Oxidising - Provides oxygen with lets other materials burn fiercely. (Liquid oxygen)
Harmful - Like toxic but not as dangerous. (Copper sulphate)
Highly flammable - Catches fire easily. (Petrol)
Irritant - Not corrosive but can cause reddening or blistering of skin. (Bleach)
Toxic - Can cause death from swallowing, breathing in, or absorption through the skin. (Hydrogen cyanide)
Corrosive - Attacks and destroys living tissues like the eyes and skin. (Concentrated sulphuric acid)
Acids & Alkalis
Substances can be Acids, Bases or Neutral.
- An Acid is a substance whith a pH lower than 7.
- A Base is a substance with a pH higher than 7.
- An Alkali is a base that dissolves in water.
- A Neutral substance has a pH of 7.
- There's a scale from strong Acid to strong base with neutral in the middle.
Neutralisation reactions with Acids and Bases make salts.
- An Acid & Base react with one another to make a salt and water.
- The products of the reaction aren't strongly acidic or alkaline but neutral.
- This is the equation for any neutralisation reaction:
- acid + base → salt + water
Neutralisation reactions can be used to make salts which can be used for many things:
- Salts are used in fertilisers (ammounium nitrate, ammounium phosphate)
- These fertilisers are good oxidising agents, they release oxygen that helps fuler burn.
- They're also used in fireworks as colouring agents. (Calcium chloride for orange, copper chloride for blue-green)
Hydrochloric Acid & Indigestion Tablets
We rely heavily on acids and alkalis, without them even eating dinner whould be much harder to do.
- The stomache makes hydrochloric acid to help with digestion. The enzymes that break down food in the stomache work best in acidic environments.
- Having acid in the stomach helps kill bacteria making the changes of food poisoning a lot less.
- Indigestion is created by too much hydrochloric acid in the stomach. Indigestion tablets hold bases like calcium carbonate to neutralise the exess acid.
- Some remedies are more effective than others.
Reactions of Acids
Metal oxides and metal hydroxides tend to be bases, this means that they can be neutralised with acids to make salt and water.
- Acid + metal oxide/metal hydroxide → salt + water
The combination of metal and acid decides the salt...
- hydrochloric acid + copper oxide → copper chloride + water
- H2SO(ag) + ZnSO4(s) → ZnSO4(ag) + H2O(l)
- hydrochloric acid + sodium hydroxide → sodium chloride + water
- Sulphuric acid + zinc oxide → zinc sulphate + water
- Sulphuric acid + calcium hydroxide → calcium sulphate + water
- Nitric acid + magnesium oxide → magnesium nitrate + water
- Nitric acid + potassium hydroxide → potassium nitrate + water
Reactions of Acids #2
Acid + metal carbonate → salt + water + carbon dioxide
Carbonates give off carbon dioxide when they neutralise acids.
Hydrochloric acid+Sodium carbonate → Sodium+Water+Carbon dioxide
2HCl + Na2CO3 → 2NaCl + H2O + CO2
Hydrochloric acid+Calcium carbonate → Calcium chloride+Water+Carbon dioxide
2HCl + CaCO3 → CaCl2 + H2O + CO2
Electrolysis means splitting up with electricity.
- It is the decomposition of a compound using electrical energy.
- The electricity comes from a direct current (d.c.) source like a battery.
- A liquid called the electrolyte is used to conduct the electricity.
- The electricity is applied to the electrolyte by two electrodes.
- The electrolyte holds the compound, that gets broken down into its component parts.
- The component parts then get released as atoms or molecules, normally as gas.
You can Electrolyse hydrochloric acid
- The electrolyte is a dilute solution of hydrochloric acid. (HCl)
- Applying a d.c. current to the electrolyte makes the acid decompose into its 2 component parts: hydrogen gas (H2) & chlorine gas (Cl2)
- The gases bubble throughout the solution and can be gathered up at the electrodes.
Testing For Chlorine & Hydrogen Gas
Chlorine bleaches damp litmus paper, making it go white. It could also turn red for a bit before because the solution would be acidic.
Hydrogen makes a squeaky pop noise with a lighted splint . The noise is created by the hydrogen burning with the oxygen in the air to make H20.
Electrolysis of salt makes chlorine.
- Sea water or sodium cloride solution (Brine) can be decomposes by electrolysis and is a good way of producing chlorine gas.
- Chlorine gas is toxic so making it is a hazardous process.
- Chlorine is used for 3 things: treating water supplies becuase it kills bacteria and other dangerous micro-organisms making it safe to drink. It's also needed for the manufacturing of bleach. Chlorine is also used to make the polymer poly(chloroethene) - PVC.
Electrolysis of water gives hydrogen and oxygen.
- Water can be decomposed by electrolysis to give hydrogen & oxygen gas.
- Oxygen can be tested for by checking if the gas relights a glowing splint.