In the gaseous state, chlorine exists as a diatomic molecule Cl2 (Molar mass = 70.9 g/mol). Calculate the number of moles of chlorine present in 140 g of chlorine gas.
The Correct Answer and Explanation is:
To calculate the number of moles of chlorine gas (Cl₂) in 140 g, we use the formula:Moles=Mass (g)Molar Mass (g/mol)\text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}Moles=Molar Mass (g/mol)Mass (g)
Given:
- Mass of chlorine gas = 140 g
- Molar mass of Cl₂ = 70.9 g/mol
Moles of Cl₂=140 g70.9 g/mol≈1.975 mol\text{Moles of Cl₂} = \frac{140 \, \text{g}}{70.9 \, \text{g/mol}} \approx 1.975 \, \text{mol}Moles of Cl₂=70.9g/mol140g≈1.975mol
Final Answer:
Approximately 1.975 moles of chlorine gas are present in 140 g of Cl₂.
Explanation
Chlorine in its natural gaseous form exists as a diatomic molecule, meaning two chlorine atoms are bonded together, forming Cl₂. The molar mass of one chlorine atom is about 35.45 g/mol. Since Cl₂ has two chlorine atoms, its molar mass is:35.45 g/mol×2=70.9 g/mol35.45 \, \text{g/mol} \times 2 = 70.9 \, \text{g/mol}35.45g/mol×2=70.9g/mol
The mole is a fundamental unit in chemistry that represents a quantity of particles, typically atoms or molecules. One mole of a substance contains Avogadro’s number of entities, which is approximately 6.022×10236.022 \times 10^{23}6.022×1023.
To determine how many moles are in a given mass of a substance, divide the mass of the sample by its molar mass. In this problem, we are given a sample of chlorine gas weighing 140 grams. Using the formula for calculating moles:Moles=MassMolar Mass=14070.9≈1.975 mol\text{Moles} = \frac{\text{Mass}}{\text{Molar Mass}} = \frac{140}{70.9} \approx 1.975 \, \text{mol}Moles=Molar MassMass=70.9140≈1.975mol
This means there are about 1.975 moles of chlorine gas molecules in the 140 g sample.
This calculation is essential in chemical reactions where stoichiometry is used to determine reactant and product quantities. Knowing the number of moles allows chemists to predict how much of a substance will be consumed or produced during a reaction. For chlorine gas, this value can be used to find how much it will react with another substance, such as hydrogen, to form compounds like HCl.
