Chemical Properties of Acids
Presence of Hydrogen Ions: Acids behave the way they do mainly because when they dissolve in water, they release tiny charged particles called hydrogen ions (H⁺). These ions are very active and are the reason acids can react strongly with other substances.
Sour Taste: Acids usually have a sour taste, which you might notice in foods like lemons and vinegar. This sourness is caused by acids such as citric acid and acetic acid. However, it is extremely unsafe to taste acids in the science lab because some acids are very strong and dangerous, so we should never taste any chemicals unless supervised by a teacher with proper safety equipment.
Corrosive Nature: Acids can be very harmful because they can corrode, or eat away at, different materials. They can damage metals, clothing, and even human skin. Strong acids, like concentrated sulphuric acid, can cause severe burns or injuries if they touch skin, so we must always handle acids with care and use gloves and goggles.
Effect on Litmus Paper: An easy and quick way to find out if a solution is acidic is by using blue litmus paper. If the solution is an acid, it will turn the blue litmus paper red. This colour change happens because the hydrogen ions in acids interact with the dye in the litmus paper.
Reaction with Bases: Acids can react with bases in a type of reaction called neutralisation. During neutralisation, the acid and the base cancel each other’s effects, forming two new products: a salt and water. This process can help bring a solution back to a neutral pH.
Reaction with Reactive Metals: When acids react with reactive metals like magnesium, zinc, or iron, a chemical reaction occurs that produces a salt and hydrogen gas. You can usually see bubbles forming during the reaction, which is the hydrogen gas being released into the air.
Reaction with Metal Carbonates: Acids also react with substances called metal carbonates, like calcium carbonate. This reaction produces a salt, carbon dioxide gas, and water. The carbon dioxide gas makes bubbles or fizzing, which is an easy way to see that a reaction is happening.
Chemical Properties of Alkalis
Presence of Hydroxide Ions: Alkalis show their special chemical properties because they release hydroxide ions (OH⁻) when they dissolve in water. These hydroxide ions are responsible for making the solution alkaline and helping the alkalis react with other substances.
Soapy Feel: If you ever touch an alkali solution carefully (for example, soap, which contains alkali), you will notice it feels slippery or soapy. This is because alkalis can react with the fats and oils on your skin to form soap-like materials.
Corrosive Nature: Strong alkalis, just like strong acids, can be very dangerous. They can break down materials, harm clothing, and cause very serious burns on skin and eyes. In some cases, strong alkalis can even cause worse injuries than acids, so handling them with safety gear is very important.
Effect on Litmus Paper: To find out if a solution is alkaline, you can use red litmus paper. If the solution is an alkali, it will turn the red litmus paper blue. This clear colour change happens because of the hydroxide ions in the alkali.
Reaction with Acids: Alkalis react with acids through a neutralisation reaction, just like acids react with alkalis. When an alkali meets an acid, they react to form a salt and water. This reaction helps to balance the pH of the solution.
Reaction with Ammonium Salts: When alkalis react with ammonium salts, they produce ammonia gas, which has a strong, sharp smell that is very easy to notice. This is one way to test if an unknown gas is ammonia.
Reaction with Metal Ions: Alkalis can react with solutions containing metal ions to form insoluble metal hydroxides. These are solid substances that do not dissolve in water and often appear as coloured precipitates, which are tiny pieces of solid that float in the liquid and give it a cloudy or coloured look.