Why care about acids, bases and salts?
Ever wonder why a lemon makes your tongue tingle or why soap feels slippery? Those sensations come from acids, bases and salts – the everyday chemistry that powers everything from cooking to cleaning. Knowing their properties helps you ace the board exam and understand the world around you.
In simple words: acids taste sour, turn blue litmus red, and love to give away a hydrogen ion. Bases feel slippery, turn red litmus blue, and love to accept a hydrogen ion. Salts are the neutral kids that form when an acid and a base finish their reaction.
What are acids, bases and salts?
Acid – a substance that releases hydrogen ions (H⁺) when dissolved in water. Think of hydrogen ions as tiny, eager messengers that want to join other particles.
Base – a substance that releases hydroxide ions (OH⁻) or accepts hydrogen ions. Imagine a base as a friendly catcher that grabs those hydrogen messengers.
Salt – the product that forms when an acid and a base neutralise each other. It’s like the peace treaty after a heated debate, leaving behind a neutral compound.
Physical properties you can see and feel
Physical properties are the traits you can observe without changing the substance.
- State at room temperature: Most acids (like hydrochloric acid) are liquids, many bases (like calcium hydroxide) are solids, and salts (like table salt) are solid crystals.
- Smell: Strong acids often have a sharp, pungent odor (think vinegar). Bases can smell soapy or like ammonia. Salts are usually odourless.
- Taste: Acids taste sour (lemon juice). Bases feel bitter and soapy (soap). Never taste chemicals in the lab!
- Conductivity: When dissolved in water, acids, bases and salts all conduct electricity because they produce ions – the charged particles that move like tiny marbles in a water pipe.
- pH value: A scale from 0 to 14 that measures how acidic or basic a solution is. Acids have pH less than 7, bases more than 7, and salts usually sit around 7 (neutral) unless they’re made from a strong acid and weak base or vice‑versa.
Chemical properties – what they do in reactions
Chemical properties describe how a substance behaves when it meets something else. Here’s the chemical properties of acids bases and salts you’ll need for class 10 and ICSE exams.
Acids
- Reaction with metals: Acids release hydrogen gas when they touch active metals like zinc or magnesium. Example:
Zn + 2HCl → ZnCl₂ + H₂↑ - Reaction with carbonates: They fizz away, producing carbon dioxide gas. Example:
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑ - Neutralisation: When mixed with a base, acids form a salt and water – the classic neutralisation reaction.
- Change in litmus colour: Turns blue litmus paper red.
Bases
- Reaction with acids: They accept hydrogen ions, forming a salt and water.
- Reaction with fats (saponification): Bases like NaOH break down fats into glycerol and soap – the science behind making soap bars.
- Change in litmus colour: Turns red litmus paper blue.
- Corrosive to organic tissue: Strong bases can burn skin, just like strong acids.
Salts
- Hydrolysis: Some salts react with water to form a weak acid or base, shifting the pH slightly. For example, ammonium chloride (NH₄Cl) makes the solution slightly acidic.
- Precipitation: When two soluble salts mix, an insoluble salt (a precipitate) may form. Example: mixing silver nitrate and sodium chloride gives solid silver chloride.
- Thermal stability: Most salts melt at high temperatures and don’t decompose easily.
Quick comparison table
| Feature | Acid | Base | Salt |
|---|---|---|---|
| Key ion in water | H⁺ (hydrogen ion) | OH⁻ (hydroxide ion) or accepts H⁺ | Combination of cation & anion (e.g., Na⁺ + Cl⁻) |
| Litmus test | Blue → red | Red → blue | No colour change (neutral) |
| Taste | Sour | Bitter & slippery | Generally tasteless |
| Reaction with metal | Produces H₂ gas | Usually no reaction | Depends on salt composition |
| Reaction with carbonate | Fizzes (CO₂ gas) | No fizz | Usually no reaction |
| Common use | Vinegar, battery acid | Soap, cleaning agents | Table salt, fertilizers |
Everyday examples that make the concepts stick
Think of a lemon as a natural acid – it contains citric acid that can dissolve tiny bits of metal (that’s why old coins get dull). Soap is a base; it grabs grease molecules like a magnet, making them wash away. Sea water is a salty solution; the salt (mainly sodium chloride) stays dissolved until you evaporate the water, leaving crystals behind.
Bullet‑point revision
- Acids donate H⁺, taste sour, turn blue litmus red.
- Bases accept H⁺ or give OH⁻, feel slippery, turn red litmus blue.
- Salts are neutral products of acid‑base reactions; they may hydrolyse.
- All three conduct electricity in aqueous solution because they produce ions.
- Typical reactions: acid + metal → H₂, acid + carbonate → CO₂, base + fat → soap, salt + water → hydrolysis.
📝 Likely Exam Questions
- State two physical and two chemical properties of acids. Answer: Physical – sour taste, conducts electricity, liquid at room temperature, pungent smell. Chemical – reacts with metals to release H₂, reacts with carbonates to produce CO₂, neutralises bases.
- Write the balanced equation for the reaction between hydrochloric acid and zinc. Answer:
Zn + 2HCl → ZnCl₂ + H₂↑ - Why does a solution of sodium carbonate feel alkaline even though it is a salt? Answer: Sodium carbonate hydrolyses in water to produce carbonate ions that react with water to form hydroxide ions, making the solution basic.
- Explain how soap is formed from a base. Answer: In saponification, a strong base like NaOH reacts with triglycerides (fats) breaking the ester bonds and producing glycerol and fatty acid salts (soap).
- Compare the pH values of a typical acid, base and salt solution. Answer: Acidic solution: pH 7 (e.g., 12 for household bleach). Neutral salt solution: pH ≈ 7 unless the salt is from a strong acid‑weak base pair, which may be slightly acidic or basic.