Page 152 - Chemistry ICSE Class X

138 ICSE Chemistry – 10

EXAMPLE 5.27. Calculate the volume of oxygen at NTP obtained by
decomposing 12.26 g of KClO .
3
Solution: KClO decomposes as follows,
3
heat
2KClO o 2KCl(s) + 3O (g)
2
3
2 mol 3 mol
2 × (39 + 35.5 + 48) g 3 × 22.4 L
(2 × 122.5) g = 245g 67.2 L
Thus,
12.26 × 67.2
12.26 g of KClO gives L = 3.36 L of oxygen
3
245
So, 12.26 g of KClO on decomposing gives 3.36 L of oxygen gas at NTP.
3
ASSIGNMENT 4
Composition of a compound, Determination of empirical and molecular formulae,
Calculations based on chemical equations

ϭ͘ ĂůĐƵůĂƚĞ ƚŚĞ ƉĞƌĐĞŶƚĂŐĞ ŽĨ ŽdžLJŐĞŶ ŝŶ ƐƵŐĂƌ ; H O Ϳ͘ ZĞůĂƟǀĞ ĂƚŽŵŝĐ ŵĂƐƐĞƐ ĂƌĞ͗ с ϭϮ͕ , с ϭ ĂŶĚ K с ϭϲ͘ [Ans. ϱϭ͘ϱ]
ϭϮ ϮϮ ϭϭ
Ϯ͘ tŚĂƚ ǁŽƵůĚ LJŽƵ ĐŽŶĐůƵĚĞ ŝĨ ƚŚĞ ŐŝǀĞŶ ŵĂƐƐ ƉĞƌĐĞŶƚĂŐĞ ŽĨ ǀĂƌŝŽƵƐ ĞůĞŵĞŶƚƐ ŝŶ ĂŶLJ ĐŽŵƉŽƵŶĚ ĚŽ ŶŽƚ ĂĚĚ ƵƉ ƚŽ ϭϬϬй͍
ϯ͘ ,Žǁ ĚŽĞƐ Ă ŵŽůĞĐƵůĂƌ ĨŽƌŵƵůĂ ĚŝīĞƌ ĨƌŽŵ ĂŶ ĞŵƉŝƌŝĐĂů ĨŽƌŵƵůĂ͍
ϰ͘ ,Žǁ ŝƐ ƚŚĞ ŵŽůĞĐƵůĂƌ ĨŽƌŵƵůĂ ŽĨ Ă ĐŽŵƉŽƵŶĚ ƌĞůĂƚĞĚ ƚŽ ŝƚƐ ĞŵƉŝƌŝĐĂů ĨŽƌŵƵůĂ͍
ϱ͘ ,Žǁ ĚŽĞƐ ƚŚĞ ŵŽůĞĐƵůĂƌ ĨŽƌŵƵůĂ ŽĨ ĂŶ ĞůĞŵĞŶƚ ĚŝīĞƌ ĨƌŽŵ ƚŚĂƚ ŽĨ Ă ĐŽŵƉŽƵŶĚ͍
ϲ͘ ĐŽŵƉŽƵŶĚ ŚĂƐ Ă ĐŚĞŵŝĐĂů ĨŽƌŵƵůĂ ů O ͘ ŶƐǁĞƌ ƚŚĞ ĨŽůůŽǁŝŶŐ ƋƵĞƐƟŽŶƐ͗
Ϯ ϯ
;ĂͿ EĂŵĞ ƚŚĞ ĞůĞŵĞŶƚƐ ƉƌĞƐĞŶƚ ŝŶ ƚŚŝƐ ĐŽŵƉŽƵŶĚ͘
;ďͿ EĂŵĞ ƚŚĞ ĐŽŵƉŽƵŶĚ ƌĞƉƌĞƐĞŶƚĞĚ ďLJ ƚŚĞ ĨŽƌŵƵůĂ͘
;ĐͿ tŚĂƚ ŝƐ ƚŚĞ ǀĂůĞŶĐLJ ŽĨ ů ĂŶĚ K͍
ϳ͘ ^ŽĚŝƵŵ ĐŚůŽƌŝĚĞ ĐŽŶƚĂŝŶƐ ϯϵ͘ϰй ƐŽĚŝƵŵ ĂŶĚ ϲϬ͘ϱй ĐŚůŽƌŝŶĞ͘ ^ŚŽǁ ďLJ ĐĂůĐƵůĂƟŽŶƐ ƚŚĂƚ ŝƚƐ ĞŵƉŝƌŝĐĂů ĨŽƌŵƵůĂ ŝƐ EĂ ů͘
ƚŽŵŝĐ ŵĂƐƐĞƐ ĂƌĞ͗ EĂ с Ϯϯ Ƶ ĂŶĚ ů с ϯϱ͘ϱ Ƶ͘
ϴ͘ >ŝƐƚ ĨĞǁ ƐƵďƐƚĂŶĐĞƐ͕ ;ĂͿ ǁŚŽƐĞ ĨŽƌŵƵůĂĞ ƉƌŽƉĞƌůLJ ƌĞƉƌĞƐĞŶƚ ƚŚĞŝƌ ŵŽůĞĐƵůĂƌ ĐŽŵƉŽƐŝƟŽŶƐ͕ ĂŶĚ ;ďͿ ǁŚŽƐĞ ƐŝŵƉůĞƐƚ ĨŽƌŵƵůĂĞ
ĚŽ ŶŽƚ ƌĞƉƌĞƐĞŶƚ ĚŝƐĐƌĞƚĞ ĂŶĚ ŝŶĚŝǀŝĚƵĂů ŵŽůĞĐƵůĞƐ͘

Let us Answer Some More Questions

1. &GſPG VJG VGTO OQNG 9JCV KU VJG PQVCVKQP QH VJG OQNG WPKV!
2. What is meant by the term molar mass?
3. What is meant by molar volume?
4. What is the molar volume of a gaseous substance under NTP conditions?
5. How will you calculate the number of moles of a gaseous substance present in V mL (at NTP) of it?
6. Describe: (a) Normal temperature and pressure (NTP) (b) Standard temperature and pressure (STP)
7. (a) State Gay-Lussac’s law of combining volumes.
(b) Illustrate the above law by taking a typical reaction involving gases.
8. State Avogadro’s law.
9. C &GſPG CVQOKEKV[ QH C OQNGEWNG
(b) Give two examples each of monatomic, diatomic and triatomic molecules.
10. Derive the relationship, Molecular mass = 2 × Vapour density.
11. How many particles are there in one mole of a substance?
12. How much volume (at NTP) would an Avogadro’s number of particles of a gaseous substance occupy?
13. What is the unit of molar mass?
14. What is the atomic mass unit? Is atomic mass unit a practical unit? Describe a practical unit for the amount of a
chemical substance.
15. Write the value of the Avogadro’s number? How much one Avogadro number of carbon atoms would weigh?