Molality Example Problem - Worked Chemistry Problems

Molality Example Problem - Worked Chemistry Problems Molality is a means of expressing the concentration of a chemical solution. Heres an example problem to show you how to determine it: Sample Molality Problem A 4 g sugar cube (Sucrose: C12H22O11) is dissolved in a 350 ml teacup of 80  °C water. What is the molality of the sugar solution?Given: Density of water at 80 ° 0.975 g/ml Solution Start with the definition of molality.  Molality is the number of moles of solute per kilogram of solvent. Step 1 - Determine number of moles of sucrose in 4 g.Solute is 4 g of C12H22O11 C12H22O11 (12)(12) (1)(22) (16)(11)C12H22O11 144 22 176C12H22O11 342 g/moldivide this amount into the size of the sample4 g /(342 g/mol) 0.0117 mol Step 2 - Determine mass of solvent in kg. density mass/volumemass density x volumemass 0.975 g/ml x 350 mlmass 341.25 gmass 0.341 kg Step 3 - Determine molality of the sugar solution. molality molsolute / msolventmolality 0.0117 mol / 0.341 kgmolality 0.034 mol/kg Answer: The molality of the sugar solution is 0.034 mol/kg. Note: For aqueous solutions of covalent compounds, such as sugar, the molality and molarity of a chemical solution are comparable. In this situation, the molarity of a 4 g sugar cube in 350 ml of water would be 0.033 M.