Olympiad Notes: Acids, Bases and Salts

Introduction

Like we individuals have certain kind of nature, likewise, every chemical substance that we come across has some nature. But in terms of chemicals, we relate nature either with acidic, basic or neutral nature. But to know exactly what is acidic, basic or neutral, we need to know about what exactly we mean by being acidic, basic or neutral. So, accordingly, different concepts were introduced to define them. So, let us study them first. Earlier, it was thought that those substances that are sour, turn blue litmus red and are corrosive are called acids.

Whereas those which are bitter, turn red litmus blue, soapy in touch are called bases. But later this concept was replaced by relevant concepts like lewis concept, bronsted lowry concept  and  Arrhenius concept.

Acids

Arrhenius Concept: According to his way of judging substances, he classified the acids and bases as given below: Acids are those that when dissolved in water, give hydrogen ion or we can write hydronium ion (H₃O⁺) This hydronium ion is formed due to the combination of hydrogen ion produced by acid with water molecule.

Example of acids are:

• hydrochloric acid (HCl)
• sulphuric acid (H₂SO₄)
• nitric acid (HNO₃)
• phosphoric acid (H₃PO₄)
• carbonic acid (H₂CO₃)

Classification of Acids: we have different classification based on different factors so let's sum up and make ourselves familiar with it.

1. Depending upon source  from which they are obtained

• Organic acids: Organic Acids are obtained from plants and animals or we can say they are present in organic matter.
  Example: in tomato,  oxalic acid is present, in apple, malic acid and in lemon, we have citric acid and so many other acids are present in different organic substances.
• Inorganic acids: Inorganic Acids are those that are obtained from minerals present in earth. These are quite reactive in nature.
  Example we have are: nitric acid, sulphuric acid, etc.

2. Classification of acids on the basis of strength

If we talk about strength, it means the amount of hydrogen ions given out when acid is dissolved in water.
On the basis of this we have two categories of acids -

• Strong acids: Strong Acid is the acid that completely dissociates into hydrogen ion. These acidstotally dissociate and leave no dissociated molecule of acid.
  Example: Hydrochloric acid, sulphuric acid, etc.
• Weak acids: Weak Acid is the acid that partially dissociates into hydrogen ions. There actually exists the equilibrium between dissociated ions and undissociated molecules of acids .
  Example: Carbonic acid.

3. Classification of acids on the basis of water content

• Dilute acid: Dilute Acid is the acid that has more amount of water in it and less salt content. They are not quite strong.
• Concentrated acid: Concentrated Acid is that which has less amount of water in it and more amount of salt content.

We can dilute the concentrated acid but need to take certain precautions as follows-
One can dilute concentrated acid by adding concentrated acid slowly in water with continuous stirring. By doing so, the heat released is comparatively less and is constantly absorbed by water. So, it prevents the reaction from becoming violent.

Bases

If we talk about bases, according to Arrhenius, they  are those that when dissolved in water give hydroxide ion (OH^-)

Example: 

• Calcium hydroxide Ca(OH)₂
• Magnesium hydroxide Mg(OH)2

Classification of bases:

1. Classification of bases on the basis of their solubility in water

• The bases that are soluble in water are called alkalis.
• Note: it is interesting to note that all bases are not alkalis but all alkalis are bases.

2. Classification on the basis of strength

• Strong bases: That completely dissociates in water to give hydroxide ions. These bases totally dissociates and leave no dissociated molecule of base.
  Example: Hydroxides of all reactive metals
• Weak bases: That do not completely dissociates in water to give hydroxide ions.
  There actually exists the equilibrium between dissociated ions and undissociated molecules of bases.
  Example: Calcium hydroxide etc.

Physical Properties Of Acids And Bases

Some physical properties of acids are as follows -

• They are sour.
• They turn blue litmus red.
• They are corrosive in nature

Some physical properties of bases are as follows -

• They are bitter.
• They turn red litmus blue.
• They are soapy in nature

Chemical Properties of acids and bases

Chemical properties of acids

1. Action with Indicators: when treated with litmus, they turned blue litmus red.

2. Reaction with Metals: They react with acid to form metal salt and hydrogen gas is released.
Acid + metal → metal salt + hydrogen gas
Example: HCL+Zn→ZnCl₂+H₂

3. Action with metal carbonate and metal bicarbonate

Whenever acids react with metal carbonate or metal bicarbonate, they form respective salts, water and carbon dioxide gas is released.
Example: acid + metal carbonate →metal salt + water + carbon dioxide gas

i.e. HCl +Na₂CO₃→NaCl +H₂O+CO₂

4. Reaction with Bases: Acids react with bases to form salt and water.
i.e. Acid + base →salt and water
HCL + NaOH → NaCl + H₂O
This reaction is regarded as neutralization reaction as salt formed is neither acidic nor basic its neutral.

5. All acids act as electrolytes in aqueous states
In aqueous state when current is passed they dissociate into ions.

Chemical properties of bases

• Action with Indicators: They turn red litmus blue
• Reaction with Metals: They react with base to form oxy salt and hydrogen gas is released.
  Example: Al + NaOH → NaALO₂ + H₂
  
• Action with ammonium salts
  Example: NH₄CL + NaOH → NaCL + NH₄OH
• Reaction with Acids: Acid react with acids to form salt and water
  Acid + base →salt and water
  HCL + NaOH → NaCl + H₂O
  This reaction is regarded as neutralization reaction as salt formed is neither acidic nor basic its neutral
• All bases act as electrolyte in aqueous states i.e. NaOH → Na⁺ +OH^-
• alts are formed when acid and base react with each other.
  i.e. acid + base→salt + water
  HCL + NaOH → NaCl + H₂O
  

The salts are formed as a result of neutralization reaction as both acid and base neutralize each others effect.

The Nature of Salts Can Be-  

1. Acidic Salt: It is formed when strong acid react with weak base. As the acid is strong, therefore, strong character is retained in the salt that is why it comes out to be acidic
Example: HCL + Ca(OH)₂ → CaCL₂ + H₂O

2. Basic Salt: It is Formed When Strong Base Reacts With weak acid
Example: NaOH + CH₃COOH → CH₃COONa + H₂O

3. Neutral Salt: It is Formed When Weak Or Strong Acid And Base React With Each other. They Cancel Each Other's Effect And Can Form Neutral Salt
Example: HCL + NaOH → NaCl  + H₂O

Ph and its biological importance, indicators

• Strength of acid and base is expressed in terms of Ph
• It is the Logarithm of Reciprocal of Hydrogen ion Concentration.
  i.e.: PH = -LOG(H+)
• The ph of any substance can be detected by using ph paper or ph scale.
• Ph scale consists of scale ranging from 0 to 14.
• Ph ranging from 0 to 7 are acids
• Ph ranging from 7 to 14 are bases And 7 is neutral

 For Measuring, We Have Ph Scale Given By:
Observations Made On The Bases Of Ph Values

Ph Range Indicate the strength of acids and bases as given below:

• 0-2: Strong Acid
• 2-4: Moderately Acidic
• More Than 4: Weak Acid
• At 7: Neutral
• 7-10: Weak Base
• 10-12: Moderately Basic
• More Than 12: Strongly Base

Effect of ph on dilution:

• In Case Of Acids On Dilution: Ph Increases as acidic strength decreases
• In Case Of Bases On Dilution: Ph Decreases as basic strength decreases

Importance of Ph

• Biological Importance: Our Body Works Within 7-7.8 Ph. The Ph Of Acid Rain Is Below 5.6 And This Water Affects Aquatic Life.
• Agriculture: Plants Also Specific Range Of Ph For Survival In Order To Grow Crops
• In Dairies: Ph Value Of Milk Is Adjusted About 6.6. If Ph Falls Below 6.6 It Turns Sour.
• In Tooth Decay: Tooth Decay Starts When Ph Of Mouth Falls Below 5.5. At That Ph Acid Reacts With Calcium Phosphate Of Tooth Enamel And Cause Its Corrosion. When We Eat Some Sugary Substance The Acids Production Is Stimulated That Corrode Enamel.
• Indicators: Are the substances that bring about change in themselves when some acid or base is added to Natural and artificial indicators
• Natural indicators: Litmus (it is extracted from lichens) original color of litmus is purple but in lab it is used as red and blue litmus.
  
• Effect of Acid: Turns blue litmus red
• Effect on Base: Turns red litmus blue
• Artificial Indicators: Phenolphthalein, methyl orange

Effect on phenolphthalein-

Original color is colorless
Acid: Remain colorless
Base: Turns pink

Effect on methyl orange: original color (orange)
Acid: from orange to red
Base:  from orange to yellow
We have olfactory indicators as well that bring about change in smell when any substance is added to it.
Like Onion Extract And Vanilla Extract

• Effect Of Acid On Vanilla Extract: same smell
• Effect Of Base On Vanilla Extract: smell changes
• Effect Of Acid On Onion Extract: same smell
• Effect Of Base On Onion Extract: smell changes

Washing Soda

Formula: Na₂CO₃.10c
Chemical name: Sodium carbonate decahydrate
Preparation: by solvays process
Reaction involved:

Na₂CO₃ + 10H₂O   → Na₂CO₃.10H₂O

The solvay process is an efficient process because the bi products can be reused in this process:

CaCO₃ → CaO+CO₂
CaO + H₂O → Ca(OH)₂
Ca(OH)₂ + NH₄CL → CaCL₂ + NH₃ + H₂o
This ammonia and water can be reused in solvay's process.

Physical properties

• It is crystalline solid
• Action of heat: Na₂CO₃.10H₂O  → Na₂CO₃ + 10H₂O
• Action  of air: Na₂CO₃.10H₂O  → Na₂CO₃ H₂O.+9H₂O
• Efflorescence: "the loss of 9 molecules of crystallization when washing soda is exposed to air ".

Uses of washing soda:

• Used for softening of hard water
• Used in detergents as it has cleansing properties
• Used in glass industry, etc

Baking Soda

Formula: NaHCO₃
Chemical name: Sodium Bicarbonate
Preparation: by Solvay's process
Reaction involved :

NH₃ + H₂O +NaCl + CO₂ → NaHCO₃ + NH₄Cl

Physical properties of Baking Soda:

1. It is white crystalline solid

2. Action of heat: NaHCO₃-HEAT→Na₂CO₃ + H₂O + CO₂

Uses of Baking Soda

• It is used as antacid
• It is used in baking cakes, etc - in cakes baking powder is added that contains baking soda and tartaric acid. in the batter of cake, baking powder is added and mixed well, then this cake is heated. On heating, the following reaction occurs
  NaHCO₃-HEAT →Na₂CO₃ + H₂O + CO₂
  The carbon dioxide so produced, being volatile, escapes and makes the cake fluffy but the cake becomes bitter due to sodium carbonate. So, to restore bitterness, the tartaric acid reacts with sodium carbonate to form sodium tartrate that neutralizes its effect and original taste of cake is retained .

3. It is used in soda acid fire extinguishers
It consist of two cylinders -

• Outer: made of metal
• Inner: made of glass

baking soda + sulphuric acid → sodium sulphate +water + carbon dioxide

The outer cylinder has baking soda and inner one has concentrated Sulphuric acid. Both the cylinders are bounded by common knob. When knob is pressed, the glass cylinder breaks, both of them react and as a result, carbon dioxide is released that forms the protective blanket and extinguishes fire.

Plaster of Paris

Formula: CaSO₄/2H₂O
Chemical name: Calcium Sulphate Hemihydrate
Preparation: from Gypsum
CaSO₄.2H₂O -Heat 100⁰C→ CaSO₄.1/2H2O + 11/2H₂O

Precaution to be taken while preparing it:

• The temperature is to be controlled because if temperature exceeds 100 degree celsius, all water will get evaporated and it will form dead burnt plaster (calcium sulphate)
  CaSO₄.2H₂O-Temp. above 100→CaSO₄ + 2H₂O

Physical Properties of POP

• white crystalline solid
• Reaction with water:  When used it has to mixed with water and following reaction occurs-POP + H₂O → Gypsum

Uses of POP

• It is used to decorate ceilings, etc
• It is used to make statues, etc
• It is used for joining fractured bones

Bleaching Powder

Formula: CaoCL₂
Chemical name: Calcium Oxychloride
Preparation: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Physical properties of Bleaching Powder

• White crystalline solid
• Action of air: CaoCL2+CO2--CaCO3+CL2

Uses of Bleaching Powder:

• It makes wool unshrinkable
• It is used for cleaning water tanks, toilets, etc.