# An aqueous solution containing 17.5 g of an unknown molecular compound in 100.g water was found to have a freezing point of-1.8°C.

An aqueous solution containing 17.5 g of an unknown molecular compound in 100.g water was found to have a freezing point of-1.8°C. Calculate the molar mass of this unknown compound. You can use the following steps to solve this problem. Show your work. What is the freezing point change (AT) from pure water? The freezing point of water is 0.0°C a. What is the freezing point depression constant (K of water? moles of solute b. What is the molality of the solution? (m= kg of solvent Horizontal (Value) Axis Major Gridlines moles of solute kg of solvent*Kr) c. S olve the moles of the solute . d. (A7-mxKf- Knowing the mass of the compound, and the moles of the compound, solve the molar mass of the compound.

Explanation:

Data

ΔT = 1.8 °C

mass = 17.5 g

mass of water = 100 g

Kc = 1.86

Process

1.- Calculate the molality using the following formula

ΔTc = mKc

solve for m

m = ΔTc/Kc

substitution

m = 1.8/1.86

result

m = 0.968

2.- Calculate the number of moles

m = # of moles/kg of solvent

kg of solvent = 0.1 kg

# of moles = m x kg of solvent

# of moles = 0.968 x 0.1

# of moles = 0.0968

3.- Calculate the molar mass

x g molar mass 1 mol

17.5 g                   0.0968 moles

x = (1 x 17.5)/0.0968

x = 178.6 g

I’m distilled water all of the dissolved substances mixed in water have been removed by evaporation.

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