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The masses of Calcium Carbonate precipitate resulting from vacuum filtering varying concentrations of Calcium Hypochlorite solution are graphed below. The masses were found to be 0.3, 0.72, and 1.93 grams at 10 g/L, 20 g/L, and 30 g/L, respectively. The mass of precipitate was found to increase with increasing concentration of solution. From these resulting masses and the known molecular weights of Calcium Hypochlorite going in, the amount of Calcium Carbonate that could precipitate out was calculated. And based on the amount of Calcium Carbonate we found that actually did precipitate out of solution, we were able to find the residual mass of Calcium left in solution that could potentially settle out at a later time and clog the hypochlorinators.
Using the reaction below (Reaction 1), we could see that for For every mole of calcium hypochlorite (Ca(ClO)2) one mole of calcium carbonate (CaCO3) precipitates out in solution.
Reaction 1: Calcium Hypochlorite Reacting in Solution to form Calcium Carbonate
2Ca(ClO)2 + 2CO2 → 2CaCO3 + 2Cl2 + O2
Using Using this and the fact that the molecular weight of calcium hypochlorite is 142.98 g/mol and the known masses of calcium hypochlorite added were 10, 20, and 30 g, the moles of calcium added were found to be 0.7, 0.14, and 0.21, respectively. Therefore the mass of calcium (molecular weight: 40.08 g/mol) going into solution was found to be 2.8, 5.6, and 8.4 g, respectively. Then using the molecular weight of calcium carbonate (100.09 g/mol) and the known masses of calcium carbonate coming out of solution (0.3, 0.72, and 1.93 at 10 g/L, 20 g/L, and 30 g/L, respectively as mentioned above), the moles of calcium carbonate and thus calcium coming out were found to be 0.003, 0.007, and 0.019, respectively. From this the mass of calcium coming out of solution was found to be 0.12, 0.29, and 0.77 g respectively. By subtracting the amount of calcium coming out of solution from the amount of calcium going into solution, the residual mass at each concentration was found.
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When starting with an initially high concentration of Calcium Hypochlorite and reducing the concentration after initial settling by adding tap water, the resulting amount of precipitate in solution was found to decrease from 0.12 in height to 0.01 in a 30g/L solution. These are dimensionless heights measured as the height of precipitate forming divided by the height of solution. This data reveals a 80% reduction in precipitate found to accumulate. The full results are shown below (Figure 4).
Figure 4: Height of
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precipitate forming at 100g/L solution and
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diluted 30g/L solution.
From this data, it can be inferred that in the first day that the 100g100 g/L solution was allowed to sit, a lot of the precipitate did settle out. Most of the precipitate found in the diluted 30g/L solution probably came from the precipitate that remained suspended on the top of 100g/L solution due to the CO2 gas risingHowever, reducing the supernatent of the 100 g/L concentration to 30 g/L after the first day and allowing it to settle again did result in the additional formation of precipitate. This additional precipitate was a result of an additional day of settling, due to the fact that this test was done in less than the 3 suggested days. This was done because of a time constraint. It is also possible that some of what was measured in the initial 100 g/L concentration as precipitate was actually calcium hypochlorite that didn't dissolve due to the saturation of solution. Thus adding additional water to the supernatant of that solution would result in more calcium hypochlorite dissolving and more precipitate forming.
Conclusions
With increasing concentration of Calcium Hypochlorite Solution, the threat of clogging becomes greater due to increased amount of precipitate forming. There are several ways however to reduce this threat.
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