Answer:
2. a. All three solutes are nonelectrolytes.
3. a. the solution of solute X
Explanation:
The freezing point depression (ΔTf) and <em>boiling point elevation</em> (ΔTb) are <em>colligative properties</em>: they depend on the <em>numbers of particles</em>.
The formula for ΔTf is
ΔTf = iKf·b
i is the van’t Hoff factor: the number of moles of particles you get from a solute.
For sucrose,
Sucrose (s) ⟶ sucrose (aq)
1 mole sucrose ⟶ 1 mol particles i = 1
For NaCl
NaCl(s) ⟶ Na⁺(aq) + Cl⁻(aq)
1 mol 1 mol + 1 mol i = 2
For Ca(NO₃)₂
Ca(NO₃)₂(s) ⟶ Ca²⁺(aq) + 2NO₃⁻(aq)
1 mol 1 mol + 2 mol i = 3
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2. <em>Freezing points
</em>
For a nonelectrolyte, i = 1.
Kf = 1.86 °C·kg⁻¹mol⁻¹
b = 1 mol/kg Calculate ΔTf
ΔTf = 1 × 1.86 × 1
ΔTf = 1.86 °C
Tf = Tf⁰ - ΔTf =0.00 °C – 1.86 °C = -1.86 °C
All the other solutions have lower freezing points, so the solutes must be <em>electrolytes</em>.
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3. <em>Boiling points</em>
The formula for ΔTb is
ΔTb = iKb·m
The solution with the <em>highest boiling point</em> will have the <em>highest value of i.
</em>
In other words, the solution with the highest boiling point will be the one with the <em>lowest freezing point</em>.
That’s the solution of solute X.
