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–
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)
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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