What is the purpose of measuring calcium, magnesium hardness? why tap water have 0 temporary hardness?

Answer 1

Hard water is water that has a high mineral content (water with a low mineral content is known as soft water). This content usually consists of high levels of metal ions, mainly calcium (Ca) and magnesium (Mg) in the form of carbonates, but may include several other metals as well as bicarbonates and sulfates. It is not generally dangerous. The simplest way to determine if water is hard or soft is the lather/froth test. If the water is very soft, soap will tend to lather up easily when agitated, whereas with hard water it will not. Toothpaste will also not froth well in hard water. More exact methods of 'hardness' detection use a wet titration method to determine hardness.

Total water 'hardness' (including both Ca2+ and Mg2+ ions) is reported as ppm w/v (or mg/L) of CaCO3. Water hardness usually measures the total concentration of Ca and Mg, the two most prevalent divalent metal ions, although in some geographical locations iron, aluminium, and manganese may also be present at elevated levels. Calcium usually enters the water from either CaCO3, as limestone or chalk or from mineral deposits of CaSO4. The predominant source of magnesium is dolomite, CaMg(CO3)2.

As carbonates of Calcium and Magnesium are relatively less soluble in water and calcium and magnesium salts of long fatty acids being used in manufacturing of the Soap are less prone to give good froth,hence measuring calcium ,magnesium hardness has been accepted as a criteria for determining the hardness of water.
Temporary Hardness of Tap water :
Temporary hardness is hardness that can be removed by boiling or by the addition of lime (calcium hydroxide). It is caused by a combination of calcium ions and bicarbonate ions in the water. Boiling, which promotes the formation of carbonate from the bicarbonate, will precipitate calcium carbonate out of solution, leaving water that is less hard on cooling.

The following is the equilibrium reaction when calcium carbonate (CaCO3) is "dissolved" in water:

CaCO3(s) + H2O (l) + CO2 (g)----> Ca+2 (aq.) +2HCO3'(aq.)

Upon heating, less CO2 is able to dissolve into the water . Since there is not enough CO2 around, the reaction cannot proceed from left to right, and therefore the CaCO3 will not "dissolve" as readily. Instead, the reaction is forced to go from right to left (i.e. products to reactants) to reestablish equilibrium, and solid CaCO3 is formed. Heating water will remove hardness as long as the solid CaCO3 that precipitates out is removed. After cooling, if enough time passes the water will pick up CO2 from the air and the reaction will again proceed from left to right, allowing the CaCO3 to "redissolve" in the water.
As at ambient temperature conditions solubility of calcium chloride is relatively more hence the tap water have 0 temporary hardness.

Answer 2

Hard water can somewhat be cured by all three, BUT the only real cure is a good water softener device. There are small ones that can attach to your sink if your hard water comes and goes. I run a full in system machine with salt and anti-rust agents only because I want it good all the time.

Answer 3

1) Hard water is not suitable for washing clothes & some other works. while it's recommended you to drink water which is hard to an extent, soft water should never be carried in lead pipes because poisonous Pb(OH)2 evolves & dissolves in water.

So,u see that for various purposes we need to know whether the water is hard or not,and if it's hard, then to what extent.

That is why,measurements of hardness of water is necessary.

2) I don't know.

Answer 4

Hard water is not suitable for home or many industrial purposes since soap will not foam in hard water and it is difficult to wet surfaces with hard water. Softening make it wetter and moreefficient for use.

Answer 5

In order to ensure that it is suitable for domestic purposes.