Question

a) find the mass of 10 moles of sodium sulphide.

b) calculate the number of molecules in 8 gm of oxygen gas.

c. convert 22 g of carbon dioxide in to mole.

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Answer 1

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Answer 2

A) No : of moles = 10
Molar mass of sodium sulphide , Na₂S = 2 × 23 + 32 = 78 g/mol
No: of moles = Given mass / Molar mass
∴ Mass = No: of moles × Molar mass
= 10 × 78 = 780 g
B)No: of moles = Given mass / Molar mass
Molar mass of 0₂ = 2 × 16 = 32 g/mol
Given mass = 8 g
∴No: of moles = 8 / 32 moles

No : of molecules = No: of moles × Avogadro no:
= 8/ 32 × 6.022 × 10 ²³
= 1.5055 × 10 ²³
≈ 1.51 × 10 ²³

C)No: of moles = Given mass / Molar mass
Molar mass of Carbon Dioxide , CO₂ = 12 + 2 ×16 = 44 g/mol
Given mass = 22 g
∴ No: of moles = 22 ÷ 44 = 1 ÷ 2 = 0.5 moles


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