If you want to lower waters freezing point by 23°C by adding #"MgF"_2#, what must the molality of the solution be?

1 Answer
Junaid Mirza
Jun 4, 2018

#"4.12 molal"#

Explanation:

Change in freezing point is given by

#"ΔT = – iK"_f"m"#

Where

  • #"i ="# Van’t Hoff factor (#3# for #"MgF"_2#)
  • #"K"_f ="# Freezing point constant (#"1.86°C/molal"# for water)
  • #"m ="# Molality of solution

#"m" = "ΔT"/("– iK"_f)#

#color(white)("m") = "– 23°C"/"– 3 × 1.86°C/molal"#

#color(white)("m") = 4.12\ "molal"#

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