Question

determine the number of grams found in 4.9 mol of li₂s. hint: you must first calculate the molar mass of the compound. options: \\(\frac{45.95}{4.9}\\) g, 45.95 g, \\(\frac{4.9}{45.95}\\) g, \\(4.9 \cdot 45.95\\) g

Explanation:

Step1: Recall the formula for mass from moles

The formula to calculate mass (in grams) from moles is \( \text{Mass} = \text{Moles} \times \text{Molar Mass} \). Here, moles of \( \text{Li}_2\text{S} \) is \( 4.9 \) mol, and molar mass is \( 45.95 \) g/mol (we assume this is already calculated as \( 45.95 \) g/mol for \( \text{Li}_2\text{S} \)).

Step2: Identify the correct expression

To find the mass, we multiply the number of moles (\( 4.9 \) mol) by the molar mass (\( 45.95 \) g/mol). So the expression should be \( 4.9 \times 45.95 \) g (or \( 4.9 \cdot 45.95 \) g). Let's analyze each option:

• Option 1: \( \frac{45.95}{4.9} \) g is incorrect as it's dividing molar mass by moles, not multiplying.
• Option 2: \( 45.95 \) g is just the molar mass, not considering the moles.
• Option 3: \( \frac{4.9}{45.95} \) g is incorrect (dividing moles by molar mass).
• Option 4: \( 4.9 \cdot 45.95 \) g is the correct expression as it's moles multiplied by molar mass.

Answer:

\( 4.9 \cdot 45.95 \) g (the last option: \( 4.9 \cdot 45.95 \) g)