Polarography Techniques and Maxima Analysis

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Questions and Answers

What is the primary purpose of polarography?

To determine the molecular weight of compounds

To analyze the concentration of ionic species (correct)

To evaluate the spectral properties of materials

To measure temperature changes in chemicals

Which device is commonly associated with polarography?

Thermal analyzer

Dropping mercury electrode (correct)

Gas chromatograph

Spectrophotometer

Which of the following methods is NOT typically classified as a polarography method?

Voltammetry

Thermogravimetric analysis (correct)

Direct current polarography

Alternating current polarography

What type of information can polarography provide?

Electrode potential vs. concentration data Signup and view all the answers

In which scenario is polarography typically applied?

Analyzing heavy metal concentrations in water Signup and view all the answers

Which of the following best describes the significance of polarography?

It offers cost-effective analysis of ionic concentrations Signup and view all the answers

What requirement should one know before studying polarography?

Fundamentals of electrochemical analysis Signup and view all the answers

Which statement about the dropping mercury electrode is true?

It provides a continuous and stable surface for reactions Signup and view all the answers

What is the typical range for the temperature coefficient?

1.5-2% Signup and view all the answers

Which factor has a sixth root power effect on the diffusion current?

Time Signup and view all the answers

How can the diffusion current be accurately controlled?

By controlling the mass flow of mercury Signup and view all the answers

What does the interfacial tension at the mercury surface affect?

The diffusion current Signup and view all the answers

Increasing the temperature affects the diffusion current how?

It increases the diffusion current Signup and view all the answers

What happens to the viscosity and diffusion current when the concentration of solution is low?

Viscosity is low; diffusion current is high Signup and view all the answers

In the context of complex formation, how does movement of metal ions vary when hydrated complexes are formed?

They show different Id than other complexes Signup and view all the answers

What variable is described in the empirical relation related to the diffusion coefficient from Stoke’s Einstein formula?

Concentration of the electrolyte Signup and view all the answers

What does E1/2 represent in a redox reaction?

The potential when the diffusion current is half of the total current. Signup and view all the answers

Which equation is utilized to understand the potential and current of a redox system?

Nernst equation. Signup and view all the answers

What must be achieved to know the exact E1/2 value?

Maxima must be eliminated. Signup and view all the answers

What happens when the voltage in a polarographic experiment is increased?

Decomposition of active ions may occur. Signup and view all the answers

In polarography, what does the equation I = [Ox] - [Oxs] represent?

The change in concentration at the DME surface. Signup and view all the answers

Which factor does NOT influence the kinetics of current in a polarographic system?

Color of the solution. Signup and view all the answers

What is the role of surface active materials in polarography?

To eliminate maxima for better current measurement. Signup and view all the answers

How can you predict the element present in a solution using E1/2?

By knowing the half wave potential as a characteristic feature. Signup and view all the answers

What effect does the addition of alcohol have on the viscosity of a solution?

It reduces viscosity by forming complexes with metal ions. Signup and view all the answers

What is the polarographic maxima?

An abnormal increase in current that eventually decreases. Signup and view all the answers

What is a distinguishing feature of the strike streaming type mechanism?

It occurs within a very short range of applied potential. Signup and view all the answers

How can the difficulties caused by polarographic maxima be managed?

By decreasing the concentration of active ions and increasing the concentration of base electrolyte. Signup and view all the answers

What causes the non-streaming maxima?

Increased pressure on the reservoir attached to the dropping mercury electrode. Signup and view all the answers

What is the outcome of polarographic maxima on the diffusion current measurement?

It can lead to inaccuracies in measuring the diffusion current. Signup and view all the answers

What happens to the V-I curve as the applied voltage increases in a polarogram exhibiting maxima?

It gradually decreases to a normal diffusion current curve. Signup and view all the answers

What is a likely result of having low viscosity in a polarographic analysis?

It leads to a faster movement of ions and potential measurement complications. Signup and view all the answers

What is the primary factor measured in a cyclic voltammetry (CV) curve to evaluate the concentration of dissolved oxygen?

The height of the curve Signup and view all the answers

In polarography, what is the significance of using a masking reagent?

To prevent interference from other ions Signup and view all the answers

What is the tolerable limit difference in E1/2 for best estimations in polarography when several ions are present?

0.4 Signup and view all the answers

When using the standard addition method in polarography, what is the first step before determining the concentration of an unknown sample?

Prepare a polarogram for the unknown sample Signup and view all the answers

For the estimation of Cu2+ in polarography, which reagent can be used to form a complex?

KCN Signup and view all the answers

What is the purpose of measuring the height between two plateaus in polarography?

To determine the concentration of ions in the solution Signup and view all the answers

What is required to estimate the concentration of an unknown ion using the internal addition of a pilot ion?

A known amount of pilot ion added to the sample Signup and view all the answers

What is the role of a maxima suppressor in the determination of ions in polarography?

To reduce the effects of competing ions Signup and view all the answers

Study Notes

Polarography

A technique that studies the relationship between current and potential, specifically at a dropping mercury electrode (DME)
Used for qualitative and quantitative analysis of electroactive species, including metals, ions, and organic molecules.
The heart of polarography is the DME, a mercury electrode that generates continuously renewable droplets, allowing for a fresh surface.

Polarographic Maxima

Abnormalities in the current-voltage curve.
Appear as abnormal increases in current before returning to the normal diffusion current curve.
Types:
- Strike Streaming Type: Caused by low base electrolyte concentration and high active species concentration, resulting in rapid diffusion.
- Non-streaming Maxima: Occurs due to increased pressure on the DME, leading to quick mercury drop formation and broad maxima.

Methods for Suppressing Maxima

Surface-active Agents: Adding substances that reduce the surface tension, such as surfactants, dyes, or capillary-active ions.

Diffusion Current (ID)

The limiting current (plateau current) reached after the potential rises beyond a certain value.
Directly proportional to the concentration of the electroactive species.
Influenced by factors such as temperature, pressure, complex formation, interfacial surface tension, and the diffusion coefficient.

Half-Wave Potential (E1/2)

The potential at which the diffusion current is half of the total current.
A characteristic feature of the electroactive species, providing qualitative information about the element present.
Measured from the middle point of the rising portion of the polarographic curve.

Measuring Concentration using Polarography

Standard Addition Method: A known amount of standard solution of the same ion is added to the unknown sample, and the change in wave height is used to determine the initial concentration.
Internal Addition of Pilot Ion: A known amount of a pilot ion (with a known E1/2) is added to the unknown sample. Comparing the wave heights of the unknown ion and the pilot ion allows for the determination of the unknown concentration.

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Description

This quiz covers the fundamentals of polarography, emphasizing the relationship between current and potential in electrochemical analysis. It explores the phenomena of polarographic maxima and methods for suppressing these abnormalities, particularly through the use of surface-active agents. Test your knowledge of this important electrochemical technique!