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 Cl1- 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 = 

(e) Calcium bicarbonate
Calcium bicarbonate Symbol Valency
Calcium Ca 2+
bicarbonate HCO3 1−

Positive ions are written first

On interchanging the valences

Formula = NO_3

(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 = 

(i) Potassium permanganate
Potassium permanganate Symbol valency
Potassium K 1+
permanganate MnO4 1−

Positive ion is written first

On interchanging the valences

Formula = 

(j) Potassium dichromate
Potassium dichromate Symbol Valency
Potassium K 1+
dichromate Cr2O7 2−

Positive ions are written first

On interchanging the valences

Formula= 

(k) Aluminium hydroxide
Aluminium hydroxide Symbol Valency
Aluminium Al 3+
Hydroxide OH 1−

Positive ions are written first

On interchanging the valences

Formula = 

(l) Magnesium nitride
Magnesium nitride Symbol Valency
Magnesium Mg 2+
Nitride N 3−

Positive ions are written first

On interchanging the valences

Formula =

(m) Sodium zincate
Sodium zincate Symbol Valency
Sodium Na 1+
Zincate ZnO2 2−

Positive ions are written first

On interchanging the valences

Formula = 

(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 = 

Copper Symbol Valency
Copper Cu 1+
S 2−

Positive ions are written first

On interchanging the valences

Formula = 

(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 = 

(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 =

(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 = 

(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 = 

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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