Module 4 Intro

Module 4—Properties of Solutions

Classification of Solutions

 

Metals such as gold are called “precious metals” because they are rare in nature and have a high economic value. Since ancient times, gold jewellery has been produced as a means of displaying wealth and status.

 

One problem with the use of gold for jewellery is the softness of the metal. You may have seen a gold ring that has been worn so long that it is no longer round because it has shaped itself to the finger of the person wearing it. Gold in its pure form is actually too soft to use in jewellery—it can bend out of shape very easily. Fortunately, the strength of most jewellery is improved significantly by mixing the gold with other metals to form a solution called an alloy.

 

Are you wearing a gold ring? Can you read the stamp on the inside of the band? You may have noticed that the stamp indicated that the gold is 10 k or 14 k. When gold is labelled as being 24 karat, it means 24 parts are pure gold and no other metal is present. If gold is 18 karat, 18 parts of the 24 total possible parts are gold and the 6 remaining parts are some other metal, which together forms the alloy. A ring that is 24-karat gold will more easily bend out of shape than a ring that is 18-, 14-, or 10-karat gold.

 

Not only does an alloy solution improve the strength of the jewellery, it can dramatically change the appearance of the jewellery too! The only difference between yellow gold and white gold is the type of metal being mixed with the gold. You will soon understand how solution chemistry plays an important role in the production of yellow gold and white gold rings.

 

Definition and Types of Solutions

 

A solution is composed of a solute dissolved in a solvent. Solutes and solvents may be solids, liquids, or gases. The following table shows how various combinations lead to different types of solutions.

 

 

Types of Solutions		Solvent
		Solid	Liquid	Gas
Solute	Solid	brass (tin in copper)	ocean water (salt in water)	does not form solutions
	Liquid	amalgam dental fillings (mercury in silver)	antifreeze (ethylene glycol in water)	does not form solutions
	Gas	1980s cold fusion experiments (hydrogen absorbed into the crystalline lattice of palladium)	club soda (carbon dioxide in water)	air (oxygen in nitrogen)

 

The most important property of a solution is homogeneity. This means that the solution will have an identical composition throughout. If you use a micropipette to analyze an extremely small sample of a solution, it will have exactly the same composition as the larger mixture. Substances like milk and fog are not considered to be solutions because they are heterogeneous mixtures. In a true solution, the solute particles will not separate from the solvent on standing, nor can they be filtered out.

 

For further information, read “Solutions and Mixtures” on pages 192 and 193 in your textbook.

 

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