Acids, Bases and salts BY TRI SIR.pptx

Acids, Bases and salts
CHAPTER- 2 SCINCE (CBSE CLASS 10)
By:
Tripurari Prajapati
M.sc. Biotechnology

 Elements are combined to form compounds.
 On the basis of their chemical properties, all the compounds
will be classified into three types :
1) Acids : Sour in taste
2) Bases : Bitter in taste
3) Salts

Indicators for testing acids and bases :
 An indicator is a dye that changes color when it is put into an
acid or a base. It tells us whether the substance we are
testing is an acid or base.

TYPES OF INDICATORS
Natural Indicators Synthetic Indicators
Eg: a) Litmus Eg: a) Methyl orange
b) Turmeric b) Phenolphthalein

Litmus :
 Litmus is a most common indicator used for testing acids and
bases in the laboratory.
 Litmus can be used in the form of litmus paper or litmus
solution.
 It is of two types : Blue litmus and Red litmus.

 An acid turns blue litmus to red.
 A base (or alkali) turns red litmus to blue.
 A neutral No color change

 If a drop of the given solution turns
blue litmus to red, then the given
solution will be acidic in nature.
Ex. Orange juice turns blue litmus
to red, so orange juice is acidic in nature.
 If drop of the given solution turns
red litmus to blue. Then given
solution will be basic in nature.
Ex. NaOH solution.

Methyl orange :
 Methyl orange is synthetic indicator.
 The neutral colour of methyl orange
is ‘orange’.
(i) Methyl orange gives red colour in acidic solution.
(ii) Methyl orange gives yellow colour in basic solution.

Phenolphthalein :
 The neutral colour of phenolphthalein is
colourless.
 The colour changes which take place in
phenolphthalein indicator as below :
(i) Phenolphthalein indicator is
colourless in acid solution.
(ii) Phenolphthalein indicator gives pink
colour in basic solution.

Some natural indicators :
1. Litmus
 Litmus is a natural indicator. Litmus solution is a purple dye
which is extracted from a type of plant called ‘lichen’
 Lichen is a plant belonging to the division
Thallophyta.
 When litmus solution is neither acidic
nor basic (it is neutral), then its colour
is purple.

2. Turmeric:
 Turmeric is also a natural indicator. Turmeric contains yellow
dye.
 It turns red in basic solutions.

3. The red cabbage:
 The red cabbage extract (obtained from red cabbage leaves)
is also a natural indicator.
 It is red in colour. The red cabbage
extract remains red in acidic solution
but turns green on adding to basic
solutions.

4. Coloured petals of some flowers:
 The coloured petals of some flowers
(such as Hydrangea, Petunia and
Geranium) which change colour in the
presence of acids or bases also act as
indicators.
 For example, the flower of Hydrangea
plant are usually blue which turn pink
in the presence of base.

Olfactory indicators :
 The term ‘olfactory’ means ‘relating to the sense of smell’.
 Those substances whose smell (or odour) changes in acidic
or basic solutions are called olfactory indicators.
 An olfactory indicator usually works on the principle that
when an acid or base is added to it, then its ‘characteristic
smell’ cannot be detected.

1. Onion
• Onion has a characteristic smell.
 When a basic solution like NaOH is added to
a cloth strip treated with onions, then the
onion smell cannot be detected.
 An acidic solution like HCl does not destroy
the smell of onions.
 This can be used as a test for acids and
bases.

2. Vanilla
 Vanilla extract has a characteristic pleasant smell.
 If a basic solution like NaOH is added to vanilla
extract, then we cannot detect the characteristic
smell of vanilla extract.
 An acidic solution like HCl does not destroy the smell
of vanilla extract.
 This can be used as a test for acids and bases.

Sample problem :
You have been provided with three test tubes. One of them contains distilled
water and the other two contain an acidic solution, respectively. If you are given
only red litmus paper, how will you identify the contents of each test-tube?

Acids
 Acids are those chemical substances
which have a sour taste.
 Acids change the colour of blue litmus
to red.
 Some common fruits such as raw
mango, raw grapes, lemon, orange and
tamarind (imli) etc. are sour in teste
due to presence of acid.

Organic Acids :
 The acids present in plant material and animals are called
organic acids.
 Organic acids are naturally occurring acids.
 Organic acids are weak acids.
 It does not harmful to eat or drink substances containing
naturally occurring acids in them.

Sources of organic acids :
Acid Sources
Acetic acid Vinegar (sirka)
Citric acid Lemon, orange
Lactic acid Curd
Tartaric acid Tamarind, unripe grapes
Oxalic acid Tomato
Formic acid (methanoic acid) Ant sting, nettle leaf sting

Mineral acids:
 Mineral acids are man made acids.
 The three most common mineral acids are :
 Hydrochloric acid
 Sulphuric acid
 Nitric acid
 Concentrated mineral acids are very dangerous. They can burn our hands
and clothes.
 Dilute acids are less harmful to us.

Concentrated and Dilute acids :
 A concentrated acid is one which contains the minimum
possible amount of water.
 Dilute acid is one which contains much more of water in it.
 The concentration of an acid is decreased by adding more
water to it.

Diluting Acids :
 The dilution of a concentrated acid should always be done
by adding concentrated acid to water gradually with stirring
and not by adding water to concentrated acid.
 This is because, when concentrated acid is added to water
for preparing a dilute acid, then the heat is evolved gradually
and easily absorbed by the large amount of water.

 If, water is added to concentrated acid to dilute it, then a
large amount of heat is evolved at once. This heat changes
some of the water to steam explosively which can splash the
acid on our face or clothes and cause acid burns.

Properties of acids :
 Acids have a sour taste.
 Acid turns blue litmus to red.
 Acid solutions conduct electricity.
When an acid dissolved in water, we get the acid solution.
The solution of all the acids conduct electricity.

Reaction with metal
• when an acid reacts with a metal, then salt and hydrogen
gas are formed.
𝑴𝒆𝒕𝒂𝒍 + 𝑨𝒄𝒊𝒅 → 𝑺𝒂𝒍𝒕 + 𝑯𝒚𝒅𝒓𝒐𝒈𝒆𝒏 𝒈𝒂𝒔
For example,
1. when dilute sulphuric acid reacts with zinc metal then
zinc sulphate and hydrogen gas are formed.
𝒁𝒏(𝒔) + 𝑯𝟐𝑺𝑶𝟒 (𝒂𝒒) → 𝒁𝒏𝑺𝑶𝟒 (𝒂𝒒) + 𝑯𝟐 (𝒈)

The reaction is carried out as follows :
• Take a few pieces of zinc granules in boiling tube and add
5ml of dil. Sulphuric acid to it.
• We will observe the formation of bubbles on the surface of
zinc granules.
• Pass the gas being formed through the soap solution taken
in a trough. Gas filled bubbles are formed in the soap
solution which rise into the air.

 Bring a burning candle near a gas filled soap bubbles. The
gas present in soap bubble burns with the pop sound.
Only hydrogen gas burns making a pop sound. This shows
that hydrogen gas is evolved during reaction.

 Example 2 :
Dilute hydrochloric acid reacts with zinc to form zinc chloride
and hydrogen gas.
𝒁𝒏(𝒔) + 𝑯𝑪𝒍(𝒂𝒒) → 𝒁𝒏𝑪𝒍𝟐(𝒂𝒒) + 𝑯𝟐(𝒈)
 Note : Curd and other sour foodstuffs such as vinegar, lemon
juice and orange juice, etc., should not be kept in metal
vessels (like copper vessels or brass vessels)
This is because foodstuffs contains acids which can react
with metal and forms poisonous metal compounds.

Reaction with metal carbonate
• When an acid reacts with a metal carbonate (or metal hydrogen
carbonate), then a salt, carbon dioxide and water are formed.
𝑴𝒆𝒕𝒂𝒍 𝑪𝒂𝒓𝒃𝒐𝒏𝒂𝒕𝒆 + 𝑨𝒄𝒊𝒅 → 𝑺𝒂𝒍𝒕 + 𝑪𝒂𝒓𝒃𝒐𝒏 𝒅𝒊𝒐𝒙𝒊𝒅𝒆 + 𝑾𝒂𝒕𝒆𝒓
𝑴𝒆𝒕𝒂𝒍 𝒉𝒚𝒅𝒓𝒐𝒈𝒆𝒏𝒄𝒂𝒓𝒃𝒐𝒏𝒂𝒕𝒆 + 𝑨𝒄𝒊𝒅 → 𝑺𝒂𝒍𝒕 + 𝑪𝒂𝒓𝒃𝒐𝒏 𝒅𝒊𝒐𝒙𝒊𝒅𝒆 + 𝒘𝒂𝒕𝒆𝒓

Example 1 :
• When dilute hydrochloric acid reacts with sodium carbonate,
then sodium chloride, carbon dioxide and water are formed.
𝑵𝒂𝟐𝑪𝑶𝟑(𝒔) + 𝟐𝑯𝑪𝒍(𝒂𝒒) → 𝟐𝑵𝒂𝑪𝒍(𝒂𝒒) + 𝑪𝑶𝟐 𝒈 + 𝑯𝟐𝑶(𝒍)

This reaction can be performed as follows :
1. Take a boiling tube and put about
0.5g of sodium carbonate in it.
2. Add about 2mL of dilute
hydrochloric acid in the boiling
tube
3. We will observe that brisk
effervescence of a gas is produced.
4. Pass the gas through lime water.
The lime water turns milky.

Carbon dioxide gas reacts with lime water as follows
:
a) When carbon dioxide gas is passed through lime water,
the lime water turns milky due to formation of a white
PPT of calcium carbonate.
𝑪𝒂(𝑶𝑯)𝟐 (𝒔) + 𝑪𝑶𝟐(𝒈) → 𝑪𝒂𝑪𝑶𝟑(𝒔) + 𝑯𝟐𝑶(𝒍)
b) If excess of carbon dioxide gas is passed through lime
water, then white PPT formed first dissolves due to
formation of soluble salt calcium hydrogen carbonate.
𝑪𝒂𝑪𝑶𝟑(𝒔) + 𝑪𝑶𝟐(𝒈) + 𝑯𝟐𝑶(𝒍) → 𝑪𝒂(𝑯𝑪𝑶𝟑)𝟐(𝒂𝒒)

Example 2 :
 When dilute hydrochloric acid reacts with sodium hydrogen
carbonate, then sodium chloride, carbon dioxide and water are
formed.
𝑵𝒂𝑯𝑪𝑶𝟑(𝒔) + 𝑯𝑪𝒍(𝒂𝒒) → 𝑵𝒂𝑪𝒍(𝒂𝒒) + 𝑪𝑶𝟐(𝒈) + 𝑯𝟐𝑶(𝒍)
 Note : If someone is suffering from the problem of acidity after
overcoming, we can suggest taking baking soda solution as
remedy. Because baking soda is sodium hydrogen carbonate
which reacts with excess HCl in the stomach and neutralizes it.

Reaction with Base
 When an acid reacts with a base, then a salts and water are
formed.
𝑨𝒄𝒊𝒅 + 𝑩𝒂𝒔𝒆 → 𝑺𝒂𝒍𝒕 + 𝑾𝒂𝒕𝒆𝒓
 When an acid is treated with a base, the base neutralizes the
acid and destroys its acidity.
 So the reaction between an acid and base to form salt and
water is called ‘neutralization reaction’.

Example 1 :
 When hydrochloric acid reacts with sodium hydroxide
solution, then a neutralization reaction takes place to form
sodium chloride and water.
𝑵𝒂𝑶𝑯 𝒂𝒒 + 𝑯𝑪𝒍(𝒂𝒒) → 𝑵𝒂𝑪𝒍(𝒂𝒒) + 𝑯𝟐𝑶(𝒍)
 Take about 5mL of dilute sodium hydroxide solution in a test
tube (or a conical flask). Add 2 or 3 drops of phenolphthalein
indicator. The solution will turn pink.

 Add dilute HCl to above NaOH solution
dropwise and shake the test tube after each
addition.
 After adding a certain volume of HCl, we will
find that the pink colour of solution in the test
tube just disappears. The solution becomes
colourless.
 At this stage all the NaOH base taken in the
test tube completely neutralized.

Reaction with metal oxides
 Acids react with metal oxides to form salt and water :
𝐀𝐜𝐢𝐝 + 𝑴𝒆𝒕𝒂𝒍 𝑶𝒙𝒊𝒅𝒆 → 𝑺𝒂𝒍𝒕 + 𝑾𝒂𝒕𝒆𝒓
 Copper (II) oxide is a metal oxide. Dilute hydrochloric acid
reacts with copper (ll) oxide to form copper (ll) chloride and
water.
𝑪𝒖𝑶(𝒔) + 𝟐𝑯𝑪𝒍(𝒂𝒒) → 𝑪𝒖𝑪𝒍𝟐(𝒂𝒒) + 𝑯𝟐𝑶(𝒍)

 Take a small amount of copper(ii) oxide in a beaker. It is
black in colour.
 Take a small amount of copper(ii) oxide in a beaker. It is
black in colour.
 Add dilute HCl slowly while stirring with a glass rod.
 We will find that copper(ll) oxide has dissolved in dilute HCl
to form blue green solution.

Acids have corrosive nature
 The mineral acids cause severe burns on the skin and attack and eat up
materials cloth, wood, metal structures and stonework, so they are said
to be corrosive.
 Acids are never stored in metal containers because they gradually
corrode and eat up the metal container.
 The strong bases such as NaOH are also very corrosive, and attack and
destroy our skin.

WHAT DO ALLACIDS HAVE IN COMMON :
 All the acids contain hydrogen.
 An acid is a substance which dissociates (or ionizes) on
dissolving in water to produce hydrogen ions.
 For example, an aqueous solution of HCl dissociates to form
hydrogen and chloride ions.
𝑯𝑪𝒍(𝒂𝒒) → 𝐻 𝐚𝐪
+
+ 𝑪𝒍 𝐚𝐪
−

 Sulphuric acid shows acidic behaviour because it ionizes in
aqueous solution to give Hydrogen ions and sulphate ions.
𝑯𝟐𝑺𝑶𝟒(𝒂𝒒) → 𝟐𝐻 𝐚𝐪
+
+ 𝑺𝑶𝟒 𝐚𝐪
𝟐−
 Ionization of Nitric acid :
𝑯𝑵𝑶𝟑 → 𝐻 𝐚𝐪
+
+ 𝑵𝑶𝟑 𝐚𝐪
−

 Ionization of phosphoric acid :
𝑯𝟑𝑷𝑶𝟒(𝒂𝒒) → 𝟑𝐻 𝐚𝐪
+
+ 𝑷𝑶𝟒 𝐚𝐪
𝟑−
 Ionization Acetic acid :
𝑪𝑯𝟑𝑪𝑶𝑶𝑯(𝒂𝒒) → 𝑪𝑯𝟑𝑪𝑶𝑶 𝐚𝐪
−
+ 𝐻 𝐚𝐪
+

 The compounds such as glucose (𝑪𝟔𝑯𝟏𝟐𝑶𝟔) and alcohol
(𝑪𝟐𝑯𝟓𝑶𝑯) also contain hydrogen but they do not show
acidic character.
 The aqueous solutions and glucose and alcohol do not show
acidic character because their hydrogen does not separate
out as hydrogen ions.

TO SHOW THAT ALL THE COMPOUND CONTAINING
HYDROGEN ARE NOT ACID:
 Take solutions of hydrochloric acid, sulphuric acid, glucose
and alcohol. All these are hydrogen containing compounds.
 Fix two iron nails on a rubber cork and place the cork in a
beaker.
 Connect the nails to the two terminals of a 6 volts battery
through a switch and a bulb.

 Pour some dilute HCl or 𝑯𝟐𝑺𝑶𝟒 solution in the beaker and
switch on the current. The bulb starts glowing.
 This shows that solution taken in beaker conducts
electricity.
 Now take glucose or alcohol solution in the beaker and
switch on the current. The bulb does not glow in this case.

 Distilled water does not conduct electricity because it does
not contain any ionic compound dissolved in it.
 On the other hand rain water conducts electricity. Rain
water while falling to the earth through the atmosphere,
dissolves acidic gas carbon dioxide from air and forms
carbonic acid (𝑯𝟐𝑪𝑶𝟑).
 Carbonic acid provides hydrogen ions and carbonate ions.

 Acids contain 𝑯+
as cation and anion such as
𝑪𝒍− in HCl,
𝑵𝑶𝟑
−
in 𝑯𝑵𝑶𝟑,
𝑺𝑶𝟒
𝟐−
in 𝑯𝟐𝑺𝑶𝟒
𝑪𝑯𝟑𝑪𝑶𝑶− in 𝑪𝑯𝟑𝑪𝑶𝑶𝑯
 Since the cation present in acids is 𝑯+, this suggests that
acids produce hydrogen ion in a solution, which responsible
for their acidic properties.

STRONG ACIDS :
 An acid which is completely ionized in
water and thus produces a large amount
of hydrogen ions is called strong acids .
Ex. 𝑯𝑪𝒍, 𝑯𝑵𝑶𝟑, 𝑯𝟐𝑺𝑶𝟒 etc.
 The strong acids react very rapidly with
other substances such as metals.
 Strong acids have a high electric
conductivity.

WEAK ACIDS :
 An acid which is partially ionized in water
and thus produces a small amount of
hydrogen ions is called weak acids.
Ex. 𝑪𝑯𝟑𝑪𝑶𝑶𝑯, 𝑯𝟐𝑪𝑶𝟑, 𝑯𝟐𝑺𝑶𝟑.
 Weak acids reacts quite slowly with
other substances.
 Weak acids have weak electrical
conductivity.

Uses of Mineral Acids in Industry :
1. Sulphuric acid is used in the manufacture of fertilisers,
paints, dyes, chemicals, plastics, synthetic fibers,
detergents, explosives and car batteries.
2. Nitric acid is used for making fertilisers, explosives, dye
and plastics.
3. HCl is used for removing oxide film from steel objects. It
is also used in dye-stuff, textile and food and leather
industries.

BASES :
 The solutions of substances like caustic soda, lime(choona)
and washing soda are bitter in taste, and soapy to touch
(slippery to touch). They called bases.
 Thus bases are those chemical substances which have a
bitter in taste.
 All the bases change the colour of red litmus to blue.

 Bases are the chemical opposite of acid. When bases are added to acids,
they neutralize the effect of acids.
 All the metal oxides and metal hydroxides are bases.
Ex:- Sodium oxide (𝑵𝒂𝟐𝑶),
Sodium hydroxide (𝑵𝒂𝑶𝑯),
Calcium oxide (𝑪𝒂𝑶),
Calcium hydroxide [𝑪𝒂(𝑶𝑯)𝟐]
Ammonium hydroxide (𝑵𝑯𝟒𝑶𝑯),
 Metal carbonates hydrogen carbonates are also considered to be bases
because they neutralize the acids.
EX. 𝑵𝒂𝟐𝑪𝑶𝟑 , 𝑪𝒂𝑪𝑶𝟑 , 𝒂𝒏𝒅 (𝑵𝒂𝑯𝑪𝑶𝟑)

WATER SOLUBLE BASES : ALKALIS
 Those bases which dissolves in water without any chemical
reaction are called alkalis, i.e a base which is soluble in water is
called an alkali.
 Some common water soluble bases are :
𝑵𝒂𝑶𝑯, 𝑲𝑶𝑯, 𝑪𝒂(𝑶𝑯)𝟐, 𝑵𝑯𝟒𝑶𝑯, 𝑴𝒈(𝑶𝑯)𝟐.
 The soluble bases are much more useful than insoluble bases
because most of chemical reactions takes place only in aqueous
solutions.

WHAT DO ALL THE BASES HAVE IN COMMON
:
 When a base is dissolved in water, it always produces
hydroxide ions 𝑶𝑯− 𝒊𝒐𝒏𝒔 .
 For example, sodium hydroxide is a base because it dissolves
in water to produce hydroxide ions.
𝑵𝒂𝑶𝑯(𝒔) 𝑵𝒂(𝒂𝒒)
+
+ 𝑶𝑯(𝒂𝒒)
−
water

 Potassium hydroxide is base which dissolves in water to give hydroxide
ions.
𝑲𝑶𝑯(𝒔) 𝑲(𝒂𝒒)
+
+ 𝑶𝑯(𝒂𝒒)
−
 Magnesium hydroxide is also a base which dissolves in water to produce
hydroxide ions.
𝑴𝒈(𝑶𝑯)𝟐(𝒂𝒒) 𝑴𝒈(𝒂𝒒)
+
+ 𝟐𝑶𝑯(𝒂𝒒)
−
water
water

STRONG BASES :
 A base which completely ionizes in water and thus produces
a large amount of hydroxide ions is called strong base (or
strong alkali).
Eg:- 𝑵𝒂𝑶𝑯 𝒂𝒏𝒅 𝑲𝑶𝑯

WEAK BASES :
 A base which is partially ionized in water and thus produces
a small amount of hydroxide ions is called a weak base.
Eg:-
𝑵𝑯𝟒𝑶𝑯, 𝑪𝒂(𝑶𝑯)𝟐, 𝒂𝒏𝒅 𝑴𝒈(𝑶𝑯)𝟐.

PROPERTIES OF BASES :
 Bases have bitter taste.
 Bases feel soapy to touch.
 Bases turn red litmus to blue.
 Bases conduct electricity in solution.

CHEMICAL PROPERTIES
 Bases react with some metals to form hydrogen gas.
𝟐𝑵𝒂𝑶𝑯(𝒂𝒒) + 𝒁𝒏(𝒔) 𝑵𝒂𝟐𝒁𝒏𝑶𝟐(𝒂𝒒) + 𝑯𝟐(𝒈)
 Bases react with acids to form salt and water.
𝟐𝑵𝒂𝑶𝑯(𝒂𝒒) + 𝑯𝟐𝑺𝑶𝟒(𝒂𝒒) → 𝑵𝒂𝟐𝑺𝑶𝟒(𝒂𝒒) + 𝟐𝑯𝟐𝑶(𝒍)
Heat

 Bases react with non- metal oxides to form salt and water.
𝑪𝒂(𝑶𝑯)𝟐(𝒂𝒒) + 𝑪𝑶𝟐(𝒈) → 𝑪𝒂𝑪𝑶𝟑(𝒔) + 𝑯𝟐𝑶(𝒍)

USES OF BASES :
 Sodium hydroxide is used in the manufacture of soap, paper
and a synthetic fibre called rayon.
 Calcium hydroxide is used in the manufacture of bleaching
powder.
 Magnesium hydroxide is used as an antacid to neutralize
excess acid in the stomach.

 Sodium carbonate is used as washing soda and for softening
hard water.
 Sodium hydrogen carbonate is used as baking soda in
cooking food, for making baking powder, as an antacids to
cure indigestion and in soda-acid fire extinguishers

STRENGTH OF ACID AND BASE SOLUTIONS :
 Water is slightly ionized into hydrogen ions and hydroxide
ions.
 In pure water the concentration of
hydrogen ions and hydroxide ions are
equal. Due to this, pure water is
neither acidic nor basic, it is neutral.

 Acids produce hydrogen ions in water. So when an acid is
added to water, then the concentration of hydrogen ions in
water increases.
 The solution of acid thus formed will have more of hydrogen
ions, and it will be acidic in nature.
 In other words acidic solutions have excess of hydrogen ions.

 Bases produce hydroxide ions in water. So, when a base is
added to water, then the concentration of hydroxide ions in
it increases.
 The solution formed by dissolving a base in water will have
more hydroxide ions, and it will be basic in nature.
 In other words, the basic solutions have excess of hydroxide
ions.

 We have learnt in the previous section about dilution and
decrease in the concentration of 𝑯+ or 𝑶𝑯− ions in the
solution.
 Can we quantitatively find the amount
of these ions present in the solution?
 Can we judge how strong a given acid
or base is?

universal indicator
We can do this by making use of
universal indicator, which is a
mixture of several indicators.
The universal indicator shows
different colours at different
concentrations of hydrogen ions in
a solution.

pH SCALE :
 A scale for measuring hydrogen ion concentration in a solution called pH
scale.
 The p in pH stands for ‘potenz’ in German, meaning power.
 On the pH generally from 0 (very acidic) to 14 (very alkaline).

 pH should be thought of simply as a number which indicates
the acidic or basic nature of a solution.
 Higher the hydronium ion concentration, lower is the pH
value.
 The pH of a neutral solution is 7.
 Value less than 7 on the pH scale
represents an acidic solution

 As the pH value increases from 7 to 14, it represents an
increase in the 𝑶𝑯−
ion concentration in the solution, that
is, increase in the strength of alkali .
 Generally paper impregnated with the universal indicator is
used for measuring pH.

COLOURS PRODUCED BY UNIVERSAL
INDICATOR AT VARIOUS pH VALUES:
pH Colour pH Colour
0 Dark red 8 Greenish blue
1 Red 9 Blue
2 Red 10 Navy blue
3 Orange red 11 Purple
4 Orange 12 Dark purple
5 Orange yellow 13 Violate
6 Greenish yellow 14 Violate
7 Green

pH VALUES OF SOME COMMON SUBSTANCES:
S.NO Solution Colour of pH paper Approximate pH value Nature
1. Saliva (before meal) Light green 7.4 Base
2. Saliva (after meal) Pale yellow 5.8 Acid
3. Lemon juice Pink red 2.5 Acid
4. Colourless aerated drink Pale yellow 6 Acid
5. Carrot juice Light orange 4 Acid
6. Coffee Orange yellow 5 Acid
7. Tomato juice Dark orange 4.1 Acid
8. Tap water Green 7 Neutral
9. 1M NaOH Violate 13-14 Base
10. 1M HCl Red 1 Acid

Sample problem :
1. You have two solutions A and B. The pH of solution A is 6 and pH of
solution B is 8
(a) Which solution has more hydrogen ion concentration?
(b) Which of the solutions is acidic and which one is basic?
2. Five solutions A,B,C,D and E when tested with universal indicator
showed pH of 4,1,11,7 and 9 respectively,
(a)Which solution is (i) neutral, (ii)strongly alkaline, (iii)strongly
acidic, (iv)weakly acidic, (v)weakly alkaline?
(b) Arrange pH in increasing order of hydrogen ion.

IMPORTANCE OF pH IN EVERYDY LIFE :
1) pH in our Digestive system :
 Our stomach produces hydrochloric acid (of pH 1.4).
 This dilute HCl helps in digestion our food without
harming the stomach.
 Sometimes, excess of acid is produced in the stomach due
to various reasons.

 The excess acid in the stomach causes
indigestion which produces pain and
irritation.
 To get rid of this pain people use bases
called antacids. These antacids
neutralize the excess acids.
 Magnesium hydroxide (milk of
magnesia), a mild base is often used for
this purpose.

2) pH change as the cause of tooth decay:
 When we eat food containing sugar, then the bacteria present in our
mouth break down the sugar to form acids.
 This acid lowers the pH in the mouth.
 Tooth decay starts when the pH of acid formed in the mouth falls below
5.5.
 Tooth is made up of calcium hydroxyapatite (crystalline form of calcium
phosphate) is the hardest substance in the body.

 It does not dissolve in water, but is
corroded when the pH in the
mouth is below 5.5.
 The best way to prevent tooth decay
is to clean the mouth thoroughly
after eating food.
 Many toothpastes contain bases. It
can neutralize the excess acid in
mouth and prevent tooth decay.

3. Plant and animals are sensitive to pH changes :
 Our body works within the pH range 0f 7.0 to 7.8.
 Living organism 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.
 Calcium carbonate is often
added to acidic lake water to
neutralize the acid.

4) What is the pH of the soil in your backyard?
 Most of the plant grow best when the pH of the soil is close
to 7
 If the soil is too acidic or too basic, the plant grow badly or
do not grow at all. The soil may be acidic or basic naturally.
 The soil pH is also affected by the use of chemical fertilizers
in the field.

 The pH of acidic soil can reach as low as 4 and that of the
basic soil can go up to 8.3.
 If the soil is too acidic then it is treated with materials like
quicklime (calcium oxide) or slaked lime (calcium hydroxide)
or chalk (calcium carbonate).
 If the soil is too alkaline then its alkalinity can be reduced by
adding decaying organic matter (manure or compost) which
contains acidic material.

 We can check pH of a soil ourselves as follows: take about 2g
soil in a test tube and add 5 mL of water to it.
 Shake the test tube well. Filter the contents of the test tube
through a filter paper and collect the filtrate.
 Find the pH of this filtrate by using the universal indicator
paper.

5) Self defence by animals and plants through chemical warfare:
 Many animals and plants protect themselves from their
enemies by injecting painful and irritating acids and bases
into their skin.
 For example, when a honey bee stings a person, it injects an
acidic liquid into the skin which causes immense pain and
irritation.

v
 If the bee stings a person, then rubbing a mild base like
baking soda solution on the stung area of the skin gives
relief.
 When a wasp stings, it injects an alkaline liquid into the skin.
So if a wasp stings a person, then rubbing a mild acid like
vinegar on the stung area of the skin gives relief.

 Some plants also give painful stings.
 For example, nettle is a herbaceous plant which grows in the
wild. The nettle leaves have stinging hair.
 When a person happens to touch the leaves of a nettle plant
accidently, the stinging hair of nettle leaves inject methanoic
acid into the skin of the person causing burning pain.
 The nettle sting being acidic can be neutralized by rubbing
baking soda.

 Even nature itself has provided remedy for the nettle sting in
the form of ‘dock’ plant.
 So, a traditional remedy for the nettle leaf sting is to rub the
stung area of the skin of the person with the leaf of dock
plant.

SALTS :
 A salt is a compound formed from an acid by the
replacement of the hydrogen in the acid by a metal.
 In HCl if we replace the hydrogen (H) by metal atom, (Na),
then we will get a salt NaCl.
 In some salts, however, the hydrogen pf acid is replaced by
ammonium group (𝑵𝑯𝟒) as in the case of ammonium
chloride.

i. The salts if hydrochloric acids are called chlorides.
ii. The salts of sulphuric acid are called sulphates.
iii. The salts of nitric acid are called nitrates.
iv. The salts of carbonic acid are called carbonates.
v. The salts of acetic acid are called acetates.

SOME IMPORTANT SALTS AND THEIR
FORMULAE:
SALT FORMULA SALT FORMULA
Sodium chloride 𝑵𝒂𝑪𝒍 Zinc sulphate 𝒁𝒏𝑺𝑶𝟒
Calcium chloride 𝑪𝒂𝑪𝒍𝟐 Copper sulphate 𝑪𝒖𝑺𝑶𝟒
Magnesium chloride 𝑴𝒈𝑪𝒍𝟐 Ammonium sulphate (𝑵𝑯𝟒)𝟐𝑺𝑶𝟒
Zinc chloride 𝒁𝒏𝑪𝒍𝟐 Sodium nitrate 𝑵𝒂𝑵𝑶𝟑
Sodium sulphate 𝑵𝒂𝟐𝑺𝑶𝟒 Potassium nitrate 𝑲𝑵𝑶𝟑
Potassium sulphate 𝑲𝟐𝑺𝑶𝟒 Sodium carbonate 𝑵𝒂𝟐𝑪𝑶𝟑
Calcium sulphate 𝑪𝒂𝑺𝑶𝟒 Calcium carbonate 𝑪𝒂𝑪𝑶𝟑
Magnesium sulphate 𝑴𝒈𝑺𝑶𝟒 Zinc carbonate 𝒁𝒏𝑪𝑶𝟑
Aluminium sulphate 𝑨𝒍𝟐(𝑺𝑶𝟒)𝟑 Sodium acetate 𝑪𝑯𝟑𝑪𝑶𝑶𝑵𝒂

Properties of salt
 Salts are mostly solids. They have high melting points and boiling
points.
 Salts are usually soluble in water.
 Just like acids and bases, solution of salts in water conduct
electricity.
 Salt solution conducts electricity due to the presence of ions in
them. Salts are ionic compounds.

FAMILY OF SALTS:
 The salts having the same positive ions (or negative ions) are
said to belong to a family of salts.
 For example 𝑵𝒂𝑪𝒍 and 𝑵𝒂𝟐𝑺𝑶𝟒 belongs to the same family
salts called sodium salts.
 Similarly 𝑵𝒂𝑪𝒍 and 𝑲𝑪𝒍 belong to the same family of salts
called chloride salts.

THE pH OF THE SALT SOLUTION:
 Salts of strong acid and a strong base are neutral with pH
value of 7.
 Salts of strong acid and weak base are acidic with pH value
less than 7.
 Salts of strong base and weak acid are basic in nature with
pH value more than 7.

Salt pH Acid used Base used
Sodium chloride 7 𝑯𝑪𝒍 𝑵𝒂𝑶𝑯
Potassium nitrate 7 𝐊𝑶𝑯 𝑯𝑵𝑶𝟑
Aluminium chloride 7 𝑯𝑪𝒍 𝑨𝒍(𝑶𝑯)𝟑
Zinc sulphate 7 𝑯𝟐𝑺𝑶𝟒 𝒁𝒏(𝑶𝑯)𝟐
Copper sulphate <7 𝑯𝟐𝑺𝑶𝟒 𝑪𝒖(𝑶𝑯)𝟐
Sodium acetate >7 𝑪𝑯𝟑𝑪𝑶𝑶𝑯 𝑵𝒂𝑶𝑯
Sodium carbonate >7 𝑯𝟐𝑪𝑶𝟑 𝑵𝒂𝑶𝑯
Sodium hydrogen carbonate >7 𝑯𝟐𝑪𝑶𝟑 𝑵𝒂𝑶𝑯

COMMON SALT (SODIUM CHLORIDE) :
 The common salt is white powder which is used in preparing
food, especially vegetables and pulses.
 Common salt is known as just salt. The chemical name of
common salt is sodium chloride.
 Common salt is a neutral salt.

 Sodium chloride can be made in the laboratory by the
combination of sodium hydroxide and hydrochloric acid.
𝑵𝒂𝑶𝑯(𝒂𝒒) + 𝑯𝑪𝒍(𝒂𝒒) → 𝑵𝒂𝑪𝒍(𝒂𝒒) + 𝑯𝟐𝑶(𝒍)
 The sodium chloride solution formed here can be
evaporated to obtain sodium chloride salt.
 But sodium chloride is never made in this way on a large
scale. Because sodium chloride is present in nature in
abundance.

HOW COMMON SALT IS OBTAINED :
Common salt from sea water :
 Sea water contains many dissolved salts in it.
 The major salt present in sea water is common salt.
 Common salt is obtained from sea water by the process of evaporation.
 This is done by as follows.

 Sea water is trapped in large, shallow
pools and allowed to stand there.
 The sun’s heat evaporates the water
slowly and common salt is left behind.
 This salt is impure because it has some
other salts mixed in it. It is purified to
obtain pure common salt.

Common salts from underground deposits.
 The large crystals of common salts
found in in underground deposits
are called rock salt.
 Rock salt is usually brown due to
the presence of impurities in it.
Rock salt is mined from
underground deposits just like coal.

USES OF COMMON SALT :
 The common salt thus obtained is an important raw material
for various materials of daily use, such as sodium hydroxide,
baking soda, washing soda, bleaching powder and many
other more.

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 chlore for chlorine and alkali for sodium
hydroxide.
𝟐𝑵𝒂𝑪𝒍(𝒂𝒒) + 𝟐𝑯𝟐𝑶(𝒍) → 𝟐𝑵𝒂𝑶𝑯(𝒂𝒒) + 𝑪𝒍𝟐(𝒈) + 𝑯𝟐(𝒈)

 Chlorine gas is given off at the anode, hydrogen gas at the
cathode.
 The three products produced in this process are all useful.

Bleaching powder :
 Chlorine gas is used for the manufacture of bleaching
powder.
 Bleaching powder is produced by the action of chlorine on
dry slacked lime.
 Bleaching powder is represented as 𝑪𝒂𝑶𝑪𝒍𝟐.(calcium
hypochloride)
𝑪𝒂(𝑶𝑯)𝟐 + 𝑪𝒍𝟐 → 𝑪𝒂𝑶𝑪𝒍𝟐 + 𝑯𝟐𝑶

Bleaching powder is used :
 For bleaching cotton and linen in the textile industry,
 for bleaching wood pulp in paper factories and
 for bleaching washed clothes in laundry.
 As an oxidizing agent in many chemical industries.
 For disinfecting drinking water to make it free from germs.

Baking soda :
 The soda commonly used in the kitchen for making tasty crispy
pakoras is baking soda. Sometimes it is added for faster cooking.
 The chemical name of the compound is sodium hydrogen
carbonate.
 It is produced using sodium chloride as one of the raw material.
𝑵𝒂𝑪𝒍 + 𝑵𝑯𝟑 + 𝑯𝟐𝑶 + 𝑪𝑶𝟐 → 𝑵𝑯𝟒𝑪𝒍 + 𝑵𝒂𝑯𝑪𝑶𝟑

 Sodium hydrogen carbonate is a non-corrosive base.
 The following reaction takes place when it is heated during
cooking
𝟐𝑵𝒂𝑯𝑪𝑶𝟑 𝑵𝒂𝟐𝑪𝑶𝟑 + 𝑯𝟐𝑶 + 𝑪𝑶𝟐
heat

Uses of sodium hydrogencarbonate :
 For making baking powder, which is a mixture of baking soda 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
 𝑪𝑶𝟐 produced during the reaction causes bread or cake to rise
making them soft and spongy.

 Sodium hydrogen carbonate is also an ingredient in antacids.
Being alkaline, it neutralizes excess acid in the stomach and
provides relief.
 It is also used in soda-acid fire extinguishers.

Washing soda :
 Washing soda (𝑵𝒂𝟐𝑪𝑶𝟑. 𝟏𝟎𝑯𝟐𝑶) is obtained from sodium
chloride.
 We have seen that sodium carbonate can be obtained by heating
baking soda, crystallization of sodium carbonate gives washing
soda.
 It is also a basic salt.
𝑵𝒂𝟐𝑪𝑶𝟑 + 𝟏𝟎𝑯𝟐𝑶 → 𝑵𝒂𝟐𝑪𝑶𝟑. 𝟏𝟎𝑯𝟐𝑶

Uses of washing soda :
 It is used in glass, soap and paper industries.
 It is used in the manufacture of sodium compounds such as
borax.
 It can be used as a cleaning agent for domestic purposes.
 It is used for removing permanent hardness of water.

Plaster of paris :
 On heating gypsum at 273 K, it loses water molecules and
becomes calcium sulphate hemihydrate. This is called plaster
of Paris.
𝑪𝒂𝑺𝑶𝟒. 𝟐𝑯𝟐𝑶 𝑪𝒂𝑺𝑶𝟒.
𝟏
𝟐
𝑯𝟐𝑶 + 𝟏
𝟏
𝟐
𝑯𝟐𝑶
Heat
Gypsum Plaster of Paris

 Plaster of Paris is the substance which doctors use as a
plaster for supporting fractured bones in the right position.
 Plaster of Paris is a white powder and on mixing with water,
it changes to gypsum once again giving the hard solid mass.
𝑪𝒂𝑺𝑶𝟒.
𝟏
𝟐
𝑯𝟐𝑶 + 𝟏
𝟏
𝟐
𝑯𝟐𝑶 𝑪𝒂𝑺𝑶𝟒. 𝟐𝑯𝟐𝑶
Gypsum
Plaster of Paris

Uses :
 Plaster of Paris is used for making toys materials for
decoration and for making surface smooth.

Why calcium sulphate hemihydrate is called plaster of Paris?
 The name plaster of Paris is derived from the large deposits
of gypsum in the ‘Montmartre hill’ in Paris.

Acids, Bases and salts BY TRI SIR.pptx

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