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Файл:English in Analytical Chemistry communicating about Methods & Techniques. Учебное пособие. Книга для студента
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4. Salt bridge known as the liquid
junction
5. The most popular reference
electrode is
6. Indicator electrodes also known
as
7. Components of biosensors
include
8. Potentiometry, amperometry, and
coulometry are all considered
types of
9. Amperometry, conductimetry,
voltammetry are
10. Ion selective electrode
11. Electrochemistry
12. Electrochemical cell l) voltmeter
13. Electrolytic cell
14. Indicator electrode potential is
transmitted to the
15. Anode electrode o) ion selective electrodes
21 Read the description of the determination of F- in toothpaste that provides an
instructive example of a typical potentiometric procedure. Then work in small
groups to consider the questions below.
Determination of Fluoride in Toothpaste
Description of the Method. The concentration of fluoride in toothpastes containing
soluble F- may be determined with a А- ion-selective electrode (ISE) using a calibration
curve prepared with external standards. Although the F- ISE is very selective (only OH–
with a KF-/OH- of 0.1 is a significant interferent), Fe3+ and Al3+ interfere with the analysis
because they form soluble fluoride complexes that do not interact with the ion-selective
electrode’s membrane. This interference is minimized by reacting any Fe3+ and Al3+ with
a suitable complexing agent.
Procedure. Prepare 1 L of a standard solution of 1.00% w/v SnF2 and transfer it
to a plastic bottle for storage. Using this solution, prepare 100 mL each of standards
containing 0.32%, 0.36%, 0.40%, 0.44%, and 0.48% w/v SnF2, adding 400 mg of malic
acid to each solution as a stabilizer. Transfer the standards to plastic bottles for storage.
Prepare a total ionic strength adjustment buffer (TISAB) by mixing 500 mL of
water, 57 mL of glacial acetic acid, 58 g of NaCl, and 4 g of disodium DCTA (trans-1,2cyclohexanetetraacetic acid) in a 1-L beaker, stirring until dissolved. Cool the beaker in
a water bath and add 5 M NaOH until the pH is between 5–5.5. Transfer the contents of
the beaker to a 1-L volumetric flask and dilute to volume. Prepare each external
standard by placing approximately 1 g of a fluoride-free toothpaste, 30 mL of distilled
water, and 1.00 mL of standard into a 50-mL plastic beaker and mix vigorously for two
min with a stir bar. Quantitatively transfer the resulting suspension to a 100-mL
d) can be a piece of filter paper saturated
with electrolytes
e) can be immersed in a single, beaker that
contains a salt solution.
f) is equal to reduction (e-gain)
g) is equal to oxidation (e-loss)
h) current can be forced to flow through the
dead cell by applying an external
electromotive force
i) method(s) in which the power supply
measures cell current
j) Ag/AgCl electrode in saturated HCL or
KCL
k) immobilized biological/biochemical
reagent
m) is selective and can measure selected
analytes
n) completes the circuit between the half-
cells and the voltmeter
81
volumetric flask along with 50 mL of TISAB and dilute to volume with distilled water.
Store the entire external standard in a 250-mL plastic beaker until you are ready to
measure the potential. Prepare toothpaste samples by obtaining an approximately 1 g
portion and treating in the same manner as the standards. Measure the cell potential for
the external standards and the samples using a F
appropriate reference electrode. When measuring the potential, stir solution and allow
two to three minutes to reach a stable potential. Report the concentration of F- in the
toothpaste %w/w SnF2.
(based on J.H. Kennedy – Analytical Chemistry Practice)
Questions to Discuss
1. The total ionic strength adjustment buffer serves several purposes in this
procedure. Identify these purposes.
2. Why is a fluoride-free toothpaste added to the standard solutions?
3. The procedure specifies that the standards and the sample should be stored in
plastic сcontainers. Why is it a bad idea to store the solutions in glass containers?
4. What effect does this have on the quantitative analysis for fluoride in
toothpaste?
22 Label the pictures using the prompt below if necessary. Resort to the Russian
sources to find the principle of their work and explain it later in English.
-
ion-selective electrode and an
1
. Schematic diagram for a manual
potentiostat
B. Schematic diagram of a manual
potentiometer
82
2
C. Schematic diagram of a
galvanostat
3
(based on D. Harvey – Analytical Chemistry 2.0)
Prompts
C is the counter electrode;
W is the working electrode;
SW is a slide-wire resistor;
T is a tap key;
i is an ammeter for measuring current;
A is the auxiliary electrode;
R is an optional reference electrode;
E is a high-impedance potentiometer.
83
Vocabulary Boost
23 Work in pairs and follow the instructions below.
1. Look at the crossword and make sure you know the meaning of all the words
you have.
2. Ask Student B to define a word for you. Ask, for example, What’s 1 down?
What’s 2 across? Write the word in.
3. Now Student B will ask you to define a word.
STUDENT A
84
1. Look at the crossword and make sure you know the meaning of all the words
you have.
2. Ask Student A to define a word for you. Ask, for example, What’s 1 down?
What’s 2 across? Write the word in.
3. Now Student A will ask you to define a word.
STUDENT B
For additional practice, follow the link:
https://quizlet.com/94567414/electrochemical-methods-flash-cards/
85
24 Study the tree below and prepare a talk on interfacial electrochemical
techniques.
Family tree highlighting a number of interfacial electrochemical techniques. The specific
techniques are shown in red, the experimental conditions are shown in blue, and the
analytical signals are shown in green.
(based on D. Harvey – Analytical Chemistry 2.0)
86
25 In small groups of “experts”, do the research on one of five concepts that
underlie electrochemistry. Think of three questions that everybody should
answer after getting acquainted with your talk.
To understand electrochemistry, we need to appreciate five important and
interrelated concepts:
1) the electrode’s potential determines the analyte’s form at the electrode’s
surface;
2) the concentration of analyte at the electrode’s surface may not be the same as
its concentration in bulk solution;
3) in addition to an oxidation–reduction reaction, the analyte may participate in
other reactions;
4) current is a measure of the rate of the analyte’s oxidation or reduction; and
5) we cannot simultaneously control current and potential.
26 Once you are ready, reform your original groups in a way that a new group
includes one member of each “expert group”. Take turns teaching each other
your part of information. Check your mates’ understanding by asking the
questions you prepared.
Check Yourself
1 Complete the gaps with the types of electrochemical methods.
1.(...) is based on an exhaustive electrolysis of the analyte. By exhaustive we mean that
the analyte is completely oxidized or reduced at the working electrode or that it reacts
completely with a reagent generated at the working electrode.
2. In (...) we measure the potential of an electrochemical cell under static conditions.
Because no current – or only a negligible current – flows through the electrochemical
cell, its composition remains unchanged.
3. In (...) we apply a time-dependent potential to an electrochemical cell and measure
the resulting current as a function of that potential.
4. (...) is a form of voltammetry in which the analyte is first deposited on the electrode
and then removed electrochemically while monitoring the current as a function of the
applied potential.
5. (...) is a form of voltammetry in which we measure current as a function of time while
maintaining a constant potential.
6. (...) is a form of voltammetry using a dropping mercury electrode or a static mercury
drop electrode.
7. (...) is an electrochemical method in which the current required to exhaustively
oxidize or reduce the analyte is measured.
2 Match the types of electrodes and their descriptions.
8) indicator electrode A. An electrode whose potential remains constant and
against which other potentials can be measured.
9) reference electrode B. The second electrode in a two-electrode cell that
completes the circuit.
87
10) counter electrode C. The electrode where oxidation occurs
11) auxiliary electrode D. The electrode whose potential is a function of the
analyte’s concentration (also known as the working
electrode).
12) anode E. The electrode where reduction occurs.
13) redox electrode F. An electrode in which the membrane potential is a
function of the concentration of a particular ion in
solution
14) ion-selective
electrode
15) cathode H. An inert electrode that serves as a source or sink for
3 Choose the correct option.
16. The statement that the current moving through a circuit is proportional to the
applied potential and inversely proportional to the circuit’s resistance (E = iR).
A Ohm’s law
B Faraday’s law
17. The current or charge passed in a redox reaction is proportional to the moles
of the reaction’s reactants and products.
A Ohm’s law
B Faraday’s law
18. A device for measuring the potential of an electrochemical cell without
drawing a current or altering the cell’s composition.
A potentiostat
B galvanostat
C potentiometer
19. A device used to control the current in an electrochemical cell.
A potentiostat
B galvanostat
C potentiometer
20. A device used to control the potential in an electrochemical cell.
A potentiostat
B galvanostat
C potentiometer
G. The third electrode in a three-electrode cell that
completes the circuit.
electrons for a redox half reaction.
21. A connection between two solutions that allows the movement of current in
the form of ionic charge.
A liquid junction potential
B mediator
C salt bridge
88
22. A potential that develops at the interface between two ionic solutions that
differ in composition, because of a difference in the mobilities of the ions (Elj).
A liquid junction potential
B mediator
C salt bridge
23. A species that transfers electrons from the electrode to the analyte.
A liquid junction potential
B mediator
C salt bridge
24. The percentage of current that actually leads to the analyte’s oxidation or
reduction.
A voltammogram
B current efficiency
C diffusion
25 The movement of material in response to a concentration gradient.
A voltammogram
B current efficiency
C diffusion
26. A plot of current as a function of applied potential.
A voltammogram
B current efficiency
C diffusion
4 Translate the sentences from Russian into English.
27. Электрохимия изучает процессы, которые вызывают движение и
перенос электронов.
28. Напряжение двух электродов в электролитической ячейке называется
потенциалом ячейки.
29. Электроды второго рода покрыты слоем труднорастворимой соли
металла, из которого состоит электрод.
30. Технологии, в которых требуются
включают гальванизацию металлов и крупномасштабное производство алюминия
и хлора.
31. В полярографии один из электродов представляет собой стеклянную
трубку, содержащую ртуть.
32.Насыщенный каломельный электрод используется в качестве электрода
сравнения.
33. Электроды должны быть погружены в раствор электролита, чтобы
процессы окисления и восстановления были постоянными, генерируя
электрический ток.
28-33 Excellent. You can use the vocabulary from Unit 4 very well.
23-27 Quite good, but you need to learn some words.
13-22 Not bad, but you need to be more persistent in your everyday practice.
0-12 This is hard for you. Learn the vocabulary from the Unit 4 and do the tasks
again.
электрохимические процессы,
89
Glossary
Basic terms are highlighted in bold.
Gravimetry
Gravimetry & its types
Gravimetry (gravimetric method) – гравиметрия
Direct analysis – прямой анализ
Indirect analysis – непрямой анализ
Precipitation gravimetry – осадительная гравиметрия
Electrogravimetry – электрогравиметрия
Volatilization gravimetry – гравиметрическая возгонка
Particulate gravimetry – гравиметрия твёрдых частиц
Definitive technique – определительные испытания
Procedure
Weighed form – взвешиваемая форма
Pure form – чистая форма
Crucible – тигель
Muffle furnace – муфельная печь
Ashless filter – беззольный фильтр
Filter aid – вспомогательный фильтр, фильтрующая среда
To collect – собирать (напр., осадок)
Precipitation – осаждение
Precipitate – осадок
Precipitant / precipitating agent – осадитель
Primary standard – первичный стандарт
Dilution – разбавление
Ignition – прокаливание
Drying – высушивание
Separation –
Impurities – примеси
To char – поджечь
Slurry – суспензия
Overall process – общий процесс
Formula weight – формульная масса / молекулярная масса
Gravimetric factor – гравиметрический фактор
General terms
Titrimetry (titration, titrimetric method) – титрование, титриметрия
Titrand (=titrated analyte) – титруемый аналит
Titrant – титрант
Titre – титр
To titrate – титровать
To perform titration – титровать
разделение (фаз)
Titration
90
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