Chapter # 09 [Acids, Bases and Salts]

 

UNIT# 09

ACID, BASES AND SALT

By the 15^thcentury, chemists recognized a group of substance which had sour taste so they named it to ACIDS. They also recognized the other group of substance which lead bitter taste and were used as good cleaning agent called BASES.

In the next century, scientists found that whenever Acids react with the Bases, it neutralizes it and form an ionic compound which is simply termed as SALT.

 

Q#	Questions	Year
Q# 01	Define pH.	[2018][2015][2012] [2008]
Q# 02	Define acids, bases and salts. Write one property of each.	[2013]
Q# 03	Write properties of acids.	[2012][2006]
Q# 04	What is salt? Discuss its types.	[2017][2012][2010] [2008]
Q# 05	What are Double salts? Describe.	[2018][2014][2012][2011] [2008] [2007]
Q# 06	Write name of any three double salts with their chemical formulae.	[2018][2014][2011]
Q# 07	Define Neutralization.	[2016][2015][2013][2012] [2011][2008][2007][2006] [2005]
Q# 08	Define Acidity of base.	[2014]
Q# 09	Define titration.	[2008]
Q# 10	Define Basicity of acids.	[2014] [2012]
Q# 11	What is a base? Write two chemical and three chemical properties of base.	[2005]
Q# 12	State Lewis concept of acids and bases.	[2017][2016][2011][2008] [2006] [2005]
Q# 13	State Arrhenius theory of acids and bases.	[2009]
Q# 14	State Bronsted Lowry theory of ionization.	[2015] [2010][2007]
Q# 15	Mention the uses of potash alum.	[2009][2007]
Q# 16	Mention the uses of Carnalite.	[2007]
Q# 17	Mention the uses of Mohr’s salt.	[2007]
Q# 18	Mention the uses of Epsom salt.	[2010]
Q# 19	Mention the uses of NaHCO3.	[2012]
Q# 20	Mention the uses of Chrome alum.	[2007]

 

Q. Give the Physical properties of acids.

PHYSICAL PROPERTIES OF ACIDS

1.      Acids have sour taste.

2.      They change the color of methyl orange and blue litmus paper to red

3.      Aqueous acids conduct electricity.

4.      Concentrated acids can destroy skin and tissues.

5.      They react with bases to forms salts and water.

 

Q. Give the Chemical properties of acids.

CHEMICAL PROPERTIES OF ACIDS

NEUTRALIZATION

Acids react with base to form salt and water.

HCl + NaOH ⟶       NaCl + H₂O

 

REACTION WITH METALS

Whenever acid react with metals, H₂ gas liberates.

Zn + 2HCl      ⟶       ZnCl₂ + H₂

 

REACTION WITH CARBONATE AND BICARBONATES

Acids produce CO₂ gas, when react with carbonates and bicarbonates

Na₂CO₃ + 2HCl         ⟶       2NaCl + H₂O + CO₂

NaHCO₃ +HCl          ⟶       NaCl + H₂O + CO₂

 

Q. Give the Physical properties of bases.

PROPERTIES OF BASES

1.      They have bitter taste

2.      They have slippery touch.

3.      Bases are electrolytes

4.      Concentrated bases can damage tissues and skin.

5.      They covert red litmus paper to blue

6.      Base reacts with acids to produce salt and water.

 

Q. Describe Arhenius theory of acids and bases.

ARHENIUS THEORY OF ACIDS AND BASES

Swedish chemist Svante Arhenius in 1887, describe the acids and bases.

ACID An acid can be defined as a substance that yields H⁺ ions when dissolved in water.

ARHENIUS ACID HCl      →       H⁺ + Cl^-

 

BASE A base can be defined as a substance that yields OH^- ion when dissolved in water.

ARHENIUS BASE NaOH     →   Na⁺ + OH^-

 

Q. Describe Bronsted Lowry theory of acids and bases.

BRONSTED-LOWRY THEORY OF ACIDS AND BASES

This theory was proposed by two scientists’ English chemist Lowry and Danish Chemist Bronsted in 1923.

HCl and hydronium ion (H₃O⁺) are proton donors which act as Bronsted Lowry acids whereas H₂O and NH₃ are proton acceptors which act as proton acceptors.

HCl + H₂O                 H₃O⁺ + Cl^-

 

ACID: Acid is a substance which has tendency to donate one or more protons.

BRONSTED-LOWRY THEORY OF ACID: A substance that can donate H⁺

 

BASE: Base is a substance having a tendency to accept the protons.

BRONSTED-LOWRY THEORY OF BASE A substance that can accept H⁺

 

Q. Describe Lewis theory of acids and bases.

LEWIS CONCEPT OF ACIDS AND BASES

In 1923, G. N Lewis proposed a more general concept of acids and bases.

ACID An acid is any specie which can accept a pair of electrons 

BASE A base is any specie which can donate a pair of electrons

 

LEWIS ACIDS An electron pair acceptor

LEWIS BASE An electron pair donor

 

Q. Define Neutralization, acidity of base and basicity of acids.

NEUTRALIZATION

When acids react with base then salt and water is formed, the process is called Neutralization.

Neutralization is example of both double displacement reaction and exothermic reaction

REACTION
HCl + NaOH →   NaCl + H₂O                                ∆H = -57.3 KJ/ mol

 

ACIDITY OF BASE

The number of ionizable or replaceable (OH^-) ions per molecule is called acidity of the bases.

 

BASICITY OF ACIDS

The number of ionizable or replaceable hydrogen atoms present in a molecule of an acid is called Basicity of the acids.

 

Q. Define salts and its types.

SALT

Salt is a substance that forms by the neutralization of acid and base.

OR

Ionic compound which is produced by the neutralization between acid and base is called Salt.

 

REACTION

NaOH + HCl              →        NaCl + H₂O

KOH + HNO₃                        →        KNO₃ + H₂O

 

CLASSIFICATION OF SALTS

Salts have been classified into following three main categories

1.      Acidic salt

2.      Basic salt

3.      Normal salts

 

ACIDIC SALTS

Salts which are formed by the partial neutralization of an acid by the base are called acidic salt.

FOR EXMAPLE

NaHSO₄, KHCO₃, NaHCO₃ etc.

 

REACTION

NaOH + H₂SO₄         →        NaHSO₄ + H₂O

BASIC SALTS

Salts which are formed by the partial neutralization of base with the acid are called Basic Salt.

FOR EXMAPLE

Mg(OH)Cl, Zn(OH)Cl

 

REACTION

Mg(OH)₂   + HCl           →   Mg(OH)Cl   + H₂O

 

NORMAL SALT

Salts which are formed by the complete neutralization of acids and base are called normal salts.

FOR EXMAPLE

NaCl, NaNO₃, K₂SO₄

 

REACTION

NaOH + HCl              →        NaCl + H₂O

 

Q. What are double salts?

DOUBLE SALT

When two specific salts are crystallized together they form a salt known as Double salt.

FOR EXAMPLE

Potash alum:             K₂SO₄(Al₂SO₄)₃24H₂O

Mohr’s salt:               FeSO₄ (NH₄)₂ SO₄ 6H₂O

Chrome alum:           K₂SO₄Cr₂(SO₄)₃24H₂O

Carnalite:                   KCl. MgCl₂.6H₂O

 

Q. Describe the construction and working of Castner Kellner cell. Also write the production of NaOH.

CASTNER KELLNER CELL [Production of NaOH]

PRINCIPLE

NaOH is prepared by the electrolysis of Brine (aqueous solution of NaCl) in Castner Kellner Cell.

 

CONCENTRATION OF BRINE

25% mass/ mass

CONSTRUCTION OF CASTNER KELLNER CELL

It is a rectangular tank of steel

Inside of tank is lined with ‘ebonite’

Anode is made of titanium

Flowing layer of mercury (Hg) at the bottom of tank serves as cathode

 

PROCEDURE

IONIZATION OF NaCl

2NaCl             ⟶       2Na⁺ + 2Cl^-

When electric current is passed through brine, +ve and –ve ions migrate towards their respective electrodes. Na⁺ ions are discharged at mercury cathode. The sodium deposited at mercury form Sodium Amalgam. The produced Chlorine at the anode is removed from the top of the cell.

 

REACTION AT CATHODE

2Na⁺ + 2e^-      ⟶       2Na

Na forms amalgam

Na + Hg          ⟶       Na/Hg

Na⁺ ions are discharged in preference to H⁺ ions due to high over voltage.

Na⁺ / Na EP= -2.71 V

H⁺/ H EP= 0.00 V

 

REACTION AT ANODE

2Cl^-                 ⟶       Cl₂ + 2e^-

 

FORMATION OF NaOH

Amalgam shifts to another chamber called ‘denuder’, where it is treated with water to produce NaOH.

2Na/Hg + 2H₂O                    2NaOH + H₂+ 2Hg

 

ADVANTAGES OF CASNTER KELLNER CELL

·        Obtained NaOH is highly pure

·        Process is very efficient

·        Possible reaction between NaOH and Cl₂ is avoided because NaOH is obtained in separated chamber

 

DISADVANTAGES OF CASTNER KELLNER CELL

·        High electricity consumption

·        Environmental pollution due to escape of Hg vapors

Q. Write chemical properties of sodium hydroxide.

CHEMICAL PROPERTIES OF SODIUM HYDROXIDE

REACTION WITH ACIDS

For the production of salts, sodium hydroxide can be treated with sulphuric acid, hydrochloric acid, nitric acid.

2NaOH + H₂SO₄       ⟶       Na₂SO₄ + H₂O

NaOH + HCl              ⟶       NaCl + H₂O

NaOH + HNO₃          ⟶       NaNO₃ + H₂O

REACTION WITH METALS

Sodium hydroxide reacts with certain metals like zinc, tin aluminium

2NaOH + Zn              ⟶       Na₂ZnO₂ + H₂

2NaOH + Sn              ⟶       Na₂SnO₂ + H₂

2NaOH + Al + 2H₂O            ⟶       2NaAlO₂ + 3H₂

REACTION WITH CARBON DI OXIDE

It reacts with carbon di oxide to produce sodium carbonate and water.

2NaOH + CO₂                       ⟶       Na₂CO₃ + H₂O

REACTION WITH CHLORINE GAS

The reaction of sodium hydroxide with chlorine gas results in the formation of sodium salt of oxy acids.

2NaOH + Cl₂             ⟶       NaOCl + NaCl + H₂O

Q. Write physical properties of sodium hydroxide.

PHYSICAL PROPERTIES OF SODIUM HYDROXIDE

·        It is highly insoluble in water

·        It produces high amount of heat

·        Its melting point is 318⁰ C

·        Its density is 2.13 gm/ml

Q. Give the industrial preparation of Sodium carbonate.

INDUSTRIAL PREPARATION OF SODIUM CARBONATE

AMMONIA SOLVAY PROCESS OR AMMONIUM SODA PROCESS

Industrially, sodium carbonate is produced by Ammonia Solvay process

RAW MATERIALS

The raw materials which are needed for the production of Sodium carbonate are given below:

·        Sodium chloride (Brine)

·        Lime stone (CaCO₃)

·        CO₂

·        Ammonium chloride (NH₄Cl)

PROCEDURE

At first stage, a saturated solution of sodium chloride is prepared which is also known as Brine.

Brine is the 28% m/m solution of NaCl

Following are the steps of the industry:

AMMONIATION OF BRINE

In this stage, saturated solution of NaCl i.e. brine is allowed to flow down from ammoniating tower. The ammoniated tower is fitted with mushroom shaped baffles which are designed to control the flow of brine and ensure the proper mixing and saturation of ammonia.

CARBONATION OF AMMINIATED TOWER

In this step, ammoniated brine is allowed to trickle down a carbonating tower called ‘Solvay tower’. Here, brine is fixed with carbon di oxide gas.

CaCO₃                        ⟶       CaO + CO₂

CO₂ reacts with ammonia to form ammonium carbonate

2NH₃ + CO₂ + H₂O   ⟶       (NH₄)₂CO₃

Ammonium carbonate further reacts with CO₂ to form ammonium bi carbonate

(NH₄)₂CO₃ + CO₂ + H₂O     ⟶       2NH₄HCO₃

Ammonium bi carbonate then reacts with NaCl to form Sodium bi carbonate.

NH₄HCO₃ + NaCl     ⟶       NaHCO₃ + NH₄Cl

Due to the exothermic nature of the above reactions, solubility of NaHCO3 increases. To oppose this effect, lower part of Solvay tower is cooled first, precipitate of NaHCO₃ are separated by vacuum filtration and then washed to remove ammonium salts.

CONVERSION OF NaHCO₃ TO Na₂CO₃

Sodium bicarbonate is heated in rotary furnace called ‘Calciner’ to produce anhydrous sodium carbonate or soda ash. Carbon di oxide is re-circulated to carbonation tower.

2 NaHCO₃      ⟶       Na₂CO₃ + CO₂ + H₂O

RECOVERY OF AMMONIA

The CaO which obtained from the heating of CaCO₃ is treated with water to form Ca(OH)₂

CaO + H₂O    ⟶       Ca(OH)₂

Quick lime is heated with NH₄Cl to form NH₃ and CaCl₂ (by product).

2 NH₄Cl + Ca(OH)₂ ⟶       CaCl₂ + 2NH₃ + 2H₂O

Ammonia is used again in this process.

 

Q. Give the physical properties of Sodium bi carbonate.

PHYSICAL PROPERTIES OF SODIUM BI CARBONATE

·        It is bitter in taste

·        Sparingly soluble in water

·        It is white crystalline compound

·        Its density is 2.11 gm/ ml

Q. Give the chemical properties of Sodium bi carbonate.

CHEMICAL PROPERTIES OF SODIUM BI CARBONATE

REACTION WITH ACIDS

Sodium bi carbonate loses carbon di oxide and water to give sodium carbonate on heating.

NaHCO₃ + HCl         ⟶       NaCl + H₂O + CO₂

ACTION OF HEAT

Sodium bicarbonate loses carbon dioxide and water to give sodium carbonate on heating.

2NaHCO₃                   ⟶       Na₂CO₃ + H₂O + CO₂

Q. Give the uses of Sodium bi carbonate.

USES OF SODIUM BICARBONATE

·        It is used in the preparation of effervescent drinks.

·        It is used in fire extinguishers.

·        It is used in the textile, tanning, paper, ceramics industries.

·        It is used in medicine as antacid to neutralize the acids.

Q. Give the physical properties of Sodium carbonate.

PHYSICAL PROPERTIES OF SODIUM CARBONATE

·        It is highly soluble in water

·        Sodium carbonate (Na₂CO₃) is an odorless, grayish white hygroscopic powder.

·        The melting point of Sodium carbonate is 1,564°F (851°C)

·        Density of sodium carbonate 2.53 g/cm³

·        It is soluble in water.

·        The water solution of soda ash has a basic pH and a strong alkaline taste. If it is placed in a slightly acidic solution, it decomposes and forms bubbles. This effect, called effervescence

·        It is used as cleaning agent in soap and detergents.

Q. Give the chemical properties of Sodium carbonate.

CHEMICAL PROPERTIES OF SODIUM CARBONATE

PRODUCTION OF SALTS

Sodium carbonate can be decomposed to produce salts

Na₂CO₃ + 2HCl         ⟶       2NaCl + H₂O + CO₂

Q. Write note on Copper Sulphate.

COPPER SULPHATE [CuSO₄.5H₂O]

It is also known as cupric sulphate or blue vitriol or blue stone.

 

PREPARATION

By reacting copper with dilute sulphuric acid in presence of air copper sulphate may produce.

2Cu + 2 H₂SO₄ + O₂      →         2CuSO₄ + 2 H₂O

CuO and CuCO₃ can also produce copper sulphate by reacting with dilute H₂SO₄.

CuO + H₂SO₄            →      CuSO₄ + H₂O

CuCO₃ + H₂SO₄        →       CuSO₄ + H₂O + CO₂

 

USES

1.      It acts as germicide and insecticide.

2.      It uses in paints and vaccines.

3.      It is use to kill fungus and molds.

4.      It is used in textiles, tanning, electric batteries, hair dyes and electroplating.

 

Q. Write note on Magnesium Sulphate.

MAGNESIUM SULPHATE [MgSO₄.7H₂O]

It is also known as Epsom salt.

 

PREPARATION

It can be prepared by the action of H₂SO₄ over magnesite [MgCO₃], dolomite [MgCO₃.CaCO₃] or heating kieserite [MgSO₄] under pressure with water.

MgCO₃ + H₂SO₄                   →        MgSO₄ + H₂O + CO₂

MgCO₃. CaCO₃ + 2 H₂SO₄  →        MgSO₄ + CaSO₄ + 2H₂O + 2CO₂

MgSO₄. H₂O + 6H₂O                        →        MgSO₄.7H₂O

 

USES

1.      It is used as mild purgative (ant acids)

2.      It is used in manufacture of ceramics, glazed tiles and match boxes.

3.      It is used in dyes and tanning processes.

4.      It is used in fire proof fabrics

5.      It is used in filter paper industry

 

Q. Write note on Alum.

ALUM

If equi molar quantities of potassium sulphate and aluminium sulphate are dissolved in water and the solution is allowed to evaporate. Crystals of potash alum are produced.

K₂SO₂ + Al₂(SO₄)₃ + 24H₂O    →        K₂SO₂ Al₂(SO₄)₃ 24H₂O

 

USES OF POTASH ALUM

1.      It is used in sizing of paper.

2.      It is used in medicines.

3.      It is used in purifying water

4.      It is used as mouth wash.

 

Q. Write chemical formula of Carnalite. Also give its uses.

CARNALITE

KMgCl₃·6(H₂O)

 

USES OF CARNALITE

·        It is mostly used in fertilizers.

·        It is an important source of potash

 

Q. Write chemical formula of Chrome alum. Also give its uses.

CHROME ALUM

KCrS₂O₈

 

USES OF CHROME ALUM

·        Chrome alum is used in the tanning of leather

·         It is also used as hardener in gelatine emulsions of photographic film

 

Q. Define Titration and pH

TITRATION

A titration is a technique in which solution of known concentration is used to determine the concentration of an unknown solution.

pH

Danish Chemist Senson proposed that the measurement of the power of ^H+ ions in aqueous solution. pH means power of hydrogen atom (H⁺) ion_.

p^H of a solution can be define as the negative logarithm of the hydrogen ion H⁺ concentration or H₃O⁺ ion concentration in moles per liter.

Mathematically

pH = -log [H⁺]

pOH = -log [OH^-]

and pH + pOH = 14