Water hardness. Temporary and permanent water hardness

Science 2023

Table of contents:

Water hardness. Temporary and permanent water hardness
Water hardness. Temporary and permanent water hardness

First of all, let's find out why it's a problem when the water is too hard. Its regular consumption of water entails the appearance of stones in the excretory system. Using it for bathing or washing can often cause skin irritation, especially in children. In addition, it can create certain inconveniences in everyday life: metal s alts (calcium and magnesium), which are responsible for water hardness, can form special compounds (insoluble) with fatty acids contained in soap.

Let's experiment:

  1. Pour water into the flask up to the "40" mark.
  2. Add all 0.2 m of calcium chloride solution from the vial.
  3. Take a fuel stove and place a candle on it. Then take off your protective gloves and light the candle. Install the flame diffuser on the stoves.
  4. Place the flask on the flame diffuser. Please wait 15 minutes.
  5. Pour all 0.3M sodium bicarbonate solution from vial.
  6. After that, the water in the flask will become cloudy.

What are the hardness of water?

Temporaryand constant water hardness. What is a constant?

Preparations for stiffness

This is such a certain value, reflecting the amount of s alts of various metals dissolved in water, such as calcium, manganese, iron. Temporary hardness (which can be extracted) and permanent hardness. The temporary one is due to calcium and magnesium bicarbonate, and the permanent tourniquet is due to their sulfates and chlorides (CaCl2 and MgCl2). We can conclude that hard water is one in which there are many metal s alts at the same time.

When we add calcium chloride to it, we artificially increase its hardness. As mentioned above, CaCl2 causes permanent non-carbonate hardness in water. And one part of our experiment demonstrated this fact: when boiling, no noticeable precipitation occurs on the walls.

Addition of sodium bicarbonate NaHCO3 leads to the formation of calcium bicarbonate in solution:2 NaHCO3 + CaCl2 =Ca (HCO3)2 + 2NaCl, and due to the formation of Ca (HCO3)2, the hardness of our water becomes temporary - now it can be removed by boiling.

Why scale builds up and how to remove it

Scale (or limescale) is an insoluble calcium carbonate that precipitates during the thermal decomposition of calcium bicarbonate. Although the thick gray scale layer does not make the food prettier, it does no harm. Moreover, it can remove excessive hardness of tap water. In addition, scale can be easily removed from teapots and pots by cleaning them withcitric acid solution.

How to soften water

Water hardness tester

Water, which contains a small amount of metal s alts, is soft. And the hardness extraction process softens it. The easiest way to soften, as shown in our experiment, is boiling. When heated, calcium and magnesium bicarbonates undergo thermal decomposition. This process only removes temporary (carbonate) hardness (permanent water hardness can be removed by other methods). Constant hardness is maintained: water saturated with calcium chloride CaCl2 leaves no residue when boiled. Distillation is closely related to this action. During the distillation process, the evaporated liquid condenses on the cooled surface and is thus collected in the form of droplets. Water purified in this way is called distilled. It is not suitable for drinking, as it leaches minerals from the body. However, it is widely used in science and industry.

Another way to soften is to use reagents. They transfer magnesium and calcium ions to a form that does not dissolve by adding certain chemicals, such as calcium hydroxide (a process called lime softening). Like boiling, softening lime only removes carbonate hardness.

Illustrating water hardness

Eliminating permanent water hardness

In order to extract permanent (non-carbonate) hardness, deeper water softening is needed, so they use carbonate in addition to slaked limesodium.

For even more efficient removal of metal ions, “big guns” – sodium phosphate are used:

Na3PO4:CA3 3Ca2+ + 2Na3PO4 → (PO4)2↓ + 6Na+

3Mg2+ + 2Na3PO4=Mg3(PO4)2=+ 6Na+.

The disadvantage of this softening method is that it is necessary to accurately dose the reagents given to us. In industry, the technology of water softening with ion-exchange resins is most widely used. Specialists pass water through a filter that retains metal ions (calcium, manganese, iron, magnesium). These “trapped” particles are replaced by potassium, sodium, or hydrogen H+ ions released into the solution. This method is also effective when persistent water hardness bothers you.

Conclusions: which is better?

Water jet

Which water is better for you - hard or soft? The answer is simple: everything is good in moderation. The ideal option for daily home use is water of medium hardness, which contains a small amount of harmful substances. The right balance is always the path to harmony.

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