Water can acquire dissolved minerals as it moves over rock formations.
Hard water is water which contains a high concentration of a variety of ions. The origin of the term likely lies in the behavior of soaps and detergents when using this type of water; a hard scum of soap typically forms on the surface of the washwater. In fact, hard water makes it difficult to use soaps precisely because the ions combine with the detergent molecules and render them useless. Hard water can also cause other problems as minerals come out of solution to form a hard deposit known as scale.
About Ions
Ions are chemical compounds, either atoms or molecules, that have acquired a charge due to either losing or gaining electrons. A compound that gains an electron becomes negatively charged and is known as an anion. Losing an electron produces a positively charged species, known as a cation. The species that cause hard water are all cations. Because water is a very polar liquid, meaning its molecules have a slight distribution of charge among their atoms, it is very good at dissolving ions.
The Main Ions
The main ions which are responsible for hard water are the doubly positive calcium cation (Ca++) and the doubly positive magnesium cation (Mg++). These ions are the most common because they frequently occur in the types of underground rock formations through which water travels. Calcium is found in the minerals calcite, gypsum and aragonite whereas both calcium and magnesium can be found in dolomite. Water can dissolve portions of these rocks, especially if it is rendered slightly acidic by dissolved carbon dioxide gas.
Other Ions
Hard water may also contain a variety of metallic ions, although the concentration of these ions is usually much, much less than that of calcium and magnesium and so is often not considered. These ions include iron (Fe++ and Fe+++), zinc (Zn++), manganese (Mn++) and strontium (Sr++). These elements also enter water as it flows over various rocks and minerals.
Measures of Hardness
The total hardness of water is a measure of the overall concentration of all dissolved cations. It is reported as the equivalent of parts per million (abbreviated as "ppm" and also known as milligrams per liter) calcium carbonate. There are several methods of finding total hardness, including EDTA titration and colormetric test strips. The relation between total hardness in ppm carbonate and the concentration of the most common cations is as follows: total hardness (ppm) = 2.5 x ppm calcium + 4.1 x ppm magnesium + 1.8 x ppm iron + 1.8 x ppm manganese.
Related posts
Ionic compounds dissociate when they dissolve in water.Ionic compounds are those where the ions are held together by electrical attraction. When an ionic compound like NaCl (table salt) dissolves,...
Even clean water has trace minerals and other substances dissolved in it.Water is one of the four basic ingredients of beer brewing, along with malt, hops and yeast. Because of this, as home brewe...
The hardness of concrete is determined basically by two things--the mixture of the ingredients and the time you allow for the concrete to set, or cure. The important elements in the mixing of conc...
Softened water can leave salt stains on tile when it dries.Hard water contains excess minerals like calcium and potassium which leaches from the soil into underground aquifers. Water softening sys...
Although you may enjoy soft water for bathing and other household uses, it's not good for your lawn and garden. Hard water contains magnesium and calcium, which counteracts any sodium found in the...
