How many grams of sodium carbonate, Na2CO3, are needed to add to 0.125 kg of water to make a 0.200 m (molal) solution

Mass = 2.65 g

Explanation:

Given data:

Mass of sodium carbonate = ?

Mass of water = 0.125 g

Molality = 0.200 m

Solution:

Formula:

Molality = number of moles of solute / mass of solvent in Kg

by putting values,

0.200 m = Number of moles of solute / 0.125 kg

Number of moles = 0.200 m × 0.125 kg

Number of moles = 0.025 mol

Mass of sodium carbonate:

Mass = number of moles × molar mass

Mass = 0.025 mol × 106 g/mol

Mass = 2.65 g

the answer is option a.