I am trying to mimic the hardness of natural waters of Ohio streams and reservoirs. Ohio sediments are rich in limestone, so our surface water is unusually high in carbonate hardness and calcium, even at pHs of 7-8. However, I know it is pretty much impossible to dissolve calcium carbonate in water at this pH. In the end, I'm going for some combination of carbonate and non-carbonate hardness, with a little magnesium and mostly calcium contributing to the hardness, and a carbonate hardness (alkalinity) of around 200 mg/L. I know I can use combinations of calcium carbonate, magnesium carbonate, or calcium and magnesium sulfates or chlorides. What is the best way to do this? How does nature do it???
Carbonate hardness (transient hardness, temporary hardness) - water hardness mainly caused by calcium bicarbonate, Ca(HCO3)2, and magnesium bicarbonate, Mg(HCO3)2. When water is heated, these compounds decompose into insoluble carbonates, which form the limescale:
Ca(HCO3)2 → CaCO3↓ + CO2 + H2O Mg(HCO3)2 → MgCO3↓ + CO2 + H2O
Due to the ease of removal of this type of hardness (it is enough to boil the water), it is called transient hardness - the resulting boiler scale, consisting of precipitated carbonates, settles on the bottom and walls of the vessel or tank.
Non-carbonate hardness (permanent hardness) - water hardness caused mainly by calcium and magnesium salts. The most common are sulphates (including CaSO4), which give gypsum stone which is difficult to remove, and chlorides. These salts can be naturally present in the water as well as re-formed, for example during cooking.
Thus, to simulate the hardness of water, for example, calcium bicarbonate and calcium sulfate (and/or chloride) should be introduced into it. Calcium bicarbonate is formed by dissolving calcium carbonate in water containing carbon dioxide:
CaCO3 + H2O + CO2 → Ca2+ + 2HCO3-
Dear Ashley Bair The following procedure is adopted from the "sciencing .com" on page titled " How to Make Hard Water":
Pour 500 milliliters of distilled water into a calibrated beaker, water level touching the 500 milliliters mark in the beaker.
Add half tablespoon of epsom salt to the distilled water. Stir well to completely dissolve the salt and make a clear solution.
Add half tablespoon of baking soda to the solution. Stir the solution well to completely dissolve the baking soda. Baking soda generally increases the temporary hardness of water.
Add half table spoon calcium chloride to the solution and stir to completely dissolve calcium chloride in the solution. Calcium chloride increases the permanent hardness of water.
Leave the solution for few hours. Generally 2 hours of time will be enough for complete dissolution of the minerals into the solution.
Make a filter cone with the filter paper. Filter the solution slowly with a filter cone into another beaker to remove any suspended material.
https://sciencing.com/make-hard-water-8191733.html
Best regards
· Absolutely. The most common example of this would be softened water. After a water softener the hardness will be near zero but the alkalinity remains unchanged.
· Total alkalinity is measured by titrating (step-wise addition of reagent) the water sample with sulfuric acid (H2SO4) to a pH endpoint of ~4.5. Once the water sample reaches a pH of 4.5, the three main forms of alkalinity (bicarbonate, carbonate, and hydroxide) have been neutralized.
· When titrating for total alkalinity, there are 2 “equivalence points,” where pH changes rapidly with small additions of acid – these lie near pH 8.3 and 4.5. These points can be determined by measuring pH as the acid is added, or by choosing indicators that change color at the pH value of the equivalence point.
· Hardness can be calculated by the procedure of Dilute 25 mL of sample (V) to about 50 mL with distilled water in an Erlenmeyer flask. Add 1 mL of buffer solution. Add two drops of indicator solution. The solution turns wine red in colour. Add the standard EDTA titrant slowly with continuous stirring until the last reddish tinge disappears from the solution. The color of the solution at the end point is blue under normal conditions. 5. Note down the volume of EDTA added (V1 ).
· When hardness/ alkalinity is expressed as ‘mg/l as CaCO3’, it’s calculated as if all the calcium and magnesium were present only as calcium carbonate. Hard water contains Carbonates, chlorides, sulphides of calcium, magnesium etc. From all of them, the molecular mass of Calcium carbonate is 100. Measuring hardness requires 1 standard value, as a constant to equate with. Hence the hardness of water is measured in terms of CaCO3, as it would be easier to equate values with respect to 100 as compared to the molecular masses of other hardness causing agents. During water softener the hardness will be near zero but the alkalinity remains unchanged. River is soft water so temporary hardness which comes lesser than alkalinity. Alkalinity and hardness values are normally similar to magnitude because calcium, magnesium, bicarbonate, and carbonate ions in water are derived in equivalent quantities from the solution of limestone in geological deposits. However, in some waters alkalinity may exceed its hardness and vice versa.
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Ashley Bair , " How does nature do it??? " I believe the answer to this question guide how you can make a solution have a hardness above the apparent solubility dictated by the alkalinity.
Groundwater dissolve carbonates by reaction with CO2 which increase in partial pressure with depth as a result of the increasing total pressure. Likewise surface water with CaCO3 stones often have partial pressure of CO2 much higher than the equilibrium with atmosphere predicts due biodegradtion of plant matter and a slow gas exchange through the water surface.
You can use this principle in the laboratory by adding CO2 to the solution from a gas bottle which will not change the alkalinity but reduce the pH and thus increase the solubility of Ca and Mg. I often use this in the laboratory.
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