Problem: A small cube of lithium (density = 0.535 g/cm3) measuring 1.0 mm on each edge is added to 0.510 L of water. The following reaction occurs: 2 Li(s) + 2 H2O(l) → 2 LiOH(aq) + H2(g)What is the freezing point of the resultant solution, assuming that the reaction goes to completion?

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We’re being asked to calculate the freezing temperature the resultant solution, assuming that the reaction goes to completion


When calculating the freezing point of a solution, we’re going to use the equation for Freezing Point Depression.

Tf=i·Kf·m

∆Tf = change in freezing point = Tf pure solvent –Tf solution
Kf = freezing point depression constant
i = van' t Hoff factor of the solute = no. of ions
m = molality


We're going to calculate the freezing point of the solution using the following steps:

Step 1: Calculate the moles of lithium (Li).
Step 2: Calculate the moles of LiOH produced.
Step 3: Calculate the molality of the solution (LiOH).
Step 4: Calculate the change in temperature (ΔTf).
Step 5: Calculate the freezing point of the solution.


Step 1: Calculate the moles of lithium (Li).

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Problem Details

A small cube of lithium (density = 0.535 g/cm3) measuring 1.0 mm on each edge is added to 0.510 L of water. The following reaction occurs: 

2 Li(s) + 2 H2O(l) → 2 LiOH(aq) + H2(g)

What is the freezing point of the resultant solution, assuming that the reaction goes to completion?

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