the hydrologic cycle Select a lesson
 

The water cycle
The hydrologic cycle
Define evaporation
Define condensation
Define Precipitation
Define transpiration
Define runoff
Define infiltrationWhat makes water hard and soft

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What is a chemical change



Hard water or soft water?


Water hardness and softness has nothing to do with its touch and feel. It is more about chemical compounds dissolved in it. They are both safe for human consumption.

Pure water (like clean rainwater) is soft water. It only becomes hard when it comes into contact with rock layers made up of compounds such as calcium or magnesium, and dissolves in it.

How does soft water become hard water?
Let us take rainwater as an example. The rainwater may be slightly acidic because of some carbon compounds in the air from pollution. Let’s assume that the rainwater falls on an area with lots of limestone rocks. Limestone contains calcium carbonate (CaCO3). As the water soaks into the limestone layers, calcium compounds dissolve in the acidic rainwater. The water is now hard water because it has calcium and magnesium ions in it.

There are various levels of hardness. It all depends on the rock types found in that region.

You will not know if water is soft or hard by just looking at it. It has to be tested. In your home, there are some signs that can help you guess if your water is hard or soft.

Here are a few:
problems of hard waterHard water does not easily lather with soap.
problems of hard waterHard water leaves a lot of scum (some whitish deposits) in the bathtubs and sinks.
problems of hard waterBoiled hard water leaves some limescale residue, which can cause pipes to block over time.
problems of hard waterIf the hard water has ferrous irons (oxidized to the ferrous form) it may leave some reddish brown stains on your clothing after laundry, or on the bathroom enamel surfaces.

Some people believe that hard water tastes better to drink. It is also known to be good for bones and teeth, and can even help reduce heart disease.

Can hard water be softened?

Hard water can be
temporal or permanent. Temporal hard water is caused by calcium bicarbonate. This hardness can be removed by just boiling the water, as this converts the carbonate to insoluble carbonate (This leaves a precipitate and can clog your boiler). Permanent hardness is usually caused by other salts.

calcium deposit in boilers from hard water

Permanent hard water can be made soft by adding sodium carbonate (also called washing soda) to it. This will soften both temporal and permanent hardness. In this chemical reaction, the calcium and magnesium ions react with sodium to form a precipitate. This also leaves limescale behind and can clog your pipes. This is not the best idea for softening water in your home.

In another process, ion exchange columns are used. In this chemical reaction, the sodium ions swap places with the calcium ions. The result is water with sodium ions instead of calcium ions. There is no limescale precipitate or residue.


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Our reading and research on this lesson included the links below:
1. The USGS Water Science School. wwww.ga.water.usgs.gov/edu/watercyclesummary.html#evapotranspiration)
2. National Weather Service, Columbia SC. www.erh.noaa.gov/cae/svrwx/hail.htm
3. Michigan Environmental Education Curriculum. The Watershed Concept. www.techalive.mtu.edu/meec/module01/Infiltration.htm
4. The Weather Notebook. Chinook Melt, http://www.weathernotebook.org/transcripts/2001/03/14.html
5. THE WATER CYCLE: A GUIDE FOR STUDENTS: www.freedrinkingwater.com/resource-water-cycle-student-guide.htm
6. FWR, Hydrological cycle. www.euwfd.com/html/hydrological_cycle.html
7. Kids Konnect. Clouds. www.kidskonnect.com/subjectindex/15-educational/science/67-clouds.html
8. World Health Organization, Hardness in Drinking-Water: http://www.who.int/water_sanitation_health/dwq/chemicals/en/hardness.pdf
9. Case Study: Hard Water: http://chemwiki.ucdavis.edu/Inorganic_Chemistry/
Descriptive_Chemistry/Main_Group_Reactions/Case_Study%3A_Hard_Water


What is condensationevaporation in the hydrologic cycle