Topic 4- Chemical changes

• What is oxidation and reduction?

  oxidation is loss of electron

  reduction is gain of electrons
• What is a displacement reaction?

  A displacement reaction is where a more reactive metal can displace a less reactive metal from a compound
• What is the general equation for a reaction between metals and acids? what type of reaction is this?

  Metal + acid >>>>>> salt + hydrogen
• What is the general equation for the reaction between an acid and metal hydroxide?

  acid + metal hydroxide >>>>>> salt + water
• What is a general equation for the reaction between metal oxides and acids? 


  acid + metal oxide >>>>> salt + water
• Give a method to make a soluble salt?

  1. measure 25cm3 of the acid in a measuring cylinder then pour into a beaker and heat with a Bunsen burner
  2. add insoluble base in excess till it no longer dissolves
  3. filter it through a funnel unsung filter paper to collect excess salt to leave a dissolved form of the salt
  4. heat this solution in a water bath until crystals start to form
  5. remove from heat and leave somewhere warm for more crystals to form
  6. then filter out the crystals
• What is a strong acid?

  Strong acids completely ionise in aqueous solutions
• What is weak acid?

  Weak acids only partially dissolve in aqueous solutions and are reversible
• What happens to the pH as concentration of H+ ions increases?

  pH decreases
• What is a concentrated solution and what is a dilute acid? is the same as strong or weak acids? 


  Concentrated acids contain more moles per unit volume than dilute and is not the same as strength of an acid
• As the pH is decreased by one unit , what Change is seen in the hydrogen ion concentration?

  increases by x10
• name the following salts LiNO3, K2CO3, MgBr2, BaSO4

  Lithium nitrate , Potassium carbonate, magnesium bromide, barium sulfate
• What is electrolysis? 


  The passing of an electrical current through ionic substances that are molten or in a solution to break them down into elements; ions are discharged at electrodes to produce electrons
• What is an electrolyte?

  An aqueous or molten solution that conducts electricity
• What is the cathode? What is the anode?

  Cathode is negative electrode

  Anode in positive electrode
• What occurs at the cathode during Electrolysis?

  reduction
• What occurs at the anode in electrolysis?

  Oxidation
• In an aqueous solution, which element is discharged at the cathode? 


  The hydrogen Is always discharged unless it’s copper which is less reactive then hydrogen
• What is produced at the anode? 


  always oxygen is produced unless a halide is involved In which case halogen molecules are produced
• What are the half equations in the extraction of aluminium?

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

  2 O2- >>>>> O2 + 4e- (anode )
• What is a chemical indicator?

  an indicator is a dye that changes colour based on the pH of the solution eg universal indicator
• What is a neutralisation reaction?

  A reaction between an acid and a base in which H+ ions are formed from the base and react with OH- ions from base H+ + OH- >>>>> H2O
• What ions do acids form in water?

  H+
• What is a base?

  a substance that can neutralise an acid
• What is an alkali?

  a base that dissolves in water to form a solution with a pH of greater then 7
• what ions do alkalis form in water?

  OH-
• What is a strong acid?

  an acid that completely ionises in an aqueous solution
• What is a weak acid?

  an acid that partially ionises in an aqueous solution
• How does pH differ between strong and weak acids if they're the same concentration?

  the strong acid will have a lower pH as it fully ionises and realises more H+ ions
• Which category of acids are weak acids?

  carboxylic acids
• why are strong acids more reactive than weak acids?

  Strong acids have a greater concentration of H+ ions so more will react in a given amount of time increasing rate of reaction
• What is the ionic equation for neutralisation?

  H+ + OH- >>>>> H2O
• What is the general word equation for the reaction between an acid and metal carbonate?

  acid + metal carbonate >>>> salt + water + carbon dioxide
• What is the effect of using reactants with increased reactivity in a reaction?

  mean reaction will take place more quickly or vigorously
• How can you investigate the reactivity of a metal using an acid?

  react metal with acid when metal reacts bubbles of hydogen will be released the faster the bubbles are produced the faster the rate of reaction is so the more reactive the metal is
• How can you investigate the reactivity of metals using temperature change?

  the more reactive the metal the greater the temperature change
• Why can it be dangerous to react very reactive metals with acids or water?

  can react explosively and produce many bubbles
• What metals don’t react with water?

  less reactive metals like zinc iron and copper
• In displacement reactions which ions are reduced? 


  metal ions are reduced meaning they gain ions
• What does electrolysis mean?

  means electricity breaking something apart