First of all, let's find out why this is 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 salts (calcium and magnesium), which are responsible for the hardness of water, can form special compounds (insoluble) with fatty acids contained in soap.
Let's make an experiment:
- Pour water into the flask to the “40” mark.
- Add there all 0.2 m calcium chloride solution from the vial.
- Take the fuel stove and install a candle on it. Then remove the protective gloves and light the candle. Install the flame diffuser on the stoves.
- Put the flask on the flame diffuser. Wait 15 minutes
- Pour all 0.3 m sodium bicarbonate solution from the vial.
- After that, the water in the flask becomes cloudy.
What are the hardness of water?
Temporary and permanent hardness of water. What is a constant?
This is such a specific value, reflecting the amount of salts of various metals dissolved in water, such as calcium, manganese, iron. Temporary hardness (which can be extracted) and constant hardness. Temporary is caused by calcium and magnesium bicarbonate, and a permanent tourniquet is caused by their sulfates and chlorides (CaCl 2 and MgCl 2 ). We can conclude that hard water is one in which at the same time there are many metal salts.
When we add calcium chloride to it, artificially increase its rigidity. As mentioned above, CaCl 2 causes a constant non-carbonate hardness of water. And one of the parts of our experiment demonstrated this fact: when boiling on the walls there is no noticeable precipitation.
Adding sodium bicarbonate NaHCO 3 leads to the formation of calcium bicarbonate in solution: 2 NaHCO 3 + CaCl 2 = 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 does scale form and how to remove it
Scale (or limescale) is an insoluble calcium carbonate precipitated by thermal decomposition of calcium bicarbonate. Despite the fact that the thick gray layer of scales does not make the dishes more beautiful, it does no harm. Moreover, it can extract excessive hardness of water from the tap. In addition, scale can be easily removed from teapots and pots by cleaning them using a solution of citric acid.
How to soften water
Water, which contains a small amount of metal salts, is soft. And the process of extracting hardness 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 removes only temporary (carbonate) hardness (constant water hardness can be eliminated by other methods). Constant hardness is maintained: water saturated with calcium chloride CaCl2 does not leave a residue upon boiling. Distillation is closely related to this action. During the distillation process, the evaporated liquid condenses on a cooled surface and is thus collected in the form of droplets. The water purified in this way is called distilled. It is unsuitable for drinking, as it washes minerals out of the body. However, it is widely used in science and industry.
Another method of softening is the use of reagents. They transfer magnesium and calcium ions into a form that does not dissolve, adding certain chemicals, such as calcium hydroxide (a process called lime softening). Like boiling, lime softening removes only carbonate hardness.
Elimination of constant water hardness
In order to extract a constant (non-carbonate) hardness, a deeper softening of the water is necessary, therefore, in addition to hydrated lime, they use sodium carbonate.
For even more efficient removal of metal ions using "big guns" - sodium phosphate:
Na3PO4: CA3 3Ca2 + + 2Na3PO4 → (PO4) 2 ↓ + 6Na +
3Mg2 + + 2Na3PO4 = Mg3 (PO4) 2 = + 6Na +.
The disadvantage of this mitigation method is that it is necessary to accurately dose the reagents given to us. In industry, the most widely used technology is water softening by ion-exchange resins. Specialists pass water through a filter that holds metal ions (calcium, manganese, iron, magnesium). These “captured” particles are replaced by potassium, sodium or H + hydrogen ions released into the solution. This method is also effective when constant hardness of water bothers you.
Conclusions: which is better?
Which water is better for you - hard or soft? The answer is simple: everything is good in moderation. Ideal for daily home use is medium hardness water, which contains a small amount of harmful substances. The right balance is always the path to harmony.