Electrolytes & Colligative Properties — Practice · Grade 11 Science

Chapter: Solutions & Dissolved Particles

What this practice covers

By the end of Electrolytes & Colligative Properties you should be able to:

8 questions, numeric and written answer, each with a worked explanation.

Vocabulary used: molality, particle factor i, osmosis.

Problem 1

Find molality of .30 mol solute in .60 kg solvent.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

0.5 mol/kg

.30/.60=.50.

Problem 2

Why can dissolved sugar fail to conduct well?
Answer and explanation

Neutral sugar molecules do not supply many mobile ions.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 3

Find ideal freezing depression for i=1, Kf=1.86, b=.30 mol/kg.
Hints

List the given quantities, select a relationship, and check units before substituting.

Answer and explanation

0.558 °C

1×1.86×.30=.558.

Problem 4

Compare molarity and molality denominators.
Answer and explanation

Molarity uses solution volume; molality uses solvent mass in kilograms.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 5

Find ΔT_f for m=0.20, i=1 and K_f=1.86°C·kg/mol. Show the reasoning, not just the conclusion.
Hints

Use molality, not molarity, for the standard freezing-point relation.

Answer and explanation

ΔT_f=iK_fm=0.372°C.

Problem 6

Why can an ionic solute conduct electricity while glucose solution usually conducts poorly?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Mobile ions carry charge; dissolved neutral glucose does not supply comparable ionic carriers.

Problem 7

A phase-equilibrium explanation is stronger than saying particles block freezingA phase-equilibrium explanation is stronger than saying particles block freezingDepression magnitude ΔTf (K)00.511.522.500.20.40.6Molality b (mol/kg solvent)Selected dilute model: slope = iKf = 3.72 K·kg/mol.
Original calculated ideal-model curve, not observed freezing data or a complete water–salt phase diagram.
Interpret the supplied visual. What does the slope describe in the selected linear model, and why should it not be extrapolated without limit?
Answer and explanation

It is iKf. At larger concentration, nonideality and other phase behavior can invalidate the simple dilute relation.

A dissolved solute changes the solvent’s chemical potential and therefore the conditions for phase equilibrium. In the selected dilute model, more effective solute particles give a larger freezing-temperature shift. This is not a literal wall of solute particles physically blocking every water molecule from crystallizing. Real phase diagrams, eutectic limits and concentration changes during freezing add detail beyond the straight-line approximation. Interpret the graph within its stated range and avoid extending it indefinitely to impossible temperatures.

It is iKf. At larger concentration, nonideality and other phase behavior can invalidate the simple dilute relation.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the chemistry relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 8

Using Kf=1.86 K·kg/mol, compare ideal freezing depressions for 0.100 mol glucose and 0.100 mol CaCl₂, each in 0.500 kg water. Assume i=1 and 3 respectively.
Answer and explanation

Both formula molalities are 0.200 mol/kg. Glucose gives ΔTf=0.372 K and ideal CaCl₂ gives 1.116 K≈1.12 K. Actual effective i and nonideality can change the measured comparison.

Both formula molalities are 0.200 mol/kg. Glucose gives ΔTf=0.372 K and ideal CaCl₂ gives 1.116 K≈1.12 K. Actual effective i and nonideality can change the measured comparison.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Browse all courses