Question

Sodium thiosulphate is used in photography because of its (a) reaction with light (b) oxidizing behaviour (c) reducing behaviour (d) complex forming behaviour

Short answer

Sodium thiosulphate is used in photography for its complex forming behaviour (option d).

Step-by-step solution

Understanding the Question

We need to identify the property of sodium thiosulphate that makes it suitable for use in photography.

Examining Sodium Thiosulphate Properties

Sodium thiosulphate is known for various chemical behaviors, including complex formation, oxidation, and reduction potential.

Connecting to Photography

In photography, sodium thiosulphate is primarily used to remove unreacted silver halides from exposed photographic film or paper, forming a soluble complex.

Identifying the Correct Behavior

The property of sodium thiosulphate that helps remove silver halides is its ability to form complexes.

Key concepts

Complex Formation

Sodium thiosulphate is particularly valued for its ability to form complexes. In chemistry, a complex forms when molecules or ions surround a central metal atom or ion. Sodium thiosulphate excels at creating these complexes due to its open molecular structure.

A significant application of this property is its interaction with silver ions. When sodium thiosulphate comes into contact with silver ions, it forms a soluble complex, silver thiosulphate. This transformation is essential in various applications, especially in photography, as it helps dissolve and remove unwanted silver residues.

Additionally, the complex formation is a reversible process; hence it plays a role in many industries, such as textile and paper, too. The versatility of sodium thiosulphate in binding with various metal ions highlights its importance in both industrial and laboratory settings.

Chemical Properties of Sodium Thiosulphate

Sodium thiosulphate, also known as hypo, possesses many interesting chemical properties. One key property is its solubility in water, which allows it to readily participate in chemical reactions. When dissolved, it dissociates into sodium and thiosulphate ions, facilitating its role in complex formation.

It also has mild reducing capabilities, though not as pronounced as its ability to form complexes. This gives sodium thiosulphate the potential to participate in redox reactions, where it donates electrons to other substances.

Furthermore, sodium thiosulphate resists oxidation, which makes it a stable compound under numerous conditions. Its stability and ability to not easily react with atmospheric oxygen are advantageous when used in chemical compositions that demand consistency and reliability.

Use of Sodium Thiosulphate

The use of sodium thiosulphate extends far beyond photography. In medicine, it's often employed as an antidote for cyanide poisoning, where it helps in converting toxic cyanide ions to less harmful thiocyanate ions.

For routine applications, sodium thiosulphate plays a crucial role in the textile industry, acting as a bleaching agent by interacting with undesired colors. Additionally, water treatment facilities utilize it to neutralize chlorine in excess, thus preventing the chlorine from causing harm to aquatic life.

In analytical chemistry, this compound often serves as a titrant due to its ability to participate in redox reactions, which are helpful in determining concentrations of substances, such as in the iodometric titration to measure the amount of iodine.

Photography Chemistry

Photography chemistry is deeply intertwined with the use of sodium thiosulphate. The compound is primarily used in the film development process to fix images. After the photographic film has been exposed to light and developed, it still contains unreacted silver halides, which need to be removed to prevent future darkening.

Sodium thiosulphate is used in the 'fixer' stage of development. It reacts with the silver halides, forming a complex that is water-soluble. This allows the silver to be washed away, stabilizing the image for long-term preservation.

The correct handling and application of sodium thiosulphate ensure that photographs remain clear and intact over time. This use highlights the importance of selecting chemistry suited to specific needs, where complex-forming behavior is essential for achieving desired results in photography.