Language of Chemistry Class-8 Dalal Simplified ICSE Chemistry Solutions Chapter-5

Language of Chemistry Class-8 Dalal Simplified ICSE Chemistry Solutions Chapter-5, Language of Chemistry Dr Viraf J Dalal Middle School Allied Publishers Solutions. Chapter-5. We Provide Step by Step Solutions to Questions and Answers of Dr Viraf J Dalal Middle School Chemistry Allied Publishers. Visit official Website CISCE for detail information about ICSE Board Class-8.

Language of Chemistry Class-8 Dalal Simplified ICSE Chemistry Solutions Chapter-5

Board	ICSE
Class	8th
Subject	Chemistry
Book Name	Dalal New Simplified
Chapter-5	Language of Chemistry
Unit-1	Language of Chemistry
Topic	Solution of exercise questions
Session	2023-24

Exercise-1

Language of Chemistry Class-8 Dalal Simplified ICSE Chemistry Solutions Chapter-5

Question: 1. Explain the term ‘symbol’. State a reason why – the symbol of calcium is ‘Ca’ & of copper is ‘Cu’.

Answer: Symbol is a short form or abbreviated name of the element.
                                                          OR
“Symbol of an element is the ‘first letter’ or the ‘first letter and another letter’ of the English name or Latin name of the element”.

As the name calcium and copper start with same letter of English alphabet ‘C’ so another letter from the name of the element is added to ‘C’.
Hence symbol of calcium is ‘Ca’ and symbol of copper or cuprum (Latin name of copper) is ‘Cu’.

Question: 2. Define the term ‘valency’. With reference to water & ammonia as compounds respectively, state the valency of oxygen & nitrogen. Magnesium [2, 8, 2] has valency 2+. Give reasons.

Answer: Valency is the number of hydrogen atoms which combine with (or displace) one atom of the element forming a Compound.

Compound water H₂O, two atoms of hydrogen combine with one atom of oxygen to form water. Hence valency of oxygen atom is 2.
Compound ammonia NH₃.
Valency of atom nitrogen is 3, as it combines with 3 atoms of hydrogen.

Valency of magnesium is 2⁺, Mg [2, 8, 2]
Electronic configuration of Mg is 2, 8, 2 i.e. there are 2 valence electrons which Mg can lose and achieve the stable configuration of nearest noble gas Neon.
Hence is cation Mg²⁺ has valency 2⁺.

Question: 3. Explain the term ‘variable valency’. Copper having electronic configuration 2,8,18,1 exhibits variable valency. Give a reason for the same & name the compound CuCl & CuCl₂.

Answer: “When an element has more than one valency, its valency is called variable valency.” Copper exhibit valency ‘1’ and ‘2’ i.e. has variable valency reason for variable valency:
Valency is the number of electrons lost or gained from the outer shell of an atom of an element – during the chemical reaction. Variation in this gain or loss results in ‘variable valency’.
Lower valency ends with – ous
Higher valency ends with – ic
CuCl is named as cuprous chloride (lower valency)
OR

Cu [I] Cl i.e. Copper [I] chloride and CuCl₂ – Cupric chloride (higher valency) i.e. Copper [II] chloride Cu[II]Cl₂        

Question: 4. State the valences of the following metallic elements –

(a) Potassium
(b) Sodium
(c) Calcium
(d) Magnesium
(e) Zinc
(f) Aluminium
(g) Chromium [write each symbol with the valency]

Answer: Metals have positive valency 1, 2 or 3 ,

Valency of:

(a) Potassium is 1⁺ = K⁺
(b) Sodium 1⁺     = Na⁺
(c) Calcium 2⁺ = Ca²⁺
(d) Magnesium 2⁺ = Mg²⁺
(e) Zinc 2⁺= Zn²⁺
(f) Aluminium 3⁺ = Al³⁺
(g) Chromium 3+ = Cr³⁺

Question: 5. Certain metals exhibit variable valences which include valences: 1+, 2+, 3+ and 4+. State the variable valency of the following metals –

(a) Copper
(b) Silver
(c) Mercury
(d) Iron
(e) tin
(f) Lead

[write each symbol with the variable valency]

Answer: 

S. No.	Element	Symbol	Valency
(a)	Potassium	K1+	1
(b)	Sodium	Na1+	1
(c)	Calcium	Ca2+	2
(d)	Magnesium	Mg2+	2
(e)	Zinc	Zn2+	2
(f)	Aluminium	Al3+	3
(g)	Chromium	Cr3+	3

 

Question: 6. State which of the following ions or radicals given below of non-metallic elements exhibit-valency: 1^–, 2^– & 3^–

(a) Chloride

(b) Bromide

(c) Iodide

(d) Nitrate

(e) Hydroxide

(f) Bicarbonate

(g) Bisulphite

(h) Bisulphate

(i) Aluminate

(j) Permanganate

(k) Oxide

(l) Sulphide

(m) Sulphite

(n) Sulphate

(o) Carbonate

(p) Dichromate

(q) Zincate

(r) Plumbite

(s) Phosphate

(t) Nitride
[write each ion or radical with the correct valency]

Answer: 

Valency	Element/Radical	Ion
1–	Chloride	Cl1-
	Bromide	Br1-
	Iodide	I1-
	Nitrate	NO31-
	Hydroxide	OH1-
	Bicarbonate	HCO31-
	Bisulphite	HSO31-
	Bisulphate	HSO41-
	Aluminate	AlO21-
	Permanganate	MnO41-
2–	Oxide	O2-
	Sulphide	S2-
	Sulphite	SO32-
	Sulphate	SO42-
	Carbonate	CO32-
	Dichromate	Cr2O72-
	Zincate	ZnO22-
	Plumbite	PbO22-
3–	Phosphate	PO43-
	Nitride	N3-

 

Question: 7. Differentiate between the terms – ‘Ion’ & ‘radical’ with suitable examples.

 Answer: Ion: “Ion is an atom or a group of atoms carrying a positive or negative charge due to loss or gain of electrons.” e.g. cation Na⁺ and Cl^1- is the anion.
Radical: “Radical is a group of atoms of elements that behaves like a single unit & show valency.”

Question: 8. Write the chemical formula of the following compounds in a step-by-step manner – 

a] Potassium chloride, b] Sodium bromide, c] Potassium nitrate, d] Calcium hydroxide, e] Calcium bicarbonate, f] Sodium bromide, g] Potassium sulphate, h] Zinc hydroxide, i] Potassium permanganate, j] Potassium dichromate, k] Aluminium hydroxide, l] Magnesium nitride, m] Sodium zincate, n] Copper [II] oxide, o] Copper [I] sulphide, p] Iron [III] chloride, q] Iron [II] hydroxide, r] Iron [III] sulphide, s] Iron [III] oxide

Answer: 

(a) Potassium Chloride:

Potassium chloride	Symbol	Valency
Potassium	K	1+
Chloride	Cl	1−

Positive ion is written first

Interchange the valences

Formula = KCl

(b) Sodium Bromide:

Sodium bromide	Symbol	Valency
Sodium	Na	1+
Bromide	Br	1−

Positive ions are written first

On interchanging the valences

Formula = NaBr

(c) Potassium Nitrate

Potassium nitrate	Symbol	Valency
Potassium	K	1+
Nitrate	NO3	1−

Positive ions are written first

On interchanging the valences

Formula = K(NO3)

(d) Calcium hydroxide

Calcium hydroxide	Symbol	Valency
Calcium	Ca	2+
Hydroxide	OH	1−

Positive ions are written first

On interchanging the valences

Formula = Ca[OH]2

(e) Calcium bicarbonate

Calcium bicarbonate	Symbol	Valency
Calcium	Ca	2+
bicarbonate	HCO3	1−

Positive ions are written first

On interchanging the valences

Formula = NO_3NO3

(f) Sodium Bisulphate

Sodium bisulphate	Symbol	valency
Sodium	Na	1+
Bisulphate	HSO4	1−

Positive ions are written first

On interchanging the valences

Formula = Na(HSO4)

(g) Potassium Sulphate

Potassium sulphate	Symbol	valency
Potassium	K	1+
sulphate	SO4	2−

Positive ions are written first

On interchanging the valences

Formula = K2(SO4)

(h) Zinc Hydroxide

Zinc hydroxide	Symbol	valency
Zinc	Zn	2+
Hydroxide	OH	1−

Positive ions are written first

On interchanging the valences

Formula = Zn[OH]2

(i) Potassium permanganate

Potassium permanganate	Symbol	valency
Potassium	K	1+
permanganate	MnO4	1−

Positive ion is written first

On interchanging the valences

Formula = K[MnO4​]

(j) Potassium dichromate

Potassium dichromate	Symbol	Valency
Potassium	K	1+
dichromate	Cr2O7	2−

Positive ions are written first

On interchanging the valences

Formula= K2​[Cr2​O7​]

(k) Aluminium hydroxide

Aluminium hydroxide	Symbol	Valency
Aluminium	Al	3+
Hydroxide	OH	1−

Positive ions are written first

On interchanging the valences

Formula = Al[OH]3

(l) Magnesium nitride

Magnesium nitride	Symbol	Valency
Magnesium	Mg	2+
Nitride	N	3−

Positive ions are written first

On interchanging the valences

Formula =Mg3​N2

(m) Sodium zincate

Sodium zincate	Symbol	Valency
Sodium	Na	1+
Zincate	ZnO2	2−

Positive ions are written first

On interchanging the valences

Formula = Na2​[ZnO2​]

(n) Copper [II] oxide

Copper [II] oxide	Symbol	Valency
Copper	Cu	2+
Oxide	O	2−

Positive ions are written first

On interchanging the valences

Formula = $CuO$

$(o)\; Copper\; [I]\; sulphide$

Copper $[I]\; sulphide$	Symbol	Valency
Copper	Cu	1+
$sulphide$	S	2−

Positive ions are written first

On interchanging the valences

Formula = Cu2​S

(p) Iron [III] chloride

Iron [III] chloride	Symbol	Valency
Iron	Fe	3+
chloride	Cl	1

Positive ions are written first

On interchanging the valences

Formula = FeCl3

(q) Iron [II] hydroxide

Iron [II] hydroxide	Symbol	Valency
Iron	Fe	2+
hydroxide	OH	1−

Positive ions are written first

On interchanging the valences

Formula =Fe[OH]2

(r) Iron [III] sulphide

Iron [III] sulphide	Symbol	Valency
Iron	Fe	3+
sulphide	S	2−

Positive ions are written first

On interchanging the valences

Formula = Fe2​S3

(s) Iron [III] oxide

Iron [III] oxide	Symbol	Valency
Iron	Fe	3+
oxide	O	2−

Positive ions are written first

On interchanging the valences

Formula = Fe2​O3

Question: 9. What is a chemical equation. How is it represented. Differentiate between a ‘word equation’ and a ‘molecular equation’ with a suitable example.

Answer: A chemical equation is a shorthand form for representing the result of a chemical change.

It is represented with the help of formulas and symbols of the reactants and products.

Word equation	Molecular equation
Zinc + sulphuric acid ⟶ zinc sulphate + Hydrogen	Zn + H2SO4 ⟶ ZnSO4 + H2

Question: 10. State the information provided by a chemical equation. Chemical equations suffer from a number of limitations. State the main limitations of a chemical equation.

Answer: Information provided by a chemical equation :

1. The formulas & symbols of the reactants & products.

2. The physical state of the substance whether it is solid, liquid or gas.

3. The special conditions required such as heat, catalyst, direction of reaction.

4. Tells the ratio in which the substances react in a balanced equation.

Chemical equation do not tell us about:

1. The physical states of the reactants & products – hence [(s) for solids, (g) for gas may be added]

2. The conditions such as temperature, pressure or catalyst which affect the reaction.

3. The concentration of the reactants & products hence [(dil.) dilute & (conc) concentrated may be added.]

4. The nature of the chemical reaction.

5. The speed of the reaction.

6. The heat changes accompanying the reaction.

7. The completion of the reaction.

Question: 11. State what is a balanced equation with a relevant example. Give a reason why an equation is balanced with reference to the law of conservation of matter.

Answer: A balanced equation is one in which the number of atoms of each element of the reactant is equal to the number of atoms of each element of the products.

Zn + H₂SO₄ ⟶ ZnSO₄ + H₂

An equation must be balanced to comply with the ‘law of conservation of matter’ because according to this law : matter is neither created nor destroyed during the chemical change.

Question: 12. Write balanced molecular equations for the following word equations :

1. Calcium + Oxygen → Calcium oxide

2. Calcium + Water → Calcium hydroxide + Hydrogen

3. Zinc + Sulphuric acid → Zinc sulphate + Hydrogen

4. Lead sulphate + Ammonium hydroxide → Ammonium Sulphate + Lead hydroxide

5. Copper hydroxide + Nitric acid → Copper nitrate + Water

6. Lead nitrate + Sodium Chloride → Sodium Nitrate + Lead Chloride

Answer:

1. 2Ca + O₂ ⟶ 2CaO

2. Ca + 2H₂O ⟶ Ca(OH)₂ + H₂

3. Zn + H₂SO₄ ⟶ ZnSO₄ + H₂

4. PbSO₄ + 2NH₄OH ⟶ (NH₄)₂SO₄ + Pb(OH)₂

5. Cu(OH)₂ + 2HNO₃ ⟶ Cu(NO₃)₂ + 2H₂O

6. PbNO₃ + NaCl ⟶ NaNO₃ + PbCl

Question: 13. Balance the following equations: 

(a) P + O₂ ⟶ P₂O₅

(b) Na₂O + H₂O ⟶ NaOH

(c) K + H₂O ⟶ KOH + H₂

(d) Fe + H₂O ⇌ Fe₃O₄ + H₂

(e) CaO + HCl ⟶ CaCl₂ + H₂O

(f) Fe + Cl₂ + FeCl₃

(g) Al + H₂O ⟶ Al₂O₃ + H₂

(h) Al + H₂SO₄ ⟶ Al₂(SO₄)₃ + H₂

(i) Fe₂O₃ + H₂ ⟶ Fe + H₂O

(j) C + H₂SO₄ ⟶ CO₂ + H₂O + SO₂

(k) Pb₃O₄ ⟶ PbO + O₂

(l) Al + O₂ ⟶ Al₂O₃

(m) NO + O₂ ⟶ NO₂

(n) ZnS + O₂ ⟶ ZnO + SO₂

(o) Pb₃O₄ + HCl ⟶ PbCl₂ + H₂O + Cl₂

(p) ZnO + NaOH ⟶ Na₂ZnO₂ + H₂O

(q) H₂S + Cl₂ ⟶ S + HCl

(r) FeCl₃ + NaOH ⟶ NaCl + Fe(OH)₃

(s) Fe₂O₃ + CO ⟶ Fe + CO₂

(t) KHCO₃ ⟶ K₂CO₃ + H₂O + CO₂

(u) CuO + NH₃ ⟶ Cu + H₂O + N₂

Answer:

(a) 4P + 5O₂ ⟶ 2P₂O₅

(b) Na₂O + H₂O ⟶ 2NaOH

(c) 2K + 2H₂O ⟶ 2KOH + H₂

(d) 3Fe + 4H₂O ⇌ Fe₃O₄ + 4H₂

(e) CaO + 2HCl ⟶ CaCl₂ + H₂O

(f) 2Fe + 3Cl₂ + 2FeCl₃

(g) 2Al + 3H₂O ⟶ Al₂O₃ + 3H₂

(h) 2Al + 3H₂SO₄ ⟶ Al₂(SO₄)₃ + 3H₂

(i) Fe₂O₃ + 3H₂ ⟶ 2Fe + 3H₂O

(j) C + 2H₂SO₄ ⟶ + CO₂ + 2H₂O + 2SO₂

(k) 2Pb₃O₄ ⟶ 6PbO + O₂

(l) 4Al + 3O₂ ⟶ 2Al₂O₃

(m) 2NO + O₂ ⟶ 2NO₂

(n) 2ZnS + 3O₂ ⟶ 2ZnO + 2SO₂

(o) Pb₃O₄ + 8HCl ⟶ 3PbCl₂ + 4H₂O + Cl₂

(p) ZnO + 2NaOH ⟶ Na₂ZnO₂ + H₂O

(q) H₂S + Cl₂ ⟶ S + 2HCl

(r) FeCl₃ + 3NaOH ⟶ 3NaCl + Fe(OH)₃

(s) Fe₂O₃ + 3CO ⟶ 2Fe + 3CO₂

(t) 2KHCO₃ ⟶ K₂CO₃ + H₂O + CO₂

(u) 3CuO + 2NH₃ ⟶ 3Cu + 3H₂O + N₂

– : End of Language of Chemistry Class-8 Dalal Simplified Solutions :–

Return to –  Dalal Simplified Chemistry for ICSE Class-8 Solutions

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