Chemistry C4

  • Created by: abbiedye
  • Created on: 25-07-18 14:11

What is the pH scale?

  • A measure of how acidic or alkaline a solution is
  • The lower the pH, the more acidic and the higher the pH, the more alkaline
  • A neutral substance has a pH of 7
  • A universal indicator indicates red, orange, or yellow for an acid, green for a neutral substance, and blue or green for an alkali
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How do acids and bases neutralise each other?

  • An acid is a substance that forms aqueous solutions in a pH less than 7 and forms H+ ions in water
  • A base is a substance with a pH greater than 7
  • An alkali is a base that dissolves in a solution that has a pH greater than 7. It forms OH- ions in water
  • acid + base -> salt + water
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What are strong and weak gases?

  • Concentration is different to strength
  • Strong acids (like sulphuric, hydrochloric and nitric acids) ionise completely in water and all acid particles dissociate to release H+ ions
  • Weak acids (like ethanoic, citric and carbonic acids) do not fully ionise in solution, only a small amount of acid particles dissociate to release H+ ions and the reactions are reversible
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How do metal oxides/hydroxides react with acids?

  • acid + metal oxide -> salt + water
  • acid + metal hyrdroxide -> salt + water
  • hydrochloric acid + copper oxide -> copper chloride + water
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How do acid and metal carbonates produce CO2?

  • Metal carbonates are also bases. They react with acids to produce a salt, water and carbon dioxide
  • acid + metal carbonate -> salt + water + carbon dioxide
  • hydrochloric acid + sodium carbonate -> sodium chloride + water + carbon dioxide
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What is the Reactivity Series?

  • Potassium - K
  • Sodium - Na
  • Lithium - Li
  • Calcium - Ca
  • Magnesium - Mg
  • Carbon - C
  • Zinc - Zn
  • Iron - Fe
  • Hydrogen - H
  • Copper - Cu

Potassium, sodium, lithium, and calcium are very reactive

Magnesium, carbon, zinc, and iron are very reactive

Hydrogen and copper are not very reactive

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How do metals react with acids?

  • Metals react with acids to produce a salt and hydrogen gas
  • acid + metal -> salt + hydrogen
  • The speed of a reaction is indicated by the rate at which bubbles of hydrogen are given off
  • The more reactive the metal, the faster the reaction
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How do metals react with water?

  • metal + water -> metal hydroxide + hydrogen
  • example - Ca(s) + 2H2O(l) -> Ca(OH)2(aq) + H2(g)
  • The metals potassium, sodium, lithium and calcium react with water and the metals zinc, iron and copper won't react with water
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How are metals separated from their oxides?

Formation of metal ore:

  • Oxidation = Gain of Oxygen
  • E.g. magnesium is oxidised to make magnesium oxide
  • 2Mg + O2 -> 2MgO

Extraction of metal:

  • Reduction = Loss of Oxygen
  • E.g. copper oxide is reduced to copper
  • 2CuO + C -> 2Cu + CO2
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What metals are extracted by reduction with Carbon

Some metals can be extracted from their ores chemically by reduction using carbon

  • In the reactivity series, if a metal is below carbon, it can be extracted by reduction using carbon. These metals are zinc, iron, and copper
  • In the reactivity series, if a metal is above carbon, it can be extracted by electrolysis. These metals are potassium, sodium, lithium, calcium, and magnesium
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What are redox reactions?

  • Displacement reactions
  • A more reactive metal will displace a less reactive metal from its compound
  • iron + copper sulfate -> iron sulfate + copper (iron is more reactive)
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What is electrolysis?

  • An electric current is passed through an electrolyte. Ions move towards the electrodes where they react and the compound decomposes
  • Positive ions move towards the cathode (negative electrode) and gain electrons (reduced)
  • Negative ions move towards the anode (positive electrode) and lose electrons (oxidised)
  • It creates a flow of charge and as they gain or lose electrons, they are discharged from the electrolyte
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How does electrolysis of aqueous solutions occur?

  • As well as ions, there is hydrogen ions and hydroxide ions from the water
  • Cathode - if H+ ions and metal ions are present, hydrogen gas will be produced is the metal is more reactive - if not, a solid layer of pure metal is produced
  • Anode - if OH- and halide ions are present, molecules of chlorine, bromine or iodine will be formed - if no halide ions, OH- ions are discharged and oxygen is formed
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