Language of Chemistry

a molecule

Reason — A molecular formula of a compound is the symbolic representation of its (one) molecule. It shows the number of atoms of each element present in it. These atoms combine in whole numbers to form the molecule.

SO₃^2-

Reason — The symbol of sulphite ion is SO₃^2-.

Lead and mercury

Reason — Lead has a variable valency of 2 and 4, while mercury has a variable valency of 1 and 2.

Neon

Reason — Neon is the element with zero valency, as it doesn't form bonds under normal conditions.

1 and 2

Reason — The valencies shown by copper are 1 and 2.

K⁺

Reason — The correct symbol for the potassium ion is K⁺.

Both A and R are true and R is the correct explanation of A.

Explanation — In a neutral atom, the number of electrons and protons are equal, so they are electrically neutral. However, when an atom gains one or more electrons, the number of electrons in an atom exceeds the number of protons, and the atom becomes negatively charged.

Both A and R are true but R is not the correct explanation of A.

Explanation — The symbol can be based on the Latin or Greek name of the element, or a combination of letters, but it’s not strictly the first letter. For example, Helium has the symbol He, Sodium has Na, and Iron has Fe, which are not simply the first letter of the element's name.

Both A and R are true but R is not the correct explanation of A.

Explanation — Magnesium burns in oxygen to form magnesium oxide, whose molecular formula is MgO. Magnesium oxide is a white amorphous solid. However, the fact that magnesium oxide is a white amorphous solid does not explain why magnesium burns in oxygen to form MgO.

Both A and R are true and R is the correct explanation of A.

Explanation — The valency of inert gases, helium, neon and argon is zero as the outermost shell of inert gases is complete.

Both A and R are true but R is not the correct explanation of A.

Explanation — A chemical equation is the symbolic representation of a chemical reaction using symbols and formulae of the substances involved in the reaction, and every chemical equation needs to be balanced to follow the law of conservation of mass. However, they are two separate facts.

(a) atom

(b) chemical reaction

(c) Cations

(d) five

(e) chemical equation

(a) False
Correct Statement — When an atom gains one or more electrons, it becomes negatively charged.

(b) True

(c) False
Correct Statement — The sulphide ion (S^2-) is a monoatomic ion.

(d) False
Correct Statement — The nitrate ion is represented as NO₃^-.

(e) False
Correct Statement — The element cobalt is represented as Co.

(a) Ammonium ion, NH₄⁺

(b) Reactants

(c) Products

(d) Skeletal equation

(e) Radical

(f) Catalyst

(a) Bicarbonate

(b) Permanganate

(c) Nitride

(d) Dichromate

(a) Potassium carbonate

(b) Phosphorus pentoxide

(c) Hydrogen sulphide

(d) Calcium hydroxide

(e) Copper sulphate

(f) Silicon dioxide

(a) A symbol is the short hand representation for the atom of a specific element. Each chemical element has its own unique symbol. For example, H represents Hydrogen, and O represents Oxygen.

(b) A molecular formula of a compound is the symbolic representation of its one molecule which shows the number of atoms of each element present in it.

(c) Radical is an atom of an element or a group of atoms of the same or different elements that behave as a single unit and has positive or negative charge.

(d) Valency is the combining capacity of an atom of an element or of a radical with the atoms of other elements or radicals to form molecules.

(a) Differences between Reactants and Products

(b) Differences between Cation and anion

(c) Differences between a balanced and an unbalanced chemical equation

The law of conservation of mass states that matter can neither be created nor be destroyed in a chemical reaction. Only it can be changed from one form to another during the reaction process.

To write the molecular formula of a compound, the following information should be available:

1. Symbols of the elements or the radicals that constitute the compound.
2. Valencies (combining capacities) of the elements or the radicals.

1. N₂ + 3H₂ ⟶ 2NH₃

2. 2H₂ + O₂ ⟶ 2H₂O

3. Na₂O + H₂O ⟶ 2NaOH

4. 2CO + O₂ ⟶ 2CO₂

5. Zn + 2HCl ⟶ ZnCl₂ + H₂

1. 2Fe + 3Cl₂ ⟶ 2FeCl₃

2. Mg + H₂SO₄ ⟶ MgSO₄ + H₂

3. 2Mg + O₂ ⟶ 2MgO

4. CaO + H₂O ⟶ Ca(OH)₂

5. 2Na + Cl₂ ⟶ 2NaCl

(a) We get the following information from the given chemical equation:

1. Zinc and Hydrochloric acid are reactants. Zinc is in solid state that reacts with dilute HCl.
2. The reaction is irreversible.
3. The products formed are an aqueous solution of zinc chloride and hydrogen gas.
4. The equation is balanced i.e., number of atoms of each element on the reactant side and the product side are equal.

(b) We get the following information from the given chemical equation:

1. The reactants, nitrogen and hydrogen, and the product, ammonia, are all gases.
2. The reaction is reversible and exothermic.
3. The reaction takes place at a temperature between 400-450°C and at a high pressure between 200-900 atmosphere.
4. The catalyst is iron and molybdenum acts as a promoter, which increases the efficiency of the catalyst.
5. The equation is balanced i.e., number of atoms of each element on the reactant side and the product side are equal.

Some elements exhibit more than one valency and they are said to have variable valency.

Examples: Iron and copper.

(a) A chemical equation is the symbolic representation of a chemical reaction using symbols and formulae of the substances involved in the reaction.

(b) It is necessary to balance a chemical equation so as to make the number of atoms of the reactants equal to the number of atoms of the products because a chemical reaction is just a rearrangement of atoms and atoms are neither created nor destroyed during the chemical reaction.

(c) The limitations of a chemical equation are:

It does not inform about:

1. the physical states of the reactants and the products i.e. whether they are solids, liquids or gases.
2. the concentration of reactants and products.
3. the time taken for the completion of reaction.
4. the rate at which a reaction proceeds.
5. the heat changes during the reaction i.e. whether heat is given out or absorbed.
6. the conditions such as temperature, pressure, catalyst, etc. which affect the reaction.
7. the nature of the reaction i.e. whether it is reversible or irreversible.

(a) The molecular formula of a compound gives the following information:

1. It represents one molecule of a compound.
2. The elements or ions present in the compound.
3. The number of each kind of atoms and ions present in one molecule of a compound and their ratio.
4. The molecular formula enables us to calculate the mass of one molecule of the compound if the atomic mass of each atom present in the molecule is known. Molecular mass is the algebraic sum of the masses of all the atoms present in a given molecule.

(b) A balanced chemical equation gives the following information:

1. It shows which substances are taking part in a chemical reaction and what products are obtained as a result of it (Qualitative).
2. It shows both the number of molecules and the number of atoms of each type involved in the reaction.
3. It enables us to calculate the actual amount (mass) of reactants and products involved and formed in the reaction if atomic mass of each of the elements involved in the reaction is known (Quantitative).
4. It makes the study of chemistry universally standardized.

A chemical equation can be made more informative in the following ways:

1. The physical state of the reactants and products can be indicated by putting (s) for solid, (l) for liquid, (g) for gas and (aq.) for aqueous state beside the symbols for the reactants and products.
2. Evolution or absorption of heat during the reaction can be denoted by adding or subtracting a heat term on the product side.
3. Temperature, pressure and catalyst can be indicated above or below the arrow (→) separating the reactants and products.
4. Concentrations of reactants and products are indicated by adding the words (dil.) for dilute and (conc.) for concentrated before their formulae.
5. By using the signs → and ⇌, information about irreversible and reversible reactions can be depicted.

(a) Copper exhibits variable valency. It shows valencies 1 and 2.

(b) NH₄⁺ ion is different from the other basic radicals because it is a polyatomic ion, whereas the others are simple metal ions.

(c) NO₃^- is the odd one out because it is the only polyatomic acid radical in the group. Cl^-, S^2- and O^2- are monoatomic ions.

(d) Using Na⁺ from basic radicals and Cl^- from acid radicals, the compound formed is sodium chloride. Its chemical formula is NaCl.