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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 9: Continuous Monitoring of Rates of Reaction

Aim: To measure how the rate of reaction changes with different concentrations of hydrochloric acid (HCl) by collecting the hydrogen gas (H₂) produced during its reaction with magnesium (Mg), and to use this data to calculate the rate of reaction over time.

Chemical Equation

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

Apparatus and Chemicals

Apparatus

Chemicals

Method

Experimental setup showing magnesium reacting with hydrochloric acid and hydrogen gas collected in a gas syringe.
  1. Setup: Assemble the gas syringe or inverted measuring cylinder and secure with clamps.
  2. Initial Reaction: Add 50 cm³ of HCl of known concentration to the conical flask. Add the magnesium ribbon, insert the bung quickly, and start the stopwatch immediately.
  3. Data Collection: Record the volume of hydrogen gas collected every 15 seconds for at least 2.5 minutes, or until the reaction stops.
  4. Repeat: Carry out the experiment with other HCl concentrations (0.25, 0.5, and 1.0 mol dm⁻³).

Example Data Table

Time (s) Volume of H2 (cm3) at 1.0 mol dm−3
00
1525
3041
4553
6060
7565
9067
10568
12068

Analysis and Calculations

Plotting Results: Plot a graph of volume of H₂ vs time. The gradient gives the rate of reaction.

Initial Rate

Rate of reaction graph showing tangent at t = 0 s to determine initial rate.

Draw a tangent at time = 0 s.
Initial Rate = ΔVolume / ΔTime

Comparative Analysis

Graphs showing how order of reaction with respect to concentration can be identified.

Sample Initial Rate Calculation

From graph: At 1.0 mol dm⁻³, 25 cm³ of gas is produced in 15 seconds.
Rate = 25 cm³ ÷ 15 s = 1.67 cm³ s⁻¹

Sources of Error

Improvements