Yes, chemical fertilizers are essential because the soil is impoverished by harvesting by breaking the natural life cycle of vegetables, in which leaves, fruits and seeds fall to the ground giving back what the plant took from it.
For example, the phenomenon of ‘vecería’, which is attributed to the cultivation of the olive tree, has this cause, since when removing the olive from the field we withdraw with it the nutrients that the tree itself needs. If these nutrients are not replenished the next harvest will be lower. Thus, since carbon is fixed from atmospheric carbon dioxide, the three elements that must be supplied to the soil are nitrogen (N), phosphorus (P) and potassium (K).
The truth is that agricultural production would not have been able to afford food for a population that continues to grow like ours using only natural fertilizers such as manure. In addition, it should not be forgotten that the availability of fertile soil has practically reached the ceiling unless one resort to practices as aggressive as deforestation. Of course, chemical fertilizers have to be applied rationally, providing the necessary doses and with the appropriate frequency.
The hardness of a water is related to the concentration of calcium and magnesium compounds in solution, which give insoluble compositions with the soap.
The hardness of a water can be defined as the sum of all the salts of non-alkali metal ions present in it. In fact, we are mainly talking about bicarbonates of calcium and magnesium, but also sulfates, chlorides, nitrates, phosphates and silicates from other metals such as barium, strontium and other minor metals.
It is called temporary hardness to that caused by bicarbonate or acid carbonate [Ca (HCO3) 2], because when heating water calcium carbonate (CaCO3) is formed, which is insoluble and forms deposits on hot surfaces. These deposits can be formed in the bottom of the kitchen vessels, in the heating resistors (thermos, dishwashers, washing machines …), in heated pipes, such as boilers, reducing the heat transfer and being able to seal them. Permanent hardness is almost always due to chlorides and sulphates and does not cause deposits on heating.
The concentration of an acid in a solution can be determined by making an acid-base titration. To this end, a known volume of the acid solution is slowly added alkali solution whose concentration is known, until a neutral pH is reached.
Knowing the reaction that occurs and according to the principle of conservation of matter, you can calculate the concentration of the acid knowing its molecular weights. Suppose the acid is hydrochloric acid (HCl), alkali sodium hydroxide (NaOH) and thus reacting:
HCl + NaOH→NaCl + H2O
One mole of HCl (36.5 g) is reacted with one mole of NaOH (40 g). The amount of spent alkali is deduced from the volume used and its concentration. Knowing the volume of starting acid can calculate the amount of acid neutralized and thus its acidity.