  You are given a vial with an unknown compound. You are told that it is a sodiumcompound. You need to determine the identity of the halide. When 1.57 g of NaX is addedto 39.2 g of distilled water, the resulting solution was cooled and the freezing point wasdetermined to be -1.45 °C. What is the identity of X? (Assume the freezing point of thedistilled water is 0.00°C.)4.halide140

Question help_outlineImage TranscriptioncloseYou are given a vial with an unknown compound. You are told that it is a sodium compound. You need to determine the identity of the halide. When 1.57 g of NaX is added to 39.2 g of distilled water, the resulting solution was cooled and the freezing point was determined to be -1.45 °C. What is the identity of X? (Assume the freezing point of the distilled water is 0.00°C.) 4. halide 140 fullscreen
Step 1

Freezing point is a colligative property that means it depends upon the amount of solute or ions in solution.

Step 2

Given here,

mass of NaX = 1.57 g

dissolved in mass of water = 39.2 g = 0.0392 kg

[1 kg = 1000 g]

freezing point of solution = -1.45 degree C

Depression in freezing point (dTf) = -1.45 - 0 = -1.45 degree C

Kf for water = 1.86 degree C/m

i (Van't hoff factor) = 2 [NaX has 2 ions Na+ and X-]

Using,

dTf = -i x Kf x m

-1.45 = -2 x 1.86 x m

molality of solution (m) = 0.39 m

with,

molality = mass of solute/kg of solvent

we get,

moles of NaX = 0.39 m x 0.0392 kg

...

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