C4 Chemical Changes

• What is an oxidation reaction?

  Where a substance often gains oxygen
• What is a reduction reaction?

  Where a substance often loses oxygen
• What always occurs together?

  Oxidation and reduction.
• What do metals react with oxygen to form?

  Metal oxides
• How can metal oxides be reduced?

  By removing oxygen
• What happens when metals react?

  Their atoms lose electrons to form positive metal ions.

  Some metals lose electrons more easily than others.

  The more easily a metal atoms loses electrons, the more reactive it is.
• What is the reaction of metals with acid and water used to do?

  Place metals in order of reactivity, this is called the reactivity series.
• What do metals react with acids to produce?

  Metal salts and hydrogen.
• What are some very reactive metals?

  Lithium, sodium and potassium.

  They react vigorously with water to produce a metal hydroxide solution and hydrogen.
• How do lithium, sodium and potassium react with dilute acids?

  So vigorously that is would not be safe to carry out the reactions.
• How do calcium, magnesium, zinc and iron react with acid and water?

  They react quickly with acids.

  They react slowly with water.
• How do unreactive metals, like copper and gold, react with acid and water?

  They do not react with acids or water.
• What does the reactivity series often include for comparison?

  Carbon and hydrogen.
• What is the reactivity series?

  Potassium, K

  Sodium, Na

  Lithium, Li

  Calcium, Ca

  Magnesium, Mg

  Aluminium, Al

  Carbon, C

  Zinc, Zn

  Iron, Fe

  Tin, Sn

  Lead, Pb

  Hydrogen, H

  Copper, Cu

  Silver, Ag

  Gold, Au

  Platinum, Pt
• What is a displacement reaction?

  Where a more reactive metal will displace a less reactive metal from a solution of it's salt.
• What does the method of extraction of a metal depend on?

  How reactive it is
• What do unreactive elements exist as?

  Elements at the earth's surface
• What are most metals found as?

  Metal oxides, or as compounds that can be easily changed into metal oxides.
• How can metals that are less reactive than carbon be extracted from their oxides?

  By heating them with carbon.

  E.g. iron oxide + carbon > iron + carbon dioxide

  The iron losses oxygen, so it is reduced.

  The carbon gains oxygen, so it is oxidised.
• How can metals that are more reactive than carbon be extracted?

  From molten compounds by electrolysis.
• What do not all reduction and oxidation reactions involve?

  Oxygen
• What do scientists define oxidation as?

  The loss of electrons
• What do scientists define reduction as?

  The gain of electrons
• What happens when substances dissolve in water?

  They dissolve into their individual ions:

  Hydroxide ions, OH-(aq), make solutions alkaline.

  Hydrogen ions, H+(aq), make solutions acidic.
• What is the pH scale?

  A measure of the acidity or alkalinity of an aqueous solution.
• What does a pH of 7 mean?

  The solution is neutral
• What does a pH less than 7 mean?

  Solutions are acidic.

  The closer to a pH of zero, the stronger the acid.
• What does a pH of more than 7 mean?

  The solution is alkaline.

  The closer to a pH of 14, the stronger the alkali.
• How can you measure the pH of a solution?

  A pH probe or universal indicator.
• What are indicators?

  Dyes that can change colour depending on whether they are in acidic or alkaline solutions.
• What does litmus do?

  Change colour from red to blue or vice versa, depending on the pH.
• What does universal indicator do?

  It is a mixture of dyes that shows a range of colours to indicate how acidic or alkaline a substance is
• What are soluble bases?

  Alkalis
• How are acids neutralised?

  Bases.

  Acid + metal hydroxide > salt + water
• What ions do acids contain?

  Hydrogen ions, H+(aq)
• What ions do alkalis contain?

  Hydroxide ions, OH-(aq)
• What happens when an acid reacts with an alkali?

  The H+ and OH- ions react together to produce water, H2O, which has a pH of 7.

  H+(aq) + OH-(aq) > H2O(l)
• Why is this reaction called neutralisation?

  Acid is neutralised by an alkali.

  The solution that remains has a pH of 7, showing it is neutral.
• What can acids also be neutralised by?

  Metal oxides and metal carbonates.

  Acid + metal oxide > salt + water

  Acid + metal carbonate > salt + water + carbon dioxide
• How is a salt produced in neutralisation?

  The hydrogen in the acid is replaced by a metal ion