- Classify solvent pairs as miscible or immiscible based on polarity principles
- Compare quantitative solubility of ionic vs. non-polar solutes in Water, Acetone, and Hexane
- Measure how surface area (particle size) affects dissolution rate
- Measure how temperature affects dissolution rate
- Apply the "like dissolves like" principle to predict solubility outcomes
🩺 Clinical Connection: Why This Matters for Nursing
Medication Preparation: Many IV medications must be dissolved in specific solvents. Understanding polarity helps you recognize why some drugs dissolve in saline (polar) while others require lipid emulsions (non-polar).
IV Fluid Selection: Normal saline (0.9% NaCl) works because salt is ionic and dissolves completely in polar water. Fat-soluble vitamins (A, D, E, K) require different delivery methods because they don't dissolve in water.
Patient Safety: Precipitation can occur when incompatible medications are mixed—understanding solubility prevents dangerous medication errors.
Not all molecules are "polar" or "non-polar"—polarity exists on a spectrum. This explains why some solvents mix with both polar AND non-polar substances.
Strong H-bonds, high dielectric constant
Polar C=O + non-polar CH₃ groups
Only C-C and C-H bonds (London forces only)
🩺 Clinical Insight: Acetone's Dual Nature
Acetone is used clinically as a defatting agent before surgical preps. Its amphipathic (dual-nature) structure allows it to dissolve both water-soluble residues AND oily/fatty substances from skin.
Use this decision tree to predict whether a solute will dissolve in a given solvent:
(e.g., NaCl, KBr)
(e.g., Sugar, Ethanol)
(e.g., Vaseline, Oil)
Ion-dipole forces
H-bonding
No attraction
Can't stabilize ions
Dipole interactions
Some interaction
No dipoles to attract
Polar ≠ Non-polar
London dispersion forces
- Example: Water (H₂O)
- Dissolves: Ionic compounds, polar molecules
- Cannot dissolve: Oils, fats, non-polar hydrocarbons
- Key force: Ion-dipole & Hydrogen bonding
- Clinical: Normal saline, most IV drugs
- Example: Hexane (C₆H₁₄)
- Dissolves: Oils, fats, waxes (Vaseline)
- Cannot dissolve: Salts, polar molecules
- Key force: London dispersion forces
- Clinical: Lipid-based drug carriers
- Example: Acetone
- Dissolves: Many polar AND some non-polar
- Structure: Polar C=O + non-polar CH₃
- Key term: Amphipathic
- Clinical: Surgical prep, defatting
- Temperature ↑ = Faster dissolution
- Surface Area ↑ = Faster dissolution
- Stirring/Agitation = Faster dissolution
- Fine particles > Coarse particles
- Hot water > Cold water
- ORGANIC WASTE: Acetone, Hexane, Vaseline mixtures
- SINK OK: Plain water, dilute salt water
- NEVER: Pour organics down sink
- Wear safety goggles at all times
- Work in fume hood with volatile organics
Why Does NaCl Dissolve in Water but NOT in Hexane?
✓ In Water (It Works!)
- Water molecules are polar with δ+ on H and δ- on O
- The δ- oxygen attracts Na⁺ ions
- The δ+ hydrogens attract Cl⁻ ions
- These ion-dipole interactions pull ions away from the crystal
- Water molecules surround each ion (hydration shell)
- Result: Complete dissolution!
✗ In Hexane (It Fails!)
- Hexane has no permanent dipole
- C-H bonds share electrons nearly equally
- No δ+ or δ- regions to attract ions
- The ionic bond energy in NaCl is NOT overcome
- Ions stay locked in crystal structure
- Result: No dissolution—crystals remain!
🩺 Clinical Application: Electrolyte Replacement
This is exactly why IV electrolyte solutions use water as the solvent! Potassium chloride (KCl), sodium bicarbonate (NaHCO₃), and calcium gluconate all rely on water's polarity to dissolve and deliver ions directly into the bloodstream.
🔥 Temperature Effect
Higher temperature = faster molecular motion
The "Traffic Jam" Analogy:
At 10°C, water molecules are sluggish—like cars in heavy traffic. They bump into salt crystals slowly.
At 50°C, water molecules zoom around with high kinetic energy—like cars on an open highway. They crash into salt crystals rapidly.
📐 Surface Area Effect
More surface = more contact with solvent
The "Doorway" Analogy:
Coarse NaCl = One big room with one doorway. Water can only enter/attack from that one entrance.
Fine NaCl = Many tiny rooms, each with its own doorway. Water can attack from hundreds of entry points!
🩺 Clinical Connection: Medication Formulation
Crushing medications: When a patient can't swallow a tablet whole, crushing it increases surface area for faster dissolution in the stomach. (Never crush extended-release formulations!)
⚠️ Pre-Lab Safety Review
- Hexane is highly flammable—NO open flames, use fume hood
- Acetone is volatile—use fume hood, avoid skin contact
- Organic waste container for ALL acetone/hexane/Vaseline mixtures
- Only dilute aqueous salt solutions may go down the sink with water
- Wear safety goggles and lab coat throughout the experiment
Before coming to lab, make sure you can:
- Classify solvent pairs as miscible or immiscible and relate results to polarity
- Compare quantitative solubility of ionic vs. non-polar solutes in varying solvents
- Measure the effects of surface area (particle size) and temperature on dissolution rates
Procedure
- Add 3.0 mL of each solvent pair to labeled test tubes
- Invert exactly 10 times. Let stand for 2 minutes
- Observe layers: 1 Layer = Miscible, 2 Layers = Immiscible
Data Table 1: Miscibility Observations
| Solvent Pair | Observation | Conclusion |
|---|---|---|
| Water + Acetone | ||
| Water + Hexane | ||
| Acetone + Hexane |
A) NaCl Solubility (Ionic Solute)
- Prepare 3 tubes with 10.0 mL of each solvent: Water, Acetone, Hexane
- Add NaCl in 0.25 g increments. Shake 15 seconds, wait 30 seconds
- Repeat until no more dissolves. Record the maximum mass dissolved
Data Table 2A: NaCl Solubility Limit
| Solvent | Polarity | Max Mass Dissolved (g) | Observation |
|---|---|---|---|
| Water | |||
| Acetone | |||
| Hexane |
B) Vaseline Solubility (Non-Polar Solute)
- Prepare 3 tubes with 10.0 mL of each solvent. Add 0.20 g Vaseline
- Cap and invert 10 times. Place in 50°C warm-water bath for 3 minutes
- Observe clarity: Fully dissolved, Partially dissolved, or Not dissolved
Data Table 2B: Vaseline Solubility
| Solvent | Polarity | Solubility Result | Appearance |
|---|---|---|---|
| Water | |||
| Acetone | |||
| Hexane |
- Prepare two containers with 20.0 mL room temperature water
- Add 2.00 g Fine NaCl to one and 2.00 g Coarse NaCl to the other
- Stir exactly 10 seconds, then stop. Record time to dissolve completely
- Repeat for 3 total trials
Data Table 3: Surface Area Effects
| Trial | Fine NaCl Time (s) | Coarse NaCl Time (s) | Observations |
|---|---|---|---|
| 1 | |||
| 2 | |||
| 3 | |||
| AVERAGE | (Trial1 + Trial2 + Trial3) ÷ 3 |
- Prepare 3 beakers with 20.0 mL water at: 10°C (Ice), ~22°C (Room), 50°C (Warm)
- Record actual temperature. Add 1.00 g Fine NaCl
- Stir consistently. Record time to dissolve completely. Repeat for 2 trials
Data Table 4: Temperature Effects
| Condition | Actual Temp (°C) | Trial 1 Time (s) | Trial 2 Time (s) | Average Time (s) |
|---|---|---|---|---|
| Cold (~10°C) | ||||
| Room (~22°C) | ||||
| Hot (~50°C) |
1Solvent Analysis: Why is Acetone considered "intermediate" in its solvent properties compared to Water and Hexane?
2Solubility Mechanics: Explain, on a molecular level, why water could dissolve NaCl but Hexane could not.
3Clinical Connection: A nurse is preparing an IV medication that must be dissolved before administration. Based on your lab results, explain why the medication is mixed with sterile water rather than a lipid solution if the drug is ionic.
4Rate Analysis: Based on your Part III and IV data, which factor had a greater effect on dissolution rate—particle size or temperature? Support with specific data.
📋 Required: Document Your Waste Disposal
Check each item after proper disposal:
⚠️ This section contains expected results, detailed explanations, and grading guidance. Do not share with students.
| Solvent Pair | Expected Result | Explanation |
|---|---|---|
| Water + Acetone | ✓ MISCIBLE (1 Layer) | Acetone is polar enough to form hydrogen bonds with water via its carbonyl oxygen. |
| Water + Hexane | ✗ IMMISCIBLE (2 Layers) | Polar vs. non-polar incompatibility. Hexane forms top layer (density ~0.66 g/mL). |
| Acetone + Hexane | ✓ MISCIBLE (1 Layer) | Acetone's methyl groups interact with hexane via London dispersion forces. |
💡 Teaching Point: The Acetone Surprise
Students often expect acetone to be immiscible with hexane because "acetone is polar." This is a great opportunity to discuss the spectrum of polarity rather than a binary classification.
| Solvent | Polarity | Expected Max Mass | Expected Observation |
|---|---|---|---|
| Water | Polar | >3.0 g | Clear, colorless solution. NaCl solubility ~36 g/100 mL at 25°C. |
| Acetone | Intermediate | 0.0–0.25 g | Cloudy suspension, white crystals remain undissolved. |
| Hexane | Non-Polar | 0.0 g | Crystals sit at bottom completely unchanged. |
| Solvent | Expected Result | Expected Appearance |
|---|---|---|
| Water | NOT Dissolved | Melted blobs float on surface. Clear phase separation. |
| Acetone | PARTIALLY Dissolved | Cloudy/milky emulsion. Some dissolution but not complete. |
| Hexane | FULLY Dissolved | Clear, colorless solution. |
Range: 15–40 sec
Range: 45–120 sec
~50 sec
~30 sec
~10–15 sec
1Why is Acetone "intermediate"?
Acetone (CH₃-C(=O)-CH₃) has an amphipathic structure. The central carbonyl (C=O) is highly polar and can accept hydrogen bonds from water. The two methyl groups (-CH₃) are non-polar and interact with hexane via London dispersion forces. This dual nature makes acetone miscible with both polar and non-polar solvents.
2Why does water dissolve NaCl but hexane cannot?
Water: Polar molecules with δ- oxygen attracting Na⁺ and δ+ hydrogens attracting Cl⁻. These ion-dipole interactions overcome the ~787 kJ/mol lattice energy. Water forms hydration shells around each ion.
Hexane: No permanent dipole—only weak London dispersion forces. Cannot overcome NaCl's high lattice energy. Ions remain locked in crystal.
| Criteria | Proficient (5 pts) | Developing (3 pts) | Needs Improvement (1 pt) |
|---|---|---|---|
| Data Recording | All trials recorded with precise units. Averages correct. | Missed one trial OR units inconsistent. | Tables largely empty or disorganized. |
| Observation Quality | Correctly identifies all miscibility and solubility results. | Confusion on acetone results. | Observations contradict basic solubility rules. |
| Safety & Waste | Organic waste used for all appropriate mixtures. | Minor prompts needed for disposal. | FAIL: Organic solvents down sink. |
| Analysis | Explains acetone's dual polarity AND ion-dipole mechanism. | Generic explanations without molecular reasoning. | Incorrectly identifies solvent polarity. |
Multiple Choice
1Waste container for Water + Acetone + NaCl?
2Why heat Vaseline to 50°C?
3Which statement about Acetone is true?
4Why did Fine NaCl dissolve faster?
5Water + Hexane produces?
Select All That Apply
6ORGANIC waste?
7Factors that INCREASED dissolution rate?
8Why does NaCl dissolve in water?
9Experimental errors affecting data?
10Acetone can dissolve?
❌ Marking Acetone + Hexane as "Immiscible"
Correction: Acetone's non-polar methyl groups interact with hexane via London forces.
❌ Expecting NaCl to dissolve in Acetone
Correction: Acetone's dielectric constant (~21) is too low to stabilize ions. Water's (~80) is required.
❌ Confusing melting with dissolution
Correction: Dissolution = molecular dispersion. Melting into floating blobs is NOT dissolution.
❌ CRITICAL: Organic solvents down sink
Response: Automatic point deduction. Review waste protocols before every lab.