C4-Chemical Changes

• Acids are substances that have a pH between 1 - 6
• Neutral solutions have a pH of 7
• Alkali solutions have a pH between 8 - 14
• Acids form H+ ions in water
• Alkalis form OH- ions in water
• Reaction between acid and base (neutralisation) :

  acid + base $\rightarrow$ salt + water
• Practical:Titration

  • pour known concentration of alkali into a beaker
  • using a volumetric pipette and a pipette filler draw up exactly 25 cm$^3$ of alkali
  • add a few drops of indicator to the alkali in the conical flask
  • set up the retort and burette then fill the burette with acid of an unknown concentration using a funnel
  • Record the starting volume of acid in the burette
  • Place the conical flask under the burette allowing acid to run into the conical flask whilst swirling
  • At the end there will be a permanent colour change, close the tap and record the volume of acid
  • Repeat process
• • Strong acids:
  • Completely dissociate in water so more H+ ions are released. This increases concentration, increasing rate of reaction making it more reactive
• • Weak acids:
  • Partially dissociate in water so less H+ ions are released. This decreases concentration, decreasing rate of reaction making it less reactive
• pH is a measure of the concentration of H+ ions in a solution
• Acid + Metal Oxide $\rightarrow$ Salt + Water
• Acid + Metal Hydroxide $\rightarrow$ Salt + Water + Carbon Dioxide
• Practical : Making Salts

  1.Measure 20 cm3 sulfuric acid into a measuring cylinder and pour it into beaker.

  2. Heat the acid gently using a Bunsen burner.

  3. Add small amounts of insoluble base in this case copper oxide in excess

  4. Filter using filter paper and funnel the solution to remove the excess copper oxide.

  5. Pour the solution into the evaporating basin. 6. Evaporate the solution using a water bath until crystals start to form. 7. Leave the evaporating basin in a cool place for at least 24 hours. 8. Gently pat the crystals dry between two pieces of filter pap
• Reactivity Series :

  • Potassium(K) Please
  • Sodium(Na) Stop
  • Lithium(Li) Literally
  • Calcium(Ca) Calling
  • Magnesium(Mg) Me
  • Aluminium(Al) A
  • Carbon(C) Careless
  • Zinc(Zn) Zebra
  • Iron(Fe) Instead
  • Tin(Sn) Try
  • Lead(Pb) Learning
  • Hydrogen (H) How
  • Copper(Cu) Copper
  • Silver(Ag) Saves
  • Gold(Au) Gold
• Acid + Metal $\rightarrow$ Salt + Hydrogen
• Metal + Water $\rightarrow$ Metal Hydroxide + Hydrogen
• Oxidation is loss of electrons
• Reduction is gain of electrons
• Metals above carbon in the reactivity series are extracted using electrolysis
• Metals below carbon in the reactivity series are extracted by reduction using carbon
• Redox reactions are when oxidation and reduction occur at the same time
• A displacement reaction is where a more reactive metal displaces a less reactive metal
• During electrolysis, positively charged ions move to the negative electrode (cathode)
• During electrolysis, negatively charged ions move to the positive electrode (anode)
• When electrolysis occurs in an aqueous solution, H+ and OH- ions are present
• What occurs at the cathode during electrolysis of an aqueous solution

  • Reduction
  • If the positive ion from compound is above hydrogen, H+ ions are discharged and hydrogen gas is produced
  • If the positive ion from compound is below hydrogen, metal ions are discharged and the metal is produced
• What occurs at the anode during electrolysis of an aqueous solution

  • Oxidation
  • If the negative ion from compound is a halide, halide ions are discharged and halide gas is produced
  • If the negative ion from compound is not a halide, OH- ions are discharged and oxygen gas is produced