Question

What mass
of oxygen, O₂, will contain
the same number of molecules as:2.5 moles of chlorine, Cl?
6.4g of sulphur dioxide SO₂ ?
6.023x102 molecules of water, H₂O?
​

Answer 1

1)2.5 moles of Cl2 contains (2.5 * Avogadro no.) Number Of molecules. Now that is equal to 2.5 moles of oxygen , which weighs 32*2.5 grams = 80 grams Hence the mass of oxygen o2 is 80 grams.

2)Given mass = 64 gm

Molecular mass = 32+(16×2) = 64 gm

No: of moles = given mass/ molecular mass = 64gm/ 64 gm = 1

Now, we get 64 gm of SO2 have 1 mole of SO2 molecules. Also 1 molecule of SO2 consists of 3 atoms ( 1 of Sulphur and 2 of oxygen).

So, 1 mole of SO2 = 6.023× 10^23 molecules of SO2 = 3× (6.023× 10^23) atoms = 18.069× 10^23 atoms.

Note: 1 mole of anything = 6.023× 10^23 anything. This number 6.023× 10^23 is called Avagadaro's number.

Answer 2

Mass of O₂ is

• 80 grams of O₂ will have the same number of molecules as 2.5 moles of Cl₂

• 3.2 grams of O₂ will contain same number of molecules as 6.4 grams of SO₂
• 32 × 10⁻²¹ grams of O₂ will contain 6.022 × 10² molecules .

GIVEN

Moles of chlorine gas = 2.5

Mass of sulphur dioxide = 6.4 grams

Number of molecules of water = 6.023 × 10²

TO FIND

Weight oxygen gas that will be equal to the given proportions.

SOLUTION

We can simply solve the above problem as follows -

We know that,

Molar mass of substance = 1 mole of molecules of substance = Nₐ

Where,

Nₐ = 6.022 × 10²³

So,

1 mole of Cl₂ = Nₐ

2.5 moles of Cl₂ = 2 × Nₐ

Now,

Molar mass of Oxygen gas (O₂) = 32 grams

Therefore,

Nₐ molecules of O₂ = 32 grams

2.5 × Nₐ molecules of O₂ Will be equal to;

$\frac{32}{Nₐ} \times 2.5 \times Nₐ$

= 80 grams

Hence, 80 grams of O₂ will have the same number of molecules as 2.5 moles of Cl₂

Similarly,

6.4 grams of SO₂ = (Nₐ/64)× 6.4 = 0.1 Nₐ

Now,

Nₐ molecules of O₂ = 32 grams

So,

0.1 moles of O₂ = 32×0.1 = 3.2 grams

Hence, 3.2 grams of O₂ will contain the same number of molecules as 6.4 grams of SO₂

Number of molecules of H₂ = 6.022 × 10²

We know that,

32 grams of O₂ = 6.022 × 10²³ molecules

1 molecule =

$\frac{32}{6.022 \times {10}^{23} }$

6.022 × 10² molecules will weigh =

$\frac{32}{6.022 \times {10}^{23} } \times 6.022 \times {10}^{2}$

= 32 × 10⁻²¹ grams

Hence, 32 × 10⁻²¹ grams of O₂ will contain 6.022 × 10² molecules.

Mass of O₂ is

• 80 grams of O₂ will have the same number of molecules as 2.5 moles of Cl₂

• 3.2 grams of O₂ will contain same number of molecules as 6.4 grams of SO₂

• 32 × 10⁻²¹ grams of O₂ will contain 6.022 × 10² molecules .

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