What is the molality of a solution prepared by dissolving 15.1 g KNO_3 in 250. g

Question

What is the molality of a solution prepared by dissolving 15.1 g KNO_3 in 250. g water? 0.0604 m 0.598 m 0.0375 m 0.150 m 1.67 m The mole fraction sucrose in an aqueous solution is 0.200. Calculate the molality of sucrose in the solution. The molar mass of sucrose is 342.3 g/mol. 13.9 m 55.6 m 2.92 m 0.200 m The mole fraction of sucrose in an aqueous solution is 0.100. Calculate the molarity of sucrose in the solution. The molar mass of sucrose is 342.3 g/mol. 0.100 m 1.98 m 6.17 m 55.6 m 2.92 m Calculate the mole fraction of sucrose in 6.00 m sucrose(aq). The molar mass of sucrose is 342.3 g/mole. 0.0975 0.903 0.0556 0.00600 0.108 Calculate the molarity of ethyl alcohol in a bottle of wine that is 19.0% C_2 H_5 OH by mass. The molar mass of ethyl alcohol is 46.1 g/ mol. 5.09 m 3.73 m 1.54 m 0.412 m 1.76 m

Explanation / Answer

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19)

Molar mass of KNO3 = Mass of K + Mass of N + 3 * Mass of Oxygen

=> 39.1 + 14 + 3 * 16

=> 101.1 gm/mol

Number of moles of solute = mass of solute/molar mass = 15.1/101.1 = 0.1493 moles

molality = 0.1493/(250/1000) = 0.1493 * 4 = 0.598 m

Hence the correct answer is Option B

20)

Molar mass of Sucrose = 342.3 gms

Assuming 1 mole of solution, it will contain 0.2 moles of sucrose and 0.8 moles of water

Mass of sucrose = 0.2 * 342.3 = 68.46 gms

Mass of water = 0.8 * 18 = 14.4 gms

molality = 0.2/(14.4/1000) = 200/14.4 = 13.88

Hence the correct answer is Option A

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