CC8 core practicals

• core practical: investigating pH.

  investigate what happens to the pH of a fixed volume of dilute hydrochloric acid when you add calcium hydroxide.

  apparatus:

  • 100cm3 beaker
  • 50cm3 measuring cylinder
  • 0.1g balance
  • spatula and stirring rod
  • white tile
  • universal indicator paper
  • pH colour chart
  • diluce hydrochloric acid
  • calcium hydroxide powder
  • graph paper
  • eye protection
• Method for investigating pH

  1. Use measuring cylinder to add 50cm3 of dilute HCl to the beaker

  2. Put universal indicator paper onto the white tile

  3. Dip the end of the glass rod into the liquid, then tap it onto the paper

  4. Wait 30 seconds, then match the colour to the appropriate pH on the colour chart

  5. Rinse the glass rod with water

  6. Measure 0.3g of calcium hydroxide powder onto a piece of paper

  7. Add to the beaker, stir, estimate and record pH of mixture

  8. Repeat step 7 around 7 times so you add a total of 2.4g of powder to the acid

  9. Plot a line graph with pH on the y axis and mass of calcium hydroxide added on the x axis, draw a curve of best fit

  10. Use the graph to determine what mass is needed to reach pH 7
• how would you improve the accuracy in finding pH?

  by using a pH meter.
• core practical- preparing a salt from an insoluble base.

  pure, dry copper sulphate crystals

  apparatus:

  • eye protection
  • 100cm3 conical flask and beaker
  • bunsen burner
  • dish/crucible
  • 100cm3 measuring cylinder
  • spatula, stirring rod, filter funnel and filter paper
  • water bath
  • copper III oxide and dilute sulphuric acid

  
• Method and reasons

  1. Pour dilute sulphuric acid into a conical flask

  2. Heat in a water bath to heat up acid and speed up reaction

  3. Add an excess of copper oxide (ensure all the acid is neutralised) using the spatula

  4. Stir until the black powder does not disappear- no acid left to react with/reaction is complete

  5. Filter the mixture into a beaker and pour into an evaporating basin

  6. Heat the basin on top of a beaker with water using a bunsen burner blue flame

  7. Heat until half the water is evaporated, and allow basin to cool and water to evaporate on its own to leave large, blue crystals

  8. Pat dry
• Preparing salt from a soluble base - titration

  1. Place acid in a (clean) burette with lots of graduations and a tap to add acid dropwise

  2. Place a known volume of alkali measured with a pipette and a few drops of indicator (phenolphthalein or methyl orange which have sharp colour changes) in a conical flask

  3. Use white tile to see clearly a colour change when you add acid to alkali

  4. Note exact volume of acid added and repeat until you have 3 almost identical volumes (concordant results)

  5. Repeat without the indicator- cannot be removed so would contaminate salt

  6. Heat to evaporate water and leave crystals to dry