Selina Concise Chemistry 2023 solutions for class 8 Chemistry. Chapter 5 – Language of Chemistry is provided here with simple step-by-step explanations. These solutions for the Language of Chemistry are extremely popular among class 10 students. The Language of Chemistry solution is handy for quickly completing your homework and preparing for exams.
| Book Name | : Concise Chemistry Middle School |
| Subject | : Chemistry |
| Class | : 8 |
| Publisher | : Selina Publisher PVT Ltd |
| Chapter Name | : Language of Chemistry |
Question 1
Define:
- Radical
- Valency
- Molecular formula
Answer
- Radical: In chemistry, a radical is a species of molecule or atom that has one or more unpaired electrons.
- Valency: Valency, also known as the combining capacity of an atom or molecule, refers to the number of electrons an atom or molecule can either gain, lose, or share to form a stable compound.
- Molecular formula: A molecular formula is a symbolic representation of a molecule that shows the number and types of atoms in the molecule.
Question 2
Give the symbols and valencies of the following radicals:
- Hydroxide
- Chloride
- Carbonate
- ammonium
- Nitrate
Answer
| Radical | Symbol | Valency |
|---|---|---|
| Hydroxide | OH⁻ | -1 |
| Chloride | Cl⁻ | -1 |
| Carbonate | CO₃²⁻ | -2 |
| Ammonium | NH₄⁺ | +1 |
| Nitrate | NO₃⁻ | -1 |
Question 3
Write the molecular formulae for the oxides and sulphides of the following elements.
- Sodium
- Calcium
- Hydrogen
Answer
| Element | Oxide | Sulphide |
|---|---|---|
| Sodium | Na₂O | Na₂S |
| Calcium | CaO | CaS |
| Hydrogen | H₂O | H₂S |
Question 4
Write the molecular formulae for the following compounds and name the elements present.
- Baking soda
- Sulphuric acid
- Common salt
- Nitric acid
Answer
| Compound | Formula | Elements |
|---|---|---|
| Baking soda | NaHCO₃ | Sodium, Hydrogen, Carbon, Oxygen |
| Sulphuric acid | H₂SO₄ | Hydrogen, Sulphur, Oxygen |
| Common salt | NaCl | Sodium, Chlorine |
| Nitric acid | HNO₃ | Hydrogen, Nitrogen, Oxygen |
Question 5
The valency of aluminium is 3. Write the valency of other radicals present in the following compounds.
- Aluminium chloride
- Aluminium oxide
- Aluminium nitride
- Aluminium sulphate
Answer
- Aluminium chloride: AlCl₃ has chloride (Cl⁻) as the other radical. Since the valency of aluminium is 3 and the valency of chloride is 1, three chloride ions are required to balance the charge of one aluminium ion. So, the valency of chloride in aluminium chloride is -1.
- Aluminium oxide: Al₂O₃ has oxide (O²⁻) as the other radical. Since the valency of aluminium is 3 and the valency of oxide is 2, two aluminium ions and three oxide ions are required to balance the charge. So, the valency of oxide in aluminium oxide is -2.
- Aluminium nitride: AlN has nitride (N³⁻) as the other radical. Since the valency of aluminium is 3 and the valency of nitride is 3, one aluminium ion and one nitride ion are required to balance the charge. So, the valency of nitride in aluminium nitride is -3.
- Aluminium sulphate: Al₂(SO₄)₃ has sulphate (SO₄²⁻) as the other radical. Since the valency of aluminium is 3 and the valency of sulphate is 2, two aluminium ions and three sulphate ions are required to balance the charge. So, the valency of sulphate in aluminium sulphate is -2.
Question 6
What is variable valency? Give two examples of elements showing variable valency.
Answer
Variable valency, also known as variable oxidation state, is the ability of an element to exhibit multiple valencies or oxidation states depending on the chemical environment.
Two examples of elements showing variable valency are:
- Iron (Fe): Iron can exhibit a valency of +2 or +3.
- Copper (Cu): Copper can exhibit a valency of +1 or +2.
Question 7
- What is a chemical equation?
- Why it is necessary to balance a chemical equation?
- What are the limitations of a chemical equation?
Answer
- A chemical equation is a symbolic representation of a chemical reaction that shows the reactants, products, and their respective stoichiometric coefficients.
- It is necessary to balance a chemical equation because it follows the law of conservation of mass, which states that matter can neither be created nor destroyed, only transformed from one form to another.
- The limitations of a chemical equation include:
- It does not show the mechanism or intermediate steps involved in the reaction.
- It assumes that the reaction proceeds to completion, which is not always the case in practice due to factors such as reversibility and side reactions.
- It assumes ideal reaction conditions, which may not be achievable in practice.
- It does not take into account the energy changes or the rate of the reaction.
- It does not account for the presence of catalysts or other factors that may affect the reaction rate or pathway.
Question 8
What are the ways by which a chemical equation can be made more informative?
Answer
The ways by which a chemical equation can be made more informative are
- State the physical state of reactants and products.
- Include the energy changes involved.
- Write the mechanism of the reaction.
- Mention the reaction conditions such as temperature, pressure, or pH.
- Indicate the type of reaction, such as acid-base, redox, or precipitation.
Question 9
State the law of conservation of mass.
Answer
The law of conservation of mass states that in any chemical reaction, the total mass of the reactants is equal to the total mass of the products.
In other words, matter can neither be created nor destroyed in a chemical reaction, only transformed from one form to another.
Question 10
Differentiate between :
- Reactants and products
- A balanced and an unbalanced chemical equation
Answer
(a) Reactants and products
| Reactants | Products |
|---|---|
| Starting substances in a chemical reaction | Substances produced by a chemical reaction |
| Appear on the left side of the arrow in a chemical equation | Appear on the right side of the arrow in a chemical equation |
(a) A balanced and an unbalanced chemical equation
| Balanced Chemical Equation | Unbalanced Chemical Equation |
|---|---|
| A chemical equation where the number of atoms of each element in the reactants is equal to the number of atoms of each element in the products | A chemical equation where the number of atoms of each element in the reactants is not equal to the number of atoms of each element in the products |
| All chemical equations should be balanced | Only incomplete chemical equations are unbalanced |
Question 11
Balance the following equations:
- N2 + H2 → NH3
- H2 + O2 → H2O
- Na2O + H2O → NaOH
- CO + O2 → CO2
- Zn + HCl → ZnCl2 + H2
Answer
- N2 + 3H2 → 2NH3
- 2H2 + O2 → 2H2O
- Na2O + H2O → 2NaOH
- 2CO + O2 → 2CO2
- Zn + 2HCl → ZnCl2 + H2
Question 12
Write balanced chemical equations for the following word equations:
- Iron + Chlorine → Iron (III) chloride
- Magnesium + dil. sulphuric acid → Magnesium sulphate + water
- Magnesium + oxygen→ Magnesium oxide (d) Calcium oxide + water → Calcium hydroxide
- Sodium + chlorine → Sodium chloride
Answer
- 2Fe + 3Cl2 → 2FeCl3
- Mg + H2SO4 → MgSO4 + 2H2O
- 2Mg + O2 → 2MgO
- CaO + H2O → Ca(OH)2
- 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 reactants of the reaction: solid zinc (Zn) and dilute hydrochloric acid (HCl).
- The products of the reaction: aqueous zinc chloride (ZnCl2) and hydrogen gas (H2).
- The stoichiometric coefficients of the reactants and products: 1 molecule of solid zinc reacts with 2 molecules of dilute hydrochloric acid to produce 1 molecule of aqueous zinc chloride and 1 molecule of hydrogen gas.
- The balanced chemical equation, which represents the chemical reaction between the reactants and products.
- The physical state of each substance in the reaction: solid (s), liquid (l), gas (g), or aqueous (aq).
