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Hazard Symbols

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)

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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.(
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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)
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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.
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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
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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

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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.
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Testing For Chlorine & Hydrogen Gas

Chlorine (Cl)

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 (H)

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.

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Electrolysis #2

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.
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