Selina Concise Chemistry Class 9 ICSE Solutions The Language of Chemistry

Selina Concise Chemistry Class 9 ICSE Solutions The Language of Chemistry

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

Page No: 8

Question 1.
What is a symbol? What information does it convey?
Solution:
A symbol is the short form which stands for the atom of a specific element or the abbreviations used for the names of elements.

1. It represents a specific element.
2. It represents one atom of an element.
3. A symbol represents how many atoms are present in its one gram (gm) atom.
4. It represents the number of times an atom is heavier than one atomic mass unit (amu) taken as a standard.

Question 5(d).
2H₂
Solution:
(a) H stands for one atom of hydrogen.
(b) H₂ stands for one molecule of hydrogen.
(c) 2H stands for two atoms of hydrogen.

1. Valency of Na is +1 because it can lose one electron.
2. Valency of O is -2 because it can accept two electrons.

Variable valency: It is the combining capacity of an element in which the metal loses more electrons from a shell next to a valence shell in addition to electrons of the valence shell.

1. for the lower valency, use the suffix -OUS at the end of the name of the metal
2. for the higher valency, use the suffix -IC at the end of the name of the metal.

Example:

Question 8.
Give the formula and valency of:

1. aluminate ………………… .
2. chromate ………….…….. .
3. aluminium ………………. .
4. cupric  ………………… .

Solution:

Question 9.b
What is the significance of formula?
Solution:
Chemical formula: The chemical formula of a substance (element or compound) is a symbolic representation of the actual number of atoms present in one molecule of that substance.
It also indicates the fixed proportion by weight in which atoms combine.
Rules:
(i) The positive and negative radicals are written side by side (+ve first) with their charge as a superscript on the right side.
(ii) Charges are then interchanged and written as a subscript.
(iii) The final formula is written without the sign of charge, e.g. Hg₂O

1. Hg¹⁺O^2-
   
2. 
3. Hg₂O

Question 10(a).
What do you understand by the following terms?
Acid radical
Solution:
Acid radical: The electronegative or negatively charged radical is called an acid radical.
Examples: Cl^–, O^2-

Question 11.

Match the following:

Solution:

Question 15.
Write the chemical names of the following compounds:

1. Ca₃(PO₄)₂
2. K₂CO₃
3. K₂MnO₄
4. Mn₃(BO₃)₂
5. Mg(HCO₃)₂
6. Na₄Fe(CN)₆
7. Ba(ClO₃)₂
8. Ag₂SO₃
9. (CH₃COO)₂Pb
10. Na₂SiO₃

Solution:
Chemical names of compounds:

1. Ca₃(PO₄)₂ – Calcium phosphate
2. K₂CO₃ – Potassium carbonate
3. K₂MnO₄ – Potassium manganate
4. Mn₃(BO₃)₂ – Manganese (II) borate
5. Mg(HCO₃)₂ – Magnesium hydrogen carbonate
6. Na₄Fe(CN)₆ – Sodium ferrocyanide
7. Ba(ClO₃)₂ – Barium chlorate
8. Ag₂SO₃ – Silver sulphite
9. (CH₃COO)₂Pb – Lead acetate
10. Na₂SiO₃ – Sodium silicate

Question 16
Write the basic radicals and acidic radicals of the following and then write the chemical formulae of these compounds.

1. Barium sulphate
2. Bismuth nitrate
3. Calcium bromide
4. Ferrous sulphide
5. Chromium sulphate
6. Calcium silicate
7. Potassium ferrocyanide
8. Stannic oxide
9. Magnesium phosphate
10. Sodium zincate
11. Stannic phosphate
12. Sodium thiosulphate
13. Potassium manganate
14. Nickel bisulphate

Solution:

Question 16.
Give the names of the following compounds.

1. NaClO
2. NaClO₂
3. NaClO₃
4. NaClO₄

Solution:

1. NaClO – Sodium hypochlorite
2. NaClO₂ – Sodium chlorite
3. NaClO₃ – Sodium chlorate
4. NaClO₄ – Sodium perchlorate

Question 18(a).
Complete the following statements by selecting the correct option :
The formula of a compound represents
i. an atom
ii. a particle
iii. a molecule
iv. a combination
Solution:
iii. The formula of a compound represents a molecule.

Question 18(b).
Complete the following statements by selecting the correct option :
The correct formula of aluminium oxide is
i. AlO₃
ii. AlO₂
 iii. Al₂O₃
Solution:
iii. The correct formula of aluminium oxide is Al₂O₃.

Question 18(c).
Complete the following statements by selecting the correct option :
The valency of nitrogen in nitrogen dioxide (NO₂) is
i. one
ii. two
iii. three
iv. four
Solution:
iv. The valency of nitrogen in nitrogen dioxide (NO₂) is four.

Page No: 13

Solution:
Balanced chemical equations:

1. 3Fe + 4H₂O → Fe₃O₄ + 4H₂
2. 3Ca + N₂ → Ca₃N₂
3. Zn + 2KOH → K₂ZnO₂ + H₂
4. Fe₂O₃ + 3CO → 2Fe + 3CO₂
5. 3PbO + 2NH₃ → 3Pb + 3H₂O + N₂
6. 2Pb₃O₄ → 6PbO + O₂
7. 2PbS + 3O₂ → 2PbO + 2SO₂
8. S + 2H₂SO₄ → 3SO₂ + 2H₂O
9. S + 6HNO₃ → H₂SO₄ + 6NO₂ + 2H₂O
10. MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂
11. C + 2H₂SO₄ → CO₂ + H₂O + SO₂
12. 2KOH + Cl₂ → KCl + KClO + H₂O
13. 2NO₂ + H₂O → HNO₂ + HNO₃
14. Pb₃O₄ + 8HCl → 3PbCl₂ + 4H₂O + Cl₂
15. 2H₂O + 2Cl₂ → 4HCl + O₂
16. 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
17. 2HNO₃ + H₂S → 2NO₂ + 2H₂O + S
18. P + 5HNO₃ → 5NO₂ + H₂O + H₃PO₄
19. Zn + 4HNO₃  → Zn(NO₃)₂ + 2H₂O + 2NO₂

Page No: 17

Question 1.
Fill in the blanks:

1. Dalton used symbol _____ for oxygen _____ for hydrogen.
2. Symbol represents _____ atom(s) of an element.
3. Symbolic expression for a molecule is called _____.  .
4. Sodium chloride has two radicals. Sodium is a _____ radical while chloride is _____ radical.
5. Valency of carbon in CH₄ is _____ , in C₂H₆ _____, in C₂H₄ ___ and in C₂H₂ is ____.
6. Valency of Iron in FeCl₂ is _____  and in FeCl₃ it is ____ .
7. Formula of iron (ill) carbonate is _____ .

Solution:

1. Dalton used symbol [O] for oxygen,[H] for hydrogen.
2. Symbol represents gram atom(s) of an element.
3. Symbolic expression for a molecule is called molecular formula.
4. Sodium chloride has two radicals. Sodium is a basic radical, while chloride is an acid radical.
5. Valency of carbon in CH₄ is 4, in C₂H₆4, in C₂H₄4 and in C₂H₂ is 4.
6. Valency of iron in FeCl₂ is 2 and in FeCl₃ it is 3.
7. Formula of iron (III) carbonate is Fe₂[CO₃]₃.

Question 2.
Complete the following table.

Solution:

Question 3.
Sodium chloride reacts with silver nitrate to produce silver chloride and sodium nitrate

1. Write the equation.
2. Check whether it is balanced, if not balance it.
3. Find the weights of reactants and products.
4. State the law which this equation satisfies.

Solution:
(a) NaCl+ AgNO₃ → NaNO₃ + AgCl↓
(b) It is a balanced equation.
(c) Weights of reactants:NaCl – 58.44, AgNO₃ – 169.87
Weights of products: NaNO₃ – 84.99, AgCl – 143.32
NaCl + AgNO₃ → NaNO₃  + AgCl
(23+35.5) + (108+14+48) → (23+14+48) + (108+35.5)
58.5 + 170 → 85 + 143.5
228.5 g → 228.5 g
(d) Law of conservation of mass: Matter is neither created nor destroyed in the course of a chemical reaction.

1. The actual result of a chemical change.
2. Substances take part in a reaction, and substances are formed as a result of the reaction.
3. Here, one molecule of zinc and one molecule of sulphuric acid react to give one molecule of zinc sulphate and one molecule of hydrogen.
4. Composition of respective molecules, i.e. one molecule of sulphuric acid contains two atoms of hydrogen, one atom of sulphur and four atoms of oxygen.
5. Relative molecular masses of different substances, i.e. molecular mass of
   Zn = 65
   H₂SO₄ = (2+32+64) = 98
   ZnSO₄ = (65+32+64) = 161
   H₂ = 2
6. 22.4 litres of hydrogen are formed at STP.

1. Magnesium reacts with hydrochloric acid to form magnesium chloride and hydrogen gas.
2. 24 g of magnesium reacts with 2(1 + 35.5) = 73 g of hydrochloric acid to produce (24 + 71), i.e. 95 g of magnesium chloride.
3. Hydrogen produced at STP is 22.4 litres.

1. A chemical equation consists of formulae of reactants connected by plus sign (+) and arrow (→) followed by the formulae of products connected by plus sign (+).
2. The sign of an arrow (→) is to read ‘to form’. It also shows the direction in which reaction is predominant.

1. N₂O₃  = N is +3
2. N₂O₅ = N is +5
3. NO₂ = N is +4
4. NO = N is +2

Solution 11.
(a) A molecular formula represent The Molecule of an element or of a Compound.
(b) The molecular formula of water (H₂O) represents 18 parts by mass of water.
(c) A balanced equation obeys the law of conservation of mass wherever unbalanced equation does not obey this law.
(d) CO and Co represent carbon-monoxide and cobalt respectively.

Solution 12.

1. Relative molecular mass of CHCl3
   = 12 + 1 + (3 × 35.5)
   = 12 + 1 + 106.5
   = 119.5
2. Relative molecular mass of (NH4)2 Cr2O7
   = (14 × 2) + (1× 8) + (52 × 2) + (16 × 7)
   = 28 + 8 + 104 + 112
   = 252
3. Relative molecular mass of CuSO4· 5H2O
   = 63.5 + 32 + (16 × 4) + 5(2 + 16)
   = 159.5 + 90
   = 249.5
4. Relative molecular mass of (NH4)2SO4
   = (2 × 14) + (8 × 1) + 32 + (4 × 16)
   = 28 + 8 + 32 + 64
   = 132
5. Relative molecular mass of CH3COONa
   = (12 × 2) + (1× 3) + (16 × 2) + 23
   = 24 + 3 + 32 + 23
   = 82
6. Potassium chlorate (KClO3)
   = 39.1+ 35.5 + (16 × 3)
   = 39.1+ 35.5 + 48
   = 122.6
7. Ammonium chloroplatinate (NH4)2PtCl6
   = (14 × 2) + (1 × 8) + 195.08 + (35.5 × 6)
   = 28 + 8 + 195.08 + 213
   = 444.08

Solution 13.

Solution 14.
Relative molecular mass of MgSO₄·7H₂O
=24 + 32 + (16 × 4) + 7(2 + 16)
=24 + 32 + 64 + 126
=246
26 g of Epsom salt contains 126 g of water of crystallisation.
Hence, 100 g of Epsom salt contains

The % of H₂O in MgSO₄·7H₂O = 51.2

Solution 15.
(a)  Relative molecular mass of Ca(H₂PO₄)₂
= 40.07 + (1 × 4) + (30.9 × 2) + (16 × 8)
= 40.07 + 4 + 61.8 + 128
= 233.87
233.87 g Ca(H₂PO₄)₂ contains 61.8 g P
So, 100 g Ca(H₂PO₄)₂ contains

The % of P in Ca(H₂PO₄)₂ is 26.42%.
(b) Relative molecular mass of Ca₃(PO₄)₂
= (40.07 × 3) + (30.9 × 2) + (16 × 8)
= 120.21 + 61.8 + 128
= 310.01
310.01 g Ca₃(PO₄)₂ contains 61.8 g P
So, 100 g Ca(H₂PO₄)₂ contains
(IMAGE)
The % of P in Ca(H₂PO₄)₂ is 19.93%.

Solution 16.
Relative molecular mass of KClO₃
= 39.09 + 35.5 + (3 × 16)
= 122.59 g

The percentages of K, Cl and O in KClO₃ are 31.9%, 28.9% and 39.1%, respectively.

Solution 17.
Relative molecular mass of urea is

[12 + 16 + 28 + 4] = 60
Hence, relative molecular mass of urea = 60

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