Experiment 5A: Preparation and Standardization of 0.1 N Silver Nitrate

Question 1

Reagents

Answer 1

Silver nitrate
Dilute Nitric acid

Question 2

Standardization
* Pipette about 40 ml of the prepared silver nitrate solution and dilute with water to about 100ml.

• Heat the solution and slowly add ___________, with continuous stirring, until the precipitation of silver chloride is complete.

Answer 2

dilute hydrochloric acid

Question 3

Dry the precipitate at ______ to constant weight.

Answer 3

• 110 °C

Question 4

Why is silver nitrate the most commonly used standard solution in official assays by precipitation method?

Answer 4

• purity and stability
• capacity to produce insoluble precipitates with a wide range of ions, especially halides
• Because it reacts with anions
  like chloride or thiocyanate to give sharp, easily observable endpoints, it is particularly preferred in argentometric methods like Mohr, Volhard, and Fajans titrations.

It is suitable for precise and reproducible tests in official analytical methods due to its non-hygroscopic nature, ease of preparation as a primary standard, and strong reactivity with several anions.

Question 5

What is the reason for heating the solution in the addition of hydrochloric acid?

Answer 5

• it improves the precipitation of silver chloride (AgCl) by promoting the formation of larger, more easily filterable particles.
• because heating reduces the tendency of the precipitate to remain dispersed as a colloid.
• heating accelerates the reaction between silver ions (Ag⁺) and chloride ions (Cl⁻), ensuring complete and rapid precipitation.
• helps remove dissolved gases such as carbon dioxide (CO₂), which can interfere with the reaction by forming unwanted silver carbonate (Ag₂CO₃).
• also aid in dissolving any residual materials or ensuring uniformity of the reaction mixture.

Question 6

commonly used standard solution in precipitation titrations

Answer 6

silver nitrate (AgNO₃)

Question 7

What is the reason for adding hydrochloric acid in the standardization of silver nitrate?

Answer 7

Hydrochloric acid is added when standardizing silver nitrate because it provides chloride ions
that react with silver ions to form a white solid called AgCl.

This helps us measure
exactly how strong the silver nitrate solution is. By knowing how much hydrochloric acid was
used, we can calculate the concentration of silver nitrate.

Question 8

Why is the mixture allowed to stand in the dark until the precipitate has settled?

Answer 8

The mixture is allowed to stand in the dark to prevent the photodecomposition of silver chloride (AgCl).

Silver chloride is photosensitive—when exposed to light, it can decompose into elemental silver (Ag⁰) and chlorine gas (Cl₂).

This results in the formation of a purplish or grayish-black color in the precipitate, indicating contamination by metallic silver. This not only affects the appearance but also leads to inaccurate mass measurement of the silver chloride, which in turn affects the calculation of the normality of silver nitrate.

Question 9

What is the most appropriate container of a silver nitrate solution?

Answer 9

clean, dry amber glass bottle with a tight-fitting, NON-METALLIC CAP

Question 10

Secondary standard

Answer 10

Silver Nitrate (AgNO₃)

Question 11

Analyte/Precipitant
- Reacts with Ag⁺ to form AgCl precipitate.

Answer 11

Hydrochloric Acid (HCl)

Question 12

Washing agent
- Prevents peptization of AgCl during washing by keeping medium acidic.

Answer 12

Dilute Nitric Acid (HNO₃)

Question 13

Endpoint Observation:

Answer 13

white AgCl precipitate

Question 14

pH at Endpoint:

Answer 14

Strongly acidic (~pH 1–2) due to excess HCl and presence of HNO₃

Question 15

What type of titration is used in this experiment?

Answer 15

Precipitation titration