investigating pH

aim

  • To investigate the changes in pH of a fixed volume of dilute HCl on addition of varying amounts of a solid base

materials:

  • Dilute HCl (0.5M or 1M), solid base such as CaO or Ca(OH)2

  • Conical flask, 25 cm3 or 50 cm3 volumetric pipette, glass rod

  • Spatula and weighing boat

  • pH probe or Universal Indicator paper

method:

  • Use a pipette to measure a fixed volume of dilute HCl into a conical flask

  • Add one spatula of calcium oxide or calcium hydroxide to the flask and swirl

  • When all the base has reacted record the pH of the solution

  • If using U.I. paper use the glass rod to extract a sample from the flask

  • Repeat for different numbers of spatula (1-10) of solid but the same volume of HCl

  • Record your results neatly in table format

analysis of results:

  • Plot a graph of the amount of the base on the X-axis against the pH recorded on the Y-axis

  • The resulting graph should look something like the one below

conclusion:

  • The graph indicates a sudden change in pH which corresponds to the vertical section of the graph

  • This indicates that the more solid base is added the higher the pH, therefore the base is neutralising the acid

  • From the sample graph it can be seen that 6 spatulas of the base are required to completely neutralise the acid

hazards, risks and precautions

  • Copper(II) oxide can cause serious eye irritation and is a skin irritant. It is harmful if swallowed or inhaled and is toxic to aquatic life

  • Dilute hydrochloric acid is not classified as hazardous at the concentrations typically used in this practical, however it may still cause harm to the eyes or the skin

  • For both substances, avoid contact with the skin and use safety goggles

  • For copper(II) oxide, care should be taken not to inhale the powder