Question

How many molecules are there in 56mg HCN?
2.Number of molecules in 43g NH3
3.No of atoms in 32.0 g Br2
4.No of atoms in 7.46 g Li

Answer 1

1. Mass of one mole of HCN = 1+12+14 = 27g 
56 mg = 0.056 g
no. of moles in 56mg of HCN = 0.056/27 = 0.00207 mole
number of molecules in 1 mole = 6.022×10²³ molecules

number of molecules in 0.00207 mole = 6.022×10²³×0.00207= 1.249×10²¹ molecules


2. Mass of one mole of NH₃ = 14+3 = 17g 
no. of moles in 43g of NH₃ = 43/17 = 2.5294 mole
number of molecules in 1 mole = 6.022×10²³ molecules

number of molecules in 2.5294 mole = 6.022×10²³×2.5294= 1.523×10²⁴ molecules


3. Mass of one mole of Br₂ = 139.8g
no. of moles in 32g of Br₂ = 32/139.8 mole
number of molecules in 1 mole = 6.022×10²³ molecules

number of molecules in (32/139.8) mole = 6.022×10²³×32/139.8= 1.378×10²³ molecules

number of atoms in 1 molecule = 2
number of atoms in 1.378×10²³ molecules = 1.378×10²³×2 = 2.756×10²³ atoms


4. Mass of one mole of Li = 7g
no. of moles in 7.46g of Li = 7.46/7 = 1.0657 mole
number of atoms in 1 mole = 6.022×10²³ atoms

number of atoms in 1.0657 mole = 6.022×10²³×1.0657= 6.418×10²³ molecules

Answer 2

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1. Mass of one mole of HCN = 1+12+14 = 27g 

56 mg = 0.056 g

no. of moles in 56mg of HCN = 0.056/27 = 0.00207 mole

number of molecules in 1 mole = 6.022×10²³ molecules

number of molecules in 0.00207 mole = 6.022×10²³×0.00207= 1.249×10²¹ molecules

2. Mass of one mole of NH₃ = 14+3 = 17g 

no. of moles in 43g of NH₃ = 43/17 = 2.5294 mole

number of molecules in 1 mole = 6.022×10²³ molecules

number of molecules in 2.5294 mole = 6.022×10²³×2.5294= 1.523×10²⁴ molecules

3. Mass of one mole of Br₂ = 139.8g

no. of moles in 32g of Br₂ = 32/139.8 mole

number of molecules in 1 mole = 6.022×10²³ molecules

number of molecules in (32/139.8) mole = 6.022×10²³×32/139.8= 1.378×10²³ molecules

number of atoms in 1 molecule = 2

number of atoms in 1.378×10²³ molecules = 1.378×10²³×2 = 2.756×10²³ atoms

4. Mass of one mole of Li = 7g

no. of moles in 7.46g of Li = 7.46/7 = 1.0657 mole

number of atoms in 1 mole = 6.022×10²³ atoms

number of atoms in 1.0657 mole = 6.022×10²³×1.0657= 6.418×10²³ molecules

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