Welcome to Learn Chemistry by Inam Jazbi — your trusted guide for mastering chemistry with clarity and speed.
Hydrolysis
Etymology:
The word “Hydrolysis” comes from:
Hydro = water, Lysis = to break
Definition
of Hydrolysis
Hydrolysis means cleavage by water. The term hydrolysis is derived from hydro meaning water and lysis meaning breaking. It is a type of double
decomposition reaction (DDR) and it is a reverse of neutralization.
Hydrolysis is a proton transfer reaction in which
cation or anion or both of a water-soluble ionic salt reacts with water along with
the splitting of water into H+
and OH⁻ ions with the production of an acid or base or both
resulting in the change pH of solution. It is the breaking up of water-soluble
ionic salts with water accompanied by the cleavage
of O–H bond of water thereby changing the pH of solution making it either
acidic or basic. Thus hydrolysis means “breakdown by water.”
OR
The reaction of cation or anion of the salt with water accompanied by the cleavage of O–H bond of water to produce hydrogen ions (H⁺) or hydroxyl ions (OH⁻) thereby changing the pH of the solution making it either acidic or basic is known as hydrolysis (hdyro; water and lysis; to break). Cation hydrolysis gives acidic solution whereas anion hydrolysis gives basic solution.
General Reaction:
Salt + Water ⇌ Acid and/or Base
A⁺ + H₂O → AOH + H⁺ (Cation hydrolysis→ Acidic solution)
B⁻ + H₂O → BH + OH⁻ (Anion hydrolysis→ Basic solution)
Conditions for Hydrolysis
⇒ hydrolysis involves the fission or cleavage of a water molecule i.e. in hydrolysis the O–H bond in water molecule is broken down.⇒ Hydrolysis is possible for water-soluble ionic salts only having either strong conjugate acid (cation) or strong conjugate base (anion).
⇒ hydrolysis of salts is only said to take place when it brings a change in the pH of solution or water (7) which is a necessary condition for the process of hydrolysis.
Explanation
Salts contain cations (C⁺) and anions (A⁻), e.g., Na⁺ and Cl⁻ in NaCl; K⁺ and Br⁻ in KBr. Salts undergo ionization in water i.e. salts being strong electrolytes, when dissolve in water, they become fully ionize (completely dissociated). Cations and anions of dissolved salt can undergo either of the following:
(i) interact with water without
its cleavage forming hydrated ions in aqueous solution (hydration)
(ii) interact with water with cleavage of water forming corresponding acids or bases depending upon the nature of salts i.e. ions of the dissolved salt can disturb the water equilibrium giving acidic or alkaline solution. This interaction of ions with water is called hydrolysis.
Some salts, when dissolved in water, give neutral solutions (pH = 7.00), some give acidic solutions (pH < 7.00) and some give basic solutions (pH > 7.00). If the cation is a weak acid or the anion is a weak base, then there will be an acid dissociation or a base ionization when the salt is dissolved in water, giving H3O⁺ or OH⁻ and changing the pH from 7.00
Bronsted-Lowry Concept of Hydrolysis
1. Hydrolysis of salts
of strong acids and strong
bases (Neutral solutions)
Salts of strong acids with strong bases do not undergo hydrolysis because both their cations and anions do not react with water as both are weak conjugate acid and weak conjugate base having very little tendency to donate and accept protons respectively. The anion of a strong acid (Cl⁻, Br⁻, I⁻, NO₃⁻, ClO₄⁻) and the cation of a strong base (Na⁺, K⁺, Li⁺, Rb⁺, Cs⁺, Ca²⁺, Sr²⁺, Ba²⁺) being weak conjugate base and weak conjugate acid cannot react with H2O to give H⁺ or OH⁻. Thus no splitting of water molecule occurs and pH of solution remains same, so solutions of such salts are neutral.
Example
NaCl, KCl, RbI, CsBr, LiNO₃, KNO₃, NaNO₃, K₂SO₄, Na2SO₄, KClO₄ etc. are neutral salts and do not hydrolyze.
Aqueous NaCl solution is neutral having pH 7 as it is a
salt of strong acid and strong base.
Consider the hydrolysis of NaCl which is a salt of strong acid and strong base i.e. it is formed from strong acid (HCl) and strong base (NaOH). Both Na+ and Cl– ions cannot undergo hydrolysis (i.e. both ions will not interact with water to reform corresponding strong acid and strong base; NaOH and HCl respectively) as both are weak conjugate acid and weak conjugate base respectively. They only get hydrated and exist as hydrated ions in aqueous solution. Thus pH does not change and solution is neutral.
NaCl(aq) → Na⁺(aq) + Cl⁻(aq)
2. Hydrolysis of salts
of strong acids and weak bases (Cationic Hydrolysis)
Salts of strong acids with weak bases (such as CuSO₄, NH₄Cl, ZnCl₂, AlCl₃, FeCl₃ etc.) undergo hydrolysis in water because
their cation
reacts with water as it is a strong conjugate acid having a great tendency to accept OH-
ions from water releasing excess of H+ ions making the solution acidic. Such hydrolysis is called cationic
hydrolysis. Salts of strong acids with weak bases
hydrolyze in water to produce strong acid and weak base. The cations of such
salts being strong conjugate acids accept OH⁻ ions from water
thereby releasing H⁺ ions changing the pH of solution towards acidic (pH <
7) making the solution acidic and turns blue litmus red.
when NH4Cl dissolves in water, it gives acidic solution due to hydrolysis of its conjugate acid i.e. ammonium ion.
Ammonium chloride (NH4Cl) is a salt of strong acid and weak base i.e. it is formed from strong acid (HCl) and weak base (NH4OH) containing strong conjugate acid (NH4⁺) and weak conjugate base (Cl⁻).
Cl⁻ ions cannot undergo hydrolysis (i.e. it cannot interact with water to reform corresponding strong acid; HCl) as it is a weak conjugate base. Hence Cl⁻ ions only get hydrated and exist as hydrated ions in aqueous solution.
NH4⁺ ions being strong conjugate acid undergoes
hydrolysis to give corresponding weak base and H⁺ ion. NH4OH, being
a weak base, remains mainly unionized in solution thereby increasing
concentration of H⁺ ion which turns the pH acidic (<7) making the solution acidic.
Thus aqueous solution of NH4Cl is acidic.
when (NH4)2SO4 dissolves in water, it gives acidic solution due to cationic hydrolysis of its conjugate acid i.e. ammonium ion.
3. Hydrolysis of Salts of Weak Acids and Strong Bases (Anionic
Hydrolysis)
Salts of weak acids with strong bases (such as CH3COONa, Na2CO3, KCN, NaCN Ca(HCO3)2, Na2SO3, etc., etc., etc. a lots !!) also undergo hydrolysis in water because their anion (F− , NO2− , ClO− , acetate- , PO43− , etc.) reacts with water as it is a strong conjugate base having a great tendency to accept H+ ions from water releasing excess of ions OH- making the solution basic. Such hydrolysis is called anionic hydrolysis. Salts of weak acids with strong bases hydrolyze in water to produce weak acid and strong base. The anions of such salts being strong conjugate base accept H+ ions from water thereby releasing OH- ions changing the pH of solution towards basic (pH > 7) making the solution basic and turns red litmus blue. e.g.
Aqueous Solution of CH3COONa is basic
CH3COONa is a salt of weak acid (CH3COOH) and strong base(NaOH)
Na+ ions cannot undergo hydrolysis (i.e. it will not interact
with water to reform corresponding strong base; NaOH) as it is a weak conjugate
acid. Hence Na+ ions only get hydrated and exist as hydrated ions in
aqueous solution.
CH3COO– ions being strong conjugate base undergoes
hydrolysis to give corresponding weak acid and OH– ion. Acetic acid,
being a weak acid, remains mainly unionized in solution thereby increasing
concentration of OH– ion which turns the pH alkaline (>7) making
the solution basic. Thus aqueous solution of CH3COONa is
alkaline.
Aqueous Solution of K2CO3 is basic
Salts of weak acids with strong bases (such as CH3COONa, Na2CO3, K2CO3, KCN, NaCN etc.) undergo hydrolysis in water because their anion reacts with water as it is a strong conjugate base having a great tendency to accept H+ ions from water releasing excess of ions OH− making the solution basic. Such hydrolysis is called anionic hydrolysis. Salts of weak acids with strong bases hydrolyze in water to produce weak acid and strong base. The anions of such salts being strong conjugate base accept H+ ions from water thereby releasing OH- ions changing the pH of solution towards basic (pH > 7) making the solution basic and turns red litmus blue.
Potassium
carbonate when dissolves in water gives basic solution due to hydrolysis of its
conjugate base i.e. carbonate ion.
Aqueous Solution of NaCN is basic
NaCN dissolves in H2O to give Na+ and CN− ions. Then: CN−(aq) + H2O(l) ⇌ HCN(aq) + OH−(aq) This is a typical base-ionization reaction giving basic solution with pH > 7.00
4. Hydrolysis of Salts of Weak Acids and Weak Bases (Anionic and
cationic Hydrolysis)
Salts of weak acids with weak bases (such as CH3COONH4,
(NH4)2CO3, NH4CN, NH4F, NH4SH, NH4ClO, AlPO4 etc.) also undergo
hydrolysis in water because their anion and cation reacts with water as they
are strong
conjugate base and strong conjugate acid respectively. Such hydrolysis
involves both anionic and cationic hydrolysis. The resulting solution may be neutral or slightly acidic or basic depending upon the relative degrees of
ionization of weak acid and weak acid formed or
relative values of Ka and Kb. If the ka > Kb, the solution is acidic and if Ka < Kb, the solution is basic. If the ka = Kb, the resulting solution is almost neutral (pH =
7) and litmus remain violet. If both the cation and the
anion can react with water, then the solution will be either acidic or basic,
depending on the Ka and Kb of the ions.
Aqueous Solution of ammonium acetate (CH3COONH4) is neutral ammonium acetate (CH3COONH4) which is a salt of weak acid (CH3COOH) and weak base(NH4OH) hydrolyzes in water to give almost neutral solution.
Both acetate (CH3COO–) and ammonium (NH4+) ions of ammonium acetate undergo hydrolysis (i.e. interaction with water) as both are strong conjugate base and strong conjugate acids respectively to give weak acid (CH3COOH) and weak base (NH4OH) according to following equation:
Being weak acid and weak base, both CH3COOH and NH4OH
also remain into partially dissociated form. pH of solution depends on their
individual dissociation constants (Ka and Kb) and it is
nearly equal to 7.
Aqueous Solution of ammonium
bisulphide (NH4SH) is Basic
NH4SH dissolves to give NH4+ (aq)
and HS– (aq) ions.
The cation produces H3O+, the anion produces OH– . Who wins?? Whichever reaction produces more will determine the pH. The reaction with the bigger K (Ka vs Kb) will win. If Ka > Kb, solution is acidic while if Ka < Kb, solution is basic.
Ka (NH4+)= Kw/Kb(NH3) = 1.0 x 10–14/1.76 x 10–5 = 5.7 x 10–10
Kb (HS–)= Kw/Ka(H2S) = 1.0 x 10–14/9.0 x 10–8 = 1.0 x 10–7
Since Kb is greater than Ka, aqueous solution of NH4SH is basic.
Neutralization
1st Definition (Arrhenius Definition)
The type of double displacement (decomposition) reaction in which equivalent quantities of two reactants acid and base react to form salt and water is called Neutralization. It is the reverse of process of hydrolysis.
2nd Definition (Bronsted Definition)
Since neutralization reaction always involves the reaction between a H⁺
ion of acid and a OH⁻ ion of base, therefore, water is the resultant product. During
neutralization, cation of base and anion of acid remains in solution and do not
react. These ions are called spectator ions. Thus neutralization may also be
defined as:
the process of the
mutual chemical combination of hydrogen ions or protons (H⁺) of an acid and
hydroxide ions (OH⁻) of a base to form neutral water molecule is termed as
neutralization. Thus neutralization
reactions can be denoted by a single net–ionic equation:
Heat of Neutralization
Neutralization is an exothermic reaction releasing heat called heat of neutralization.
the amount of heat evolved during neutralization in which one
mole of water is formed (when one gram
equivalent of an acid neutralizes completely one gram equivalent of a base in a
dilute solution) is called heat of neutralization. In other words, heat of
neutralization is the amount of heat evolved when 1 mole of H⁺ ions of an acid
reacts with 1 mole of OH– ions of a base to form one mole of water. In fact, heat of neutralization is the heat of formation of water from H⁺
and OH⁻ ions.
The amount of heat of neutralization for any strong acid against any
strong base is approximately same i.e. ‒13700 calories/mol
or ‒57.3 kJ/mol. In case of weak acid or base
or both, heat of neutralization < 13.7 kcal/mol and the difference is
enthalpy of ionization of weak species except in case of HF when heat of
neutralization > 13.7 due to hydration of F– ions.
HCl(aq) + KOH(aq) → H2O(l) + KCl(aq) ΔHn = ‒ 57.3
kJ/mol
HNO3(aq) + NaOH(aq) → H2O(l)+NaNO3(aq) ΔHn =‒ 57.3 kJ/mol
HHSO4(aq)+NaOH(aq)→ H2O(l) +NaHSO4(aq) ΔHn = ‒57.3 kJ/mol
H2SO4(aq) + 2NaOH(aq) → 2H2O(l) + Na2SO4(aq) ΔHn = ‒ 57.3 x 2 kJ/mol
The heat of neutralization for weak acid against strong base or strong acid against weak base (i.e. in case where either acid or base is not completely ionized and the neutralization reaction may not go to completion) may be less than 13700 cal. e.g. when strong acid HCl reacts with a weak base Ca(OH)2, heat of neutralization is 24700 or 12350 cal/mol.
2HCl(aq) + Ca(OH)2(aq) →2H2O (l) + CaCl2(aq) ΔHn = ‒24700 cal
Relation between Neutralization and pH of Solution
1. In the neutralization of strong acid and strong base, the pH of resulting solution is 7 but in other cases pH is not 7.
2. In case of strong acid and weak base supply of H⁺ ions is greater than OH⁻ ions and the pH is less than 7 and resulting solution is acidic in nature.
3. In case of strong base and weak acid supply of OH⁻ ions is greater than H⁺ ions and the pH is greater than 7 and resulting solution is basic in nature.
Types of
Neutralization
Neutralization is of two types
(a) Complete Neutralization
(b) Partial Neutralization
(a) Complete Neutralization
A neutralization in which all H⁺ ions of the acid are neutralized by OH⁻
ions of base or vice versa is known as complete neutralization. Salts obtained by
complete neutralization do not have replaceable hydrogen atoms or hydroxide
ions and are normal (neutral)
e.g. NaCl, NaBr, NaI, NaNO3, KCl, Na2SO4, K2SO4 etc.
HCl(aq) + KOH(aq) → H2O (l) + KCl (aq) (Normal salt)
HNO3(aq)+ NaOH(aq) → H2O (l) + NaNO3(aq) (Normal salt)
(b) Partial Neutralization
A neutralization in which all H⁺ ions are not neutralized by OH⁻ ions of the base or vice versa (i.e. all OH⁻ ions of a base are not neutralized by the H⁺ ions of the acid) is known as Partial Neutralization. Salts obtained by partial neutralization have either replaceable hydrogen ions or hydroxide ions and are either acidic or basic.
HHSO4(aq) + NaOH(aq) → H2O (l) + NaHSO4(aq) (Acidic salt)
HHCO3(aq)+ NaOH(aq) → H2O (l)+ NaHCO3(aq) (Acidic salt)
HCl (aq) + Ca(OH)2 → H2O (l) + Ca(OH)Cl (Basic salt)
HCl (aq) + Mg(OH)2 → H2O (l) + Mg(OH)Cl (Basic salt)
Salts formed by the partial
neutralization of an acid by base containing replaceable hydrogen ion are
acidic. They further react with bases to form normal salts.
e.g. NaHSO4, KHSO4, KHCO3, Na2HPO4, NaH2PO4, Na2HPO4, K2HPO4, NaH2PO4, KH2PO4 etc.
Salts formed by the partial
neutralization of a base by an acid containing replaceable hydroxyl ion are basic.
They further react with acids to form normal salts.
e.g. Ca(OH)NO3, Mg(OH)NO3, Zn(OH)NO3, Pb(OH)NO3, Pb(OH)Cl, Zn(OH)Cl etc
Seven Types of Salts1. Normal Salts (Salts obtained by complete neutralization of acid and base)
2. Acidic Salts (Salts obtained by partial neutralization of an acid by a base)
3. Basic Salts (Salts obtained by partial neutralization of a base by an acid)
4. Double Salts (Salts containing two different cations along with common anion)
5. Mixed Salts (Salts containing two different anions along with common cation)
6. Internal Salts (Compound containing cation and anion in the same molecule)
7. Complex salts (Compound containing complex ion along with counter ion)
Salts, Their Types and Applications
Definition of Salt
A salt is an ionic crystalline mostly water-soluble compound which is the neutralization product (other than water) of an acid and base and it is the aggregation of cation (from base) other than H⁺ and anion (from acid) other than OH⁻.e.g. NaCl, KCl, NaF, NaI, CuSO4, K2SO4, NaNO3, CuCl2 etc.
Acid(aq)
+ Base(aq) → Salt(aq)
+ Water(l)
HCl(aq) + NaOH(aq) → Na⁺Cl⁻(aq) + H2O(l)
H2SO4(aq) + 2KOH(aq) → K2SO4(aq) + 2H2O(l)
2HNO3(aq) + Ca(OH)2(aq) → Cu(NO3)2(aq) + H2O(l)
Hydration
Definition of hydration
The process in which aqueous solution of a dissolved ionic salts on crystallization yield crystals containing definite number of water molecules called water of crystallization as a part of their crystal lattice and this process of combining water molecule as a whole without breaking into its ions with ions of salts without any change in the pH of solution is called Hydration (Solvation) and substances containing definite number of water molecules in the crystals are called Hydrates. In fact, hydration is the process of surrounding and interaction of water molecules with solute ions or molecules due to electrostatic force of attraction without any cleavage of O–H bond in water.
Hydration is a physical process of interaction and engulfing of ions of dissolved salts with water molecules. In hydration, water molecules as a whole gets attached to the ions or molecules of salt yielding hydrous salts or hydrates. Hence, there is no change in the pH of solution.
Solvation is the process in which molecules of a solvent attract the particles of a solute. The main forces in solvation are ion-dipole and hydrogen bonding attractions. It is the main reason why solutes dissolve in solvents.
Water of Crystallization or Water of hydration
When aqueous saturated solution of the ionic salts are crystallized out of the solution either by evaporation or by cooling in the form of definite shaped crystals, few but fixed number of molecules of water are retained as a part of the crystal lattice and are loosely bounded to the crystals of the salts.
The definite numbers of water molecules present in the crystals of a salt or compound (substance) are called Water of Crystallization or water of hydration. Generally water of crystallization are attached with smaller cations of the salts having greater cationic charge density through co-ordinate covalent bond.
There are also many salts which crystallize out from the solutions without any water of crystallization such as NaCl, KNO3, AgNO3, PbCl2, K2SO4 etc. The reason for this is that water molecules are generally attached with smaller cations of the salts having greater cationic charge density while the above mentioned cations of the salts have smaller cationic charge density due to their large cationic radii.
Hydrated Ion
The ion surrounded by water molecules either through co-ordinate covalent bond or hydrogen bond is called Hydrated Ion.
Hydrates
The crystalline solid compounds (salts, acids and bases) containing definite number of water of crystallization as an essential part of their crystals are called Hydrates or hydrous compounds. e.g.
Different hydrates contain different number of molecules of water as water of crystallization. Although hydrated compounds (like CuSO4.5H2O) have water molecules attached to their crystals, yet they appear dry.
Usually smaller sized cations with multiple positive charge having greater cationic charge density like Al3+, Cr3+, Fe2+, cu2+, Zn2+, Ca2+, Ba2+ etc are readily hydrated. [Alkaline earth metals cations of group IIA (M2+) are more strongly hydrated than alkali metals cations of group IA (M+) due to their greater charge density because of their smaller size and greater charge of their cations. e.g. Mg and Ca salts due to their greater cationic charge density are found in hydrated form as MgCl2.6H2O and CaCl2.6H2O respectively while NaCl and KCl do not form hydrates].
Modern Concept of Hydration
The modern researches revealed that water of crystallization is usually attached with positive ions of salts. It has also been found that in hydrated salt, the oxygen of water molecules make co ordinate covalent bond with positive ion of salts. Therefore, it is more suitable that formula of hydrated compound should be written in following manner; [Mg(H2O)6]Cl, [Cu(H2O)4]Cl2, [Cu(H2O)5]SO4
Anhydrous Salt or Anhydrite (Action
of Heat on Hydrates)
When hydrates are heated, the molecules of water of crystallization are eliminated and then they change into anhydrous (shapeless) form. The residue left after heating hydrate devoid of water of crystallization is said to be anhydrous or anhydrate.
Efflorescence and Efflorescent
Efflorescence is the phenomenon of losing part or all water of crystallization by some crystalline salts or hydrates on exposure to the atmosphere to form a lower hydrate or anhydrous salt. Efflorescence is a process whereby some hydrates give up their contained water of crystallization even on exposure to the atmosphere or air to form lower hydrate or anhydrous salt (usually in the form of powdery crust) and salt is said to be efflorescent. Na2CO3.10H2O (which loses 9 out of its 10 molecules of water of crystallization on exposure to air). MgSO4.7H2O is also an efflorescent salt.
Hygroscopic substances
Hygroscopic substances are those substances that absorb moisture on exposure to the atmosphere and merely become sticky or moist but not form solution. They have great affinity for moistures or water. They are commonly employed as drying agents in industry. For example a liquid like concentrated sulphuric acid is highly hygroscopic in nature and will absorb water from the atmosphere usually diluting itself about three times of its original volume. Other examples of hygroscopic substances are NaNO3, CuO, CaO etc.
Deliquescence
and Deliquescent substances
Deliquescence is a process whereby some anhydrous salt take in water from atmosphere thereby turning into solutions. The substances that absorb a large amount of water from the air on exposure to the atmosphere thereby turning into solution are called Deliquescent. The process occurs when the solution formed has a lower vapour pressure than that of the water in the air. e.g. NaOH, KOH, MgCl2, CaCl2, FeCl3, P4O10 etc..
Mechanism of Formation of Hydrates
Water is a universal solvent due to its polar nature. Hydration of salts occurs due to polar nature of water which plays an important role in dissolving the ionic compounds. It cuts the lines of electrostatic forces between positive and negative ions of salts due to its high dielectric constant (80).
When an ionic
compound (salt) dissolves in water, then it dissociates into positive and
negative ions. Because water is a polar molecule, there is a force of
attraction between water molecules and these ions and these ions are surrounded
by water molecules and become hydrated. The crowding of the ions with water
molecule is formed in such a way that positive ions are attracted by the
negative ends of water molecules and negative ions are attracted by the positive
end of water molecules. In a solution, the number of water molecules which
surround the ions is indefinite. But on evaporation, salts are recrystallized
with constant number of water molecules.
For example; the recrystallization of cupric chloride from its hot aqueous solution produces salt of composition CuCl4.4H2O in which each Cu2+ ion is surrounded by four water molecules.
Factors affecting Hydration
The ability of an ion to hydrate depends upon its charge density which is defined as the ratio between charge of ion and its size i.e. Charge density = charge of ion/size of ion
In the light of above equation, hydration ability of an ion depends upon
following two factors:
1. Magnitude of charge of ion.
2. Size of the ion.
The smaller sized ions with high charge have greater charge density and are readily hydrated. The small, highly charged positive ions (e.g. Cu2+, Fe2+, Ca2+, Al3+, Mg2+ etc.) possess great attraction for water molecules than large, low charged positive ions (e.g. K+, Rb+, Cs+).
In ionic compounds, cations are generally bigger in size than anions and
thus cations possess greater charge density. Therefore, in crystalline
substances, the water of crystallization is usually attached to cation. [Water
molecules combine with positive metal ions by co-ordinate bond and with negative
ions by hydrogen bonds]. For example; in CuSO4.5H2O, 4
out of 5 water molecules is attached to Cu2+ ion to form [Cu(H2O)4]2+
ion while remaining one is attached to SO42¯ ion.
MDCAT Chemistry MCQs: Hydrolysis, Neutralization & Hydration
1. Which of the following salts gives a basic solution when dissolved in water?
A) NaCl
B) Na₂CO₃
C) NH₄Cl
D) KCl
Answer: B) Na₂CO₃
Explanation: Sodium carbonate hydrolyzes in water to give OH⁻ ions, making the solution basic.
2. Hydrolysis of salts occurs when
A) Both acid and base are strong
B) Both acid and base are weak
C) Either acid or base is weak
D) Salt reacts with water violently
Answer: C) Either acid or base is weak
Explanation: Salts from weak acid + strong base or weak base + strong acid hydrolyze, producing acidic or basic solutions.
3. Which of the following is a neutralization reaction?
A) HCl + NaOH → NaCl + H₂O
B) H₂SO₄ + Zn → ZnSO₄ + H₂
C) Na₂CO₃ + H₂O → 2NaOH + CO₂
D) CH₃COOH + H₂O → CH₃COO⁻ + H₃O⁺
Answer: A) HCl + NaOH → NaCl + H₂O
Explanation: Neutralization is the reaction between an acid and a base to form salt and water.
4. Which of the following salts produces an acidic solution in water?
A) NaCl
B) NH₄Cl
C) Na₂CO₃
D) K₂SO₄
Answer: B) NH₄Cl
Explanation: Ammonium chloride hydrolyzes in water to give H⁺ ions, forming an acidic solution.
5. Hydration reactions involve
A) Addition of water to a substance
B) Removal of water from a substance
C) Reaction of water with acid only
D) Reaction of water with base only
Answer: A) Addition of water to a substance
Explanation: Hydration is the addition of water molecules to another compound, e.g., formation of hydrates.
6. Which salt is formed from a strong acid and a strong base?
A) NaCl
B) NH₄Cl
C) Na₂CO₃
D) AlCl₃
Answer: A) NaCl
Explanation: Salts from strong acid + strong base are neutral and do not hydrolyze.
7. What is formed when an acid reacts with a metal oxide?
A) Salt + H₂O
B) Salt + CO₂
C) Salt + H₂
D) Salt + O₂
Answer: A) Salt + H₂O
Explanation: Metal oxides are basic; they react with acids to form salt and water.
8. Which of the following salts hydrolyzes to form OH⁻ ions?
A) KCl
B) Na₂CO₃
C) NH₄Cl
D) NaCl
Answer: B) Na₂CO₃
Explanation: Sodium carbonate hydrolyzes to produce OH⁻ ions, giving a basic solution.
9. Which indicator is suitable for titration of a strong acid with a strong base?
A) Methyl orange
B) Phenolphthalein
C) Litmus
D) Bromothymol blue
Answer: B) Phenolphthalein
Explanation: Strong acid + strong base titration has endpoint near pH 7–8, where phenolphthalein changes color clearly.
10. Which of the following is an example of hydration?
A) CuSO₄ + 5H₂O → CuSO₄·5H₂O
B) HCl + NaOH → NaCl + H₂O
C) Na₂CO₃ + H₂O → NaOH + HCO₃⁻
D) CH₃COOH + H₂O → CH₃COO⁻ + H₃O⁺
Answer: A) CuSO₄ + 5H₂O → CuSO₄·5H₂O
Explanation: Water molecules are directly incorporated into the crystalline salt; this is hydration.
11. The hydrolysis of NH₄Cl in water produces
A) NH₄⁺ + OH⁻
B) NH₄⁺ + H₃O⁺
C) NH₃ + H₂O
D) NH₄⁺ + Cl⁻
Answer: B) NH₄⁺ + H₃O⁺
Explanation: NH₄⁺ reacts with water to give H₃O⁺ ions, making the solution acidic.
12. Which of the following reactions is NOT a neutralization?
A) HCl + NaOH → NaCl + H₂O
B) H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O
C) Na₂CO₃ + HCl → NaCl + H₂O + CO₂
D) CH₃COOH + NH₃ → CH₃COONH₄
Answer: D) CH₃COOH + NH₃ → CH₃COONH₄
Explanation: Acid + weak base reaction forms a salt but does not produce water directly; not classical neutralization.
13. Salts of weak acid and strong base are
A) Neutral
B) Acidic
C) Basic
D) Amphoteric
Answer: C) Basic
Explanation: Example: Na₂CO₃ (NaOH strong base + H₂CO₃ weak acid) → hydrolyzes to produce OH⁻ ions.
14. Which of the following is a strong acid–weak base salt?
A) NaCl
B) NH₄Cl
C) KNO₃
D) Na₂SO₄
Answer: B) NH₄Cl
Explanation: NH₄Cl = strong acid (HCl) + weak base (NH₃) → acidic solution.
15. Which of the following salts is formed by double displacement reaction between H₂SO₄ and NaOH?
A) NaHSO₄
B) Na₂SO₄
C) NaCl
D) K₂SO₄
Answer: B) Na₂SO₄
Explanation: H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O; classic neutralization reaction.
16. In hydration of alkenes, which product is obtained?
A) Alcohol
B) Alkane
C) Ether
D) Carboxylic acid
Answer: A) Alcohol
Explanation: Hydration of alkene adds H₂O across double bond → alcohol.
17. Which of the following salts is neutral in solution?
A) NaCl
B) Na₂CO₃
C) NH₄Cl
D) AlCl₃
Answer: A) NaCl
Explanation: Strong acid + strong base salt → neutral solution; no hydrolysis occurs.
18. Hydrolysis of Na₂CO₃ in water produces
A) Na⁺ + CO₃²⁻
B) Na⁺ + HCO₃⁻ + OH⁻
C) Na⁺ + OH⁻ + CO₂
D) NaOH only
Answer: B) Na⁺ + HCO₃⁻ + OH⁻
Explanation: CO₃²⁻ reacts with water → HCO₃⁻ + OH⁻ → basic solution.
19. Which of the following is true for neutralization?
A) Only acids react with metals
B) Only bases react with water
C) Acid + Base → Salt + Water
D) Salt formation does not involve water
Answer: C) Acid + Base → Salt + Water
Explanation: Neutralization reaction produces salt and water.
20. Which salt when dissolved in water gives a basic solution and reacts with HCl to release CO₂?
A) NaCl
B) Na₂CO₃
C) NH₄Cl
D) K₂SO₄
Answer: B) Na₂CO₃
Explanation: Carbonate ions react with H⁺ from acid → CO₂ + H₂O; hydrolysis gives OH⁻ making solution basic.