I/GCSE Chemistry Revision Core - 7&8

In the I/GCSE chemistry curriculum:

• Rate of reaction - how fast two components completely react with one another, can be affected by:
  1. Concentration (same as pressure in gases) - increases the amount of reactant particles therefore more of them can collide, increases rate of frequent collision of particles.
  2. Temprature - Increases KE of particles, more chance of frequent successful collisions between particles
  3. Catalyst - provides an alternatice pathaways for the reaction to travel to with lower EA, enzymes have the same thing but need certain OPTIMUM temperature needed or they become denatured.
  4. Particle Size - The smaller the particle size of a reactant, the more surface area is available for reactions, which mean there are more frequent successfull collisions.
  5. Practical method - CaCO3 (marble chips) to react with dilute hydrochloric acid. You could repeat the experiment, changing one aspect of it every time( chip size, concentration of HCl, Temperature of reaction) and time the amount of time it takes to produce a certain amount of CO2 gas. The less time it takes, the faster the rate of reaction.

• In flour mills and coal mines - Fine powder such as saw dust, sugar,coffee and flour dust is such fine powders with incredibly BIG surface areas, if it comes into contact with a spark or a flame, it can immediately be set off and cause an explosion as they are combustible.
• Reversible reactions - Reactions that can go both ways forwards and backwards depending on the conditions of the reaction (temperature,pressure).
• Hydrated copper sulphate (blue) - Anhydrous copper sulfate (white)
• Hydrated cobalt chloride (burgundy red) - Anhydrous cobalt chloride(blue)
• Oxidation reactions - Gain oxygen, Reduction - Lose oxygen , an oxidising agent is one that makes the other reactant gain oxygen, reducing agent is the reactant that makes the other reactant lose oxygen.

• In the I/GCSE chemistry, by definiton, ACIDS - reactions with metals/bases/carbonates to form metal salts
• Acid and metal make metal salt and HYDROGEN
• Acid and metal oxide/hydroxide (base) make a metal salt and WATER (netralisation reaction)
• Acid and a metal carbonate make a metal salt, CARBON DIOXIDE and WATER
• To charecterise and acid - turns BLUE litmus paper RED

• ALKALIS - react with an acid to form a metal salt and WATER- turn RED litmus paper BLUE
• All alkalis displace an ammonium compund, to make ammonia.
• Universal indicator paper - shows pH of a substance (acids-1-6), (alkalis-8-14) and a neutral substance has the pH of 7 (water).
• Plants grow best at a pH of 7 of the soil, if the soil is too acidic, they cannot grow so need to be neutralised with alkali's (LIME).

• OXIDES - oxides of metals are usually BASIC, oxides of non-metals ACIDIC.
• Preparation of salts - Soluble base (metal) - add excess metal to acid , when the bubbling has stopped the reaction is done, filter off any excess solid. If wanted crystals, you would heat the mixture gently untill solids appear, leave them to dry in a cool, damp room.

• Cations
  • Aluminium (NaOH - white ppt, soluble in excess, colourless sol/Ammonia- white ppt, insol in excess)
  • Ammonium - (NaOH-ammonia gas produced on warming-sharp pungent smell, turns red litmus blue)
  • Calcium (NaOH-white ppt, insol in excess, ammonia-same)
  • Copper (NaOH, blue ppt, insoluble in excess, ammonia-blue ppt, sol in excess giving a dark blue solution)
  • Fe2 (NaOH-green ppt insol in excess, same for ammonia)
  • Fe3 (Na OH-red-brown ppt insol in excess, same for ammonia)
  • Zinc (NaOH-white ppt soluble in  excess, colourless sol, ammonia same thing)
• Anions
  • Carbonate (add dilute acid, effervescence, Co2 produced,)
  • Chloride (add dilute nitric acid, aq silver nitrate- white ppt)
  • Iodide (dilute nitric acid, aq silver nitrate- yellow ppt)
  • Nitrate (add aq NaOH, aluminium foil , warm carefully- ammonia produced)
  • Sulphate (acidify, aq barium nitrate-white ppt)

Please remember the highlights in the I/GCSE chemistry curriculum:

• Chlorine - bleaches damp litmus paper
• CO2 - turns limewater milky
• Oxygen - relights a glowing splint
• Hydrogen - squeaky pop with lighted splint
• Ammonia - turns damp red litmus blue

End of this topic!

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