely

ionized, and their ionization doesn’t affected by

dilution, and they are good conductors of

electricity

2-weak electrolytes as CH3COOH are partially

ionized and their ionization increases by

dilution and their electric conductivity increases

by dilution HCL H

+ + Cl

- (Complete ionization)

CH3COOH CH3COO- + H

+

(Partial ionization)


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No free hydrogen ion (protons) is present in aqueous of ionized acids? Bec. This ion is attract to the lone pair of electrons on the

oxygen atom of the water molecule and connected to a water

molecule by a co-ordinate bond. This proton is called hydrated

proton or hydroxonium ion [H3O] +.

HCl + H2O [H3O] + + Cl -

Electrolyte (electrolytic substance)

A material that dissolves in water to produce ions in

solutions which conduct the electric current

Ionization A process in which unionized molecules are changed

into ions.

Hydronium ion The positive ion that produced from the

combination of water molecule with the positive

hydrogen ion.


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1- Two opposite processes are found in the solution which are:

A-dissociation of molecules into ions.

B-combination between the ions to give molecules.

2- A state of equilibrium is achieved between ions and

molecules as the following.

AB A+ + B-

The law of mass action can't be applied on strong electrolyte solutions? Bec. It doesn’t contain un-dissociated molecules, since they are

completely ionized

Complete Ionization A process in which all unionized molecules are

changed into ions and takes place in strong

electrolytes.

Incomplete Ionization A process in which small fraction of unionized

molecules is changed into ions and takes place in

weak electrolytes.

Ionic equilibrium It is the equilibrium arising between molecules of a

weak electrolyte and ions resulting from it.

Weak electrolyte Dissociated ions


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The law of mass action can be applied only in the case of weak electrolyte solutions?

Bec . their solutions (molecules and ions) and a state of

equilibrium arises between them while strong electrolyte

solutions don’t un-ionized molecules.

1- When one mole of a weak acid (HA) dissolves in (V) liter of

the solution, then at equilibrium:

2- If the number of dissociated moles is ( ) mole then, the

number of un dissociated moles from HA= (1- ) and the

number of moles of (H+) and (A-) produced equals mole.

3- Ostwald's Law for dilution: The

concentration of the substance (mole/ liter) at equilibrium is

Ostwald

In 1888 Ostwald described the relation between the

extent of ionization - alpha ( ) and concentration

( C ) mole/liter for solution.


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4- Ostwald's Law : At constant temperature, the degree of

ionization ( ) increases by dilution (so that Ka value remains

constant ) .

5- In case of weak electrolytes , the degree of ionization ( ) is

small enough and can be neglected. Consequently the value

(1- ) is considered approximately one and the relation

becomes : Since the concentration of the weak acid

male /liter. The above equation becomes:

6- This means that increasing dilution (decrease in

concentration) causes an increase in dissociation degree and

vice versa .

Calculate the degree of dissociation of 0.1 molar

hydrocyanic acid (HCN) at 25C0 providing that Ka = 7.2× 10-10

……………………………………………………………………

………………………………………………………………….....

Ostwald law At a constant temperature the degree of ionization

( ) of weak electrolytes increases by dilution

CKa 2


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When a weak acid such as acetic acid with a concentration (c)

dissociates in water according to the equation:

From the above equation, the quantity of acetate ion (CH3COO-)

released equals the quantity of hydronium ion (H3O+) produced:

[H3O+] = [CH3COO-]

The equilibrium constant is:

Since the acid is weak, the amount dissociated is small and can be

neglected.

So, the concentration of acetic acid at equilibrium equals the

original acetic acid concentration (C) Consequently:

Calculate the hydrogen ion concentration in 0.1 molar acetic

acid at25C0, Ka = 1.8× 10-5

……………………………………………………………………

……………………………………………………………………

……………………………………………………………….……


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When ammonia, a weak base , is dissolved in water the fallowing

equilibrium reaction takes place :

This equation reveals that one mole of both NH3+ and OH- ions is

formed.

Since the dissociation constant of ammonia is small, a small

portion of ammonia dissociates and at equilibrium , the

concentration of the remaining ammonia [NH3] equals the original

concentration of ammonia (Cb)


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Pure water is a very poor conductor of electricity.

The number of unionized water molecules can be considered as a

constant value. Therefore, the above relation can be rewritten as

follows;

Kw = [H+][OH-] = 10-14

Since the concentration of H+ equals the concentration of OH-

Then Kw(ionic product of water ) = [10-7][ 10-7] = 10-14

Water has a neutral (No) effect on litmus? Bec. The conc. of [H+

] (responsible for the acidic properties) equals

the conc. of [OH-] (responsible for basic properties)

The ionic product of water The resultant of multiplying the concentration of

the hydrogen ion [H+] times that of hydroxide ion

[OH-].It is a constant value equals 10-14 mole/liter.

Kw = [H+][OH-] = 10-14


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pH = -log [H3O+] , The symbol (p) means (-log) .

pKw = pH + pOH= 14

In case of a neutral solution, the pH=7 and pOH =7.

For solution of pH 5 , the pOH=9 and

For solution has a pH 8 , the pOH =6.

The pH value of the acidic solutions is < 7 and pOH is >7.

For basic solutions the pH is >7 and pOH is<7.

-logKw = - log [H3O+] + - log [OH-] = -log 10 -14

pH = -log [H3O+] POH = - log[OH-]

pH = 14 – POH POH = 14 - pH

[H3O+] = shift log – pH [OH-]= shift log – poH

If the PH > 7 The solution is basic

If the PH < 7 The solution is acidic

If the PH = 7 The solution is neutral

pH value It is the negative logarithm of hydrogen ion

concentration pH = -log [H3O

+]


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Calculate the value of PH and POH for a solution in which

[H+] = 5 × 10-3 molar.

…………………...…………………………………………………

…………………...…………………………………………………

………………..……………………………………………….……

……………………………………………………………………..

1- Strong electrolytes are completely ionized, and their ions

can't combine again to form their molecules.

2- Weak electrolytes are partially ionized, and their ions can

combine together again to form molecules.

Strong acids Weak acids Strong bases Weak bases

1- HCl

2- H2SO4

3- HNO3

1- CH3COOH

2- H2CO3

1-NaOH

2-KOH

1-NH4OH


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1- HYDROLYSIS OF SODIUM CARBONATE

The solution of sodium carbonate has a basic effect? Bec. 1- PH value is more than 7

2-the concentration of [OH-] ˃ [H+]

3- It is derived from strong base and weak acid

2-HYDROLYSIS OF AMMONIUM CHLORIDE

The solution of ammonium chloride has an acidic effect? Bec. 1- PH value is less than 7

2-the concentration of [OH-] [H+]

3- It is derived from strong acid and weak base


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3-HYDROLYSIS OF AMMONIUM ACETATE

The solution of ammonium acetate a neutral effect? Bec. 1- PH value equal to 7


3- It is derived from weak acid and weak base

4-HYDROLYSIS OF SODIUM CHLORIDE

The solution of Sodium chloride has a neutral effect? Bec. 1- PH value equal to 7


3- It is derived from strong acid and strong base


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Calculate the solubility product of silver chloride, if the degree of

solubility is 10-5 mol / L

……………………………………………………………………

……………………………………………………………………

……………………………………………………………………

……………………………………………………………………

……………………………………………………………………..

Solubility product Ksp The solubility product for any sparingly soluble

ionic compound is the product of multiplication of

the concentration (expressed by mole / liter) of its

ions, raised to the power of the number of ions,

which exist in equilibrium with its saturated solution

chapter three 2016 كامل ان شاء الله لاتنسونا من الدعاء 1

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