Chemical changes

• Explain the properties of alkalis and acids

  Acids: form H+ ions when dissolved in water, measured using pH scale, 1 being highly acidic, 6 being not highly acidic

  Alkalis: forms OH- ions when dissolved in water, an alkali is a type of base
• Describe the pH scale and it's features

  pH of 7 = neutral

  pH < 7 = acid

  pH > 7 = alkali

  Strong acids: pH close to zero, H+ ions

  Strong alaklis: close to 14 pH, form OH-
• Define the three main metal reactions

  Metal + oxygen = metal oxide

  Metal + water = metal hydroxide + hydrogen

  Metal + acid = salt + hydrogen
• What are the main three rules for ionic equations and what are they used for?

  ionic equations are used to show displacement reactions

  (displacement reaction = when a more reactive element dispalces a less reactive element)

  RULES:

  -do not include spectator ions

  -include all charges

  -include state symbols
• explain OILRIG

  Oxidation

  Is

  Loss (electrons)

  Rig

  Is

  Gain (electrons)
• define strong and weak acids

  Strong acid = will ionise completely in a solution

  Weak acid = will not ionise completely in a solution

  Dilute = low concentration (little bit)

  Concentrated = high concentration (lots of it)
• Define the three neutralisation reactions

  Acid + metal carbonate = salt + water + carbon dioxide

  Acid + base = salt + water

  Acid + Alkali = salt + water
• What are the two alternative ways to extract metal?

  Phytomining: plants growing on low-grade ore contaminated land, absorbs copper ions, plants then harvested and burnt, ash contains a large concentration of copper ions [ negative: too much space, burning plants ] [positive: no mining, no fossil fuel emmissions/land scarring]

  Bioleaching: bacteria mixed with low-grade ores, bacteria mixed with ores, bacteria converts copper creating a leachate solution [slow!]
• What is a displacement reaction?


  A reaction where a more reactive metal displaces a less reactive metal a compound
• How are unreactive metals found in earth?


  In their natural state!
• How can metals less reactive than carbon be extracted?


  -Reduction with carbon - carbon displaces the metal in a metal oxide - gets oxidised to carbon oxides - metal from the metal oxide gets reduced to the pure metal!
• How are metals more reactive than carbon extracted?


  By electrolysis
• How are oxidation and reduction defined in terms of electron transfer?


  Oxidation - loss of electrons

  Reduction - gain electrons
• Which metals in the reactivity series will react with acid?


  Those above hydrogen
• What is a redox reaction?


  A reaction where both oxidation and reduction occurs!
• How is a soluble salt formed?


  -React the excess acid with some insoluble chemical

  -Filter off the leftovers

  -Crystallise the product
• What do acids and alkalis produce in aqueous solutions?


  Acids produce hydrogen ions and alkalis produce hydroxide ions!
• What are bases, acids and alkalis?


  -Bases are compounds that neutralise acids, acids produce hydrogen ions in aqueous solutions, alkalis are soluble bases - which produce hydroxide ions in aqueous solutions!
• What is electrolysis?


  The passing of an electric current through ionic substances that are molten or in a solution to break them down into elements ; ions are discharged (the lose/gain electrons) at electrodes to produce these
• What is an electrolyte?


  The liquid/solution which conducts electricity
• What is a cathode and what is an anode?


  Cathode is the negative electrode and anode is the positive electrode!
• What occurs at the cathode and anode during electrolysis?


  Reduction occurs at the cathode

  Oxidation occurs at the anode
• In aqueous electrolysis, which element is discharged at the cathode? Oxygen is produced at the anode unless what?


  The less reactive element discharges at the cathode - hydrogen is produced unless there is a less reactive metal, in which case the said metal is produced, oxygen is produced at the anode unless the solution contains halide - in which the halogen molecules are produced!
• How is aluminium manufactured? Why is it expensive?

  Aluminium is made through the electrolysis of aluminium oxide and cryolite - lots of energy is needed to produce the current in electrolysis which makes this process expensive!
• What are the half equations in the extraction of aluminium?


  Al3+ + 3e- -> Al (cathode)

  202- -> 02 + 4e- (anode)

  Oxygen reacts with c of the anode producing CO2 also!
• Why is cryolite used in manufacturing of aluminium?


  It lowers the melting point of the aluminium oxide, reducing energy costs!
• What are the half equations in electrolysis of the aqueous Na2S04?


  CATHODE : 2H+ + 2E- -> H2

  ANODE : 40H- -> 2H20 + 4E-
• In electrolysis, what is the positive and negative electrode called?


  NEGATIVE ELECTRODE = CATHODE

  POSITIVE ELECTRODE = ANODE
• When an ionic substance is molten or dissolved, what are its ions free to do?


  Move about through its liquid or solution
• What is electrolysis?


  The process of passing a current through a substance that is either a solution or molten so that the substance can be broken down into two elements - this is electrolysis and the substance being broken down is the electrolyte!
• During electrolysis, which ions go where?


  Negatively charged ions move to the positive electrode and Positively charged ions move to the negative electrode (THINK OPPOSITES)
• Describe electrolysis of a molten ionic compound!


  -when a simple ionic compounds (ie) lead bromide, is electrolysed in the molten state, the metal (lead) is produced at the cathode and the non-metal is produced at the anode - this is because the metal is the positive ions and the non-metal is the negative!
• How can electrolysis be used to extract metals?


  Metals that are more reactive than carbon (PSCMAZINTC), so too reactive to be extracted by reduction with carbon are extracted by electrolysis!

  -large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current!
• How is aluminium manufactured?

  Aluminium is manufactured by the electroylsis of a molent mixture of aluminium oxide and cryolite using carbon as the anode!

  -aluminium oxide has a very high melting point - expensive - therfore it is mixed with cryolite to lower the melting point

  -the positive electrodes also need to be continually replaced because oxygen is formed - which reacts with the carbon of the positive electrodes forming CO2!
• What occurs during the electrolysis of aqueous solutions?


  The ions discharged depend on the relative reactivity of the elements involved.
• What is produced at the cathode during electrolysis of an aqueous solution?


  Hydrogen is produced unless the metal is less reactive than hydrogen.
• Why do more reactive ions prefer to stay within the solution during electrolysis?


  Because they are less likely to be discharged compared to less reactive ions.
• What occurs during the electrolysis of aqueous solutions?


  The ions discharged depend on the relative reactivity of the elements involved.
• What happens at the anode if OH- and halide ions are present during electrolysis?


  One of the halide ions will be produced.
• What determines the ions discharged at the cathode during electrolysis?


  It depends on whether the metal is less reactive than hydrogen.