LANGUAGE OF CHEMISTRY

LANGUAGE OF CHEMISTRY

EXERCISE

1. Calculate the molecular mass of the following:

i. Water

ii. Carbon dioxide

iii. Nitric acid

iv. Sulphuric acid

v. Ammonium sulphate

vi. Washing soda

vii. Blue vitriol

(Given : H=1, C=12, O=16, N= 14, S= 32,Na=23, Cu=65)

2. Calculate the percentage of oxygen in the following compounds:

i. Water

ii. Sulphur dioxide

iii. Carbonic acid

iv. Sodium carbonate

v. Blue vitriol

LANGUAGE OF CHEMISTRY

Chemical Symbols:

It is the short hand representation of an atom of an element.

Each element is denoted by a symbol. Usually the first letter of its name is used as its symbol. However, when more than one element has the same first letter, two letters are used to denote the symbol.

Significance of symbol:

It represents:

1. The name of an element.

2. One atom of an element

Chemical Formula:

A formula represents one molecule of a pure substance (elements and compounds). So it is also called molecular formula.

E.g. N₂ represents one molecule of nitrogen; HNO₃ represents one molecule of nitric acid.

Radical:

It is an atom or group of atoms of same or different elements that behave as a single unit. They are charged particles. They also have a valency and chemical formula.

If a radical has positive charge it is called basic radical (cation) and if it has negative charge it is called an acidic radical (anion).

E.g. NH₄⁺ is a basic radical and NO₃^- is an acidic radical.

Valency:

It is the combining capacity of an atom of an element or radical. The valency of an element or of a radical is defined as the number of hydrogen atoms that will combine with it or displace one atom of that element or radical.

E.g. 2 atoms of H combine with one atom of oxygen. So the valency of oxygen is 2.

Note: The elements having valency 1, 2, 3 and 4 are called monovalent, divalent, trivalent and tetravalent elements.

Variable valency:

Certain elements have been found which show more than one valency.

E.g. In ferric chloride,the valency of iron is +3 while the valency of iron in ferrous chloride is +2.

When an element exhibits two different valencies, for the lower valency we use the suffix ous and for the higher valency we use the suffix ic. Modern chemists have started using Roman numerals in place of these trivial names.

e.g. Instead of writing FeCl₂ as Ferrous chloride they are writing it as Iron (II) chloride and FeCl_3,as iron (III) chloride instead of ferric chloride.

Non metals can also exhibit variable valency. Sulphur has been found to show a valency of 2, 4 & 6 while phosphorus shows a valency of 3& 5.

Valency of radicals:

Radical Formula

Valency 1: Monovalent

Bromide Br ^-1

Acetate CH₃COO^-1

Chloride Cl^-1

Ammonium NH₄⁺

Cuprous or copper (I) Cu⁺¹

Bicarbonate (hydrogencarbonate) HCO₃^-

Fluoride F^-1

Bisulphate (hydrogensulphate) HSO₄^-

Bisulphite (hydrogensulphite) HSO₃^-

Iodide I^-1

Chlorate ClO₃^-

Mercurous or mercury (I) Hg⁺²

Chlorite ClO₂^-

Potassium K¹⁺

Cyanide CN^-

Silver Ag¹⁺

Hydroxide OH^-

Sodium Na¹⁺

Hypochlorite ClO^-

Nitrate NO₃^-

Nitrite NO₂^-

Perchlorate ClO₄^-

Permanganate MnO₄^-

Valency 2: Divalent

Barium Ba⁺²

Carbonate CO₃^2-

Cadmium Cd⁺²

Chromate CrO₄^2-

Calcium Ca⁺²

Dichromate Cr₂O₇^2-

Cobalt Co⁺²

Peroxide O₂^2-

Cupric or copper (II) Cu⁺²

Silicate Si₄O₃^2-

Ferrous or iron (II) Fe⁺²

Sulphate SO₄^2-

Plumbous or lead (II) Pb⁺²

Sulphite SO₃^2-

Magnesium Mg⁺²

Manganous or manganese (II) Mn⁺²

Mercuric or mercury (II) Hg⁺²

Oxide O^2-

Stannous or tin (II) Sn⁺²

Sulphide S^2-

Zinc Zn⁺²

Valency 3: Trivalent

Aluminium Al⁺³

Ferricyanide [Fe(CN)₆]^3-

Auric or gold (III) Au⁺³

Phosphate PO₄^3-

Chromic or chromium (III) Cr⁺³

Phosphite PO₃^3-

Ferric or iron (III) Fe⁺³

Nitride N^-3

Valency 4: Tetravalent

Ferrocyanide [Fe(CN)₆]^4-

Plumbic or lead (IV) Pb⁺⁴

Stannic or tin (IV) Sn⁺⁴

Writing Chemical Formulae:

How to write a formula using criss cross method:

The following steps have to be followed to write a formula:

1. Write the symbol of the respective radicals. The positive radical is written on the left hand side and negative radical on the right hand side.

2. The valency of the radicals is written on top of the symbol.

3. The valency of the radicals will be interchanged without the positive and negative signs.

4. The interchanged valencies are written to the lower right of the radicals.

5. If the radical contains more than one atom it should be enclosed within brackets.

Illustration:

Formula of sodium chloride: Formula of magnesium chloride:

Na⁺¹ Cl^-1Mg⁺² Cl^-1

Na₁ Cl₁Mg₁Cl₂

NaCl MgCl₂

Formula of calcium hydroxide: Formula of ammonium sulphate:

Ca⁺² OH^-1NH₄⁺SO₄^2-

Ca₁ (OH)₂ (NH₄)₂(SO₄)₁

Ca(OH)₂ (NH₄)₂ SO₄

NAMING OF COMPOUNDS:

1. A metal and non- metal: When we write the name of a binary compound consisting of a metal and non- metal we write the name of the metal first and add a suffix ide to the non metallic part.

E.g. MgCl₂ is named as magnesium chloride.

2. Two non metals: If a compound contains two non metals prefix mono, di, tri, tetra etc are used to indicate the number of atoms present.

E.g. CO₂ is named as carbon dioxide; PCl₃ is named as phosphorus trichloride.

3. Two elements and oxygen: Oxygen is the last element in the formula.

a. If only one compound is possible then the suffix ate is added.

b. If two compounds are possible for the compound containing less number of oxygen, suffix ite is used and for the compound containing more number of oxygen suffixes ate is used.

c. If any compound contains less number of oxygen than the compound which ends with ite then the prefix hypo is added and if it contains more number of oxygen then the compound with suffix ate, then the prefix per is used.

E.g.

KClO – Potassium hypochlorite

KClO₂ – Potassium chlorite

KClO₃ – Potassium chlorate

KClO₄ – Potassium perchlorate

Acids:

a. While writing the names of binary acids the prefix hydro is added and the suffix ic is added to the name of the non-metal.

E.g. HCl – hydrochloric acid, HBr - Hydrobromic acid

b. Acids containing polyatomic radicals are named on the basis of the second element. The prefix hydro is not used for them.

E.g. H₂SO₄ is called sulphuric acid.

Chemical Equation:

A shorthand representation of a chemical reaction in terms of symbols and formulae of the substances involved in the reaction is called chemical equation. A reaction can be represented by a word equation or a chemical equation.

E.g. Word Equation: Hydrogen + Oxygen → Water

Chemical Equation: H₂ + O₂ → H₂O

Reactant and Product:

The substances that react among themselves in a chemical reaction are known as reactants, whereas the substances that are produced as a result of the chemical reaction are known as products.

How to write a Chemical Equation:

1. The reactants are written on the right hand side and the products on the left hand side.

2. A plus sign (+) is placed between any 2 reactants and any 2 products.

3. The reactants and products are separated by an arrow (→) pointing towards the product. The ‘→’ means to produce or give.

Skeletal Equation: An unbalanced chemical equation in which only the symbols and formula of the reactants and products are written.

E.g. Fe + H₂O → Fe₃O₄ + H₂

Balanced Chemical Equation: It is a chemical equation in which the number of atoms of each kind on the reactant side and the product side are equal.

E.g. 2H₂ + O₂ → 2H₂O

BALANCING A CHEMICAL EQUATION BY HIT AND TRIAL METHOD:

1. Count the number of times each element occurs on either side of the equation.

2. The element which occur the least number of times should be balanced first.

3. If two or more elements occur the same number of times, then balance the metal atom first.

Illustration:

Balance the following skeletal equation.

Fe + H₂O → Fe₃O₄ + H₂

Step 1: Find the number of atoms on both sides of the equation:

Reactant side Product side

Fe = 1 Fe = 3

H = 2 H = 2

O = 1 O = 4

Step 2: To balance Fe atoms, Fe on the reactant side is multiplied by 3.

Step 3: Now to balance O atoms, write 4 before water on the reactant side.

3Fe + 4H₂O → Fe₃O₄ + H₂

Step 4: Hydrogen atoms are not yet balanced. So to balance hydrogen, write 4 before hydrogen on the product side.

3Fe + 4H₂O → Fe₃O₄+ 4H₂

The equation is finally balanced.

Exercise:

Balance the following equations:

1. Zn + HCl → ZnCl₂ + H₂

2. Pb(NO₃)₂ → PbO + NO₂ + O₂

ASSIGNMENTS

The following questions should be done in class work copy.

Q.1. Write the chemical formula of the following by criss-cross method:

i. Sodium oxide

ii. Potassium sulphate

iii. Zinc hydroxide

iv. Ferrous sulphate

v. Ferric chloride

vi. Ammonium phosphate

vii. Calcium bicarbonate

viii. Cupric sulphide

ix. Lead(II) nitrate

x. Aluminium Nitride

2. An element Y shows variable valency of +2 and +3. Write the formula of its:

i. Nitrite

ii. Bisulphide

iii. Zincate

iv. Permanganate

v. Dichromate

Note: Write the answer in a tabular form as shown below:

S. No.	Radical	Valency 2	Valency 3
1.	Nitrite	Y(NO₂)₂

3. Write the name of the following compounds:

i. HNO₃

ii. H₂SO₄

iii. HCl

iv. K₂SO₄

iv. CuCO₃

4. Identify the basic and acidic radical in the compound Potassium nitrate.

5. Balance the following equations:

i. Mg + N₂→ Mg₃N₂

ii. S + HNO₃ → H₂SO₄+ H₂O +NO₂

conc

iii. P₂O₅ +H₂O → H₃PO₄

iv. P + conc HNO₃→ H₃PO₄+ H₂O +NO₂

v. ZnCO₃ + HCl → ZnCl₂ + H₂O + CO₂

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LANGUAGE OF CHEMISTRY _ CLASS 9

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