Laboratory Experiment on Barium Sulfate Analysis

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Questions and Answers

What is the primary reaction when Ni2+ interacts with H2DMG?

A nickel hydroxide precipitate is formed.

Ni(HDMG)2 is formed with liberation of H+ ions. (correct)

H2DMG is oxidized to a higher oxidation state.

Ni2+ is completely converted into nickel metal.

What is the temperature range required for heating the solution during the titration process?

90 - 100 °C

80 - 90 °C (correct)

60 - 70 °C

70 - 80 °C

What is the solubility characteristic of the precipitate formed by Ni(HDMG)2?

Soluble in all organic solvents.

Insoluble in mineral acids.

Insoluble in dilute ammonia solution. (correct)

Soluble in distilled water.

What indicates the end point of the titration during the procedure?

A faint permanent pink tinge is observed Signup and view all the answers

Why must an excess of H2DMG be avoided during the precipitation process?

It can cause the precipitation of H2DMG itself. Signup and view all the answers

What should be done if the temperature of the solution falls below 60 °C during the titration?

Reheat the solution Signup and view all the answers

What is the impact of temperature on the precipitate formed from nickel(II) solutions?

The precipitate remains unchanged in composition up to 170°C. Signup and view all the answers

Which volume of sulfuric acid is recommended to be added to the H2O2 solution during the determination of volume strength?

10 mL of 50 % v/v sulfuric acid Signup and view all the answers

What type of complexes are formed when using organic reagents like dimethylglyoxime?

Chelate complexes that often incorporate five to six-membered rings. Signup and view all the answers

What is the main indicator used in the Mohr Method of titration?

Chromate Signup and view all the answers

In what type of medium should the Mohr Method be conducted?

Neutral Signup and view all the answers

How is the concentration of the H2O2 solution determined in the procedure?

Using the balance equation and a specific relationship Signup and view all the answers

What is the main reason for adding the dimethylglyoxime solution in ethanol?

The reagent itself is almost insoluble in water. Signup and view all the answers

Which precipitate is formed first in the Mohr Method during titration?

AgCl Signup and view all the answers

Which of the following ions could partially precipitate along with nickel ion under specified conditions?

Palladium ions. Signup and view all the answers

What characteristic do organic precipitants typically possess in terms of molecular weight?

They have high molecular weights, leading to smaller gravimetric factors. Signup and view all the answers

What is the primary purpose of the Volhard Method in titration?

To determine chloride concentration indirectly Signup and view all the answers

What is formed when Fe3+ reacts with SCN- in the Volhard titration?

Fe(SCN)2+ Signup and view all the answers

Which reaction describes the end point of the Volhard titration?

Ag+ + SCN- → AgSCN(s) Signup and view all the answers

What issue may arise due to the use of a dilute chromate solution in the Mohr Method?

Need for excess Ag+ for Ag2CrO4 formation Signup and view all the answers

What type of reaction is described in the Volhard Method?

Back-titration Signup and view all the answers

What is the purpose of heating the sample at red heat for 5 minutes in the gravimetric analysis?

To drive off water and ensure complete conversion to barium sulfate Signup and view all the answers

Among the following, which steps should be performed after the initial heating of the sample?

Transfer to a desiccator and allow to cool to room temperature Signup and view all the answers

What is the significance of the $2 ext{ mg}$ (or $0.002 ext{ g}$) mass difference in the weighing step?

It defines acceptable precision for the measurement Signup and view all the answers

What role does dimethylglyoxime serve in the gravimetric determination of nickel?

It precipitates nickel as a colored compound Signup and view all the answers

What is the final compound obtained after the gravimetric determination of nickel?

Nickel dimethylglyoximate Signup and view all the answers

Why is the precipitate washed with cold water in the nickel determination?

To remove impurities and unreacted reagents Signup and view all the answers

What is the primary measurement recorded on the data sheet during sulfate analysis?

Weight of the sulfate ion (SO4^2-) Signup and view all the answers

What is the main characteristic of the nickel compounds formed in this experiment?

They are colored and sparingly soluble Signup and view all the answers

What is the volume strength of a solution if 1 g of H2O2 generates 329.2 mL of O2?

329.2 mL/g Signup and view all the answers

Which solution is primarily used to determine the percent weight of iron (as Fe2+) in an unknown sample?

Potassium dichromate Signup and view all the answers

In the context of redox titration, how does potassium permanganate (MnO4-) function?

As an oxidizing agent Signup and view all the answers

What is the relationship between the weight of H2O2 and the volume of O2 produced?

Directly proportional Signup and view all the answers

Which of these oxidants can be used for the determination of reducing agents by titration?

Iodine and dichromate Signup and view all the answers

What is the standardization of KMnO4 typically done with?

Sodium oxalate Signup and view all the answers

During the determination of Iron (III), what form is iron (II) oxidized to?

Fe3+ Signup and view all the answers

Which of the following indicates a reduction during titration?

Decrease in oxidation number Signup and view all the answers

Study Notes

Gravimetric Analysis of Sulfate

Continue heating at red heat for 5 minutes, cool for 3 minutes, then transfer to a desiccator.
Record mass after cooling and reheat for 5 minutes, repeating the cooling and weighing process.
Mass should be consistent within 2 mg (0.002 g).
Calculate percentage of sulfate (BaSO4) in the original sample.
Create a formal laboratory report with all observations and data.

Data Sheet for Sulfate Analysis

Enter volume of unknown solution and weight of empty crucible.
Document weight of crucible with precipitate (BaSO4) and weight of BaSO4 alone.
Note weight of sulfate ion (SO42-) and calculate its concentration in mg per liter.

Gravimetric Determination of Nickel

Nickel determination involves precipitation using organic reagents to form colored, sparingly soluble compounds.
Dimethylglyoxime (C4H7O2N2) is used to precipitate nickel from a hot, slightly acidic solution, generating a bright red precipitate.
The precipitation reaction: Ni2+ + 2H2DMG → Ni(HDMG)2 + 2H+.
Organic reagents form chelate complexes, aiding in selective precipitation.
Precipitate characteristics: crystalline, good filterability, and washability, with stability up to 170°C.

Precipitation and Solubility

The dimethylglyoxime precipitate is insoluble in dilute ammonia and slightly soluble in mineral acids.
A 1% ethanolic solution of dimethylglyoxime suffices for precipitation of 2.5 mg of nickel.
Excess reagent should be avoided to prevent complications with solubility.

Silver Determination Methods

Mohr Method: Uses chromate as an indicator to detect silver ion presence. Requires neutral pH to prevent unwanted reactions.
Volhard Method: Involves titration with SCN- and uses Fe3+ as an indicator to detect excess silver ions through back-titration, forming a red complex.

Titration Process for Fe2+ Determination

Use a standard solution of potassium dichromate (K2Cr2O7) for oxidizing Fe2+ to Fe3+ in the presence of harsh oxidants.
Various compounds can be analyzed through this standard titration method.

Oxidation-Reduction Reactions (Redox Titration)

Strong oxidants such as permanganate and dichromate are essential for determining reducing agents, particularly iron (II).
The experiment aims to calculate the weight percent of Fe2+ in an unknown sample using potassium dichromate.

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Description

This quiz tests your knowledge of the procedures involved in determining the percent of sulfate in the form of barium sulfate through systematic heating and cooling in a laboratory context. Be prepared to record data and report results formally as required in laboratory experiments.