Class 9 Sindh Chemistry Cha 9 Acids, Bases, and Salts Pdf Download

A Swedish chemist Svante Arrhenius, in 1984 placed his acid-base theory. According to this, acid is a species that contains hydrogen and can give hydrogen ions (H⁺) in an aqueous solution. For example, hydrochloric acid (HCl) gives H⁺ ion in its aqueous solution. The reaction is,
HCl ⇔ H⁺ + Cl^–
As water accepts the H+ ion, it forms H3O+ as follows.
HCl + H₂O ⇔ H₃O⁺ + Cl^–
According to Arrhenius, bases are the substances that produce OH^– ions when it is dissolved in water. For example, NaOH is a base that gives OH^– ions in water.
NaOH ⇔ Na+ + OH^–
It also explains when acids and bases react together yield a neutral product salt and water.
HCl + NaOH ⇔ NaCl + H₂O
This theory was very helpful to explain some acids and bases, but still, there were some limitations. Like,
i) Arrhenius did not explain the behavior of acids and bases in non-aqueous solutions.
ii) It only applies to substances that produce the only hydrogen (H⁺) ions or hydroxide (OH^–) ions.
iii) Arrhenius’s theory fails to explain acids such as AlCl₃, and BF₃, which have no ‘H’ atom.

In 1923, G.N, Lewis extended the definition of Bronsted-Lowry acids and bases. He noticed that Bronsted limited his theory on the transfer of protons (H⁺). Lewis proposed his theory to describe acids and bases. He explained what happens when an H⁺ ion combines with an OH^– ion to form water.

a) Properties of acids:
1) Acids have a sour taste, vinegar gives the taste of acetic acid, and lemons and other citrus fruits contain citric acid.
2) They change the color of blue litmus to red.
3) Acids react with certain metals, such as (Zn, Mg, and Fe) to produce (H₂) gas, for example, when diluted, (HCl) reacts with (Zn) metal, producing (H₂) gas.
Zn + 2HCl → ZnCl₂ + H₂
4) Acids react with carbonates and bicarbonates to produce carbon dioxide gas.
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
5) Acids react with oxides and hydroxide of metals, forming salt and water.
FeO + 2HCl → FeCl₂ + H₂O
6) Aqueous acid solutions conduct electricity.
7) They react with bases to form salts and water.

b) Properties of bases:
1) Bases have a bitter taste.
2) Bases have a slippery touch.
3) They change the color of red litmus to blue.
4) Aqueous solutions of bases conduct electricity.
5) They react with acids to form salts. When acids and bases are mixed in the right proportions, the acidic and basic properties disappear and new substances salt and water are formed and the reaction is a neutralization reaction.

a)  Strong acid:
A strong acid is one, that completely dissociates in water and produces a large number of (H⁺) ions in an aqueous solution. For example, H₂SO₄ is a strong acid.
H₂SO4 + H₂O → 2H⁺ + SO₂^-4

b) Weak acid:
A weak acid is one, that partially dissociates in water and produces a small fraction of (H⁺) ions in water. For example, H₂CO₃ is a weak acid.
H₂CO³ + H₂O ⇔ 2H⁺ + CO2^-3

c) Strong base:
A strong base is one, that completely dissociates in water and produces a large number of (OH^–) ions in water. For example, NaOH is a strong base.
NaOH + H₂O → Na⁺ + OH^–

d) Weak base:
A weak base is one, that partially dissociates in water and produces a small fraction of (OH^–) ions in water. For example, NH₃ is a weak base.
NH₃ + H₂O ⇔ NH₄⁺ + OH^–

H₂SO₄ is diprotic acid. It has two H+ ions for dissociation in water. So both H⁺ ionizes very easily in water so H₂SO₄ is a strong acid. While HSO₄ is monoprotic and its H⁺ does not ionize in water. So it is a weak acid.

b) Strong acid and strong base.
c) Strong acid and weak base.
d) Weak acid and strong base.
Answer:
a. i) Acidic solution:
If H⁺ ion concentration is greater than OH^– then the solution is basic.
ii) Basic solution:
If H⁺ ion concentration is less than OH^– then the solution is basic.
iii) Neutral solution:
If H⁺ and OH^– ions concentrations are equal then the solution is neutral.
b) Strong acid and strong base:
When strong acid reacts with a strong base then a neutral solution is formed. For example,
HCl + NaOH → H₂O + NaCl
c) Strong acid and weak base:
When a strong acid reacts with a weak base then the solution is called acidic. For example,
NH₃ + HCl → NH₄ ⁺ + Cl^–
d) Weak acid and strong Base:
When a weak acid reacts with a strong base then the basic solution is formed. For example,
CH₃COOH + NaOH → H₂O + CH₃COO^–Na⁺

It is an ionic compound formed by the neutralization of acids and bases. For example,
HCl + NaOH → NaCl + H₂O
In this case, HCl is an acid, which reacts with base NaOH and gives a compound known as salt (NaCl) and water. NaCl is also called table salt which is used in our food. Salts are ionic compounds and have high melting and boiling points. For example, NaCl has a melting point of 801°C.

Four Examples of Salt:
i) NaCl Table salt
ii) NH₄F Ammonium fluoride
iii) MgCO₃ Magnesium carbonate
iv) Fe₂(HPO₄)₃ Iron (III) Hydrogen Phosphate

i) Mono-protic acid:
Acids, when dissolved in water, produce 1 mole of (H⁺) ion in solution, which is called mono-protic acids.
For example, HCl, HNO_3, and HCN are mono-protic acids.

ii) Di-protic acid:
Acids, when dissolved in water, produce 2 moles of (H⁺) ions in solution, which are called di-protic acids. For example, H₂SO₄ is di-protic acid.

iii) Tri-protic acid:
Acids, when dissolved in water, produce 3 moles of (H⁺) ions in solution, which are called tri-protic acids. For example, H₃PO₄ is a tri-protic acid.

a) NH₃
b) H₃PO₄
c) LiOH
d) HCOOH (formic acid)
e) H₂SO₄
f) H₂CO₃
g) Ba (OH)₂

Answer:
a) Weak base
b) Weak acid
c) Weak base
d) Weak acid
e) Strong acid
f) Weak acid
g) Strong base

Molarity:
Molarity is the number of moles of a solute dissolve per dm3 of solution. It is denoted by M.
M (Molarity) = number of moles of solute / dm3 or liter of solution.

Molar Solution:
The molar solution is defined as one mole of solute dissolved in one liter of solution. For example, if 58.8g of NaCl is dissolved in enough water to make it 1 liter of the solution then the solution will be 1 molar.

Answer:
Data:
Mass of H₂SO₄            = 9.8g
Volume of solution    = 500ml = 0.5 litre
Molarity of H₂SO₄ = ?
Solution:
Molar mass of H₂SO₄             = 1 × 2 + 32 + 4 × 16 = 98g
98g of H₂SO₄                       = 1 mol
1 g of H₂SO₄                         = 1 / 98
9.8g of H₂SO₄ 1/98 × 9.8     = 0.1 M
Molarity of H₂SO₄               = No. of mol / Solution in litre
                                             = 0.1 / 0.5
                                              = 0.2 M

Answer:
pH:
the pH of the solution is defined as the negative logarithm of the hydrogen ion (H+) concentration or (H3O+) ion concentration in moles per liter. Mathematically it is written as,
pH = -log [H+]

A neutral solution is said to have a pH of seven, it means the solution is neither acidic nor basic. pH is a measure of the number of Hydrogen ions (H+) in a solution. Ions are just atoms that have an electric charge on them, so (H+) is a hydrogen atom with a charge of 1. The amount of H+ in a neutral solution is about equal to a pH of 7 that is why the neutral solution is said to have 7 pH.

Dissociation of water:
Water dissociates into an H+ ion or oxonium ion (H3O+). The equation for the dissociation of water is,
H2O + H2O ⇔ H3O+ + OH-
In the ionization of water, proton transfers from one water molecule to the other water molecule forming an H₃O⁺ ion and OH^– ion.

Amphoteric:
Any substance that behaves both as an acid and as a base is called amphoteric. For example, water reacts with NH3 (base), during this reaction water donate proton and act as an acid.
H2O + HN3 → HN4+ + OH-
However, when water reacts with HCl (acid), it behaves as a base by receiving a proton.
H₂O + HCl → H₃O⁺ + Cl^–

a) .001 M-HCl
b) 5.2 x 10-4 M-HNO₃

Answer:
a) 0.001 M HCl:
[H⁺] = 0.001 mole / litre
pH = -log [H]⁺
= – log [0.001]
= – log [1 × 10^-3]
pH = – [-3]
= 3
b) 5.2 × 10^-4M HNO₃
[H+] = 5.2 × 10^-4 mole / litre
pH = -log [H]⁺
= – log [5.2 × 10^-4]
= – (log 5.2 × log10^-4)
= -[0.716 + (-4)]
= -(0.716 – 4)
= 3.284