Chemistry in action

Chemistry is the study of matter. It discusses the composition, structure, properties, and change of matter on the level of molecules and atoms. The job of a chemist ranges from researching the structure and characteristics of a substance, to analyzing chemical reactions and applying them to produce desired substances. Starting from the use of fire, mankind has discovered hundreds of elements, thousands of compounds, and chemical reactions. Alchemists, who strived to create gold via chemical reactions, have contributed significantly in the development of chemistry, though their struggle to produce gold was never successful. More recently, physicists and chemists revealed the structure of an atom, which substantially enhanced mankind's understanding in nature. Thanks to these efforts, nowadays we can use chemistry knowledge to help the society in various ways, by producing medical drugs, synthesizing plastics, or extracting metals.

In this introductory quiz, you will be asked to explain various chemical phenomena. Since this quiz is mainly focused on daily-life chemistry, you will find many of the contents familiar. In spite of how familiar it is, the explanation of why or how it happens might not be so easy. Here are some tips to get started:

• Relate the problem to previous similar experiences you had in your life.
• Use your intuition and understanding of other processes to reason about the one at hand.
• Carefully read all of the options, and rule out the wrong solutions starting from the most improbable one.
• Try stating a hypothesis, and see if you can logically back it up using your knowledge.
• Read the chemistry wikis and try the practice problems.

Detergents have the powerful ability to remove contaminants from our clothes, thereby making them clean. This even applies to stains that cannot be removed by soaking in water alone. Why is that?

The figure above schematically illustrates the structure of a detergent molecule. It consists of a hydrophilic (meaning it mixes with water) head and a hydrophobic (meaning it mixes with oil) tail. Compounds having both hydrophilic and hydrophobic groups are referred to as surfactants. As contaminants are mostly hydrophobic, they do not wash out well with water alone, but the detergents bind well to the contaminants using their hydrophobic tail. After binding with the contaminant, they bond with water molecules with their hydrophilic head, so that the contaminant-detergent complex can be washed away.

• Brief intro to the different areas of chemistry. Links to other chemistry wikis, that help explain basic chemistry phenomenon.