14.3 Mixtures, Solutions, Tinctures & Emulsions
Key Takeaways
- Mixtures combine substances physically without fixed chemical ratios; homogeneous mixtures look uniform, heterogeneous mixtures do not
- Solutions are homogeneous mixtures of solute dissolved in solvent; dilute vs concentrated and percent concentration describe relative amounts
- Tinctures are solutions that use alcohol as the solvent; emulsions are mixtures of immiscible liquids stabilized so one is dispersed in the other
- Suspensions have large settling particles; colloids have intermediate particles that scatter light and usually do not settle quickly
- Solubility depends on temperature, pressure (for gases), and solute–solvent polarity—“like dissolves like”
14.3 Mixtures, Solutions, Tinctures & Emulsions
Quick Answer: A mixture blends substances without a new fixed chemical formula. Homogeneous mixtures (including solutions) are uniform; heterogeneous mixtures are not. Know solute/solvent, dilute vs concentrated, intro percent concentration, tinctures (alcohol solvent), emulsions (immiscible liquids dispersed), and suspension vs colloid. Solubility follows like dissolves like plus temperature/pressure effects—daily language of nursing meds and IV fluids.
Chemistry blueprint items on mixtures are highly testable because they map onto bottles and bags you will actually handle: normal saline, oral suspensions, tinctures, and fat emulsions.
Mixtures vs Pure Substances
- Pure substance: element or compound with definite composition (water, oxygen, NaCl as a pure crystal).
- Mixture: two or more substances combined physically, variable proportions, components retain their chemical identities and can often be separated by physical means (filtration, evaporation, distillation, centrifugation).
| Type | Appearance | Particle mixing | Example |
|---|---|---|---|
| Homogeneous mixture | Uniform throughout; one phase visible | Even at microscopic scale | Salt water, air, vodka, D5W |
| Heterogeneous mixture | Not uniform; regions differ | Distinct phases or chunks | Sand in water, blood (on standing), vinaigrette before shaking, many suspensions |
Blood is a clinical nuance: circulating blood can look uniform but is a complex suspension/colloid system of cells in plasma; on standing it separates—heterogeneous character becomes obvious.
Solutions: Solute and Solvent
A solution is a homogeneous mixture of two or more substances.
- Solute: substance being dissolved (present in lesser amount, typically)
- Solvent: substance doing the dissolving (present in greater amount)
In aqueous solutions—the most important for nursing—the solvent is water. Example: in 0.9% NaCl, NaCl is the solute; water is the solvent.
Solutions can be:
- Gas in gas (air: O₂ and others in N₂)
- Liquid in liquid (alcohol in water)
- Solid in liquid (glucose in water)
- Gas in liquid (O₂ or CO₂ dissolved in blood plasma—conceptually)
Once dissolved at the molecular/ionic level, solutes in a true solution do not settle, pass through ordinary filters, and the mixture is clear (though colored solutions can still be true solutions).
Concentration Concepts
Concentration describes how much solute is present relative to solvent or solution.
Dilute vs Concentrated
- Dilute: relatively small amount of solute per amount of solution
- Concentrated: relatively large amount of solute per amount of solution
These are comparative words, not exact numbers. A solution can be concentrated yet still unsaturated (able to dissolve more), or dilute yet saturated for a poorly soluble solute.
Percent Concentration (Intro)
NEX-level percent ideas you should recognize:
- Mass/volume percent (% m/v): grams of solute per 100 mL of solution. Example: 0.9% NaCl means 0.9 g NaCl per 100 mL solution—the classic “normal saline” idea.
- Volume/volume percent (% v/v): mL solute per 100 mL solution (common for alcohol solutions).
- Mass/mass percent (% m/m): grams solute per 100 g solution.
You are not being asked to run pharmacy calculations here; you need to interpret what “percent” is saying: parts of solute per 100 parts of solution (in the specified units).
Related clinical terms (recognition level):
- Isotonic IV fluids match plasma tonicity conceptually (linked to osmosis from Biology).
- Labels may also use mg/mL, mEq/L, or molarity in coursework—percent is the Chemistry outline’s explicit intro focus.
Tinctures
A tincture is a solution in which the solvent is alcohol (ethanol), or alcohol–water, rather than water alone. Plant extracts and some antiseptics historically appear as tinctures (e.g., tincture of iodine—iodine dissolved in alcohol).
Why alcohol?
- Dissolves some substances poorly soluble in water alone
- Can act as a preservative
- Evaporates readily when applied topically
Nursing caution (conceptual): alcohol-based preparations are flammable, may irritate tissue, and are not interchangeable with aqueous solutions of the “same” drug without checking the label—solvent changes concentration, absorption, and safety.
Emulsions
An emulsion is a mixture of two immiscible liquids (typically oil and water) in which one liquid is dispersed as fine droplets throughout the other. Emulsions are often cloudy/opaque and may require an emulsifying agent (emulsifier) to keep droplets from coalescing and separating.
Types (intro):
- Oil-in-water (O/W): oil droplets in water (many lotions, some oral emulsions)
- Water-in-oil (W/O): water droplets in oil (some ointments/creams)
Clinical examples to recognize: intravenous lipid emulsions for parenteral nutrition; some oral liquid vitamins; topical creams. Shaking instructions on labels exist because emulsions can cream or separate over time even when emulsified.
Emulsions sit between simple solutions and coarse suspensions: droplets are larger than dissolved molecules but often stabilized against rapid settling.
Suspensions vs Colloids
| Feature | True solution | Colloid | Suspension |
|---|---|---|---|
| Particle size | Tiny (ions/molecules) | Intermediate (≈1–1000 nm range in many texts) | Large (often visible) |
| Settling | No | Usually no (or very slow) | Yes, on standing |
| Filter (ordinary) | Passes | Often passes | May be trapped |
| Appearance | Clear | May be cloudy; Tyndall effect (scatters light) | Cloudy/opaque; particles visible |
| Example | Saline, D5W | Milk, protoplasm, many plasma proteins in water | Milk of magnesia, many oral antibiotic suspensions |
Suspension nursing rule: “Shake well before using”—particles settle. Injecting an unsettled suspension or giving without resuspending underdoses/overdoses unpredictably.
Colloids: particles large enough to scatter light (Tyndall effect) but small enough to remain dispersed. Blood plasma proteins, homogenized milk, fog, and some IV colloids (conceptual category) fit here. Do not confuse clinical “colloid IV fluids” branding with the Chemistry definition—but the particle-size idea is the same family.
Solubility Factors (Overview)
Solubility is the maximum amount of solute that dissolves in a given amount of solvent at specified conditions.
Factors:
- Nature of solute and solvent (polarity) — Like dissolves like. Polar/ionic solutes dissolve in polar solvents (water). Nonpolar solutes dissolve in nonpolar solvents (oils, hexane). Mixed polarity limits solubility.
- Temperature — For most solid solutes in water, solubility increases as temperature rises (more sugar dissolves in hot tea). For many gases in water, solubility decreases as temperature rises (warm soda goes flat faster).
- Pressure — Strongly affects gas solubility (Henry’s law idea): higher pressure → more gas dissolved (think carbonated drinks sealed under pressure; conceptual link to dissolved O₂/CO₂ in blood under different partial pressures).
- Particle size / stirring — Affect rate of dissolving more than the final solubility limit: powder dissolves faster than a chunk; stirring brings fresh solvent to the surface.
Saturated solutions hold the maximum solute at those conditions; unsaturated can dissolve more; supersaturated hold more than the normal maximum (unstable—seed crystal can crash out solute).
Nursing and NEX Connections
- IV crystalloids (NS, LR, D5W): true aqueous solutions—clear, no shaking for settling of the drug itself.
- Oral suspensions: heterogeneous until shaken; dose accuracy depends on resuspension.
- Tinctures: alcohol solvent—storage, flammability, and patient alcohol exposure matter.
- Emulsions: lipid IV emulsions and topical creams—immiscible liquids kept dispersed.
- Reconstitution: adding solvent to powder creates a solution or suspension per manufacturer design.
Exam Traps
- Solution vs suspension: Solutions do not settle; suspensions do.
- Homogeneous ≠ always liquid: Air is a homogeneous gaseous mixture.
- Tincture solvent: Alcohol (or alcohol–water)—not “any medicine bottle.”
- Emulsion: Two immiscible liquids dispersed—not a solid settling in water (that’s suspension).
- Concentrated vs saturated: Concentrated means “a lot of solute”; saturated means “full at those conditions”—different ideas.
- Percent: Parts solute per 100 parts solution—identify what the label is measuring.
Sort every mixture question with three filters: uniform or not? Settling particles or dissolved? Water, alcohol, or oil continuous phase? Those filters place almost every 14.3 item correctly.
A medication bottle labeled “shake well before using” most likely contains a:
A tincture differs from a typical aqueous solution primarily because the tincture uses:
Oil and water form an emulsion when: