Leaving Cert Chemistry Gas Laws & Properties: Define a mole of a substance.

Define a mole of a substance - Leaving Cert Chemistry - Question b - 2005

Question b

Define a mole of a substance. State Avogadro's law. A foil balloon has a capacity of 10 litres. How many atoms of helium occupy this balloon when it is filled wi... show full transcript

Worked Solution & Example Answer:Define a mole of a substance - Leaving Cert Chemistry - Question b - 2005

Step 1

Define a mole of a substance.

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Answer

A mole of a substance is defined as the amount of that substance that contains as many entities (atoms, molecules, or particles) as there are in 12 grams of carbon-12. This quantity is known as Avogadro's number, approximately equal to $6.022 imes 10^{23}$ particles.

Step 2

State Avogadro's law.

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Avogadro's law states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules (or moles).

Step 3

How many atoms of helium occupy this balloon when it is filled with a 10% (v/v) mixture of helium in air at room temperature and pressure?

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Calculate the volume of helium in the balloon:

Volume of helium = 10 litres * (10 cm³ / 100 cm³) = 1 litre
Use the ideal gas law to find moles of helium:

At STP, 1 mole of gas occupies 22.4 litres.

Moles of helium = $rac{1}{22.4} ext{mol} \approx 0.04464$ moles of helium.
Convert moles of helium to atoms:

Atoms of helium = $0.04464 ext{mol} * 6.022 \times 10^{23} ext{ atoms/mol} \approx 2.68 \times 10^{22}$ atoms.

Thus, the number of helium atoms occupying the balloon is approximately between $2.4 \times 10^{21}$ to $2.5 \times 10^{22}$ atoms.

Define a mole of a substance - Leaving Cert Chemistry - Question b - 2005

Worked Solution & Example Answer:Define a mole of a substance - Leaving Cert Chemistry - Question b - 2005

Define a mole of a substance.

State Avogadro's law.

How many atoms of helium occupy this balloon when it is filled with a 10% (v/v) mixture of helium in air at room temperature and pressure?

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