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Class-8 Dalal Simplified Language of Chemistry ICSE Solutions

Class-8 Dalal Simplified Language of Chemistry ICSE Dr Viraf J Dalal Middle School Allied Publishers Solutions. Chapter-5. We Provide Step by Step Solutions of Exercise/Lesson -5 Language of Chemistry with Objective Type Questions, Fill in the blanks and Give reason , Match the following of Dr Viraf J Dalal Middle School Chemistry Allied Publishers. Visit official Website CISCE for detail information about ICSE Board Class-8.

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Language of Chemistry Class-8 Dalal ICSE New Simplified Dr Viraf J Dalal Middle School Allied Publishers Solutions. Chapter-5


EXERCISE-5

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

Symbol is a short form for the name of an element. It is the first letter and another letter of the name of an element.

For calcium, ‘C’ is the first letter and ‘a’ is another letter, hence ‘Ca’ for calcium.

For copper, cuprum is the latin name of copper. ‘C’ is the first letter and ‘u’ is another letter, hence ‘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 2:

Valency is the number of particular atoms combined with or displaced with another atom to form a compound.

Water which is H_2O, two atoms of hydrogen combine with one atom of oxygen. The valency of oxygen is 2, because it needs two atoms of hydrogen to form water.

Ammonia which is NH_3 , One atom of nitrogen combines with 3 atoms of hydrogen. The valency of nitrogen is 3 because it needs 3 atoms of hydrogen to form ammonia.

Magnesium has valency equal to 2+ because the electronic configuration of Mg is [2,8,2]. The nearest noble gas to magnesium is neon with electronic configuration of [2,8], to achieve this stable electronic configuration Mg can lose 2 valence electrons, hence its valency is 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 CuCI & CuCl2.
Answer 3:
When an element does not have a specific valency, its valency is called variable valency. Copper has valency ‘1’ and ‘2’ that is the number of electrons lost or gained is 1 or 2 in different compounds..

Cu [I] Cl i.e. Copper [I] chloride

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

Question 4.
State the valencies 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 4:
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 valencies which include valencies: 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 5:

(a) Copper: Valency = 1 and 2,

Cu{1+} is cuprous and Cu{2+} is cupric

(b) Silver: Valency is 1 and 2,

Ag{1+} is argentous and Ag{2+} is argentic

(c) Mercury: Valency is 1 and 2,

Hg{1+} is mercurous and Hg{2+} is mercuric.

(d) Iron: Valency is 2 and 3,

Fe{2+} is ferrous and Fe{3+} is ferric.

(e) Tin: Valency is 2 and 4,

Sn{2+} is stanous and Sn{4+} is stanic.

(f) Lead: Valency is 2 and 4,

Pb{2+} is plumbous and Pb{4+} and plumbic.

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 6:

write each ion or radical with the correct valency

new-simplified-chemistry-class-8-icse-solutions-language-of-chemistry - 6

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

An atom or group of atoms which carry a positive or negative charge due to loss or gain of electrons are called ions. Positive ions are cation Na+ and negative ions are anion Cl1-

A group of atoms of elements that behave like a single unit and have charge /valency are called radicals.

Positive radical [NH41+ ] Ammonium
Negative radical [NO31-] Nitrate

An Ion “is an atom or a group of atoms carrying a positive or negative charge due to loss or gain of electrons.”

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 bisulphate

(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 8:

(a) Potassium Chloride:

Symbol Valency
Potassium K 1+
Chlorine Cl 1-

Positive ions are written first

On interchanging the valencies

Formula =

(b) Sodium Bromide

Symbol Valency
Sodium Na 1+
Bromide Br 1-

Positive ions are written first

On interchanging the valencies

Formula = NaBr

(c) Potassium Nitrate

Symbol Valency
Potassium K 1+
Nitrate NO3 1-

Positive ions are written first

On interchanging the valencies

Formula = K(NO3)

(d) Calcium hydroxide

Symbol Valency
Calcium Ca 2+
Hydroxide OH 1-

Positive ions are written first

On interchanging the valencies

Formula =

(e) Calcium bicarbonate

Symbol Valency
Calcium Ca 2+
Bicarbonate [[> widget id=”10″ <]] 1-

Positive ions are written first

On interchanging the valencies

Formula = NO_3

(f) Sodium Bisulphate

Symbol Valency
Sodium Na 1+
Bisulphate HSO4 1-

Positive ions are written first

On interchanging the valencies

Formula = Na(HSO4)

(g) Potassium Sulphate

Symbol Valency
Potassium K 1+
Sulphate SO4 2-

Positive ions are written first

On interchanging the valencies

Formula = K2(SO4)

(h) Zinc Hydroxide

Symbol Valency
Zinc Zn 2+
Hydroxide OH 1-

Positive ions are written first

On interchanging the valencies

Formula =

(i) Potassium permanganate

Symbol Valency
Potassium K 1+
Permanganate MnO4 1-

Formula =

(j) Potassium dichromate

Symbol Valency
Potassium K 1+
Dichromate Cr2O7 2-

Positive ions are written first

On interchanging the valencies

Formula=

(k) Aluminium hydroxide

Symbol Valency
Aluminium Al 3+
Hydroxide [OH] 1-

Positive ions are written first

On interchanging the valencies

Formula =

(l) Magnesium nitride

Symbol Valency
Magnesium Mg 2+
Nitride N 3-

Positive ions are written first

On interchanging the valencies

Formula =

(m) Sodium zincate

Symbol Valency
Sodium Na 1+
Zincate ZnO2 2-

Positive ions are written first

On interchanging the valencies

Formula =

(n) Copper [II] oxide

Symbol Valency
Copper Cu 2+
Oxide O 2-

Positive ions are written first

On interchanging the valencies

Formula =

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