C6 - Detergents

Question 1

What are detergents ?

Answer 1

Substances that can surround fat or oil molecules in stains and remove them from the clothes or plates.

Question 2

Describe the structure of a detergent molecule. How does this structure help it lift stains?

Answer 2

• They have a hydrophilic head, and a hydrophobic tail.
• The hydrophilic end of the detergent molecule forms strong intermolecular forces with water molecules in the wash.
• The hydrophobic end of the detergent molecule forms strong intermolecular forces with the fat or oil molecules in greasy stains.
• The detergent molecules can surround the fat or oil molecules in the stain, lifting them from the fabric and into the washing water.

Question 3

What are the main 5 ingredients in washing powder? What is their function?

Answer 3

Active detergent - does the cleaning
Bleaches - remove coloured stains by destroying the dye
Optical brighteners - give fabrics a ‘whiter than white’ appearance
Water softener - softens hard water to avoid ‘scum’ on the clothes
Enzymes - remove food stains in low-temperature washes

Question 4

What are biological powders? How do they work? Advantages?

Answer 4

Biological powders = contain enzymes.

• These must be used in low-temperature washes in which the water is at 40 °C or less because the enzymes will be denatured at higher temperatures and so will stop working.
• Clean clothes in cooler water = less energy used to heat water for washing machine.
• Some fabrics are damaged by high temperatures, so a greater range of clothing can be cleaned.

Question 5

What are the 4 main ingredients in washing up liquid and what are their functions?

Answer 5

Active detergent - does the cleaning
Water - makes the liquid thinner and less viscous, so it pours easily
Colouring agent and fragrance - make the washing-up liquid more attractive to use
Rinse agent - helps the water drain from the crockery

Question 6

Define the following terms : insoluble, soluble, solvent, solute, solution

Answer 6

Insoluble = when a substance will not dissolve in a particular liquid. 
Soluble = the substance will dissolve in a particular liquid to form a solution. 
Solution = contains a solute and a solvent 
Solute = the dissolved substance
Solvent = the liquid that does the dissolving

Question 7

What is dry cleaning? How does it work? What is the solvent used? Why?

Answer 7

A way to clean clothes without using water. A different solvent such as tetrachloroethene is used. Solvents like this are good at dissolving greasy stains, and other stains that do not dissolve in water. The clothes are cleaned in a machine with equipment to stop solvent fumes escaping. The clothes are washed in the dry-cleaning solvent, rinsed with fresh solvent, and dried in warm air. Used solvent is distilled so that it can be reused.

Question 8

How does dry cleaning work in terms of intermolecular forces?

Answer 8

There are weak intermolecular forces between molecules of grease in a stain, and also weak intermolecular forces between solvent molecules. However, the solvent molecules can also form intermolecular forces with grease molecules.
The solvent molecules surround the grease molecules, lifting them off the fabric and into the bulk of the solvent.

Question 9

Why must clothes be rinsed with fresh solvent during dry cleaning?

Answer 9

The solvent itself becomes dirty during the cleaning cycle as the stains dissolve in it.