At first glance, sodium carbonate and calcium chloride may appear to have nothing in common. One, sodium carbonate, acts as a strong base, the other, calcium chloride, forms a soluble salt solution in water. While their unique chemical properties have practical applications individually, together they provide a classic precipitation reaction that has practical applications for your household water supply.
Sodium Carbonate
Sodium carbonate contains two atoms of sodium or Na, one molecule of carbon or C, and three molecules of oxygen or O for every molecule of sodium carbonate. In chemical formula form, sodium carbonate is written as Na2CO3. A white, odorless powder, sodium carbonate absorbs the moisture in air. In solution, sodium carbonate exists as a strong alkali or base. When associated with about 10 water molecules per molecule of sodium carbonate, sodium carbonate decahydrate or Na2CO3*10H2O, appears as a transparent colorless crystalline solid, also known as sal soda, soda ash or washing soda. Natural sources of sodium carbonate include mines in Wyoming and lake brines in California. Industrially, sodium carbonate helps make glass, paper, soaps, detergents and other chemicals, and plays a significant role in water softening.
Calcium Chloride
Calcium chloride consists of one atom of calcium or Ca and two atoms of chloride or Cl2 for every one molecule of calcium chloride--chemically written as CaCl2. While sodium carbonate usually contains 10 molecules of water associated with it, calcium chloride contains about two, designated as CaCl2*2H2O. Solutions of calcium chloride are used to help treat hypocalcemia, or low plasma calcium levels, which can be dangerous as your nervous system and muscles, particularly your heart, depend upon a specific calcium concentration in your blood. Calcium chloride also helps treat overdoses of magnesium sulfate, high levels of potassium in the blood, known as hyperkalemia, and in cardiac resuscitation if epinephrine fails to improve heart function.
Reaction
Sodium carbonate and calcium chloride readily react with each other producing sodium chloride or ordinary table salt, along with calcium carbonate. This classic reaction illustrates the principle of precipitation of solids out of liquids. The word "precipitation" refers to the process, while the word "precipiate" refers to the solid created. In the reaction of sodium carbonate and calcium chloride, sodium carbonate, the alkali, reacts with the calcium chloride salt to create the calcium carbonate precipitate and sodium chloride, which stays in solution. The calcium carbonate precipitate can be separated away from the sodium chloride solution by filtration.
Hard Water
The reaction between sodium carbonate and calcium chloride has a practical application with hard water issues. Hard water refers to water containing high levels of minerals, mostly calcium and magnesium. Hard water is a problem for many households. Clothes washed in hard water can look dingy and become scratchy. Minerals in the water combine with soils on the clothing, forming insoluble salts that are difficult to remove. Similarly, dishes washed in hard water can have spots and soap scum on them. Bathing in hard water leaves the same sticky soap scum on your skin. Even if the spots and scum do not irritate you or your body, the scale of calcium and magnesium on water-using appliances leads to costly and inefficient operation of the appliances. Calcium and magnesium scale build-up reduces water flow, clogs water pipes, increases energy bills and eventually leads to pipe replacement. While hard water is not a health hazard, water softening agents such as sodium carbonate help pull calcium minerals out of water, softening the water--thereby reducing the hard water's negative effects.
Swimming Pools
The white particulates seen on your backyard swimming pool tiles contain calcium carbonate. Calcium carbonate precipitates out of the pool water when the water contains high levels of calcium. This precipitation reaction proceeds very similarly to the reaction used to soften water; alkaline reacts with calcium in the water, causing precipitation. Low levels of calcium in the water can also be problematic for pools, as the reaction will still tend to occur--this time in the opposite direction. To bring calcium into the pool water, the reaction proceeds by pulling calcium carbonate from cement or plaster, causing the plaster to etch and the concrete to pit. Ideally you can avoid these problems by keeping the calcium in your pool in the range of 200 and 400 ppm, or parts per million.
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