CC8 & electrolysis

• Ions that make aqueous solutions acidic

  Hydrogen ions (H+)
• Ions that make aqueous solutions alkaline

  Hydroxide ions (OH-)
• what is the pH scale?

  the measurement of how acidic or alkaline a solution is
• pH ranges


  • Acid - Less than pH 7 (pH 1 is most acidic)
  • Neutral - pH 7
  • Alkali - Greater than pH 7 (pH 14 is most alkaline)
• Methods to measure pH

  • Universal indicator
  • pH probe
• Blue litmus paper in alkali

  Stays blue
• Red litmus paper in acid

  Stays red
• Red litmus paper in alkali

  Turns blue
• Problem with using universal indicator to test pH is that the colour of the solution is matched to a pH colour on the chart, which is quite subjective as people may disagree with which colour the solution matches. It doesn't provide an exact pH value.
• Acid X has a pH 1. What does this mean in terms of its concentration?


  High concentration of hydrogen ions, making it a strong acid
• Alkali Y with pH 8.5


  Low concentration of hydroxide ions, making it a weak alkali
• If pH decreases by one unit, the hydrogen ion concentration increases by a factor of 10
• Neutralisation reaction


  Reaction between an acid and a base where H+ ions from the acid react with OH- ions from the alkali to form water
• Ionic equation for neutralisation

  H+(aq) + OH-(aq) → H2O(l)
• Concentrated vs dilute acid

  Concentrated acids have a great amount of acid compared to the volume of water than dilute acids. Concentration is not the same as strength, which refers to whether the acid has completely dissociated in water or not.
• What do you call a partially dissociating acid?

  Weak acid
• Base


  Any substance that reacts with an acid to form salt and water only
• Alkalis are soluble bases, not insoluble bases
• Products of acid reacting with metal

  Salt and hydrogen
• Products of acid reacting with metal oxide


  Salt and water
• Products of acid reacting with metal hydroxide

  Salt and water
• Products of acid reacting with metal carbonate

  Salt, water and carbon dioxide
• Metal oxides are bases rather than alkalis because they are normally insoluble
• What are the products when an acid reacts with a metal hydroxide?

  Acid + metal hydroxide → salt + water
• What are the products when an acid reacts with a metal carbonate?

  Acid + metal carbonate → salt + water + carbon dioxide
• Metal oxides


  Normally bases rather than alkalis because they are insoluble, while alkalis are soluble
• Magnesium sulfate


  The name of the salt formed from magnesium and sulfuric acid
• Zinc nitrate


  The name of the salt formed from zinc oxide and nitric acid
• Calcium chloride


  The name of the salt formed from calcium carbonate and hydrochloric acid
• Describe the chemical test for hydrogen

  Light a splint and place it at the neck of a test tube. If hydrogen is present a 'squeaky pop' will be heard
• Describe the chemical test for carbon dioxide

  Bubble the gas through limewater (calcium hydroxide). Limewater turns cloudy if carbon dioxide is present.
• Excess of the insoluble reactant


  Added when preparing a soluble salt from an acid and an insoluble reactant, to ensure all the acid reacts
• How and why is the excess reactant removed?

  By filtration, to leave a pure solution of the salt
• What method must be used to prepare a salt from an acid and a soluble reactant?

  Titration, since both reactants are soluble and this allows combining them exactly to avoid excess
• Filtration


  The method that could be used to prepare a sample of soluble copper sulfate from insoluble copper oxide and sulfuric acid
• What 3 steps are required when producing a pure dry salt from an acid and alkali?

  Complete a titration to find the volume of acid that reacts exactly with a set volume of alkali. 2. Use the results from the titration to mix the acid and alkali in the correct proportions. 3. Evaporate the water from the solution, leaving pure dry salt crystals.
• Describe how to carry out an acid-alkali titration


  Use a pipette to add a measured volume of acid to the conical flask then add a few drops of indicator. Place on a white tile. 2. Fill the burette with the alkali, noting the initial volume. 3. Add the alkali to the conical flask. First complete a rough trial to find the end point (the point at which the indicator first changes colour). 4. Repeat, adding the alkali drop by drop near the end point and swirling the flask constantly to mix. 5. Record the final volume in the burette. Repeat until you have concordant results.
• Silver chloride and lead chloride


  The two exceptions to most common chlorides being soluble
• All nitrates are soluble
• All common sodium, potassium and ammonium salts are soluble