A chemist weighed out 20.0 g of magnesium. Calculate the number of moles of magnesium she weighed out.
The correct answer and explanation is:
To calculate the number of moles of magnesium in 20.0 grams, use the mole formula: Moles=Mass (g)Molar Mass (g/mol)\text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}
The molar mass of magnesium (Mg) is approximately 24.31 g/mol. Moles of Mg=20.0 g24.31 g/mol≈0.823 mol\text{Moles of Mg} = \frac{20.0\ \text{g}}{24.31\ \text{g/mol}} \approx 0.823\ \text{mol}
✅ Final Answer: 0.823 moles of magnesium
✍️ Explanation (300 words):
In chemistry, the mole is a fundamental unit in the International System of Units (SI) used to express the amount of a substance. One mole of any element contains Avogadro’s number of particles, which is approximately 6.022×10236.022 \times 10^{23} atoms, molecules, or ions. The molar mass is the mass of one mole of an element or compound, expressed in grams per mole (g/mol), and is numerically equal to the atomic or molecular weight found on the periodic table.
Magnesium (Mg) is an element with an atomic number of 12 and a molar mass of approximately 24.31 g/mol. This means that one mole of magnesium weighs 24.31 grams. If a chemist weighs 20.0 grams of magnesium, to determine how many moles this represents, we use the formula: Moles=MassMolar Mass\text{Moles} = \frac{\text{Mass}}{\text{Molar Mass}}
Substituting the values: Moles=20.024.31≈0.823\text{Moles} = \frac{20.0}{24.31} \approx 0.823
This tells us that 20.0 grams of magnesium corresponds to approximately 0.823 moles of magnesium atoms.
Understanding how to convert between grams and moles is essential in chemistry for tasks such as preparing solutions, balancing chemical reactions, and calculating yields. It allows chemists to relate a measurable quantity (mass in grams) to the number of particles involved in a reaction, which is critical when performing stoichiometric calculations in laboratory and industrial settings.