Pre lab experiment 19 erovO CHEM 111 Name: Experiment #19: Freezing Point Depres

Question

Pre lab experiment 19

erovO CHEM 111 Name: Experiment #19: Freezing Point Depression Pre-Lab Questions 2 I. How is the van't Hoff number for the following substances? a) NaCI b) Ca(NO3)2 Tab 8 2. What is the equation of calculating molality? Why do we use molality rather than molarity as our concentration unit for this experiment? CapsLk 5 2. 0 3. It is -3.00°C outside and I have friends coming over for dinner. Not wanting them to get hurt (and possible sue me), how much road salt CaCl should I use to melt the ice if there are about 7.50 kg of snow on my porch? Assume ice is pure H20. (H20: Kr 1.86 °C/m)

Explanation / Answer

1) For non electrolyte i.e.- which does not undergoes dissociation, the van't Hoff number becomes 1, for example in case of C6H22O11

In case of electrolyte the Van't Hoff number is equals to the number of ions they produce on dissociation.

NaCl dissociates to give two ions i.e.- Na+ and Cl- ion, hence, the Van't Hoff number is 2

Ca(NO3)2 dissociates to give 3 ions, i.e.- one Ca2+ ion and two NO3- ion, hence, the Van't Hoff number is 3

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