Name
How determine the pka of a acid-base indicator by means of UV/visible spectroscopy?
Topic
Analytical Chemistry
Learning time
9 hours
Designed time
10 hours and 15 minutes
Size of class
10
Description
How determine the pka of a acid-base indicator by means of UV/visible spectroscopy? This project focuses on the study of the components of visible light in order to investigate the relationship between dyed substances pH and absorption of light. The lessons are aimed at students that between 16 and 19 years old
Aims
Three methods, two graphs and a mathematical, will be used to estimate the acid dissociation constant (pKa) and the isosbestic point by means of absorbance measurements.
Outcomes
Knowledge, Formulate, Describe reasons for, Distinguish between, Prepare, Calculate, Compute, Distinguish between, Construct, Conclude, Evaluate
Editor
entropia61
Edit
Orientation. Orientation is focused on stimulating students’ interest and curiosity towards the problem at hand. The Orientation phase is also used to activate students’ prior and new knowledge.
120 minutes)
  • Read Watch Listen
    15
    0
    How determine the pka of an acid-base indicator by means of UV/visible spectroscopy? This project focuses on the study of the components of visible light in order to investigate the relationship between dyed substances pH and absorption of light.
  • Discuss
    45
    0
    The students are divided into groups of two students. This is the orientation phase, in which students will be introduced to the problem to be investigated. After a brief introduction of the teacher, groups will be asked to read and discuss a scientific article.
  • Collaborate
    60
    0
    After a careful reading, they can plan their laboratory activities. At the conclusion of this phase, the construction of a concept map can help students visualise the relationships between the various concepts.
Notes:
Connection to the curriculum: 1. Introduction to optical methods; 2. Molecular orbitals; 3. Volumetric Analysis; 4. Acid-base equilibria.
Resources linked: 1
Conceptualization. Conceptualization is a process of understanding a concept belonging to the stated problem.
60 minutes)
  • Read Watch Listen
    15
    0
    This activity is divided into two sub-phases: 1. Research question formulation 2. Hypothesis generation
  • Discuss
    20
    0
    Warm-up: Students discuss their concept maps and repeat key words to each other. Worksheet 1 (Colours) helps students to link the two core concepts of transmittance and absorption.
  • Collaborate
    25
    0
    The students help each other to formulate research questions and to decide what they want to know by doing the experiment. The hypothesis phase consists in a reading activity that uses different diagrams (spectra, graphs) to illustrate a relationship between absorption and wavelength, absorption and pH.
Notes:
Resources linked: 0
Investigation. This is a crucial phase because with appropriate practical technique students must be able to carry out experiments.
240 minutes)
  • Read Watch Listen
    20
    0
    Perform a UV-Visible spectrophotometric investigation by a scaffolding technique: in a virtual lab at the beginning, then in an analytical chemistry lab. A video (How a simple UV-visible spectrophotometer works) allows students to see a spectrophotometer in action and to identify its components (Worksheet 2)
  • Investigate
    180
    0
    Procedure a) Preparation of the solutions Initially, three solutions will be prepared: 1. 0.1 M sodium acetate in 100 ml (CH3COONa) 2. 100 ml 0.1 M acetic acid (CH3COOH) 3. 1M potassium chloride in 100ml (KCl). Subsequently, we will be prepared two methyl red solution in 100 ml volumetric flasks, one acidic and one basic, composed respectively by:  1ml of indicator methyl red, 10 ml of acetic acid and 10 ml of KCl;  1ml of indicator methyl red, 10 ml of sodium acetate and 9 ml of KCl. The ionic strength of all the prepared solutions will be held constant for the presence of KCl. From these solutions are obtained 6 buffer solutions, by mixing different volumes of acid and base solution, (V ml of the basic solution with (20-V) ml of the acid solution). All solutions are prepared with distilled water. b) pH measurements For each buffer solution, the pH value is measured using a digital pH-meter, Each of the pH value is obtained from the average of three measurements. c) c) Measurements of absorbance UV-visible absorbance spectra of all solutions at different pH value will be registered by using a UV-spectrophotometer V-630 of JASCO. The absorbance measurements will be performed in the intervals of wavelengths between 350 and 650 nm. Data were collected for each 1 nm. Distilled water will be used as a reference solution.
  • Produce
    40
    0
    The final activity of this phase is a Data viewer. It consists of an application tool that allows loading a data set and creating a diagram (data table) with parameters measured during experimental activity in a laboratory.
Notes:
Resources linked: 0
Conclusion. The Conclusion phase is where the outcomes of the Investigation phase are compared to the output of the Conceptualization phase and conclusions are drawn.
90 minutes)
  • Produce
    60
    0
    The open answers final test (Quiz) requires that students summarise what they have learnt through this project. The teacher evaluates students by crossing data obtained from: 1. Progress report A - observing how they work during practical activity (interest and participation); 2. Progress report B - observing how they learn to write scientific explanations linking their hypothesis with the evidence collected during the investigation phase; 3. Progress report C - evaluating the results of the final test
  • Collaborate
    30
    0
    The assessment rubric is produced and shared between teacher and students. The rubric is constructed with the tool: forallrubrics
Notes:
Resources linked: 0
Results and discussion. In all phases, from Orientation to Conclusion, the processes of the Discussion phase are also possible. Both Communication and Reflection can be seen as on-going processes, which help students receive feedback about their learning process by sharing their domain related outcomes and   process-related   ideas   with   others.   This   means   direct communication among peer students, teacher, etc.
105 minutes)
  • Discuss
    60
    0
    The Discussion phase is about sharing one’s inquiry process and results. It involves the process of describing, critiquing, evaluating and discussing the whole inquiry process or a specific phase. It contains two sub-phases - Communication and Reflection - which help students to communicate their findings to others and prompt them to reflect on their actions in order to learn from their experiences.
  • Produce
    15
    2
    The work done will be evaluated through a digital presentation. A rubric of evaluation is linked to this phase. This project can be evaluated also as CLIL activity. Attached to this TLA it is possible downloaded a rubric of assessment.
  • Collaborate
    30
    0
    Utilise tools, for example, instaGrok to design a concept map
Notes:
Resources linked: 0

Learning Experience

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