Language of Chemistry

“Language of Chemistry” chapter lays the groundwork for understanding chemical reactions. It starts with the symbols of elements, which are concise abbreviations (like ‘H’ for Hydrogen) often drawn from English or Latin names. Next is valency, an element’s combining power, which dictates how atoms bond; it’s tied to electron transfer or sharing, and some elements even exhibit variable valency. The chapter then introduces radicals, which are charged groups of atoms that function as a single unit, crucial for constructing chemical formulae. These formulae are symbolic blueprints of compounds, indicating constituent elements and their precise ratios (e.g., H₂O).

Building on this, chemical equations are presented as symbolic depictions of reactions, with starting materials (reactants) on the left, an arrow, and newly formed substances (products) on the right. A key skill taught is balancing chemical equations, a process vital for upholding the Law of Conservation of Mass by ensuring an equal count of each type of atom on both sides. While balanced equations effectively convey reactants, products, and their relative quantities, the chapter also highlights their limitations: basic equations typically don’t reveal physical states, necessary reaction conditions, energy changes, or whether a reaction is reversible.

Exercise

Question 1.
Define:
(a) Radical
(b) Valency
(c) Molecular formula
Answer:
(a) Radical: Think of it like a charged group of atoms that sticks together and joins in on the action during chemical reactions.

(b) Valency: This is basically how many connections an atom or radical can make with others – its bonding power.

(c) Molecular formula: It’s a quick way to see exactly how many of each type of atom are in one molecule of a substance.

Question 2.
Give the symbols and valencies of the following radicals:
(a) Hydroxide (b) Chloride
(c) Carbonate (d) ammonium
(e) Nitrate
Answer:

Question 3.
Write the molecular formula for the oxide and sulphide of the following elements.
(a) Sodium (b) Calcium
(c) Hydrogen
Answer:
(a) Sodium oxide Na2O
Sodium sulphide Na2S
(b) Calcium oxide CaO
Calcium sulphide CaS
(c) Hydrogen oxide H2O
Hydrogen sulphide H2S

Question 4.
Write the molecular formulae for the following compounds and name the elements present.
(a) Baking soda (b) Common salt
(c) Sulphuric acid (d) Nitric acid
Answer:
(a) Baking soda — NaHCO3
Elements present in baking soda are sodium, hydrogen, oxygen and carbon.
(b) Common salt — NaCl
Elements present are: Sodium and chlorine.
(c) Sulphuric acid — H2SO4
Elements present are: Hydrogen, sulphur and oxygen.
(d) Nitric acid — HNO3
Elements present are: Hydrogen, nitrogen and oxygen.

Question 5.
The valency of aluminium is 3. Write the valency of other radicals present in the following compounds.
(a) Aluminium chloride
(b) Aluminium oxide
(c) Aluminium nitride
(d) Aluminium sulphate
Answer:
(a) Aluminium chloride — (AlCl3) here valency of Al is 3.
Other radical – Chloride (Cl–)
Valency of chloride = 1
(b) Aluminium oxide — (Al2O3)
Here valency of Al is 3
Other radical presents = oxide (O2-)
Valency of O2- = 2
(c) Aluminium nitride — (Al N)
Here valency of aluminium = 3
Another radical = Nitride (N3-)
Valency of nitride (N3-) = 3
(d) Aluminium sulphate — Al2(SO4)3
Here valency of aluminium is 3
Another radical = Sulphate (SO42-)
Valency of (SO42-) = 2

Question 6.
What is variable valency? Give two examples of elements showing variable valency.
Answer:
Variable valency refers to the property of certain elements to exhibit more than one combining power or oxidation state in their compounds. This means that an atom of such an element can form a different number of chemical bonds depending on the specific reaction or the other elements it is bonding with. This usually happens when the element can either lose or share a different number of electrons from its outermost and/or penultimate shells.

Two examples of elements showing variable valency are:

1. Iron (Fe):
   
   • Iron commonly shows a valency of 2 in compounds like iron(II) chloride (FeCl$_2$) or iron(II) oxide (FeO), also known as ferrous chloride and ferrous oxide, respectively. Here, the iron atom loses two electrons.
   • It also commonly shows a valency of 3 in compounds like iron(III) chloride (FeCl$_3$) or iron(III) oxide (Fe$_2$O$_3$), also known as ferric chloride and ferric oxide. In this case, the iron atom loses three electrons.
2. Copper (Cu):
   
   • Copper exhibits a valency of 1 in compounds such as copper(I) oxide (Cu$_2$O) or copper(I) chloride (CuCl), also known as cuprous oxide and cuprous chloride. Here, the copper atom loses one electron.
   • It also shows a valency of 2 in compounds like copper(II) oxide (CuO) or copper(II) sulfate (CuSO$_4$), often called cupric oxide and cupric sulfate. In this instance, the copper atom loses two electrons.

Question 7.
(a) What is a chemical equation?
(b) Why is it necessary to balance a chemical equation?
(c) What are the limitations of a chemical equation?
Answer:
(a) What is a chemical equation?

A chemical equation is a shorthand representation of a chemical reaction using chemical formulas, symbols, and coefficients. It shows the reactants (starting materials) on the left side, the products (substances formed) on the right side, and an arrow pointing from reactants to products, indicating the direction of the reaction.

(b) Why is it necessary to balance a chemical equation?

It is necessary to balance a chemical equation to satisfy the Law of Conservation of Mass.

Balancing ensures that the equation accurately reflects the actual proportions in which substances react and are formed, upholding this universal law.

(c) What are the limitations of a chemical equation?

While chemical equations are powerful tools, they have certain limitations:

1. Does not indicate the rate of reaction: A chemical equation does not tell us how fast or slow a reaction will occur. Some reactions are instantaneous, while others might take years.
2. Does not give information about the physical state of reactants/products (unless explicitly mentioned): Although states (solid (s), liquid (l), gas (g), aqueous (aq)) can be added, they are not inherently part of just the balanced chemical formulas. Without them, the equation doesn’t specify if a substance is a solid, liquid, or gas.

Question 8.
What are the ways by which a chemical equation can be made more informative?
Answer:
Chemical equations are a powerful shorthand for describing reactions. They include states of matter like solid (s) or aqueous (aq), and energy changes are shown by heat values (released if on the product side, absorbed if on the reactant side). Reaction conditions, such as temperature or catalysts, are often written above the arrow. Solution strength can be indicated by (dil) for dilute or (conc) for concentrated.

Question 9.
State the law of conservation of mass.
Answer:
The law of conservation of mass states that matter is neither created nor destroyed in any ordinary chemical or physical change. Although substances may transform (like water freezing or wood burning), the total mass of the reactants will always equal the total mass of the products. Essentially, matter simply changes form, it doesn’t disappear or spontaneously generate.

Question 10.

Differentiate between:
(a) Reactants and products
(b) A balanced and an unbalanced chemical equation

Ans :

(a) Reactants and products

Feature	Reactants	Products
Definition	The starting substances that undergo a chemical change during a reaction.	The new substances that are formed as a result of a chemical reaction.
Position in Equation	Written on the left side of the arrow in a chemical equation.	Written on the right side of the arrow in a chemical equation.
Transformation	Are consumed or used up during the reaction.	Are generated or produced during the reaction.
Chemical Identity	Have a specific set of chemical and physical properties before the reaction.	Have a new and distinct set of chemical and physical properties different from the reactants.
Example	In 2H2​+O2​→2H2​O, H₂ and O₂ are reactants.	In 2H2​+O2​→2H2​O, H₂O is the product.

(b) A balanced and an unbalanced chemical equation

Feature	Balanced Chemical Equation	Unbalanced Chemical Equation (Skeletal Equation)
Law of Conservation of Mass	Obeys the Law of Conservation of Mass.	Does not obey the Law of Conservation of Mass.
Atom Count	The number of atoms of each element is the same on both the reactant and product sides.	The number of atoms of at least one element is different on the reactant and product sides.
Coefficients	Has appropriate stoichiometric coefficients placed in front of chemical formulas to equalize atom counts.	Lacks the necessary stoichiometric coefficients to equalize atom counts, or has incorrect ones.
Accuracy/Realism	Represents the true quantitative relationship between reactants and products in a real reaction.	Represents only the qualitative aspect (what reacts and what is formed) but not the correct proportions.
Example	2H2​+O2​→2H2​O (4 H, 2 O on both sides)	H2​+O2​→H2​O (2 O on left, 1 O on right)

Question 11.
Balance the following equations:

Answer:

Question 12.

12. Write balanced chemical equations for the following word equations:
(a) Iron + Chlorine → Iron (III) chloride
(b) Magnesium + dil sulphuric acid → Magnesium sulphate + water
(c) Magnesium + oxygen → Magnesium oxide
(d) Calcium oxide + water → Calcium hydroxide
(e) Sodium + chlorine → Sodium chloride
Answer:
(a) Iron + Chlorine → Iron (III) chloride
4Fe + 3Cl2 → 2F2Cl3
(b) Magnesium + dil sulphuric acid → Magnesium sulphate + water
2Mg + 2H2SO4 → 2MgSO4 + 2H2
(c) Magnesium + oxygen → Magnesium oxide
2Mg + O2 → 2MgO
(d) Calcium oxide + water → Calcium hydroxide
CaO + H2O → Ca(OH)2
(e) Sodium + chlorine → Sodium chloride
2Na + Cl2 → 2NaCl

Question 13.
What information do you get from the following chemical equation:
Zn(s) + 2HCl (dil) → ZnCl2 (aq) + H2(g)
Answer:The equation Zn(s) + 2HCl(dil) → ZnCl₂(aq) + H₂(g) demonstrates a single displacement reaction: solid zinc reacts with dilute hydrochloric acid to yield aqueous zinc chloride and hydrogen gas. The notation clearly shows the states of matter and the balanced proportions of reactants and products in this irreversible chemical change.