7.2.1Additional lessons
Applying Technology to Collect Data in Chemistry — IB Chemistry HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 161 of 172
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 6Sensors and Data Loggers
Technology lets experimenters collect larger and more precise data sets than manual reading.
Sensor
- Sensor A probe converts a physical quantity such as temperature, pH, gas pressure or conductivity into an electrical signal.
Data logger
- Data logger The signal is recorded automatically at set time intervals and stored for later analysis on a computer.
Advantages
- Advantages Readings are frequent, free from human reaction time and can follow very fast or very slow changes with little effort.
Limitations
- Limitations Probes need calibration, have a limited range and response time, and may drift, so results still need critical checking.
Section 2 of 6Spectroscopic Methods
Spectroscopic Methods
Colorimetry
- Colorimetry A coloured solution absorbs light, and the absorbance is proportional to concentration within a limited range.
Calibration curve
- Calibration curve Absorbance is measured for solutions of known concentration, and an unknown is read from the resulting graph.
Filter choice
- Filter choice The filter or wavelength is chosen to be absorbed strongly by the solution, which is usually the colour complementary to the solution.
Blank
- Blank A cuvette containing only solvent sets zero absorbance and removes the effect of the container.
Section 3 of 6Planning Automated Data Collection
1
Decide which variable the sensor will measure and check that its range includes the expected values.
2
Calibrate the probe with standards, such as buffers of known pH for a pH probe.
3
Set a logging interval short enough to capture the fastest change and long enough to avoid unmanageable data.
4
Start logging before the reaction begins so that the starting baseline is also recorded.
5
Save the file, check for gaps or spikes, and export the data for processing.
Section 4 of 6Other Technologies
Digital imaging
- Digital imaging Photographs and video record colour changes or precipitation, so timings can be checked afterwards frame by frame.
Gas sensors
- Gas sensors Pressure sensors in a sealed flask follow gas production and give a smooth curve rather than a few spot readings.
Conductivity probes
- Conductivity probes These follow reactions where the number of ions changes, such as the neutralisation of an acid with a base.
Remote data
- Remote data Online databases and shared files let results be compared with accepted values quickly.
Section 5 of 6Worked Example
Question
- A calibration line for a coloured complex follows A = 840 × c, where c is in mol dm⁻³.
- A sample gives an absorbance of 0.42.
- Find its concentration.
- Rearrange the calibration equation to c = A ÷ 840.
- c = 0.42 ÷ 840.
- c = 5.0 × 10⁻⁴ mol dm⁻³.
Answer c = 5.0 × 10⁻⁴ mol dm⁻³
Section 6 of 6Exam Checklist & Tips
7.2.1 – Key Points for the Exam
- Data logger A device that records sensor readings automatically over time.
- Absorbance A measure of how much light a solution takes in at a chosen wavelength.
- Calibration curve A graph of a measured signal against known concentrations, used to find unknown values.
- Sensor A probe that converts a physical or chemical quantity into an electrical signal.
- Blank A reference sample containing everything except the substance being measured.
Common Mistakes
- Assuming that a digital reading is automatically accurate, when an uncalibrated probe can give consistently wrong values.
- Using a filter of the same colour as the solution, which gives very little absorbance.
- Reading a concentration from a calibration curve far outside the range of the standards.
- Starting the logger after the reaction has begun, which loses the first and most important readings.
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