Question

the largest number of molecules are present in
*3.6gm of H2O *4.8gm of C2H5OH
*2.8gm of CO *5.4 gm of N2O5​

Answer 1

Answer:-

We have to calculate the number of molecules of each compound given and then find the compound which has the highest number of molecules.

We know that;

Number of molecules = n × Nᴀ.

This implies ;

⟹ Number of molecules = (Given mass/molecular weight) × Nᴀ.

where;

• n is the number of moles [ ∵ n = given mass/molecular weight]
• Nᴀ. is Avogadro's number [ Nᴀ. = 6.023 × 10²³ ]

1) 3.6 gms of H₂O.

• Given mass = 3.6 g
• Molecular weight of H₂O = 2 × 1 + 1 × 16 = 18 g/mol

⟹ Number of molecules of H₂O = (3.6/18) × 6.023 × 10²³

⟹ Number of molecules of H₂O = 0.2 × 6.023 × 10²³

⟹ Number of molecules of H₂O = 2 × 6.023 × 10²²

⟹ Number of molecules of H₂O = 12.046 × 10²²

_________________________

2) 4.8 gms of C₂H₅OH

• Given mass = 4.8 gms
• Molecular weight of C₂H₅OH = 2 × 12 + 6 × 1 + 1 × 16 = 46 g/mol

⟹ Number of molecules of C₂H₅OH = (4.8/46) × 6.023 × 10²³

⟹ Number of molecules of C₂H₅OH = 0.1 × 6.023 × 10²³

⟹ Number of molecules of C₂H₅OH = 6.023 × 10²²

_________________________

3) 2.8 gms of CO

• Given mass = 2.8 gms
• Molecular weight of CO = 1 × 12 + 1 × 16 = 28 g/mol

⟹ Number of molecules of CO = (2.8/28) × 6.023 × 10²³

⟹ Number of molecules of CO = 0.1 × 6.023 × 10²³

⟹ Number of molecules of CO = 6.023 × 10²²

_________________________

4) 5.4 gms of N₂O₅

• Given mass = 5.4 gms
• Molecular weight of N₂O₅ = 2 × 14 + 5 × 16 = 108 g/mol

⟹ Number of molecules of N₂O₅ = (5.4/108) × 6.023 × 10²³

⟹ Number of molecules of N₂O₅ = 0.5 × 6.023 × 10²²

⟹ Number of molecules of N₂O₅ = 3.011 × 10²²

On comparing;

The largest number of molecules are present in 3.6 gms of H₂O i.e., 12.046 × 10²².

Answer 2

Information provided with us :

• 3.6 gm of H2O
• 4.8 gm of C2H5OH
• 2.8gm of CO
• 5.4 gm of N2O5

To Find:

• Which of these given gases contains largest number of molecules ?

Performing Calculations :

1) 3.6 gm of H2O :

• In order to find out the number of molecules we would be using the formula of calculating the number of molecules.

No. of molecules:-

• No. of molecules = (Mass of molecular substance / Molecular weight) × 6.023× 10²³

Finding out molecular weight of H2O (Hydrogen):-

➺ Molecular weight = (1)(2) + (1)(16)

➺ Molecular weight = 1 × 2 + (1)(16)

➺ Molecular weight = 2 + (1)(16)

➺ Molecular weight = 2 + 1 × 16

➺ Molecular weight = 2 + 16

➺ Molecular weight = 18 g

We have :

• Mass of molecular substance is 3.6
• Molecular weight of hydrogen is 18

Putting the required values :

➺ No. of molecules = (3.6 / 18) × 6.023 × 10²³

➺ No. of molecules = (36 / 18 × 10) × 6.023 × 10²³

➺ No. of molecules = (36 / 180) × 6.023 × 10²³

➺ No. of molecules = (1 / 5) × 6.023 × 10²³

➺ No. of molecules = 1 × 6.023 × 10²³ / 5

➺ No. of molecules = 0.2 × 6.023 × 10²³

Henceforth, of molecules of hydrogen are 0.2 × 6.023 × 10²³!

2) 4.8 gm of C2H5OH :

• We would be first find out the molecular weight of it and then simply apply the values in the formula of calculating the no. of molecules. (Ethanol)

Finding out the molecular weight :

We know that Carbon (C) contains 12 atoms, hydrogen (H) contains 1 atom and oxygen (O) contains 16 atoms.

➺ Molecular weight = 24 + 5 + 16 + 1

➺ Molecular weight = 24 + 5 + 17

➺ Molecular weight = 29 + 17

➺ Molecular weight = 46 g

We have :

• Mass of molecular substance that is ethanol is 4.8g
• Molecular weight is 46g

Putting the values :

➺ No. of molecules = (4.8 / 46) × 6.023 × 10²³

➺ No. of molecules = (48 / 46×10) × 6.023 × 10²³

➺ No. of molecules = (48 / 460) × 6.023 × 10²³

➺ No. of molecules = (24 / 230) × 6.023 × 10²³

➺ No. of molecules = (12 / 115) × 6.023 × 10²³

➺ No. of molecules = (0.1) × 6.023 × 10²³

➺ No. of molecules = 6.023 × 10²²

Henceforth, of molecules of ethanol are 6.023 × 10²²!

Note:-

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