Question

1. what mass of nacl is needed to prepare 125ml of a 2.5m solution? (remember that m = molarity = moles solute per liter of solution.)

Explanation:

Step1: Convert volume to liters

$125\ \text{mL} = \frac{125}{1000}\ \text{L} = 0.125\ \text{L}$

Step2: Calculate moles of NaCl

Moles = Molarity × Volume
$\text{Moles of NaCl} = 2.5\ \text{mol/L} \times 0.125\ \text{L} = 0.3125\ \text{mol}$

Step3: Find molar mass of NaCl

Molar mass of Na = 23 g/mol, molar mass of Cl = 35.5 g/mol
$\text{Molar mass of NaCl} = 23 + 35.5 = 58.5\ \text{g/mol}$

Step4: Calculate mass of NaCl

Mass = Moles × Molar mass
$\text{Mass of NaCl} = 0.3125\ \text{mol} \times 58.5\ \text{g/mol}$

Answer:

$18.28125\ \text{g}$ (or rounded to $18.3\ \text{g}$)