A 2% by weight aqueous solution of NaCl (MW= 58.45) has a boiling point of 100.31 °C. What is the van't Hoff factor for NaCl?
The experimental value of the van't Hoff factor is 1.7.
The formula for boiling point elevation is
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This can be rearranged to give
We must now calculate the molality of the solution.
Calculating the molality
Assume that we have 100 g of the solution.
Then we have 2 g of NaCl and 98 g of water.
The formula for molality is
#color(blue)(|bar(ul(color(white)(a/a) "molality" = "moles of solute"/"kilograms of solvent"color(white)(a/a)|)))" "#
Now we can calculate the
The van't Hoff factor for NaCl is 1.7.