GH MBreda test Determination of total water hardness. 

The determination of total water hardness is associated with the main sources of enrichment, which are limestone rocks, which can come from calcitic (CaCO3), magnesium (MgCO3) or dolomitic limestones (mixture of the two previous ones).

These, when added to the water, are solubilized, releasing calcium (Ca2+) and/or magnesium (Mg2+) ions and carbonate ions into the solution, which, depending on the pH of the water, can appear as carbonates (CO32-), bicarbonates ( HCO3-) or carbonic acid (H2CO3) The pH of the water is strongly influenced by the solubilization of these limestones, since the carbonate ion, when dissolved, undergoes a hydrolysis reaction, obtaining bicarbonate (HCO3-) and hydroxyl (OH-) ions as products, the latter being responsible for the pH elevation.

Calcitic limestones, when added to pure water, can raise the pH of the water to 9.91; Magnesians can reach 10.20 and dolomites 10.06. For this reason, monitoring the pH of aquarium water must be carried out when rocks are added, especially if they are calcareous.

However, the water hardness parameter, although commonly linked to the pH change, are not necessarily correlated, since the water hardness parameter monitors the concentration of dissolved calcium and magnesium ions, and not the pH, which changes with the concentration. of bicarbonate/carbonate ions.

The concentration of Ca2+ and Mg2+ can be increased without necessarily changing the pH. We recommend using the GH+ MBreda to raise these parameters correctly and safely for aquariums.

For this reason, for the monitoring of water quality it is important to determine two parameters, the total hardness (Ca2+ and Mg2+), also called “GH” and the buffering capacity (species that influence the pH), also called “ Kh”.

The determination of the total hardness is carried out through a chemical reaction with the complexing agent, called Ligand (Solution 3) in an alkaline medium. The ligand reacts with calcium and magnesium to produce a stable compound.

This chemical stability is exploited in an analytical technique called volumetry, in which, with the addition of controlled volumes of ligand and the use of a complexation indicator, it is possible to determine the total concentration of Ca and Mg in the solution. Chemical fundamentals of the MBreda Analysis Kit for total hardness Considering that the parameter Total hardness considers the concentration of Ca and Mg present in the water, we will use the stable reaction of the ligand (solution 3) with these metals.

Chemical reaction 1 and 2 show the reactions. Image title We can verify in equations 1 and 2 that the formation constant of the calcium complex is greater than that of magnesium, consequently, more stable as well.

This greater stability prioritizes this reaction over that of magnesium, that is, all Solution 1 initially added reacts preferentially with calcium and only after all calcium has reacted will the reaction with magnesium begin.

This reaction generates colorless complexes as a product, so it is not possible to determine when we have reached the stoichiometric point, that is, the concentration at which the addition of Solution 3 equals the concentration of Ca and Mg.

To solve this, we used a complexation indicator that also acts as a complexing agent, differentiating that the product of this reaction has a characteristic color.

In this case, as we want to monitor the total hardness, that is, the sum of Ca and Mg, we need to monitor the complexation of the last species to be complexed, in this case, magnesium. For this we use a specific indicator for magnesium present in solution 2.

The indicator of Solution 2 is a weak complexing agent, which when in the presence of magnesium forms a red complex and in the absence it has a blue color. The procedure to determine the Ca and Mg content of the water starts with the adjustment of the pH to 10 (Solution 1), in which the complexation reaction presents the best performance, and then with the addition of the complexation indicator.

At this time, the added indicator complexes with the magnesium present, turning the solution red, according to equation 3. Image title With the dropwise addition of Solution 3, a second reaction occurs, which is the complexation of the ligand with calcium, initially, and then with magnesium.

Preferably, the ligand will react with the free metals in the ionic form and, after its depletion, will start a competition for bound metals. When we add the indicator to the water, a small part of the free magnesium is complexed, and it is this compound formed that will be the last to compete with the binder. how was it

Operating procedure of the MBreda Analysis Kit for total hardness:

1) Transfer 5 ml of aquarium water with the syringe into the glass bottle of the kit

2) Add 5 drops of solution 1

3) Add 1 drop of solution 2

4) Shake the tube, homogenizing the solution (red color)

5) Add a drop of solution 3 and shake, observe if the color changes from red to blue, if not, add another drop and shake again, observing the color. Repeat this procedure until the color changes.

Note: It is very important to shake after the addition of each drop and to position the dropper in an upright position. If after adding solution 1 the sample already turns blue, it is because the hardness is too low (pure water)

6) Knowing the number of drops of solution 3 used,

See the classification in Table 1

Composition:

Ammonium chloride, ammonium hydroxide, eriochrome black, hydroxylamine hydrochloride, methyl alcohol, EDTA, distilled water.

Guidelines:

Always keep this package closed, protected from light and out of the reach of children.

In contact with the skin, wash with water and neutral soap. In case of contact with eyes, rinse immediately with water and seek medical advice.

In case of ingestion, consult a doctor taking this package with you.