SC8

• 1. Moderate Health Hazard - skin irritation
  2. Serious Health Hazard - breathing difficulties
  3. Toxic - cause death if swallowed or inhaled
  4. Corrosive - damaged skin and clothing
  5. Flammable - catches fire easily
  6. Oxidising - makes flammable substances burn more fiercely
  7. Harmful to the Environment - cause damage to animal and plant life

  
• Precautions to reduce the risk of harm:

  • use less hazardous substances (e.g. dilute acids)
  • wearing protective clothing (e.g. gloves/eye protection)
  • choosing different equipment/methods (e.g. water bath is safter than a bunsen burner)
• H+ ions are found in all acidic and alkaline solutions and determines the pH of the solution:

  • 7pH is neutral (water)
  • 1-6pH is acidic (sulfuric acid)
  • 8-14pH is alkaline (sodium hydroxide)

  The pH scale is that the concentration of H+ ions is multiplied by 10 the lower the number
• Indicators:

  • Litmus Paper - red is acidic, purple is neutral, blue is alkaline
  • Methyl Orange - red is acidic, yellow is neutral and alkaline
  • Phenolphthalein - colourless is acidic and neutral, pink is alkaline
• Acids - substances that react with water to release H+ ions

  • the higher the concentration of H+ ions in an acidic solution, the lower the pH
  • strong acids fully dissociate into water - more reactive
  • concentrated acids have more reactant particles moving together - more reactive
• Acid Types:

  • Dilute - small amount of acid and lots of water (low concentration of H+ ions)
  • Concentrated - large amounts of acid and a bit of water (high concentration of H+ ions)
  • Weak - don't completely dissociate in water to produce minimum H+ ions
  • Strong - completely dissociate in water to produce maximum H+ ions
• Bases - substances that react with acids to form salt and water (sometimes CO2) in neutralisation

  • This includes metal oxides/hydroxides and carbonates
  • In neutralisation, a salt will always be produced
• Neutralisation Reactions:

  • metal + acid ---> salt + hydrogen
  • metal oxide + acid ---> salt + water
  • metal hydroxide + acid ---> salt + water
  • metal carbonate + acid ---> salt + water + carbon dioxide
  • ammonia + acid ---> ammonium salt
• Crystal Practical - make soluble salt from an acid and insoluble reactant:

  1. Add powdered insoluble reactant to acid in beaker one spatula each time
  2. Stir and continue until excess or all acid has reacted
  3. Filter mixture in beaker to remove excess solid so filtrate only contains salt and water
  4. Heat solution on evaporating dish over water bath and stop when small crystals appear around the edges (solution now saturated)
  5. Leave saturated solution at room temperature for 1-2 days to allow large crystals to form
  6. Dry crystals by dabbing gently with filter paper (pure salt crystals)
• Alkalis are a special type of base that reacts with water to release OH- ions.

  They're soluble bases that also react with acids to neutralise into salt and water (e.g. ammonia)
• During neutralisation, the H+ ions from the acid join with the OH- ions from the alkali which is what forms water.

  Titration is used to prepare soluble salts due to the absence of surplus insoluble reactants that require a filtration methods for removal
• Acid-Alkali Titration Practical:

  1. Use pipette/filler to add 25cm3 alkali to clean conical flask
  2. Add few drops of indicator and put conical flask on white tile
  3. Fill burette with acid and note starting volume
  4. Slowly add acid from burette to alkali in conical flask, swirling to mix
  5. Stop adding acid when appropriate colour change in indicator happens (end point reached) and note final volume reading
• Metal in an Acid:

  • metal gets smaller as its used up in the chemical reaction
  • bubbles (effervescence) produced from hydrogen gas
• Test for Hydrogen:

  Hold a burning splint over the area with the gas. If H2 is present then a small explosion making a squeaky pop will he heard
• Metal Carbonate in an Acid:

  • CO2 causes bubbling (effervescence)
  • exothermic reaction
  • adding sodium carbonate solution will create CO2 in any acid
• Test for Carbon Dioxide:

  Pass the gas through limewater. If it turns cloudy there is CO2 present
• Soluble in Water:

  • all common sodium/potassium/ammonium salts
  • all nitrates
  • most chlorides/sulfates
  • sodium/potassium/ammonium carbohydrates and hydroxides
• Insoluble in Water:

  • silver/lead chlorides
  • lead/barium/calcium sulfates
  • most carbonates
  • most hydroxides
• Formation of precipitate, when mixing 2 solutions, can be predicted using solubility rule table:

  • if products meet soluble rules, no precipitate will form
  • if at least one product meets insoluble rule, precipitate will form
• Making Insoluble Salts Practical:

  1. 1 spatula lead nitrate into test tube and add deionised water to dissolve it, shaking thoroughly
  2. Tip 2 solutions into small beaker and stir so lead chloride precipitates
  3. Put filter paper into filter funnel that goes into conical flask
  4. Pour beaker contents into filter paper middle (avoid overflowing)
  5. Swill out beaker with deionised water and tip into filter paper to ensure all precipitate goes
  6. Wash away all soluble sodium nitrate with deionised water in filter paper
  7. Scrape lead chloride onto fresh filter paper and leave to dry in oven/desiccator