Acids Bases and Salts class 10 notes Chapter 2

Compound are classified into three group on the basis of their chemical properties
i)Acids
ii)Bases
iii) Salts

Indicators:
An indicators are used for testing a substance wheather it is acid or base by change in its colour .There are three most common indicators are use to testing for acid and bases are following
i) Litmus
ii)Methyle orange
iii)Phenolphthealein

Litmus paper:
Litmus can used in form of paper. there are two type of Litmus paper
i) Red Litmus paper
ii) blue Litmus paper
When a blue Litmus turn into red the it is acidic in nature and when red Litmus turn into blue then it is basic in nature

Methyle orange:
Methyle orange indicator give red color in acid solution and yellow colour in basic solution
Phenolphthealein:
Phenolphthealein indicator is colourless in acid solution and pink colour in basic solution

Olfactory Indicators:
The substance whose smell change in acidic or basic solution are known as olfactory indicator . The following olfactory indicator are:
i)Onion When basic solution is added to cloth strip treated with onion the onion smell cannot detectd but in case of acidic solution smell can be detected because it cannot destroy the smell of onion
ii) Vanilla vanilla has a pleasant smell. if basic solution is added to vanilla extract the we cannot detected smell but in case of acidic solution smell can be detected because it cannot destroy the smell of vanilla extrac

Acids

• The chemical substance which are sour in test are called acids
  
• Acids are the substance which when we dissolve in water produce H⁺ (aq) or hydronium ions (H₃ O⁺ )as the only positive charged ions e.g HCl
• Acid Solution cunduct electricity
• Acids turn blue litmus to red

Organin acids :The acids which are obtained from animal and plant materials are known as organic acids for example: Citric acids , Acetic acids, latic acids etc
Inorganin acids :are the acids which are usually obtained from minerals for example Hydrochloric acid ,Sulphuric acid and nitric acids

Strong and Weak Acids:
i)All the Inorganic(mineral) acid like Hydrochloric acid , sulphuric acid etc are strong acid except carbonic acids This is because it completely ionised in water and produce large amount of hydrogen ions
ii) All organic acid like citric acid , acetic acids etc are weak acid This is because it is partially ionised in water and produce small amount of hydrogen ions

Concentrated Acids : Concentrated Acids contain minimum amount of water

Dilute Acids : Dilute Acids contain more amount of water

Acids react with metal :

Metal + Acid → Salt + Hydrogen gas
Zn(s) + H₂SO₄(aq) → ZnSO₄(aq)+ H₂(g)
Most of the acids react with metals to form salts and evolve hydrogen gas .

Note : Curd and other sour foodstuffs contain acid which can react with the metal of the container to form poisonous metal compounds which can cause food poisonoing and damage our health

Acids react with metal carbonates and metal hydrogencarbonates :
When acids react with metal carbonates and metal hydrogencarbonates to form salt ,carbon dioxide and water

Metal carbonate + Acid → Salt + Carbon dioxide + Water
Na₂CO(s) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(s)
Metal Hydrogencarbonates +Acids → Salts + carbon dioxide + Water
NaHCO₃+ HCl(aq)→ NaCl(aq) H₂O(l) + CO₂(s)
i) On passing the carbon dioxide gas evolved through lime water

ii)On passing excess carbon dioxide the following reaction takes place

Limestone, chalk and marble are different forms of calcium carbonate. All metal carbonates and hydrogencarbonates react with acids to give a corresponding salt, carbon dioxide and water.

Acids react with bases: When acids react with base to form Salt and water
Acids + Base → Salt + Water
NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)

Neutralisation reaction :
The reaction between an acid and a base to give a salt and water is known as a neutralisation reaction. In general, a neutralisation reaction

Reaction of Metallic Oxides with Acids :
Acids react with metal oxide to form salt and water
Metal oxide + Acid → Salt + Water
CuO(s) + 2 HCl(aq) → CuCl₂(aq) + H₂O(l)
When metal react with metal hydroxide to form salt and Water

WHAT DO ALL ACIDS HAVE IN COMMON? :
All acids contain hydrogen .An acids is substance which dissociates on dissolving in water to produce hydrogen ions (H⁺) for example
HCl → H⁺ + Cl^-

The separation of H+ ion from HCl molecules cannot occur in the absence of water.
HCl + H₂O → H₃O⁺ + Cl

Note :Hydrogen ions cannot exist alone, but they exist after combining with water molecules. Thus hydrogen ions must always be shown as H+(aq) or hydronium ion (H3O+).
H⁺ + H₂O → H₃O⁺

Note : Such compound like glucose and alcohol also contain hydrogen but do not show acidic charecter this is because their hydrogen does not separate out as hydrogen ions on dissolving in water

Q : Why acids do not show acidic behaviour in the absence of water
Ans: acids do not show acidic behaviour in the absence of water because acid do not form hydrogen ions

Base

• It is bitter in taste
• Turn red litmus to blue
• Base conduct electricity in solution

Alkali
A base which is soluble in water produce Hydroxyl ion as the only negetive charged ions are known as Alkali. for example Sodium Hydroxide, Potassium Hydroxide

WHAT DO ALL BASE HAVE IN COMMON? :
When base dissolve in water to produce hydroxide ions (OH^- ) in solution

Strong and Weak Base:
i)When base completely ionised in water and produce large amount of hydroxide ions (OH^- ) is known as strong base
ii) When Base partially ionised in water and produce small amount of hydroxide ions (OH^- ) is known as weak base

Base react with metal
When base react with metal to form metal salt and hydrogen

Base react with acid
When base react with acid to form salt and water

Base react with non-metal oxide
When base react with non-metal oxide to form salt and water
Non-metal + Base → Salt + Water

Universal indicator
A universal indicator is a mixture of many different indicator which has a pH range from 0 to 14 that indicates the acidity or alkalinity of a solution. A neutral solution has pH=7
pH
pH value of solution is given as pH= -log[H⁺] where [H⁺] = molar concentration of [H⁺] ion in solution
pure water, [H⁺]=[OH⁻]=10−7 mol/L. Hence, the pH of pure water is 7.
The pH scale ranges from 0 to 14.
If pH rane 0- 6 : acidic solution
If pH=7 Neutral Solution
If pH rang 8- 14 : basic solution

pH in Everyday Life

plants and animals pH sensitive
Our body works within the pH range of 7.0 to 7.8. Living organisms can survive only in a narrow range of pH change. When pH of rain water is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.

pH in our digestive system
our stomach produces hydrochloric acid. It helps in the digestion of food without harming the stomach. During indigestion the stomach produces too much acid and this causes pain and irritation. To get rid of this pain, people use bases called antacids.

pH of a soil
The pH of a soil optimal for the growth of plants or crops is 6.5 to 7.0.

pH change as the cause of tooth decay
Tooth decay starts when the pH of the mouth is lower than 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.

Self defence by animals and plants through chemical warfare
Bee-sting leaves an acid which causes pain and irritation. Use of a mild base like baking soda on the stung area gives relief. Stinging hair of nettle leaves inject methanoic acid causing burning pain.

SALTS
When acid react with base form a salts

Family of Salts
Salts having the same positive or negative radicals are said to belong to a family. example Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate and ammonium chloride are families of salts.

pH of Salts
i)Salts of a strong acid and a strong base are neutral with pH value of 7.
ii) salts of a strong acid and weak base are acidic with pH value less than 7
iii) strong base and weak acid are basic in nature, with pH value more than 7.

Common salt
The chemical name of common salt is Sodium chloride and it is obtained from sea water by the process of evaporation

Sodium hydroxide
When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. The process is called the chlor-alkali process because of the products formed– chlor for chlorine and alkali for sodium hydroxide.
2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)
Chlorine gas is produce at the anode, and hydrogen gas at the cathode. Sodium hydroxide solution is formed near the cathode.

Bleaching powder
Prepartion
Bleaching powder is produced by the action of chlorine on dry slaked lime [Ca(OH)₂]


.Properties
i)Bleaching powder is white powder which give a smell of chlorine
ii)it is soluble in cold water
Bleaching powder is used –
(i) for bleaching cotton and linen in the textile industry, for bleaching wood pulp in paper factories and for bleaching washed clothes in laundry;
(ii) as an oxidising agent in many chemical industries; and
(iii) for disinfecting drinking water to make it free of germs.

.Baking soda
.
.Prepartion
The chemical name of the compound is sodium hydrogencarbonate (NaHCO₃). It is produced using sodium chloride with ammonia and carbon dioxide

Properties
i) Baking soda consist of white crystal which are sparingly soluble in water
ii) After Heat

Uses of sodium hydrogencarbonate (NaHCO3) or baking soda
(i) For making baking powder, which is a mixture of baking soda (sodium hydrogencarbonate) and a mild edible acid such as tartaric acid. When baking powder is heated or mixed in water, the following reaction takes place –
NaHCO₃ + H⁺ → CO₂ + H₂O + Sodium salt of acid
Carbon dioxide produced during the reaction causes bread or cake to rise making them soft and spongy.
(ii) Sodium hydrogencarbonate is also an ingredient in antacids. Being alkaline, it neutralises excess acid in the stomach and provides relief.
(iii) It is also used in soda-acid fire extinguishers.

Washing soda
Prepartion
i) CO₂ is passed through a concentrated solution of sodium chloride and ammonia:
NaCl + NH₃ + H₂O + CO₂ → NaHCO₃ + NH₄Cl
ii) On Heating of sodium hydrogencarbonate

iii) recrystallisation of sodium carbonate gives washing soda

Properties
i) Washing soda is a transparent crystalline solid
ii) it is soluble in water
Uses of washing soda
(i) Sodium carbonate (washing soda) is used in glass, soap and paper industries.
(ii) It is used in the manufacture of sodium compounds such as borax.
(iii) Sodium carbonate can be used as a cleaning agent for domestic purposes.
(iv) It is used for removing permanent hardness of water

Crystals of salts
The water molecules which form part of the structure of a crystal are called water crystallisation

Plaster of Paris
Prepartion
On heating gypsum at 373 K, it loses water molecules and becomes calcium sulphate hemihydrate ( 1CaSO₄.2H₂O). This is called Plaster of Acids, Bases and Salts 33 Paris,

Properties
i)it is white in colour
Uses of Plaster of Paris
i)doctors use as plaster for supporting fractured bones in the right position
ii) Plaster of Paris is used for making toys, materials for decoration and for making surfaces smooth