Applying Technology to Collect Data in Chemistry (HL IB Chemistry)

• Computational chemistry is an advanced field that involves the use of computer simulations and theoretical methods to study chemical systems and investigate chemical reactions
• It also involves the use of computers to identify trends and make predictions from large data sets, for example of reactivity or molecular properties
• These large data sets can be collected experimentally for example, via the use of sensors, from existing databases or from models and simulations

Collecting data using data loggers and sensors

• Using a data logger and different sensors are essential in many scientific experiments for obtaining and analysing reliable results

Data loggers

• Sensors can be used to measure various physical and chemical properties of substances
• Sensors are input devices that detect and respond to specific changes in their surroundings, converting the detected information into electrical signals stored within the data logger
• Sensors allow chemists to easily collect large sets of data in a short space of time 
• Here are some common types of sensors used in chemistry and how they can be applied:

pH meters

• pH meters measure the acidity or alkalinity of a solution expressed as a pH value
• A pH value is a measure of the concentration of hydrogen ions (H⁺) in the solution
• A pH meter consists of two electrodes, one is a reference electrode and the other contains a special glass membrane that is sensitive to changes in the concentration of H⁺ ions in the solution
• When the pH meter is immersed in the solution, the pH electrode's glass membrane interacts with the H⁺ ions in the solution, the reference electrode provides a stable reference potential, and the pH meter measures the potential difference between the two electrodes
• Uses of pH meters include:
  • To determine the end point in acid-base titrations
  • To measure the pH of various solutions to study the behaviour of acids, bases, and salts in different chemical reactions
  • To study buffer solutions, for example, to monitor their effectiveness to resist changes in pH on small additions of acid or base

Temperature probes

• Temperature sensors are used to measure the temperature of a system or a reaction
• They are crucial for carrying out experiments that require specific temperature conditions or monitoring exothermic/endothermic reactions
• Temperature sensors can be used instead of thermometers in practical investigations and enable 
• For examples of investigations where temperature is measured, see our revision notes on Calorimetry Experiments

Pressure sensors

• Pressure sensors measure the pressure of gases or liquids
• In chemistry, they can be used in gas law experiments or to monitor changes in pressure during chemical reactions

Conductivity sensors

• Conductivity sensors measure the electrical conductivity of a solution, which is related to the concentration of ions present
• They are commonly used to determine the concentration of ions in a solution or to study the behaviour of electrolytes
• The changes in the conductivity of a reaction mixture can be used to determine the rate of reaction
• For more information on using conductivity to determine the rate of a reaction, see our revision notes on Measuring Rates of Reaction

Data logging in chemistry

Data logging is a useful part of the chemist's laboratory toolkit

Identifying and extracting data from databases

• A database is a structured collection of data so it can be searched, sorted, filtered and analysed quickly
• Data in a database can be any type of data including text, images, videos, sound

• Databases that you may come across during your studies include:
  • Formulae of polyatomic ions, used to write formulae of compounds containing the ion and equations
  • Physical properties, e.g. melting points, boiling points
  • Thermodynamic data such as enthalpy values, entropies, Gibbs energy values
  • Kinetic data, such as rate constants
  • Equilibrium constants
  • Spectroscopic data, such as NMR and IR spectra
  • Chemical structures and properties
  • Organic synthesis information, including reaction conditions and procedures for the preparation of specific organic compounds
  • Bond lengths
• This is by no means an exhaustive list

Useful websites for databases

• The Spectral Database for Organic Compounds - contains a range of information about a compound including molecular formulae, weight, atomic structure, spectra (13C NMR, 1H NMR, IR)
• MolCalc - provides a 3D molecule of different molecules and gives a range of their properties including enthalpy values, heat capacity, entropy, vibrational frequencies, molecular orbitals and polarity 
• PubChem - a large database containing lots of information about over 700,000 chemicals including 2D and 3D structures, names, chemical and physical properties
• ChemSpider - includes chemical properties and spectra
• NIST WebBook - includes formulae and properties and also allows you to search for reactions

Generating data from models and simulations

• A model is a simplified version of reality
  • For example, the ball-and-stick model is a three-dimensional model which represents compounds, using balls to represent atoms and sticks to represent chemical bonds, giving us a visual representation of the structure and bond angles within compounds
• Models in chemistry are often used to represent and explain various phenomena, structures, and interactions at the atomic and molecular level 
  • The model can then be analysed or tested to learn more about how the system works and to predict how the system might respond to change

• Some models can be very simple, such as a child’s model car, whilst other models can be highly complex and require the power of supercomputers, such as the computer models that are currently being used to predict how our climate will change in the future
  • To some extent, due to their very nature, all models involve some level of approximation or simplification, and therefore some loss of accuracy (even the very powerful and complex models)

• Chemists also use simulations which use models based on the fundamental principles of chemistry to predict the behaviour of atoms, molecules and chemical systems
• Simulations are a valuable tool to be able to explore scenarios that may not be feasible or safe to investigate in a physical laboratory
  • For example, to predict the reactions between Group 1 metals towards the bottom of the group with water which are dangerously vigorous based on models of the reactions of other Group 1 metals with water
    
    
• The accuracy and reliability of the simulation depend on the quality of the models and assumptions used to create them
• Simulations allow you to alter variables in a particular scenario and allow you see to the effect of these changes, for example:
  • Simulations of gas particles allow you to explore how gases behave
  • The simulation uses models of gas laws to predict how the system will respond to changes in temperature, pressure and volume which are controlled by the user
  • Data can be collected from these predictions of behaviour

The PhET Simulations Website

There is a range of online resources that allow you to run simulations of chemical phenomena, a particularly useful site is PhET, which includes simulations of molecule shapes, the pH scale and states of matter