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Q. 22

What is meant by the term ‘mole’? Calculate the number of moles in

(a) 3.011 × 10²³ atoms of C

(b) 32 g of oxygen gas

[N_A = 6.022 × 10²³ mol^–1, At. mass of O = 16 u and C = 12 u]

Class 9th Together with Science 3. Atoms and Molecules

Answer :

Mole: One mole of any species (Atoms, molecules, ions or particles) is that quantity in number having a mass equal to its atomic or molecules mass in grams.

(a) We will convert 1.0505 × 10²³ atoms of C into number of moles:

We know, 1 mole = 6.022 × 10²³(N_a = Avogadro’s number)

Number of moles = 0.5

Thus, the number of moles in 3.011 × 10²³ atoms of C is 0.5.

(b) Given mass: 32g

Molar mass of oxygen gas (O₂) = 2 × atomic mass of oxygen = 2 × 16 u = 32g /mol

To calculate the number of moles, we will apply the formula given below:

Number of mole = 1

Thus, the number of mole in 32 g of oxygen gas is 1.

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PREVIOUSCalculate:(a) the mass of 1.0505 × 1023 molecules of carbon dioxide (CO2).(b) the number of molecules of 0.25 moles of NH3,(c) the formula unit mass of Na2SO3.[Atomic mass: Na = 23 u, S = 32 u, O = 16 u, H = 1 u, NA = 6.022 × 1023 mol–1]NEXT(a) Calculate the number of moles in 112 g of iron.(b) Calculate the mass of 0.5 mole of sugar (C12H22O11).[Atomic mass of Fe = 56 u, C = 12 u, H = 1 u, O = 16 u]

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