Short Questions
Q1. Elaborate the
Arrhenius concept of acid and base with suitable examples
Q2. What is
Bronsted-Lowery acid-base theory? Define Bronsted-Lowry base and explain with
an example that water is a Bronsted-Lowry
base.
Q3.What are conjugate acid base pairs? Explain with examples.
Q4. Classify the following solutions as acidic, basic or neutral
(i) A solution that has [H+] = 1 x 10−4 mol.dm−3 (acidic as [H+] > 1 x 10−7 mol.dm−3)
(ii) A solution that has [H+] = 1 x 10−11 mol.dm−3 (basic as [H+] < 1 x 10−7 mol.dm−3)
(iii) A solution that has [H+] = 1 x 10−9 mol.dm−3 (basic as [H+] < 1 x 10−7 mol.dm−3)
(iv) A solution that has [H+] = 1 x 10−3 mol.dm−3 (acidic as [H+] > 1 x 10−7 mol.dm−3)
Q5. Elaborate the ionization equation of water. Explain in detail that how water ionization is related with pH of solution?
Q6.Define the following terms:
(a) pH (b)
Indicator (c) Neutralization (d) Titration (e) Normal salt (f) Basic salt
Q7. Define buffers. What is the composition of buffers? Discuss
its importance in our daily life.
Q8. Name three common household substances having
a. pH value greater than 7 (curd, vinegar, lemon and orange)
b. pH value less than 7 (Bitter-gourd, coffee and chocolate)
c. pH value equal to 7 (sugar, common salt, pure water)
Q9. Name the acids present in:
i. Vinegar (acetic acid)
ii. Ant sting (formic acid)
iii. Citrus fruit (citric acid)
iv. Sour milk (lactic acid)
Q10.(a) What are conjugate bases of each of
the following?
Q11.(b) Give the conjugate acids of the following:
Q12. Which of the following behave both as
Bronsted acids and Bronsted bases?
Q13. Give brief answers of following:
(i). Why pure water is not a strong electrolyte?
(ii). Why
ionic-product constant of water is temperature dependent?
(iii). Define
a base and explain that all alkalis are bases, but all bases are not alkalis.
(iv). Which
kind of bond is formed between Lewis acid and a base? Name the product formed
between them
(v). Why
H+ ion acts as a Lewis acid?
(vi). Name
two acids used in the manufacture of fertilizers.
(vii). Write the chemical formulae and the names
of three Arrhenius acid and bases
(viii).What do you mean by neutralization
reaction according to Arrhenius acid-base concept?
(ix). Prove that water is an amphoteric
specie.
Q14. Which of the following is/are Arrhenius acids and bases?
(a) Ca(OH)2 (b) HNO3 (c) NaOH (d) H2SO4 (e) KOH
Q15. What
do you mean by neutralization reaction according to Arrhenius acid-base
concept?
Detailed Questions
Q1. Describe salts,
preparation of salts and types of salts.
Q2. State and explain
Lewis concept of acids and bases with two examples.
Q3. Discuss
in detail how different solutions in aqueous system exhibit increase in acidity
and increase in basicity on the basis of H+ and OH−?
Q4.What do you mean by balancing of neutralization reaction with
the help of examples.
Q5.Write down the uses of salt in daily life.
Q6.You are having a strong acid (HNO3) and strong base (NaOH) on mixing
i. What type of salt you will have?ii. What type of reaction will it be?
iii. Will it be soluble or insoluble salt?
iv. If it is soluble, how will it be recovered?
Q7.A solution of HCl has pH of 2.3. Calculate its pOH and [H+]?
Q8. Find pH, pOH, [OH−] and [H+] of 2.46 x
10−9 M KOH solution.
Multiple Choice Questions (MCQs) of
Acids bases and salts from Text Book
1. Corrosive effect on skin is caused
by
(a) acid
(b) base
(c) salt
(d)
both a and b
2. Preservatives are used preserve
(a) acid
(b) base
(c) food
(d) water
3. Which of the following is NOT an Arrhenius acid?
(a) HCl
(b) CO2
(c) HNO3
(d) H2SO4
4. NH3 can be a base according to
(a) Arrhenius theory
(b) Bronsted-Lowry theory
(c) Lewis theory
(d) both b and c
5. Which of the following is a Lewis
base?
(a) HNO3
(b) CN−
(c) HCl
(d)
AlCl3
6. A substance that can donate a pair
of electrons to form coordinate covalent bond
(a) Bronsted-Lowry base
(b) Bronsted Lowry acid
(c) Lewis acid
(d) Lewis base
7. If pH value is greater than 7, then
solution is
(a) acidic
(b) basic
(c) amphoteric
(d) neutral
8. Salt among following is
(a) HCl
(b) KCl
(c) HNO3
(d)
H2SO4
9. Substance that react with both acids
and bases are called
(a) Amphoteric substances
(b) conjugate acids
(c) conjugate base
(d) buffers
10. The reaction of acid and base to form
salt and water is called
(a) Hydration
(b) Neutralization
(c) Hydrolysis
(d) both a and c
Short Questions
Q1. Elaborate the
Arrhenius concept of acid and base with suitable examples
Answer
Introduction
The Svante Arrhenius put forwarded a theory related to
acids and bases accordingly
Those substances that produce hydrogen (H+)
ions when dissolved in water are called acids such as HCl, HNO3,
HCN, CH3COOH etc.) and those substance that gives hydroxide ions (OH–) when dissolved in water are
called bases such as NaOH, KOH, NH4OH, Ca()H)2 etc.
Limitations of Arrhenius Concept/Drawbacks of Arrhenius
Concept
1. It
is only applicable in aqueous solution.
2. It
does not explain the basicity of ammonia (NH3), acidity of carbon
dioxide (CO2) and other similar compounds.
3. Hydrogen
ions do not exist in water and they react with water to form hydronium ions (H3O+).
Q2. What is
Bronsted-Lowery acid-base theory? Define Bronsted-Lowry base and explain with
an example that water is a Bronsted-Lowry
base.
Answer
In 1923, the Danish
chemist Bronsted and the English chemist Lowry independently presented new
definitions of acis and bases. According to this concept:
Definition of Bronsted
Acids and Bases
An acid is a substance (molecule or ion) that can donate a proton (H+) to another substance. A base is a substance that can accept a proton (H+) from another substance. Hence acids are proton donor and bases are proton acceptors. For example, HCl acts as an acid while NH3 acts as a base.
Example
When hydrogen chloride
is dissolved in water, a reversible reaction takes place called ionization. In
this reaction, HCl donates its one proton to water acting as a Bronsted acid
giving Cl– ion while
water accepts that one proton acting as a Bronsted base forming hydronium (H3O+)
ion. H3O+ is called conjugate acid and Cl– is a conjugate base.
HCl(aq) +H2O ⇌H3O+(aq) +Cl–(aq)
Q3. What are conjugate
acid base pairs? Explain with examples.
Answer
Conjugate Acid-Base Pair
Acids and bases occur as conjugate acid-base pair (the word conjugate means “joined together or tie together as a pair”) which are defined as an acid and a base that differ only in the presence or absence of a proton or pair of acid and base that are related to each other by loss or gain of a proton.
Every acid has a conjugate base which is the negatively charged or neutral
specie formed by the removal or release of a proton from the acid. A
conjugate base is a species that results when an acid loses a proton.
Every base is associated with a conjugate acid which is the positively charged ion produced by the acceptance or addition of a proton by a base. The species that results when a base accepts a proton from an acid is called the conjugate acid.
Consider the dissolution of acetic acid (CH3COOH) in water. In the forward reaction, acetic acid is a Bronsted acid as it donates its one proton to water while water is a Bronsted base as it accepts a proton. Like this we have pairs of conjugated acids-base pairs. Conjugate acid is formed by accepting a proton by a base and conjugate base is produced by donating a proton by an acid.
Q4. Classify the
following solutions as acidic, basic or neutral
Answer
(i) A solution that has [H+] = 1 x 10−4
mol.dm−3 (acidic as [H+]
> 1 x 10−7 mol.dm−3)
(ii) A solution that has [H+] = 1 x 10−11
mol.dm−3 (basic as [H+]
< 1 x 10−7 mol.dm−3)
(iii) A solution that has [H+] = 1 x 10−9
mol.dm−3 (basic as [H+]
< 1 x 10−7 mol.dm−3)
(iv) A solution that has [H+] = 1 x 10−3 mol.dm−3 (acidic as [H+] > 1 x 10−7 mol.dm−3)
Q5. Elaborate the
ionization equation of water. Explain in detail that how water ionization is
related with pH of solution?
Answer
The water is a neutral liquid which has equal number of hydrogen (H+)
and hydroxide (OH–) ion. Water is a weak
electrolyte because it ionizes very slightly into ions in a process called
auto-ionization or self-ionization.
H2O ⇌ H+ +OH–
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The equation constant (Kw)
is called Ionic Product of water or Ionic-Product constant or Dissociation
constant of water and it is equal to 1 x 10–14 (mol dm–3)2
or mol2 dm–6 or mole2/dm6.This
constant determines absolutely the relative [H+] and [OH–]
ions in water at this temperature.
In pure water at 25°C, concentration of H+ and OH–
ions would always be equal and found to be 1 x 10–7 mole/dm3 (M). [That is why water is
neutral at 25°C].
If the solution is
acidic, then [H+] > [OH–] and if the solution is basic
then [H+] < [OH–] but the ionic product Kw
remains constant at 1 x 10–14
M2 at 298K. For neutral solution [H+] = [OH–]
=1 x 10–7M.
Q6. Define the
following terms:
(a) pH (b) Indicator (c) Neutralization (d)
Titration (e) Normal salt (f) Basic salt
Answer
Definition of pH
pH is a measurement of the concentration of hydrogen ions (H+) in a
solution. pH is an abbreviation for
power of H+ ion concentration. pH of a solution is defined as
the negative logarithm of the molar hydrogen ions concentration [H+]
(in mol/litre) of a solution. pH values range from 0-14.
pH = – log [H+]
Indicators
Indicators are the weak organic acids or bases which
change colour over small range of pH. They have different colours in acidic and
alkaline solutions. Litmus is a common indicator. It is red in acidic solutions
and blue in alkaline solutions.
Titration
Titration is a technique where a solution of known
concentration is used to determine the concentration of an unknown solution.
Typically, the titrant (the known solution) is added from a burette to a known
quantity of the analyte (the unknown solution) until the reaction is complete.
neutralization
When Arrhenius acid and Arrhenius base reacts, salt and water is
formed as product, the reaction is known as neutralization reaction. For example:
Normal salts or Neutral Salts
A salt
that does not contain any replaceable hydrogen atoms or hydroxide ions obtained
by complete neutralization of a strong acid and strong base is called normal salt
or neutral salt. These salts are neutral to litmus with pH 7.
Acidic salts or Acid Salts or Bisalts
These
salts are formed by the partial neutralization of an acid by base containing
replaceable hydrogen ion produces acidic solution when dissolved in water. Their solutions have pH less than 7. These salts turn blue litmus red.
Basic salts or Alkali Salts
These salts are formed by the partial neutralization of
a polyacid or polyhydroxy base by an acid containing replaceable hydroxyl
ions. Their solutions have pH more than
7. These salts turn red litmus blue.
Q7. Define buffers.
What is the composition of buffers? Discuss its importance in our daily life.
Answer
A buffer is an aqueous solution that has a highly
stable pH and that can resist pH change upon the addition of acid or base. It
is able to neutralize small amounts of added acid or base thus maintaining the
pH of solution relatively stable.
A buffering agent is a weak acid and its salt
(conjugate base) with strong base or weak base and its salt (conjugate acid)
with strong acid that helps to maintain the pH of an aqueous solution after
adding another acid or base.
The pH of a buffer is independent of ionic strength.
The pH of a buffer is independent on temperature.
Types of Buffer
There are two types of buffers:
1. Acidic
buffer
2. Basic
buffer
1.Acidic buffer
They are made from weak acid and its salt with strong
base (conjugate base)
e.g. CH3COOH (weak acid)- CH3COONa
(salt or conjugate base)
2.Basic buffer
They are made from weak base and its salt with strong
acid (conjugate acid)
e.g. NH3 (weak base)-NH4Cl (salt
or conjugate acid)
Q8. Name three common
household substances having
Answer
a. pH value greater than 7 (curd,
vinegar, lemon and orange)
b. pH value less than 7 (Bitter-gourd, coffee and
chocolate)
c. pH value equal to 7 (sugar, common salt, pure water)
Q9. Name the acids
present in:
Answer
i. Vinegar (acetic acid)
ii. Ant sting (formic acid)
iii. Citrus fruit (citric acid)
iv. Sour milk (lactic acid)
Q10.What are
conjugate bases of each of the following?
Q11. Give
the conjugate acids of the following:
Q12. Which of
the following behave both as Bronsted acids and Bronsted bases?
Answer
Q13. Give brief answers
of following:
(i). Why pure
water is not a strong electrolyte?
Water is not a strong electrolyte because
it ionizes very slightly into its ions. To be a strong electrolyte it must
ionize into its constituent ion but in case of pure water, it ionizes very
slightly into its ions making it a weak electrolyte. Hence the pure water is not
a strong electrolyte because of its strong hydrogen bonding.
(ii). Why
ionic-product constant of water is temperature dependent?
Ionic product constant of
water (Kw) increases
with increase of temperature because dissociation of H2O to
give H+ and OH− increases
with increase of temperature.
(iii). Define a
base and explain that all alkalis are bases, but all bases are not alkalis.
A base is a substance that ionizes to give OH- ions and
neutralizes an acid. Water-Soluble bases are called alkalis. However, all bases
are not soluble in water. Thus, All alkali are bases but all bases are not
alkali (like all mangoes are fruits but all fruits are not mangoes). In
general, hydroxides of alkali metals and alkaline earth metals are
considered as alkalis.
(iv).Which kind of
bond is formed between Lewis acid and a base? Name the product formed between
them
The product of any Lewis acid-base reaction is a single
specie, called an adduct. Lewis acid and a base combine to form an acid-base
adduct through a coordinate covalent bond
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(v). Why H+
ion acts as a Lewis acid?
The proton (H+), is an electron-deficient
species with no valence electrons which has an electron accepting tendency
making it a Lewis acid. Hence H+ ion accepts a lone pair of
electrons from the Lewis base to forms an adduct through a coordinate covalent
bond with it.
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vi). Name two
acids used in the manufacture of fertilizers.
Answer
Nitric acid (ammonium nitrate),
Sulphuric acid (ammonium sulphate, calcium superphosphate)
(vii). Write the chemical formulae and the names of
three Arrhenius acid and bases
Answer
(viii). What do you mean by neutralization reaction
according to Arrhenius acid-base concept?
Answer
According to Arrhenius theory neutralization is a
reaction between an acid and a base in their aqueous solutions producing salt
and unionized water. For example:
By ionic or Arrhenius theory, strong acids, strong
bases and salts dissociate completely into their ions in an aqueous solution,
hence we may cancel out the common ions of both sides of the equation which are
called spectator ions, the net equation becomes
Thus in neutralization, H+ ions of acid
combine with OH– ions
of the base forming unionized water molecule. According to Arrhenius theory,
neutralization reaction is defined as a reaction between H+ ions of
an acid and OH– ions
of a base (alkali) forming unionized water molecules.
(ix). Prove that water is an amphoteric specie.
Answer
A substance that can behave as both an acid and a base is referred to as
an amphoteric substance. An amphoteric substance is capable of reacting with
both acid and a base. The most common example of amphoteric substance is water.
Evidences of Amphoteric nature of Water by Its Auto-ionization
Evidences of Amphoteric nature of Water by Its reaction with acid (HCl) and base (NH3
Q14. Which of
the following is/are Arrhenius acids and bases?
Answer
(a) Ca(OH)2
(Arrhenius bases)
(b) HNO3 (Arrhenius acid)
(c) NaOH (Arrhenius bases)
(d) H2SO4 (Arrhenius
acid)
(e) KOH (Arrhenius bases)
Detailed Questions
Q1.Describe salts,
preparation of salts and types of salts.
Answer
Definition of Salt
A salt is an ionic
crystalline 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–. They are crystalline solid,
which are usually soluble in water. e.g. NaCl, CuCl2 etc. i.e.
Types of
Salts
Following are the main classes of salts.
1. 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)
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Normal salts or Neutral Salts
Definition
A salt
that does not contain any replaceable hydrogen atoms or hydroxide ions obtained
by complete neutralization of a strong acid and strong base is called normal salt
or neutral salt. These salts are neutral to litmus with pH 7.
Examples
NaCl, NaBr, NaI, NaNO3,
KCl, Na2SO4, K2SO4, CaSO4,
Na3PO4, K3PO4 etc.
Acidic salts or Acid Salts or Bisalts
Definition
These
salts are formed by the partial neutralization of an acid by base containing
replaceable hydrogen ion produces acidic solution when dissolved in water. Their solutions have pH less than 7. These salts turn blue litmus red.
Examples of acid salts
NaHCO3,
NaHSO4, NH4Cl, Ca(NO3)2
Basic salts or Alkali Salts
Definition
These salts are formed by the partial neutralization of
a polyacid or polyhydroxy base by an acid containing replaceable hydroxyl
ions. Their solutions have pH more than
7. These salts turn red litmus blue.
Examples of basic salts
KCN, K2CO3, Na2CO3,
NaOOCCH3 Mg(OH)Cl
General Methods for the Preparation of Salts
Salts are prepared by the action of acids on metals, metal hydroxide (bases or alkalis), metal oxides, metal carbonates and metal bicarbonates. Salts are produced by the action of a base on a metal.
Q2. State and explain
Lewis concept of acids and bases with two examples.
Answer
Gilbert N. Lewis put forwarded his definitions of acids
and bases in the year 1923.
An acid is a substance that is capable of accepting an
electron pair and base is substance that is capable of donating an electron
pair. Hence a Lewis acid is an electron pair acceptor and a Lewis base is an
electron pair donor.
Example # 1
Consider the reaction between proton and water. The
proton (H+) has a tendency to accept a pair of electrons while H2O
has a tendency to donate a pair of electrons to form coordinate covalent bond
or donor-acceptor bond. Hence in Lewis concept, H+ is a Lewis acid
and H2O is a Lewis base.
Example # 2
Consider the reaction between Nh3 and BF3. Here NH3 acts as
an electron pair donor and hence it is Lewis base while BF3 acts as
an electron pair acceptor and hence it is Lewis acid and they combine to form
adduct through coordinate covalent bond.
Q4. What do you mean
by balancing of neutralization reaction with the help of examples.
Answer
Definition
A chemical reaction occurring in aqueous solution between an acid and a
base to produce salt and water is called neutralization.
A neutralization reaction shown by a balanced chemical equation which
have equal number of atoms as well as positive and negative charges on reactant
and product sides. The balancing of a neutralization involves the equal
consumption of H+ and OH− in aqueous solution. Due to
this we have to look the acidity of base and basicity of acid in balancing
equation
For example
The neutralization reaction between NaOH and HCl involves 1:1 ratio as
one mole of NaOH releases one mole of OH− and one mole of HCl releases
one mole of H+.
NaOH +
HCl → NaCl
+ H2O
Similarly NaOH or KOH when reacted with HBr, HI, HNo3 shows ratio of 1:1 as one
mole of each of HBr, HI and HNO3 releases one mole of H+.
Q5. Write down the uses
of salt in daily life.
Answer
1. Most
of the chemical fertilizers used in agriculture by farmers are salts.
For example; ammonium chloride, ammonium nitrate,
ammonium phosphate, potassium chloride, and nitrogen, phosphorus and potassium
(NPK) fertilizers.
2. Certain
salts are used as pesticides to kill or destroy insects, pests, weeds and
fungi.
For
example; copper(II) sulphate, iron(II) sulphate and mercury chloride.
3. In
medical field, hydrated calcium sulphate (CaSO4.2H2O) is
found in Plaster of Paris to make plaster casts for supporting broken bones.
4. Patients
suffering form anemia use iron(II) sulphate heptahydrate (FeSO4.7H2O)
is an ingredient in ‘iron pills’ as food supplement.
5. Sodium
hydrogen carbonate is used as a anti-acid to neutralize the excess acid secreted
by the stomach.
6. Barium sulphate is used to make
barium meals for patients who need to take an X-ray of their stomach. The salt
helps to make internal organs like intestines appear on X-ray films.
7. Potassium
permanganate(VII) is used as a disinfectant to kill bacteria.
Q6. You are having a
strong acid (HNO3) and strong base (NaOH) on mixing
Answer
(i) What type of salt you
will have?
Strong acid and strong base
undergo complete neutralization forming normal salt
ii. What type of reaction will it be?
The reaction between acid and
base is called neutralization
iii. Will it be soluble or insoluble salt?
Nitric acid form nitrate
salts with bases which are always water soluble.
iv. If it is soluble, how will it be recovered?
Water soluble salts are
recovered from the solution by crystallization.
Q7. A solution of HCl
has pH of 2.3. Calculate its pOH and [H+]?
Answer
Solution
Calculation of pOH
pH + pOH = 14
pH = 14 – pOH
= 14 – 2.3 = 11.7
Calculation of [H+]
pH = – log [H+]
10x = [H+]
10−pH = [H+]
[H+] = 10−2.3
Q8. Find pH, pOH, [OH−]
and [H+] of 2.46 x 10−9 M KOH solution.
Solution
Ionization Equation
KOH → K+ + OH−
2.46 x 10−9 M 2.46 x 10−9 M 2.46 x 10−9 M
Calculation of [OH−]
Since KOH is strong base, it
is completely ionized. Hence concentration of KOH is equal to concentration of
OH− ions
[OH−] = [KOH] = 2.46 x 10−9 M
Calculation of [H+]
[H+][OH−] = Kw
[H+] x 2.46 x 10−9 = 1 x 10−14
[H+] = 1 x 10−14/2.46 x 10−9
= 4.07 x 10−6
Calculation of pH
pH = – log [H+]
pH = – log [4.07 x 10−6]
= 5.39
Calculation of pOH
pH + pOH = 14
pOH = 14 – pH
= 14 – 5.39 = 8.61
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