Class 9
Chapter 3 Class 9 - Atoms And Molecules

Example 3.5 - Chapter 3 Class 9 - Atoms And Molecules

Last updated at April 16, 2024 by

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Example 3.5 Calculate the number of particles in each of the following: (i) 46 g of Na atoms (number from mass) Atomic Mass of Na atom = 23 u Molar Mass of Na atom = 23 g Now, Number of moles = (𝐺𝑖𝑣𝑒𝑛 π‘šπ‘Žπ‘ π‘ )/(π‘€π‘œπ‘™π‘Žπ‘Ÿ π‘šπ‘Žπ‘ π‘ ) = 46/23 = 2 Thus, Number of Moles = (π‘π‘’π‘šπ‘π‘’π‘Ÿ π‘œπ‘“ π‘ƒπ‘Žπ‘Ÿπ‘‘π‘–π‘π‘™π‘’π‘ )/(π΄π‘£π‘œπ‘”π‘Žπ‘‘π‘Ÿπ‘œ π‘π‘’π‘šπ‘π‘’π‘Ÿ) Number of particles = Number of moles Γ— Avogadro number = 2 Γ— 6.022 Γ— 1023 = 12.044 Γ— 1023 Example 3.5 Calculate the number of particles in each of the following: (ii) 8 g O2 molecules (number of molecules from mass) Atomic Mass of O atom = 16 u Molar Mass of O2 molecules = 2 Γ— 16 g = 32 g Now, Number of moles = (𝐺𝑖𝑣𝑒𝑛 π‘šπ‘Žπ‘ π‘ )/(π‘€π‘œπ‘™π‘Žπ‘Ÿ π‘šπ‘Žπ‘ π‘ ) = 8/32 = 𝟏/πŸ’ Thus, Number of Moles = (π‘π‘’π‘šπ‘π‘’π‘Ÿ π‘œπ‘“ π‘ƒπ‘Žπ‘Ÿπ‘‘π‘–π‘π‘™π‘’π‘ )/(π΄π‘£π‘œπ‘”π‘Žπ‘‘π‘Ÿπ‘œ π‘π‘’π‘šπ‘π‘’π‘Ÿ) Number of particles = Number of moles Γ— Avogadro number = 1/4 Γ— 6.022 Γ— 1023 = 1.5055 Γ— 1023 Example 3.5 Calculate the number of particles in each of the following: (iii) 0.1 mole of carbon atoms (number from given moles) Now, Number of Moles = (π‘π‘’π‘šπ‘π‘’π‘Ÿ π‘œπ‘“ π‘ƒπ‘Žπ‘Ÿπ‘‘π‘–π‘π‘™π‘’π‘ )/(π΄π‘£π‘œπ‘”π‘Žπ‘‘π‘Ÿπ‘œ π‘π‘’π‘šπ‘π‘’π‘Ÿ) Number of particles = Number of moles Γ— Avogadro number = 0.1 Γ— 6.022 Γ— 1023 = 1/10 Γ— 6.022 Γ— 1023 = 6.022 Γ— 1022

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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo