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# Lime water

Lime water or milk of lime is the common name for saturated calcium hydroxide solution. Its chemical formula is Ca(OH)2. The term is based on the mineral sense of lime, rather than the fruit sense of lime. Lime water used as a paint is called lime wash (see whitewash).

## Etymology

• Middle English lim, from Old English līm, birdlime.

## Making lime water

Lime water can be made by adding calcium hydroxide to distilled water. The mixture needs to be shaken every few hours for a period of 24 hours to ensure that as much calcium hydroxide dissolves as possible. It is then left to settle and the solution is siphoned off the sediment.

## Uses of Lime water

### Chemistry

In chemistry, lime water can be used to test the presence of carbon dioxide because lime water reacts with carbon dioxide to produce a precipitate of calcium carbonate:

Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l)

Lime water is also used in fermentation, to determine whether carbon dioxide was produced. When lime water reacts with CO2 it becomes milky.

### Medicine

When the old vaudeville style medicine shows promoting various patent medicines were in full swing, lime water was often used as a part of the act. The salesperson would have an audience member blow through a straw into a glass of lime water. Since their exhalations contained carbon dioxide, the water would turn cloudy; the huckster then announced that this reaction proved that the audience member suffered from some ailment. If too much carbon dioxide comes into contact with the cloudy limewater, it will cause the calcium carbonate precipitate to redissolve to form soluble calcium hydrogencarbonate.

CaCO3(s) + CO2(g) + H2O(l) $\rightarrow$ Ca(HCO3)2(aq)

The huckster had a patent medicine bottle filled with vinegar or some similar acid. He then would pour some of the acid into the glass of cloudy limewater. The acid reacted with the calcium carbonate, and the water would instantly clear. This demonstrated the potent effect of the nostrum he was selling to eliminate the "disease" demonstrated by the reaction.

### Meals

Lime water is also used in the traditional making of Tortilla [1]

### Arts

In buon fresco painting, lime water is used as the colour solvent to apply on fresh plaster.

### Misc

Lime water is widely used by marine aquarists and is a primary supplement of calcium and alkalinity for reef aquariums. Corals of order scleractinia build their endoskeletons from aragonite (a polymorph of calcium carbonate) and by doing so, usually form a reef. Calcium concentration in natural seawater is about 420 ppm[2].

When used for this purpose, lime water is also referred to as "kalkwasser".

## References

1. ^ Hambidge KM; Krebs NF, Westcott JL, Sian L, Miller LV, Peterson KL, Raboy V (July 2005). "Absorption of calcium from tortilla meals prepared from low-phytate maize.". The American Journal of Clinical Nutrition 82 (1): 84-7. PMID 16002804. Retrieved on 2006-10-02.
2. ^ A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH.