Mole Calculations Study Notes

Mole Calculations #2

Question: What volume, in liters (at STP), would be occupied by 4.81 x 10²¹ atoms of helium gas?
Relevant Concepts:
- STP (Standard Temperature and Pressure):
- Defined as 0°C (273.15 K) and 1 atm pressure.
- At STP, 1 mole of any gas occupies a volume of 22.4 liters.
Calculation Steps:
- Find moles from atoms:
- Use the Avogadro's number: $N_A = 6.022 imes 10^{23}$ atoms/mole.
- Moles of He = ( ext{Moles} = rac{4.81 imes 10^{21} ext{ atoms}}{6.022 imes 10^{23} ext{ atoms/mole}} )
- Calculate volume:
- Use the volume occupied by 1 mole at STP:
- Volume = moles x 22.4 L/mole.

Question: What is the mass, in grams, of 34.99 liters of oxygen gas (O2), at STP?
Relevant Concepts:
- Moles of oxygen gas: Use the volume at STP (22.4 L/mole) to find moles.
Calculation Steps:
- Find moles from liters:
- Moles of O2 = ( ext{Moles} = rac{34.99 ext{ L}}{22.4 ext{ L/mole}} )
- Determine mass from moles:
- Molar mass of O2 = 32 g/mole (since O has an atomic mass of 16 g, O2 = 2 × 16 g).
- Mass = moles x molar mass.

Question: How many moles are equal to 393.6 grams of aluminum sulfate?
Relevant Concepts:
- Molar Mass Calculation:
- Formula of aluminum sulfate: Al2(SO4)3.
- Molar mass = 2(27) + 3(32) + 12(16) = 342 g/mole.
Calculation Steps:
- Find moles from grams:
- Moles = ( ext{Moles} = rac{393.6 ext{ g}}{342 ext{ g/mole}} )

Question: How many atoms are equal to 0.056 liters of chlorine (Cl2) gas, at STP?
Relevant Concepts:
- Moles of Cl2 from liters:
- Calculation Steps:
- Moles of Cl2 = ( ext{Moles} = rac{0.056 ext{ L}}{22.4 ext{ L/mole}} )
- Atoms = moles x Avogadro's number: ( ext{Atoms} = ext{Moles} imes 6.022 imes 10^{23} ext{ atoms/mole} ).

Question: What volume, in liters (at STP), would be occupied by 0.78 moles of carbon monoxide gas?
Relevant Concepts:
- Volume Calculation at STP:
Calculation Steps:
- Volume = moles x 22.4 L/mole = ( 0.78 ext{ moles} imes 22.4 ext{ L/mole} ).