Colligative Properties Practice
Why does 2M Fe2(SO4)3 have a higher boiling point than 2 M FeCl3?
Which solution has a higher melting point, 2 M FeCl3, 4 M NaCl, or 3 M MgCl2? Why?
What is happening at the molecular level that causes a solute to elevate the boiling point of a solvent?
What will the new boiling point be if 121 g FeCl3 is dissolved in 1,201 mL water?
(+.51 °C/m)
What will the new freezing point be if 45 g NaCl is dissolved in 121 mL water?
(-1.86 °C/m)
Colligative Properties Practice
KEY
Why does 2M Fe2(SO4)3 have a higher boiling point than 2 M FeCl3?
FeCl3makes 4 particles
Fe2(SO4)3 makes 5 particles
More particles = more attractions and greater impact of colligative properties at the same concentration.
Which solution has a higher melting point, 2 M FeCl3, 4 M NaCl, or 3 M MgCl2? Why?
2 M FeCl3 = 8 m particles
4 M NaCl = 8 m particles
3 M MgCl2 = 9 m particles
2 M FeCl3 and4 M NaCl have the least m particles, therefore the least mp depression; therefore, they would both have a higher melting point
What is happening at the molecular level that causes a solute to elevate the boiling point of a solvent?
As solute dissolves, more attractions are formed with the solvent.
These attractions need to be broken to boil the solvent so more energy (higher temp) is needed.
What will the new boiling point be if 121 g FeCl3 is dissolved in 1,201 mL water?
(+.51 °C/m)
121 g FeCl3 (1 mol FeCl3 /162.20 g FeCl3) = .75 mol FeCl3
.75 mol FeCl3 /1.021 kg H2O = .62 m FeCl3
.62 m FeCl3 (4 mol particles/1 m FeCl3) = 2.48 m particles
2.48 m particles (+.51 C/1 m particles) = 1.27 C
New BP = 101.27 C
What will the new freezing point be if 45 g NaCl is dissolved in 121 mL water?
(-1.86 °C/m)
45 g NaCl (1 mol NaCl/58.44 g NaCl) = .77 mol NaCl
.77 mol NaCl/.121 Kg H2O = 6.36 m NaCL
6.36 m NaCl (2 m particles/1 m NaCl) = 12.73 m particles
12.73 m particles (-1.86 C/1 m particles) = -23.66 C
New MP = -23.66 C