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*Revision Materials and Past Papers* 2.1.1 Atomic structure and isotopes 2.1.2 Compounds, formulae and equations 2.1.3 Amount of substance 2.1.4 Acids 2.1.5 Redox 2.2.1 Electron structure 2.2.2 Bonding and structure 3.1.1 Periodicity 3.1.2 Group 2 3.1.3 The halogens 3.1.4 Qualitative analysis 3.2.1 Enthalpy 3.2.2 Reaction Rates 3.2.3 Chemical equilibrium 4.1 Basic concepts and hydrocarbons 4.1.2 Alkanes 4.1.3 Alkenes 4.2.1 Alcohols 4.2.2 Haloalkanes 4.2.3 Organic synthesis 4.2.4 Analytical techniques 5.1.1 How fast? 5.1.2 How far? 5.1.3 Acids, bases and buffers 5.2.1 Lattice enthalpy 5.2.2 Enthalpy and entropy 5.2.3 Redox and electrode potentials 5.3.1 Transition elements 5.3.2 Qualitative analysis 6.1.1 Aromatic compounds 6.1.2 Carbonyl compounds 6.1.3 Carboxylic acids and esters 6.2.1 Amines 6.2.2 Amino acids, amides and chirality 6.2.3 Polyesters and polyamides 6.2.4 Carbon–carbon bond formation 6.2.5 Organic synthesis 6.3.1 Chromatography and qualitative analysis 6.3.2 Spectroscopy Required Practicals

Required Practicals

1 Moles determination 2 Acid–base titration 3 Enthalpy determination 4 Qualitative analysis of ions 5 Synthesis of an organic liquid 6 Synthesis of an organic solid 7 Qualitative analysis of organic functional groups 8 Electrochemical cells 9 Rates of reaction – continuous monitoring method 10 Rates of reaction – initial rates method 11 pH measurement 12 Research skills

Core Practical 11: pH Measurement

Aim: To determine the pH of a series of unknown solutions and identify them by comparison with expected values.

Safety and Disposal

Apparatus and Chemicals

Apparatus

Chemicals (all 0.1 mol dm⁻³, unknown to the student)

Method

Sample Preparation

Adding samples of unknown solutions to boiling tubes for pH testing.

Add 5 cm³ of each unknown solution (labelled A–G) into separate boiling tubes.

Indicator Testing

Universal indicator paper test with colour chart comparison.
  1. Dip universal indicator paper into each solution.
  2. Compare the colour to the pH chart and record approximate values.

Precise pH Measurement

pH meter being used to measure solution pH after calibration.
  1. Rinse the pH probe with distilled water and gently blot dry.
  2. Place the probe into each solution and record the pH from the digital meter.
  3. Rinse between each measurement to avoid contamination.

Acid/Base Classification

Example Results (Typical pH Values)

Solution pH Likely Identity
A1.5Hydrochloric acid
B3.0Methanoic acid
C4.7Ethanoate buffer
D5.0Ethanoic acid
E9.8Ammonia (weak base)
F13.0Sodium hydroxide
G1.2Sulfuric acid

Optional Titration Curve

Use a data logger to monitor pH changes during titration of a suspected base into a suspected acid.

Burette setup for titration with pH probe to monitor pH change.

The shape of the curve helps confirm whether the acid/base is strong or weak.

Titration curve strong acid vs strong base. Titration curve weak acid vs strong base. Titration curve strong acid vs weak base. Titration curve weak acid vs weak base.

Evaluation and Sources of Error

Improvements