Water hardness is the content of certain minerals in the water, generally ionkalsium (Ca) and magnesium (Mg) in the form garamkarbonat. Hard water or hard water is water that has a high mineral content, while soft water is water with a low mineral levels. In addition to calcium and magnesium ions, can also cause the hardness of the other metal ions or salts, bicarbonates and sulfates.
The simplest method for determining water hardness is with soap. In soft water, soap will generate a lot of foam. In the hard water, soap will not produce foam or produce very little foam. Total water hardness is expressed in units ppmberat per volume (w / v) of CaCO 3. Water hardness is classified into two types based on the type anion iikat by cations (Ca 2+, Mg 2+), namely:
a) Water hardness while
Hidrokarbonat contain salt such as Ca (HCO 3) 2 or Mg (HCO 3) 2.
- While hard water can be removed by heating the water kesadahannya so that karbonatnya salt precipitate, the reaction:
Ca (HCO 3) 2 (aq) CaCO3 (s) + H2O (l) + CO2 (g) -> Mg (HCO 3) 2 (aq) MgCO3 (s) + H2O (l) + CO2 (g)
- In addition to heating water, hardness while also eliminated kesadahannya by reacting a solution containing Ca (HCO 3) 2 or Mg (HCO 3) 2 with lime (Ca (OH) 2):
Ca (HCO 3) 2 (aq) + Ca (OH) 2 (aq) -> 2CaCO3 (s) + 2H2O (l)
b) The water hardness remains
Salts containing sulfate (CaSO4 or MgSO4) sometimes also contains salt chloride (CaCl2 or MgCl2). Hard water can still be eliminated kesadahannya use way:
- Reacting with Na2CO3 soda and lime Ca (OH) 2, so that the precipitation of carbonate salts and hydroxides:
CaSO4 (aq) + Na2CO3 (aq) -> CaCO3 (s) + Na2SO4 (aq)
- Zeolites process with sodium zeolite (a silicate), then the position will be replaced by calcium ions and magnesium ions or calcium zeolite.
EDTA titration method
o Total hardness is Ca2 + and Mg 2+ can be determined by titration with EDTA as titrant and using indicators that are sensitive to all of these cations. The total incidence can be analyzed separately for example by AAS method (automic Absorption Spectrophotometry).
o Ethylenediamine tetraacetic acid sodium salt and this (abbreviation EDTA) forms a chelate complex soluble when added to a solution containing certain metal cations. If a small amount of Eriochrome Black T or Calmagite added to a solution containing calcium and magnesium ions in a pH of 10.0 ± 0.1, the solution becomes pink. If EDTA is added as the titrant, calcium and magnesium will be a complex, and when all the magnesium and calcium have widened the complex, the solution will change from pink into blue which indicates the end point of the titration. Magnesium ions should appear to generate an end point of the titration. For this mememastikankan, complex neutral magnesium salt of EDTA is added to the buffer solution.
o Determination of Ca and Mg in the water has been done by EDTA titration. pH titration was 10 indicators Eriochrom Black T (EBT). At higher pH, 12, Mg (OH) 2 will precipitate, so that EDTA can be consumed only by Ca2 + indicators murexide. The disruption of the free Cu-pipe plumbing can be in masking with H2S. EBT are mashed together with solid NaCl is also sometimes used as an indicator for the determination of Ca or hidroksinaftol. Ca ought not participate terkopresitasi with Mg, therefore, recommended EDTA.
o Clarity of titik- end of the lot with pH increase. However, the pH level can not indefinitely as a result of the danger precipitated calcium carbonate, CaCO3, or magnesium hydroxide, Mg (OH) 2, and because of changes in altitude coloring dye pH value. Defined pH of 10.0 ± 0.1 is a compromise satisfaction. One barrier of 5 min is set for a period of titration to minimize the tendency toward CaCO 3 precipitation.
a) Pipette volume of 10.0 mL
a) solution of EDTA
b) Buffer solution pH 10
c) indicators EBT
How it works:
a) pipette 10 mL of water was added to erlenmeyer.
b) Add indicator EBT until the solution becomes pink.
c) Add the buffer solution pH 10 as much as 1-1.5 mL.
d) titrated with EDTA solution to become blue.
e) Record the volume of EDTA used.
mg / L CaCO3: mL EDTA X factor EBT X 10 mL sample