How many grams of CaCl_2 are required to be dissolved in 0.700 kg of water to prepare a 1.25 m (molal) solution?

• A. 87 g
• B. 156 g
• C. 121 g
• D. 98 g

Answer: (C)

Verified step by step guidance

1. Identify the given data: molality (m) = 1.25 mol/kg, mass of solvent (water) = 0.700 kg, and the solute is CaCl_2.
2. Recall the definition of molality: molality (m) = moles of solute / kilograms of solvent. Rearrange this to find moles of solute: moles of CaCl_2 = molality \times mass of solvent in kg.
3. Calculate the moles of CaCl_2 needed by multiplying 1.25 mol/kg by 0.700 kg.
4. Find the molar mass of CaCl_2 by adding the atomic masses: Ca (40.08 g/mol) + 2 \times Cl (2 \times 35.45 g/mol).
5. Convert moles of CaCl_2 to grams by multiplying the moles calculated in step 3 by the molar mass found in step 4.