Question

What quantity of \(\text{H}_2\text{O}\) in gram is present in \(0.25\) mol of it?

• A. \(4.5\) g
• B. \(0.25\) g
• C. \(18\) g
• D. \(5.4\) g

Hint:

Mass equals moles times molar mass, and the molar mass of water is 18 g per mol.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
One mole of a substance has a mass in grams equal to its molar mass.
So the mass of any amount is moles multiplied by molar mass.

Step 2: Find the Molar Mass of Water:
\(\text{H}_2\text{O}\): \(2\times 1 + 16 = 18\) g per mol.

Step 3: Calculate the Mass:
\[ m = n \times M = 0.25 \times 18 = 4.5 \text{ g} \]

Step 4: Check the Other Options:
\(0.25\) g is just the number of moles written as grams, a unit mix-up. \(18\) g is the mass of one full mole, four times too large. \(5.4\) g would come from using a wrong molar mass of 21.6 g per mol. So (A) is correct.

Final Answer:
0.25 mol of water has a mass of 4.5 g, which is option (A). \[ \boxed{\text{(A) } 4.5\ \text{g}} \]