Quick Summary
- Solvents dissolve solutes to make solutions
- Two main types: aqueous (water-based) and organic (carbon-based)
- Aqueous solvents are polar; organic solvents can be polar or non-polar
- Choice of solvent depends on what you want to dissolve
- “Like dissolves like” – polar solvents dissolve polar solutes
What Are Solvents?
A solvent is the liquid part of a solution that dissolves another substance called the solute. When you add sugar to water, water acts as the solvent and sugar is the solute. The mixture you get is called a solution.
Solvents are everywhere in daily life. The water you drink is a solvent. The petrol that powers generators and cars is a solvent. Even the nail polish remover your sister uses contains a solvent called acetone.
Main Types of Solvents
1. Aqueous Solvents
Aqueous solvents are water-based solvents. The word “aqueous” comes from the Latin word for water. Water is the most common and important aqueous solvent.
Properties of aqueous solvents:
- They are polar (have positive and negative ends)
- They dissolve ionic compounds like salt and sugar
- They are safe to drink (when pure)
- They have high boiling points
- They conduct electricity when ionic compounds dissolve in them
Examples you see in Nigeria:
- Water used for cooking and drinking
- Salt water from the Atlantic Ocean
- Sugar water (soft drinks)
- Saline solution used in hospitals
2. Organic Solvents
Organic solvents are carbon-based liquids. They can be polar or non-polar. Most organic solvents come from petroleum (crude oil) or plants.
Properties of organic solvents:
- Most are non-polar (no charge separation)
- They dissolve oils, fats, and other organic compounds
- Many are flammable (catch fire easily)
- Most have strong smells
- They evaporate quickly
- Most are harmful if swallowed or inhaled
Common organic solvents in Nigeria:
- Petrol (gasoline): Used in cars, generators, and motorcycles
- Kerosene: Used in stoves and lamps in many Nigerian homes
- Diesel: Used in trucks and buses
- Benzene: Used in making plastics and dyes
- Acetone: Found in nail polish remover
- Ethanol (alcohol): Used in drinks and as hand sanitizer
- Turpentine: Used by painters to thin paint
- Paint thinner: Used to clean paint brushes
Classification by Polarity
Chemists also group solvents by their polarity. This helps predict what they will dissolve.
| Solvent Type | Polarity | Examples | What They Dissolve |
|---|---|---|---|
| Aqueous | Polar | Water | Salt, sugar, ionic compounds |
| Polar Organic | Polar | Ethanol, acetone, methanol | Sugars, some salts, polar organic compounds |
| Non-polar Organic | Non-polar | Petrol, benzene, hexane, kerosene | Oils, fats, grease, wax |
The “Like Dissolves Like” Rule
This is the most important rule about solvents. Polar solvents dissolve polar solutes. Non-polar solvents dissolve non-polar solutes.
Example 1: Salt (polar) dissolves in water (polar) but not in petrol (non-polar).
Example 2: Oil (non-polar) dissolves in petrol (non-polar) but not in water (polar). This is why oil floats on water.
Example 3: When mechanics in Lagos wash greasy hands, they use kerosene (non-polar) to remove engine oil (non-polar). Water alone cannot do this job.
Uses of Different Solvents
In Everyday Life
- Water: Cooking, washing clothes, making drinks
- Kerosene: Fuel for stoves, removing grease stains
- Petrol: Fuel for vehicles, cleaning metal parts
- Ethanol: Making perfumes, hand sanitizers, drinks
- Acetone: Removing nail polish, cleaning tools
In Industry and Laboratories
- Water: Making medicines, cooling systems, washing equipment
- Benzene: Making plastics, rubber, dyes, detergents
- Ethanol: Making drugs, extracts from plants
- Ether: Extracting oils from seeds, as anesthetic (makes people sleep during surgery)
- Chloroform: Used to be used as anesthetic (now rarely used)
Safety with Organic Solvents
Most organic solvents are dangerous. Students should know these safety rules:
- Keep away from fire: Petrol, kerosene, and alcohol catch fire easily
- Use in open spaces: Fumes from paint thinner and petrol can make you dizzy
- Do not inhale: Breathing in solvent fumes damages the lungs and brain
- Do not swallow: Even small amounts can kill. Keep away from children
- Avoid skin contact: Wear gloves when using strong solvents
- Store properly: Keep in sealed containers away from heat
In Nigeria, NAFDAC warns against misuse of organic solvents. Some people abuse solvents to get high, which causes brain damage and death.
Environmental Impact
Organic solvents can harm the environment:
- Air pollution: Evaporated solvents contribute to smog
- Water pollution: Spilled petrol or kerosene kills fish and plants
- Soil pollution: Solvents in soil prevent crops from growing
This is why mechanics in Lagos should not pour used engine oil on the ground. It should be collected and recycled.
Common Exam Mistakes
Based on WAEC Chief Examiner reports, students often make these errors:
- Calling all solvents “organic”: Water is NOT an organic solvent. It is aqueous.
- Saying water is non-polar: Water is polar. That is why it dissolves salt.
- Listing only one type of solvent: When asked to list types, give BOTH aqueous and organic.
- Not explaining polarity: When asked why oil does not dissolve in water, explain that oil is non-polar and water is polar (unlike substances).
- Mixing up examples: Petrol and benzene are different. Do not use them interchangeably.
- Poor expression: Write “water dissolves salt” not “water is dissolving salt.” Use simple present tense for facts.
Practice Questions
Multiple Choice Questions
1. Which of the following is an aqueous solvent?
(a) Benzene
(b) Petrol
(c) Water ✓
(d) Kerosene
2. The principle “like dissolves like” means:
(a) All solvents dissolve all solutes
(b) Polar solvents dissolve polar solutes ✓
(c) Water dissolves everything
(d) Only organic solvents work
3. Which solvent would best dissolve engine oil?
(a) Water
(b) Salt solution
(c) Kerosene ✓
(d) Sugar solution
4. Why does oil float on water?
(a) Oil is lighter
(b) Oil is heavier
(c) Oil is non-polar and water is polar ✓
(d) Water is non-polar
Essay Questions
1. (a) Define the term solvent. (2 marks)
(b) State THREE differences between aqueous and organic solvents. (3 marks)
(c) Give TWO examples of each type of solvent. (2 marks)
Examiner Tip: For part (b), use a table format. Do not just list properties without comparing. For example: “Aqueous solvents are polar while organic solvents can be polar or non-polar.”
2. (a) State the “like dissolves like” rule. (2 marks)
(b) Using this rule, explain why sugar dissolves in water but not in petrol. (3 marks)
(c) State TWO safety precautions when using organic solvents. (2 marks)
Examiner Tip: In part (b), mention that both sugar and water are polar, so they dissolve. Petrol is non-polar, so sugar does not dissolve in it.
3. A student wants to remove grease stains from his school uniform.
(a) Should he use water or kerosene? (1 mark)
(b) Explain your answer in terms of polarity. (3 marks)
(c) State THREE dangers of using organic solvents at home. (3 marks)
Memory Aids
To remember types of solvents: A.O.
A = Aqueous (water-based)
O = Organic (carbon-based)
To remember “like dissolves like”: Think of friends – polar solvents and polar solutes are “friends” that mix well. Non-polar solvents and non-polar solutes are also “friends.”
To remember water is polar: Water has an “H” shape (H-O-H). The oxygen side is slightly negative, and the hydrogen side is slightly positive. This makes it polar.
To remember which solvents are dangerous: If it smells strong and burns easily, it is dangerous. Water does not smell and does not burn, so it is safe.
Related Topics
- Solubility and factors affecting it
- Properties of solutions
- Methods of separation (evaporation, distillation)
- Polar and non-polar molecules
- Uses of organic compounds