Pollutants in Water

 

Heavy Metal Ions

 

Many metal ions, such as iron, potassium and calcium, are essential to life on this planet.  However, there are ions that dissolve in water which are detremental to the health of living beings.  Heavy metal ions are those ions, such as lead (Pb+2) and mercury (Hg+2), that dissolve easily in water and can damage proteins in the body. These heavy metal ions bind to the proteins, preventing the proteins from performing their intended tasks.  This can cause serious problems such as a decrease in the immune system, brain tissue damage and developmental problems in young children.

 

Acids and Bases

 

Acids and Bases are simple compounds that are very reactive and can corrode materials, both metallic and organic, very easily.

 

Properties of Acids and Bases:

 

Property Acid Base
Taste Sour Bitter
Touch Sting, especially on open sore Slippery, eatng away skin
Reactivity Metals Organic materials
Conductor Yes Yes
Reaction with phenolphthalien (an indicator) Colorless Pink - Purple

 

Indicators - An indicator is a substance that has a different color in an acid than in a base.  Indicators come in many different colors and change colors at different places on the pH scale.

 

Neutralization - When acids and bases are mixed, they retain none of the properties of either an acid or base.  The products of a neutralization are always a salt and water.

 

pH

The pH scale, designed by Sorensen, was a proposal that expresses acidity and basicity in a more compact form.  Rather than using concentrations of acids and bases, this logarithmic-based scale converts the concentrations into numbers between 0 and 14.

 

A pH of 0 is very acidic.  A pH of 14 is very basic.  A pH of 7 is neutral. The closer you get to 7 the weaker the acid or base becomes.

 

The picture at left has a pH scale with common materials located at their pH level.

Diagram Courtesy of ChemCom, 4th Edition  

 

Molecular Substances

Molecular substances are usually organic in nature, but do not have to be.  These substances are held together by covalent bonds, which are different from ionic bonds.  These substances dissolve in water, but do not form charged ions, like organic compounds.  These substances when dissolve, break up into molecules, not ions.

 

These substances can be polar or nonpolar. Water is a polar molecule, in which it has a positive end and a negative end (picture at left).  Nonpolar molecules do not have charged ends like polar molecules.  Rather, nonpolar molecules have their charge evenly distributed throughout the whole molecule.

 

Polar molecules are very good at dissolving other polar substances.  Likewise, nonpolar molecules are very good at dissolving other nonpolar substances.  This pattern has led to the common phrase “like dissolves like”, meaning like materials can dissolve one another.  Because water and salt are both polar, salt can dissolve in water.  This general rule also explains why nonpolar liquids are ineffective at dissolving polar materials.

 

Diagram Courtesy of ChemCom, 4th Edition