Chapter 4 The language of Chemistry Class 9 Frank Chemistry

Frank Solutions for Chapter 4 The Language of Chemistry Class 9 Chemistry ICSE

1. What do you understand by the terms symbol and formula ?

Answer

Symbol- It is the short form or abbreviation used for the name of an element. It represents one atom of that element.

Formula– Formula of a compound represents the composition of a molecule of the substance in terms of the symbols of the elements present in the molecule.

2. Write the formula for the following compounds.

(a) Calcium carbonate

(b) Magnesium sulphate

(c) Ferric sulphate

(d) Calcium bicarbonates

(e) Cuprous iodide

(f) Potassium dichromate

(g) Potassium permanganate

(h) Sodium sulphate

(i) Magnesium nitrate

(j) Calcium phosphate

Answer

(a) CaCO₃

(b) MgSO₄

(c) Fe₂(SO₄)₃

(d) CaHCO₃

(e) Cul

(f) K₂Cr₂O₇

(g) KMnO₄

(h) Na₂SO₄

(i) Mg(NO₃)₂

(j) Ca₃(PO₄)₂

3. (a) Define the term valency.

(b) Arrange the following elements in the increasing order of the their valencies: phosphorous, helium, carbon, sodium, magnesium.

Answer

(a) Valency – The combining capacity of an element is called its valency.

(b) Helium < Sodium < Magnesium < Carbon < Phosphorous

4. Which law govern a completely balanced equation ?

Answer

Law of conservation of matter governs a completely balanced equation. It states that “matter can neither be created nor destroyed”.

5. What does a symbol signify?

Answer

A symbol signifies one atom of that element.

6. What are the latin name of iron, tin, lead, sodium, potassium and mercury?

Answer

Latin names of the following compounds are –

Iron – Ferrum

Tin - Stannum

Lead - Plumbum

Sodium - Natrium

Potassium - Kalium

Mercury - Hydragyrum

7. What is balanced chemical equation ?

Answer

The equation in which the total number of atoms of each element in the reactants, on the left side of the equation is same as number of atoms in the products formed, on the right side of the equation is called as balanced chemical equation.

8. Write down balanced chemical equation, giving as much information as possible, for the following reactions.

(a) A piece of magnesium, when burnt in nitrogen, forms solid magnesium nitride.

(b) A piece of potassium violently reacts with water to form an aqueous solution of potassium hydroxide and to liberate hydrogen.

Answer

(a) 3Mg + N₂ → Mg₃N₂

(b) 2K + 2H₂O → 2KOH + H₂

9. What information is conveyed by a chemical equation?

Answer

A chemical equation gives information about –

1. What substances enter into a given reaction (reactants) and what products are formed as a result of the reaction.
2. (The quantities of the reactants and the product formed.
3. The optimum conditions of temperature and pressure.

10. Balance the following equations by hit and trial or partial equation methods:

(a) FeCl₃ + NaOH → Fe(OH)₃ + NaCl

(b) NH₃ + O₂ → NO + H₂O

(c) P₂O₅ + H₂O → H₃PO₄

(d) H₂S + SO₂ → S + H₂O

(e) KMnO₄ + HCl → KCl + MnCl₂ + H₂O + Cl₂

Answer

(a) FeCl₃ + 3NaOH → Fe(OH)₃ + 3NaCl

(b) 4NH₃ + 5O₂ → 4NO + 6H₂O

(c) P₂O₅ + 3H₂O → 2H₃PO₄

(d) 2H₂S + SO₂ → 3S + 2H₂O

(e) 2KMnO₄ + 16HCl → 2KCl + 2MnCl₂ + 8H₂O + 5Cl₂

11. What do the symbols H₂, O₄ and S mean in the formula H₂SO₄ ?

Answer

H₂ means hydrogen, O₄ means oxygen and S means sulphur in the formula of H₂SO₄.

12. An element for ‘Z’ forms an oxide ZO₃.

(a) What is the valency of the element Z ?

(b) What will be the formula of the fluoride of Z ?

Answer

(a) The highest valency of the element Z is six.

(b) The formula of the fluoride of Z will be ZF₆.

13. An element ‘X’ forms the following compounds with hydrogen, carbon and oxygen : H₂X, CX₂, XO₂, XO₃. State the three valencies of element ‘X’. Which are illustrated by these compounds ?

Answer

The three valencies of element are –

1. Two – Since the element X combines with two hydrogen to form H₂X and two atoms of X combines with one carbon to form CX₂.
2. Four – Since the element X combines with two oxygen to form XO₂.
3. Six – Since the element X combines with three oxygen to form XO₃.

14. Explain the term variable valency. Why some elements show variable valency, give examples.

Answer

Variable valency – Some elements are capable of showing more than one valency in their compounds called variable valency. i.e. Some elements show variable i.e. more than one valency since these elements have more than one common valency state.

15. What is a chemical formula ? What is the rule for writing a formula correctly?

Answer

Chemical formula – It represents the composition of a molecule of the substance in terms of the symbols of the elements present in the molecule. The rule for writing the formula is criss – cross method.

1. The positive and negative radicals are represented by their symbols and written side by side with the correct valency written below each.
2. The valencies are divided by their highest common factor if any to get the simplest ratio.
3. These numbers are then interchanged and written as subscripts.

16. Write the following equations and balance them :

(a) Iron + Sulphuric acid → Ferrous sulphate + Hydrogen

(b) Copper + Nitric acid → Copper nitrate + Nitric oxide + Water

(c) Ammonia + Oxygen → Nitric oxide + water

(d) Zinc sulphide + Oxygen → Zinc oxide + Sulphur dioxide

(e) Aluminium + Sodium hydroxide + Water → Sodium aluminate + Hydrogen

Answer

(a) Fe + H₂SO₄ → FeSO₄ + H₂

(b) 3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 4H₂O

(c) 2NH₃ + O₂ → 2NO + 3H₂O

(d) ZnS + O₂ → ZnO + SO₂

(e) 2AI + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂

17. Name the following compounds:

(a) NaHCO₃

(b) Na₃Fe(CN)₆

(c) Mn₃(BO₃)₂

(d) Ca₃(PO₄)₂

(e) K₂MnO₄

Answer

(a) Sodium hydrogencarbonate

(b) Sodium hexacyanoferrate (III)

(c) Manganese (II) borate

(d) Calcium phosphate

(e) Potassium manganite (VI)

18. What is the difference between Co and CO?

Answer

Co stands for cobalt which is an element while CO stands for carbon monoxide which is a compound.

19. What is radical? Give two examples monovalent and trivalent radicals.

Answer

Radical - A radical is an atom or a group of atoms of same or different elements that behaves in the manner of positive or negative ion. Radicals have their own combining power (valency) and chemical formulae.

Examples:

Monovalent radicals – H^- , OH^- , Cl - , NO3- , H+, Na+, K+, NH₄⁺

Trivalent radicals – PO₄^3-, Fe(CN)₆^3-, AsO₃^3-, N^3-, Fe³⁺, Al³⁺, Bi³⁺, Au³⁺

20. What are the modifications made in a chemical equation to overcome the limitations of it in providing information ?

Answer

The modifications made in a chemical equation to overcome the limitations of it in providing information are –

(i) Physical states of the reactants and products are abbreviated and written after the substance in brackets. Ex solid(s), liquid(l), gas(g), aqueous(aq), dilute(dil.), concentrate(conc.).

(ii) Substances evolving as gases in the products are shown by the upward arrow (↑), ex – H₂ (↑). The substances precipitating down in reaction are shown by downward arrow (↓), ex – BaSO₄ (↓)

(iii) Condition of temperature, pressure or catalyst written above and below the horizontal arrow (→) after the reactants.

(iv)

 21. What do you understand by (a) Anion, (b) Cation?

Answer

(a) Anion - Negatively charged radicals are termed as anions.

(b) Cation – Positively charged radicals are termed as cations.

22. What are the disadvantages associated with hit and trial method of balancing the equations.

Answer

Disadvantages associated with hit and trial method of balancing of equations –

1. It is tedious and takes a long time.
2. The methods is rather difficult for balancing such equations which contain the same element being repeated in a number of compounds.
3. It does not give any information regarding the mechanism of the reaction.