Hydrocarbons – Study Notes for Medical Lab Technology
(Chemistry – Graduate‑Level Practical Course)
1. Simple Explanation
Hydrocarbons are organic compounds that consist only of carbon (C) and hydrogen (H) atoms. They form the backbone of many laboratory reagents, solvents, gases, and biochemicals used in medical diagnostics. Their structure determines their physical behaviour and chemical reactivity, which is crucial for safe handling and for predicting how they will interact with other lab reagents.
2. Key Points
| Topic | Detail |
|---|---|
| Classification | 1. Alkanes – single bonds, saturated (CnH₂n+2) 2. Alkenes – double bonds, unsaturated (CnH₂n) 3. Alkynes – triple bonds (CnH₂n‑2) 4. Cycloalkanes – rings, saturated (CnH₂n) 5. Aromatic hydrocarbons – conjugated rings (C₆H₆, derivatives) |
| General Formula | Alkanes: CₙH₂ₙ₊₂ Alkenes: CₙH₂ₙ Alkynes: CₙH₂ₙ‑₂ |
| Bonding & Geometry | - Single C–C: tetrahedral, 109.5° - Double C=C: planar, 120° - Triple C≡C: linear, 180° |
| Physical Properties | - Boiling & melting points rise with chain length. - Density ≈ 0.5–0.8 g cm⁻³ (alkanes). - Low polarity → poor solubility in water. |
| Chemical Properties | - Alkanes: very stable, undergo combustion, substitution (free‑radical). - Alkenes & Alkynes: electrophilic addition (hydrogenation, halogenation). - Aromatic: undergo substitution (nucleophilic/electrophilic). |
| Common Lab Hydrocarbons | Ethanol, methanol, acetone, hexane, toluene, benzene, isopropanol, dichloromethane (CCl₄), cyclohexane. |
| Medical Relevance | - Solvents for chromatography and electrophoresis. - Gases for sterilisation (ethane, propane). - Precursors for radiopharmaceuticals. |
| Safety | • Flammable: keep away from heat sources. • Toxic vapours: use fume hoods. • Some (benzene, toluene) are carcinogenic – use personal protective equipment (PPE). |
3. Worked Example
Problem:
Name the following hydrocarbon and determine its molecular formula.
CH3–CH2–CH2–CH3
Solution:
-
Identify the longest chain
The chain has 4 carbon atoms → “butane” is the parent hydrocarbon. -
Check for double/triple bonds or rings
All C–C bonds are single → it is an alkane. -
Assign the IUPAC name
- For alkanes, the name is n‑alkane if no branches exist.
- Thus the compound is n‑butane.
-
Write the molecular formula
Carbon atoms: 4
Hydrogen atoms: 2n+2 = 2(4)+2 = 10 → C₄H₁₀.
Answer: n‑butane, C₄H₁₀.
Another Example – Balancing a Combustion Reaction
Reactant: Ethane (C₂H₆)
Product: CO₂ and H₂O
C2H6 + O2 → CO2 + H2O
Balancing Steps:
| Species | Coeff. |
|---|---|
| C₂H₆ | 1 |
| O₂ | 7/2 |
| CO₂ | 2 |
| H₂O | 3 |
Multiplying all by 2 to avoid fractions:
2 C2H6 + 7 O2 → 4 CO2 + 6 H2O
4. Quick Revision Summary
| Concept | Quick Note |
|---|---|
| Alkanes | Saturated, single bonds, formula CₙH₂ₙ₊₂. |
| Alkenes | Unsaturated, one double bond, formula CₙH₂ₙ. |
| Alkynes | Unsaturated, one triple bond, formula CₙH₂ₙ₋₂. |
| Cycloalkanes | Rings, saturated, formula CₙH₂ₙ. |
| Aromatic | Conjugated ring, e.g., benzene (C₆H₆). |
| Reactivity | Alkanes → combustion; Alkenes → addition; Aromatics → substitution. |
| Lab Solvents | Hexane, toluene, benzene, acetone, isopropanol. |
| Safety | Flammable → keep away from ignition; toxic vapours → fume hood; PPE always. |
| Naming | Use longest chain, check for unsaturation/r |